Type 2 Diabetes Mellitus as a Multisystem Disease: From Insulin Resistance to Organ Crosstalk—A Narrative Review

Type 2 Diabetes Mellitus (T2DM) is a complex metabolic disorder characterized by insulin resistance, chronic low-grade inflammation, and progressive metabolic dysfunction affecting multiple organs. This review explores the molecular and physiological mechanisms underlying T2DM, emphasizing the role of intracellular metabolic signaling pathways, mitochondrial function, and inter-organ communication in the development and progression of metabolic dysregulation. Particular attention is given to key regulatory pathways such as AMP-activated protein kinase (AMPK) and the mechanistic target of rapamycin (mTOR), which play central roles in cellular energy sensing, glucose metabolism, and lipid homeostasis. Dysregulation of these pathways contributes to impaired insulin signaling, mitochondrial dysfunction, oxidative stress, and altered adipogenesis, all of which are critical factors in the pathophysiology of T2DM. In addition, growing evidence highlights the importance of metabolic crosstalk between skeletal muscle, adipose tissue, liver, pancreas, and the gut microbiota through signaling molecules including adipokines, myokines, hepatokines, and gut-derived metabolites. These inter-organ networks influence systemic inflammation, metabolic flexibility, and glucose homeostasis. Lifestyle factors such as physical activity, nutritional patterns, and micronutrient status have also been shown to modulate these molecular pathways, improving mitochondrial function and insulin sensitivity while reducing inflammatory signaling. Despite significant advances in understanding the molecular basis of T2DM, important challenges remain, including heterogeneity in disease progression and variability in individual metabolic responses. In conclusion, T2DM should be understood as a multisystem metabolic disorder driven by complex interactions between molecular signaling pathways and systemic metabolic regulation. Future research integrating molecular mechanisms with clinical and lifestyle interventions may help develop more effective strategies for prevention and treatment.