Type 2 diabetes mellitus (T2DM) is characterized by progressive metabolic reprogramming in which lipid metabolism imbalance links nutrient excess to insulin resistance, organelle stress, and tissue dysfunction. Although mitochondria, the endoplasmic reticulum (ER), and lipid droplets (LDs) each have established roles in metabolic homeostasis, how their coordinated interactions govern lipid remodeling in T2DM remains incompletely defined, owing in part to the technical difficulty of resolving these highly dynamic contact sites in space and time. In this Review, we integrate current evidence on mito-ER-LD interactions in T2DM, spanning advances in omics, imaging, and biochemical approaches, and summarize their structural organization, regulatory machinery, tissue-specific remodeling, and therapeutic modulation. Emerging data identify this tri-organelle network as a central metabolic interface that couples phospholipid synthesis and trafficking, calcium flux, mitochondrial dynamics, LD biogenesis and turnover, fatty-acid oxidation, autophagy, and stress signalling. Disruption of this network, including mitochondria-associated ER membrane (MAM) instability, altered balance between cytoplasmic and peridroplet mitochondria, and pathological LD expansion, reprograms lipid handling across liver, adipose tissue, skeletal muscle, and pancreatic β cells, thereby promoting lipotoxicity, oxidative and ER stress, mitochondrial dysfunction, β-cell failure, and systemic insulin resistance. Notably, glucose-lowering drugs and lifestyle interventions may exert part of their metabolic benefit by restoring organelle crosstalk and re-establishing lipid homeostasis. Together, this Review positions mito-ER-LD contact sites not simply as structural interfaces, but as core nodes that regulate lipid metabolic reprogramming in T2DM, thereby providing a mechanistic framework for targeting organelle crosstalk in metabolic disease.
