BACKGROUND: Mulberry (Morus alba L.) leaf is a Chinese herb used clinically to treat type 2 diabetes mellitus (T2DM) and has been proven to improve T2DM by regulating gut microbiota dysbiosis. However, it is currently unclear whether mulberry leaf can improve intestinal inflammation and metabolic dysfunction by restoring gut microbiota to promote short-chain fatty acids (SCFAs) level and thus activate relevant signaling pathways.
PURPOSE: This work aimed to explore the role that microbiota-SCFAs-G protein-coupled receptors (GPRs) signaling pathway plays in the anti-T2DM effect of mulberry leaf.
METHODS: Mice with T2DM, induced by intraperitoneal injection of streptozotocin after four weeks of high-fat and high sucrose diet, were randomly allocated to receive mulberry leaf water extract (MLWE) and ethanol extract (MLEE), metformin (Glucophage), or distilled water for ten consecutive weeks. Changes in metabolic parameters, pro-inflammatory cytokines, fecal microbiota, and bacterial metabolites (lipopolysaccharide (LPS) and SCFAs), were detected. Furthermore, microbiota deprivation was performed to confirm the anti-diabetic effect of MLWE-regulated gut microbiota in pseudo-germ-free T2DM mice.
RESULTS: MLWE and/or MLEE could enhance insulin sensitivity via activating GPR43/109A in colon and adenosine 5'-monophosphate-activated protein kinase (AMPK) pathway in liver, improving the expression of pro-inflammatory factors such as tumor necrosis factor α, interleukin (IL)-1β, IL-6 and IL-10 in liver, elevating intestinal barrier to decrease circular LPS level via enhancing the expression of tight junction proteins such as Zonula occludens-1 and Occludin, and decreasing intestinal inflammation via inhibiting toll-like receptor 9- myeloid differentiation primary response protein 88- interferon-γ signaling pathway in colon, accompanying by the increased abundances of beneficial bacteria, such as Akkermansia, Bifidobacterium, Dubosiella, and Muribaculaceae_unclassified, and the decreased abundances of harmful bacteria, such as Acetatifactor, Clostridiales_unclassified, Colidextribacter, Desulfovibrionaceae_unclassified, GCA-900066575, Lacchnospiraceae_unclassified, Lachnospiraceae_NK4A136_group, Oscillibacter, Murinomas, and Tuzzerella, and the corresponding elevation of fecal SCFAs levels in T2DM mice.
CONCLUSIONS: Gut microbiota-SCFAs-GPRs axis and AMPK pathway may involve in the alleviation of inflammation and insulin resistance in T2DM mice intervened with mulberry leaf, which provides new insights to elucidate the potential mechanism of mulberry leaf in the treatment of T2DM.
