Stem Cell Problems and Ways to Restore Them in Ageing: New Progress in Regenerative Medicine

Genomic instability and accumulation of DNA damage a primary hallmark of ageing, which contributes to cellular dysfunction and diseases (González-Meljem et al., 2018). Genomes are unstable due to the continual induction of DNA damage, primarily from endogenous sources. It is noteworthy that DNA damage differs from DNA mutations. DNA damage causes physical changes in the structure of nucleic acids, such as breaks, crosslinks, depurination, depyrimidination, and base changes, whereas mutations occur as errors during the DNA repair or replication process, or sometimes spontaneously (Vijg and Montagna, 2017). Therefore, genomic instability is referred to as a range of DNA modifications, including point mutations, chromosomal rearrangements, deletion and insertion mutations and whole chromosome numerical alterations which irreversibly change the genome information content, contributing to genomic instability (Aghamir et al., 2025). Genomic instability contributes to the compromise of cell function and can trigger cancer, as well as cell loss (Maldonado et al., 2023). Stem cells rely on intact genomes for renewal, so genomic instability severely limits their regenerative capacity (Tsai, 2016).

Telomeres are the genomic segments located at the ends of the linear chromosomes. The shortening of these telomeres, serving as a cap on each arm of all chromosomes, contributes to cellular senescence and ageing (Eppard et al., 2023). According to the telomere hypothesis, senescence occurs when telomeres in somatic cells reach a critical length known as the Hayflick limit (Hayflick, 1965; Hayflick and Moorhead, 1961; Hirt et al., 2013; Razgonova et al., 2020). The loss of nucleotides in the telomeric region disrupts the T-loop and opens the exposed overhang to the DNA damage response (DDR), as the telomere is now recognized as a double-strand break (DSB), eventually leading to senescence and apoptosis (Harley et al., 1990; Shay, 2018; Verdun et al., 2005). Research also indicates that the shortening of telomere leads to DDR activation and cellular senescence in various animal models resembling aspects of ageing and age-associated diseases (Rossiello et al., 2022). Despite a halt in the telomere attrition process due to cell cycle arrest, the chronic inflammatory environment created by SASP can contribute to the slow progression of various age-related conditions (Coppé et al., 2008; Cuollo et al., 2020; Libby et al., 2009; Shakeri et al., 2018). This trend may occur due to the negative impacts on other cells in the microenvironment, for instance, increased reactive oxygen species (ROS) generation and senescent cell accumulation (Fossel et al., 2022; Sahin and DePinho, 2012).

One of the most preserved signs of ageing is epigenetic alterations that include DNA methylation, histone alterations, chromatin remodeling and noncoding RNAs. Various biological processes and markers play crucial roles in the developmental process of ageing, but epigenetic changes stand out due to their vital role in gene regulation and cellular identity (Ermolaeva et al., 2018; Izadi et al., 2024). The process of methylation occurs because of the transfer of a methyl group from S-adenosyl methionine (SAM) to the fifth carbon present in cytosine to form 5-methylcytosine by the catalytic action of three DNA methyltransferases (DNMTs) called DNMT1, DNMT3a, and DNMT3b (Xiao et al., 2019). Post-translational histone changes can control the ageing process and either stimulate or suppress gene expression. ADP ribosylation, methylation, acetylation, ubiquitination, and phosphorylation are some examples of histone modifications. The most extensive research on those known to impact ageing is methylation and acetylation at lysine residues.

On the other hand, chromatin is a flexible and dynamic entity consisting of DNA and histones, which can exist as either euchromatin or heterochromatin (Nothof et al., 2022). The term ‘chromatin remodeling’ refers to a set of nuclear architecture alterations that occur throughout the genome and are discernible at the level of individual chromosomes or chromosomal domains like centromeres. Cellular senescence has been found to cause significant chromatic structural remodeling that ranges from modifications and changes in histone components to changes in chromatin compartments and topologically associating domains (TADs) (Chandra et al., 2015; Liu et al., 2022; Zhao and Chen, 2022). From yeast to human, the global canonical histone loss is thought to be a typical aspect of ageing (Dang et al., 2009; Hu et al., 2014; O’Sullivan et al., 2010). Finally, non-coding ribonucleotides have a significant role in regulating epigenetic modifications. MicroRNAs are endogenous non-coding RNAs that can inhibit gene expression via post-translational alterations. Various evidence suggests that miRNAs regulate other ageing processes, such as mTOR, AMPK, and sirtuin pathways (Jin Jung and Suh, 2012; Turko et al., 2025). In 2018, a systematic study found that miR-125b regulates MAPK, which is linked to Alzheimer’s dementia and early life stress (Lemche, 2018). Thus, changes in miRNA expression can be a sign of early ageing and can help us recognize various age-related disorders like atherosclerosis, Alzheimer’s disease (AD) and cancers.

Mammalian cells regulate the process of protein synthesis, protein folding, their transport, post-translational changes and their destruction to maintain protein equilibrium. This entire process comes under proteostasis or protein homeostasis. Any impairment or loss of protein homeostasis can lead to ageing, and therefore, it is considered a hallmark of ageing. By eliminating aberrant proteins through ubiquitin molecules, the multi-subunit proteolytic complex known as proteasome plays a critical role in preserving mammalian cellular proteostasis (Tang and Xiao, 2023). Numerous studies show a link between disrupted protein homeostasis and ageing that ultimately contributes to the progression of age-related diseases (Cai et al., 2022). Protein quality control (PQC) also contributes to maintaining a healthy proteome, necessary for cellular homeostasis. However, along with ageing progression, the efficiency of PQC pathways to regulate proteostasis weakens, and hence, the rise of hazardous misfolded proteins increases within the cell (Kumar et al., 2023). The disruption of PQC pathways is a significant sign in the pathogenesis of neurodegenerative diseases like AD, PD, amyotrophic lateral sclerosis (ALS), and Huntington’s disease (HD) (Ruz et al., 2020).

Autophagy, a Greek word meaning self-eating, is a catabolic process that is very crucial for the normal functioning of the body as it recycles many cellular processes like excess constituents, abnormally accumulated or damaged macromolecules, organelles and pathogens, that are no longer required by the body or may cause harm to the body. It is a protective pathway to maintain cellular equilibrium, and its maintenance is necessary for longevity. Dysregulation of autophagy is a primary factor in the development of various age-related diseases (Nieto-Torres and Hansen, 2021). Many studies across different organisms have shown that reduced autophagy contributes to ageing, with cells from long-lived animals and humans having elevated autophagy levels (Hansen et al., 2018; Leidal et al., 2018). Studies in Caenorhabditis elegans, Drosophila, rats, and human cells have shown that lysosomal proteolytic function declines with age, impairing autophagic flux and hence contributing to the development of age-related diseases. In addition, along with molecular chaperones and ubiquitin proteasome system (UPS), autophagy plays a role as a central regulator of cellular proteostasis. In line with this, genetic manipulation of core autophagy machinery components or regulators increases age-related protein aggregation, shortens lifespan, and exacerbates clinical characteristics in animal models (Aman et al., 2021).

Nutrient sensing is a biological process by which an organism detects changes in nutrient availability via dedicated biochemical sensors or surrogate factors and responds adaptively to preserve energy and nutrient homeostasis (Graupera and Claret, 2018). Nutrient-sensing pathways (NSP) play a vital role in the ageing process. For example, restricting dietary intake can increase the longevity of many organisms by suppressing nutrient sensing. In contrast, dysregulation of nutrient sensing is frequently reported in elderly individuals and age-related diseases such as type 2 diabetes (T2D) (Yu et al., 2024). These NSPs work as a link between ageing and diet. Modifications in these pathways have emerged as a new research topic in ageing, as they can be modulated both pharmacologically and by dietary treatments. Some NSPs that are impaired by ageing are IGF1/PI3K/AKT/mTOR and AMPK/Sirtuin/PGC1α. These pathways regulate protein synthesis, cell cycle, autophagy, DNA replication, stress response and glucose homeostasis. Recent studies also suggest that microRNAs play a crucial role in influencing nutrient-sensing pathways (Micó et al., 2017).

Mitochondria are crucial for health and diseases, regulating energy production through ATP generation, hormone production and neurotransmitter production. It also plays a vital role in shaping communication by interacting with organelles and the environment (Casanova et al., 2023). Any alteration in mitochondrial function can significantly impact ageing and chronic age-related diseases as mitochondria regulate cellular energy, oxidative balance, and calcium levels. During dysfunction, mitochondria exhibit decreased ATP production, changes in apoptosis regulation, increased ROS production and impaired calcium signaling (Nehlin, 2023; Norat et al., 2020). The accumulation of mutations in mitochondrial DNA (mtDNA) is the principal cause of mitochondrial anomalies, which contribute to ageing and associated disorders (Kujoth et al., 2007; Paraskevaidi et al., 2017). Increased ROS generation and mitochondrial apoptotic pathway activation in aged cells contribute to systemic degradation of numerous tissues, resulting in overall organ and tissue functions, like the heart, liver, brain, and muscle. Moreover, dysfunction in mitochondrial proteostasis is also associated with altered cellular activities in aged cells (Somasundaram et al., 2024).

Cellular senescence is a steady growth arrest caused by events like DNA damage, telomere dysfunction, organelle stress and oncogene activation. Hayflick and Moorhead first reported senescence in human fibroblasts in 1961. Senescence prevents uncontrolled cell growth but also contributes to the process of ageing by reducing tissue regeneration (Alcorta et al., 1996; Hayflick, 1965; Hayflick and Moorhead, 1961; Serrano et al., 1993). Furthermore, accumulation of senescent cells secretes inflammatory factors and hence disrupts tissue functions as well (González-Meljem et al., 2018). Characteristics of senescence include increased β-galactosidase activity, enhanced cell cycle inhibitors, chromatin alterations and SASP, which causes inflammation and tissue failure. While senescence inhibits tumors and helps in wound healing, its persistence contributes to chronic age-related diseases. Experiments on transgenic mouse models also indicate that eliminating senescent cells delays ageing and age-related disease progression (Di Micco et al., 2021).

Stem cell exhaustion refers to the age-related decline in the number, self-renewal and regenerative potential of tissue stem and progenitor cells that reduce tissue maintenance and repair, thereby contributing to the age-related pathologies (Ermolaeva et al., 2018; Hambright et al., 2020). This depletion emerges from DNA damage, telomere attrition, epigenetic modification, metabolic and proteostasis dysfunction, chronic inflammation and altered systemic signals that regulate the aberrant activation and loss of quiescence. Studies demonstrated that both cell intrinsic damage and extrinsic changes together reduce the stem cell functions, while interventions targeting metabolism and other causative factors can partially restore the regenerative abilities of these stem cells (López-Otín et al., 2013; López-Otín et al., 2023; Mi et al., 2022; Picerno et al., 2021).

Altered intercellular communication is a significant characteristic marker of ageing, which influences numerous biological processes and contributes to the functional decline associated with ageing. This impairment in intercellular communication can occur due to alterations in various mechanisms that include alterations in SASP, modifications in ligand-receptor interactions, and changes in extracellular vesicles (EVs) composition, either by elevating or mitigating the phenomenon of ageing (Tenchov et al., 2023). Along with pro-inflammatory cytokines, SASP constitutes proteases and growth factors as well, and altogether they contribute to tissue dysfunction and poor intercellular communication, thereby promoting age-related conditions (Ribeiro-Rodrigues et al., 2023). EVs are composed of microvesicles and exosomes, which are crucial mediators of intercellular communication as they contain proteins, RNAs and microRNAs. Age-related modification in EVs composition includes abnormal protein aggregation, and modified microRNAs can alter cellular homeostasis and proteostasis (Bhunia and Kasturi, 2024; V. Wagner and Keller, 2024). EVs can either propagate damage or facilitate the repair mechanism process, depending on their cargo and their release (Romero-García et al., 2023). Additionally, modifications in ligand receptor interaction, which are very common in ageing, can also affect the immune response and tissue regeneration process (Chen et al., 2024; García-Domínguez, 2025).

Inflammageing, also referred to as chronic inflammation, is a significant cause of ageing, characterized by a persistent low-grade inflammatory condition that contributes to various age-related diseases. Chronic inflammation is widespread across almost all major diseases, as it is associated with immune dysfunction, dysbiosis, and cellular senescence. This created a cyclical association that alleviated the decline in health among the elderly population (Andonian et al., 2024; Baechle et al., 2023). Decreased thymic production and increased immune cell senescence are caused due to ageing, which ultimately leads to chronic inflammation (Saavedra et al., 2023). One study indicated that the other hallmark of ageing, dysbiosis, allows inflammatory factors to enter tissues and thus contributes to worsening of the inflammatory process (Tan and Norhaizan, 2021). Similarly, the association of altered nutrient sensing and chronic inflammation further increases the chances of age-related dysfunctions. Inflammageing also contributes to greater risks of cardiovascular diseases, neurodegenerative diseases, and cancer. Systematic inflammation also plays a crucial role in increasing mortality risk, as it correlates with biological ageing markers such as DNA methylation and age acceleration. Despite the notion that chronic inflammation is the key cause of ageing, some evidence suggests this is not always true and that it may differ across groups (McDade, 2023).

An imbalance in the composition of the gut microbiome is known as dysbiosis. It is linked to both ageing and systemic inflammation (Schmauck-Medina et al., 2022). Based on some studies, it is suggested that ageing might lead to a decline in good bacteria and microbial diversity, which can worsen age-related problems by increasing pathobionts (Kelso, 2024). According to D’Amico et al. (2024), centenarians exhibit a more resilient and diversified microbiome, which is considered one of the specific microbial fingerprints related to ageing. Dysbiosis can also cause inflammation, which can further influence conditions such as gastrointestinal disorders (Mathur et al., 2024; Ragonnaud and Biragyn, 2021). Therefore, altering the gut microbiome by dietary and lifestyle modifications can provide several treatment approaches to reduce dysbiosis and related health risks in older adults (D’Amico et al., 2024; Ragonnaud and Biragyn, 2021).

Mesenchymal Stem Cells (MSCs) were first characterized as adherent stromal progenitors which are multipotent, non-hematopoietic stem cells and have the potential to differentiate into several mesodermal forms, including adipocytes, osteoblasts, and chondrocytes (Friedenstein et al., 1970). They can also differentiate into endodermal and ectodermal lineages, demonstrating their vast differentiation potential in stem cell therapeutics, thereby making it a highly recommended and promising approach in regenerative medicine. It also possesses the ability to immunomodulate and self-renew (Lykov, 2023; Slaba, 2024). The therapeutic efficiency of MSC is mediated by the release of bioactive molecules such as cytokines, growth factors, and extracellular vesicles (EVs), which play critical roles in modulating the local cellular environment, promoting cell survival, tissue repair and angiogenesis, as well as exerting anti-inflammatory properties. MSCs can even interact with immune cells, including T-cells, B-cells, macrophages, and dendritic cells, to modulate the immune responses through direct cell-to-cell interactions and immunoregulatory chemicals and can inhibit inflammation (Han et al., 2025; Vohra and Arora, 2023). MSCs have also shown promise in treating conditions like liver fibrosis, diabetes, spinal cord injuries and COVID-19 (Aulia et al., 2024). And currently, they are being actively investigated for their potential as regenerative medicines to bring change to the medical world (Slaba, 2024).

Hematopoietic stem cells (HSCs) are multipotent adult stem cells capable of long-term self-renewal and differentiation into numerous mature blood cells, including myeloid lineage and lymphoid lineage cells (Till and McCulloch, 1961; Weissman, 2000; Lee and Hong, 2019; Tang et al., 2023). Since their functions are reduced with age, these HSCs can cause various health issues and hence are very critical to the ageing phenomenon. According to studies, HSCs increase their regenerative capacity, thereby reducing efficiency and, ultimately, declining in function as age increases. All these processes lead to the progression of various hematological diseases and lowered immunological responses (Fujino et al., 2022; Li X. et al., 2025). Also, ageing results in impaired self-renewal and reduced differentiation potential of HSCs, ultimately leading to a shift towards the myeloid lineage at the expense of lymphoid cells. Some factors, like oxidative stress and epigenetic modifications, can also contribute to the HSCs’ ageing process (Chatterjee and Thakur, 2021; Shevyrev et al., 2023). Niche ageing can also influence the cells, for instance, the bone marrow microenvironment, which can also age, thereby affecting the functions of HSCs and resulting in chronic inflammation, which exacerbates age-related diseases (Shevyrev et al., 2023; Zhang et al., 2024). Recent studies also showed that transplanting young HSCs into older mice reduces ageing traits, indicating a possible therapeutic pathway. Furthermore, platelet factor 4 (PF4) also plays a crucial role in sustaining HSCs’ function and declines with age. Restoring PF4 levels in aged mice has shown promising benefits for regenerating HSCs (Wang et al., 2025; Zhang et al., 2024).

Neural stem cells (NSCs) are stem cells found in the nervous system and, during development, form the nervous system. In adults, very few NSCs persist and are generally dormant; yet considerable evidence supports their critical functions in the nervous system, including ageing, diseases, plasticity, and regeneration (Zhao and Moore, 2018). Ageing can cause metabolic abnormalities, reduced genetic stability, and metabolic dysfunction, thereby reducing the regeneration potential of HSCs (Zhong et al., 2025). Age slows the transition of NSCs from the quiescent to the proliferative phase, leading to reduced neurogenesis and greater cognitive decline (Nicaise et al., 2020; Ruetz et al., 2024). Secretome therapy and stem cell transplantation are among the strategies that can open new frontiers in restoring NSC function and improving neurodegenerative symptoms (Zhong et al., 2025). Also, induced NSCs engineered through miR-302a have demonstrated delayed ageing and better cognitive functions in animal models, thereby offering insight into enhancing NSCs viability (Li Y. et al., 2023).

Pluripotent stem cells that are derived from adult somatic cells are known as induced pluripotent stem cells (iPSCs). They are reprogrammed into pluripotent cells by the stimulation of genes and factors (Ye et al., 2013). These iPSCs provide a model to study cellular mechanisms and thus contribute to understanding ageing and age-related disorders. Various studies have indicated that aged iPSCs exhibit impaired mitochondrial bioenergetics, leading to increased ROS generation. In addition to this, these stem cells have reduced mitochondrial mass and impaired mitochondrial networking as compared to the young iPSCs (Lejri et al., 2024). iPSCs can replicate various diseases pathology and help in the facilitation of the drug development process for the mimicked diseases and hence provide an upper hand in regenerative medicine approaches (Esteves et al., 2023; Jothi and Kulka, 2024).

iPSCs have also revolutionized in vitro research and offer great promise for regenerative medicines because of their unlimited expansion, genetic engineering, and somatic cell differentiation. The establishment of iPSCs from centenarians offers novel insights into lifespan and resistance to age-related disorders and their applications in human development and diseases, drug screening, and various cell therapies also show their growing potential in the field of regenerative medicine (Cerneckis et al., 2024; Dowrey et al., 2025).

Embryonic stem cells (ESCs) are unique pluripotent cells found in the inner cell mass of human blastocysts, an early stage of embryonic development. They disappear after the seventh day and form three germ layers. However, ESCs derived from blastocysts can be grown in the laboratory and proliferate indefinitely under the right conditions. These undifferentiated ESCs possess the ability to differentiate into all three germ layers (El-Hashash, 2021; National Research Council and Institute of Medicine Committee on the Biological and Biomedical Applications of Stem Cell Research, 2002). Research on human ESCs (hESCs) raises ethical concerns because the embryos used to derive ESCs are destroyed. These hESCs undergo numerous cellular, molecular, and epigenetic alterations as they age, and hence impacting their self-renewal and differentiation potential (Patni et al., 2021). In addition, hESCs can differentiate into several cell types making them possible treatment options for age-related disorders, organ failure as well as neurodegenerative diseases. Current research focuses on generating a pure hESCs-derived cell population for safer clinical applications (Whirledge et al., 2006; Yabut and Bernstein, 2011).

Apart from the hallmarks of ageing, intrinsic and extrinsic ageing can also influence stem cells, their normal functioning, and their regenerative potential. This functional decline can occur due to internal and external agents that progress with age, leading to improper tissue maintenance and an earlier onset of age-related disorders. DNA damage, telomere shortening, and loss of protein homeostasis are among the intrinsic factors that contribute to the progressive deterioration of stem cell function. Accumulation of DDR is a major contributor to stem cell ageing, which further leads to weakening of the rejuvenation potential of stem cells (Devaraj et al., 2021; Montazersaheb et al., 2022). Similarly, the shortening of telomeres with age restricts the replicative property of stem cells and leads to stem cell exhaustion (Hambright et al., 2020). Modification in epigenetic factors alters gene expression and stem cell behaviour (Montazersaheb et al., 2022). Also, altered mitochondrial function leads to increased oxidative stress and more ROS generation, which are the major contributors to stem cell senescence and the ageing process (Tian and Dai, 2021).

On the other hand, extrinsic factors, including alterations in the stem cell niche, chronic inflammation, circulating factors like cytokines and hormones and systemic metabolic changes, also have the same effect. The stem cell niche comprises the surrounding cells and the extracellular matrix. This is necessary to maintain stem cell functioning. Age-related abnormalities in niche composition can result in weakened and impaired signaling pathways, affecting cellular behaviors and regeneration (Nalapareddy et al., 2022; Perdiguero et al., 2023). Metabolic changes and inflammation can lead to an increase in ROS and hence can initiate senescence in stem cells (Tian and Dai, 2021; Hambright et al., 2020; Montazersaheb et al., 2022). Table 1 provides a comprehensive overview of the intrinsic and extrinsic ageing of stem cells in the context of the hallmarks of ageing and their significant effects on the stem cells.

Age-related alterations in tissue homeostasis include decreased stem cell function and increased chronic inflammation, leading to impaired tissue maintenance and regeneration. Tissue homeostasis can also be altered by different cellular and molecular changes with ageing and hence disrupts tissue equilibrium. Ageing also contributes to modification in the stem cell population as it reduces their numbers and alters the growth properties and thus impairs tissue regeneration (Ortells and Keyes, 2014). Certain stem cells, like intestinal or hematopoietic stem cells, can enhance DNA damage and decreased regenerative abilities as age progresses (Jones and Passegue, 2023). An increase in the myeloid-derived suppressor cells and regulatory T-cells leads to a condition where while protecting against severe damage, enhanced tissue degeneration also takes place (Salminen, 2021). Lymphatic efficiency can be lowered by decreased fluid balance and improper immune responses, leading to limited transfer of antigens and immune cells, resulting in weakened tissue integrity, and thus worsening the diseases associated with age (Baranwal and Rutkowski, 2019). Some studies revealed that specific changes related to age may also start tissue resilience under specific scenarios, thereby suggesting a complex relationship between tissue homeostasis and ageing (Pomatto and Davies, 2017).

Stem cell microenvironment plays as much of a role as other factors in maintaining stem cells’ health. Any loss in the stem cell niche due to ageing directly affects their functioning and tissue integrity. Due to the progression of ageing, the structural and functional abilities of the stem cell niche begin to compromise the regulatory mechanisms that are vital to the management of the stem cell growth and population. This loss is recognized by the modifications in signaling pathways, cellular interactions and spatial organization that further lead to worsening the regenerative capacity of the stem cells. The structural change can be the dislocation of niche nuclei, which results in spatial regulation of stem cells (Urman et al., 2023; Urman et al., 2024). It was observed in bone marrow that age-related declines in niche-derived factors like netrin-1, which is a critical regulator, result in the accumulation of DNA damage, further contributing to impaired functioning of stem cells by premature ageing phenotypes and impaired hematopoietic stem cell health (Ramalingam et al., 2023). The loss of niche integrity is linked with reduced stem cell activity, as demonstrated in both germline and hematopoietic stem cells, resulting in lower tissue homeostasis and regeneration capacity. Notably, the shift in germline stem cells caused by niche ageing affects their functional control, contributing to male reproductive problems (Farahzadi et al., 2023; La and Hobbs, 2020). Figure 1 shows the significant differences between the young and aged niche, along with how pathways like NF-κB, PI3K/AKT and TGF-β/SMAD can affect these stem cell niches, leading to a change in the microenvironment that ultimately results in worsening of the condition.

While ageing hallmarks impact various cell types, their functional effects are especially evident in stem cell populations, where accumulated molecular damage directly reduces regenerative capacity. In contrast to differentiated cells, stem cells must maintain long-term genomic integrity while remaining responsive to environmental signals, making them particularly susceptible to age-related dysfunction. Recent findings suggest that stem cell ageing results from both intrinsic damage buildup and niche-mediated signalling changes, rather than from singular molecular defects. For instance, epigenetic drift and mitochondrial dysfunction hinder stem cell self-renewal, while inflammatory environments disturb quiescence and lineage equilibrium (Rossi et al., 2008; Schultz and Sinclair, 2016).

Notably, various hallmark processes have a more significant impact on stem cell populations than on differentiated tissues. Cellular senescence and inflammatory signaling in the stem cell niche diminish regenerative capacity, while systemic metabolic changes additionally affect stem cell response to repair signals (Oh et al., 2014; López-Otín et al., 2023). These findings highlight the necessity of interpreting ageing biology from a stem cell-focused perspective, prioritizing functional outcomes over mere molecular descriptions. This method improves translational relevance and facilitates focused therapeutic strategies aimed at restoring regenerative potential rather than broadly altering ageing pathways.

Stem cell rejuvenation approaches have considerable clinical significance due to their potential to address the root cause of ageing instead of merely alleviating disease symptoms. Methods like senolytic therapy, stem cell preconditioning, epigenetic reprogramming and designed biomaterial niches have demonstrated potential in revitalising stem cell function and enhancing tissue repair ability in ageing organisms. Senolytic compounds such as dasatinib and quercetin have shown targeted elimination of senescent cells, leading to enhanced tissue repair and reduced inflammation in preclinical studies. Early-stage clinical trials have indicated enhanced physical function and lower frailty-related biomarkers post senolytic treatments, emphasising their potential for translation (Justice et al., 2019; Kirkland and Tchkonia, 2020). Similarly, EVs derived from stem cells are becoming important therapeutic options as they can transport bioactive molecules without the risks associated with direct stem cell transplants. EV-derived therapies have demonstrated promising outcomes in tissue repair, neuroprotection and inflammation management, indicating their potential for clinical application in age-associated disorders (Mendt et al., 2019; Phinney and Pittenger, 2017). Stem cell delivery systems supported by biomaterials and engineered niches improve the efficiency of engraftment and cell-survival, leading to better clinical outcomes in regenerative medicine fields like skin rejuvenation, musculoskeletal repair and cardiac regeneration (Cruz-Gonzalez et al., 2025; Sun et al., 2019). Additionally, using specific transcription factors for partial cellular reprogramming has demonstrated potential in reversing epigenetic ageing indicators and rejuvenating tissue function in experimental models thereby presenting a possible approach for delaying age-related decline (Ocampo et al., 2016). In general, these rejuvenation approaches have significant potential to enhance clinical outcomes in age-related conditions such as osteoarthritis, neurodegenerative diseases, cardiovascular issues and frailty. Nonetheless, extensive randomized clinical trials and prolonged safety assessments are still crucial prior to regular clinical applications.

Stem cells, particularly MSCs and iPSCs, are advancing to clinical trials as regenerative therapies for tissue loss, ischemic injury, immune-mediated diseases, and other various conditions. MSCs exhibit dual benefits: they differentiate into lineages of damaged tissues and secrete immunomodulatory trophic factors and extracellular vesicles that stimulate endogenous repair mechanisms. Clinical translation approaches have demonstrated safety and early efficacy indications in cardiac repair, osteoarthritis, chronic wounds, corneal and cartilage regeneration and some ageing-related indications like frailty and skin ageing. Understanding the functional enhancements reported in clinical trials on frailty and ageing is challenging due to variability in patient groups, outcome metrics and follow-up duration. Many studies have shown that improvements in physical performance measures have been limited, leading to ongoing debate over whether the observed benefits reflect true regenerative repair or transient immunomodulatory effects (Golpanian et al., 2017; Schulman et al., 2018; Tompkins et al., 2017). Standardizing endpoints and conducting longer-term assessments are crucial for addressing these uncertainties.

However, therapeutic results vary by cell source, dose, delivery route and even manufacturing quality. Major challenges, including engraft durability, pulmonary entrapment after intravenous delivery, and trial design variability, can constitute different efficacy conclusions. Ongoing randomized, controlled trials and longer follow-ups are addressing safety, standardized manufacturing, and mechanistic biomarkers to move the applications of stem cells to the next level, meaning approved, evidence-based treatments (Garay, 2023; Margiana et al., 2022). Recent clinical trials are provided in Table 2 for better understanding of the clinical applications of stem cells in the regenerative medicinal field.

Even with the promising experimental outcomes, the application of stem cell therapies in clinical environment is still inconsistent. Although various early-stage studies show safety and feasibility, effectiveness results vary significantly across various disease contexts. For instance, advancements in musculoskeletal repair tend to be modest and affected by factors like patient age, disease progression and delivery methods (Pittenger et al., 2019). Likewise, cardiovascular applications have produced varied functional improvements, highlighting the need for standardized endpoints and prolonged outcome monitoring (Terashvili and Bosnjak, 2019). These findings emphasize the importance of differentiating between mechanistic plausibility and clinically confirmed advantages when analyzing regenerative outcomes.

While rejuvenation strategies utilizing stem cells demonstrate considerable potential, the robustness of the evidence varies in different experimental models and clinical contexts. Many mechanistic insights come from in vitro systems, and small animal studies often highlight the improvements in tissue repair, inflammation regulation and functional recovery. Nevertheless, translating to human clinical results remains inconsistent due to biological complexity and differences in the study design. Clinical trials with MSCs have typically shown satisfactory safety profiles, but the therapeutic effectiveness varies significantly among different disease types. For instance, research on cardiovascular disease has indicated slight improvement in cardiac function metrics, but outcomes differ based on the method of delivery, selection of patients and protocols for cell preparation (Banerjee et al., 2018; Kahlon et al., 2018).

One major mechanistic uncertainty is whether the advantages of stem cells stem mainly from direct engraftment and differentiation or from paracrine signaling facilitated by secreted bioactive factors such as EVs and cytokines, Growing evidence supports the paracrine hypothesis, therefore, indicating that the modulation of inflammation and tissue repair through secretome may be primary therapeutic mechanism (Gnecchi et al., 2008; Levy et al., 2020). Another important key factor is the variability of clinical results among trials. Differences in stem cell origin, growth methods, dosage approaches and outcomes measures greatly affect the reported effectiveness. Numerous studies are still in Phase I or Phase II, concentrating mainly on safety instead of a clear therapeutic advantage (Trounson and McDonald, 2015). Consequently, although stem cell rejuvenation approaches demonstrate significant translational promise, existing evidence supports measured optimism, highlighting the necessity for standardized methods, extensive randomized trials, and prolonged follow-up to validate therapeutic efficacy as well as safety.

This review has various significant advantages that boost its scientific importance. It first combines recent developments in cell research with new rejuvenation approaches offering a thorough insight into the association between stem cell impairment and ageing processes. Additionally, the inclusion of clinical trial data reinforces the translation viewpoint and emphasizes current initiatives aimed at the therapeutic use. Moreover, the analysis systematically links molecular characteristics of ageing with regenerative strategies and thus providing mechanistic understanding for therapeutic targeting.

In spite of these advantages, there are some limitations that should be acknowledged. The review mainly relies on published studies which could lead to publication bias and limit the addition of unpublished or negative results. Also, the rapidly changing landscape of regenerative medicine indicates that certain new therapies may still lack adequate clinical validation. Additionally, differences in stem cell sources, delivery techniques and trial methodologies across research hinder the capacity to reach uniform conclusion about safety and effectiveness (Mahla, 2016; Trounson and McDonald, 2015). Another limitation lies in the heterogeneity of ageing processes among individuals and tissues, making it difficult to translate experimental results into standard clinical treatments. Future systematic reviews and meta-analyses that include standardized outcome measures are needed to strengthen evidence based clinical decisions in stem cell rejuvenation therapies.