Islet inflammatory macrophages drive MSC loss and multiple interactions involved in β-cell adaptation during diabetes

While the functional adaptation of β-cells during type 2 diabetes progression is well-established, the role of non-β islet cells remains largely unexplored. Utilizing single-cell RNA sequencing, we identified a substantial expansion of the macrophage population and a concomitant reduction in the proportion of mesenchymal stem cells (MSCs) within the islets of diabetic mice transitioning from metabolic compensation to decompensation. Under conditions of metabolic stress, macrophages extensively infiltrated the islets and adopted a pronounced pro-inflammatory phenotype. This phenotypic shift impaired β-cell glucose-stimulated insulin secretion and induced β-cell apoptosis. Simultaneously, macrophage-derived inflammatory factors, notably TNF-α, suppressed MSC proliferation and downregulated Wntless (Wls), thereby reducing extracellular Wnt transport. The resultant loss of Wls diminished MSCs' capacity to provide trophic support to β-cells and hindered the transition of macrophages to an anti-inflammatory phenotype. This self-perpetuating cycle establishes a chronic pro-inflammatory environment within the islets, culminating in β-cell functional deterioration and the onset of diabetes. Experimental intervention involving macrophage elimination and MSC administration was shown to disrupt this detrimental cycle, restoring β-cell function and glycemic control. Collectively, our findings reveal that macrophages and MSCs jointly govern β-cell adaptation through intricate paracrine crosstalk. Modulating these macrophage-MSC interactions holds significant therapeutic implications for maintaining β-cell integrity and underscores the considerable potential of MSC-based therapies for type 2 diabetes treatment.