The Edges of Pancreatic Islet β Cells Constitute Adhesive and Signaling Microdomains

Pancreatic islet β cells are organized in rosette-like structures around blood vessels and exhibit an artery-to-vein orientation, but they do not display the typical epithelial polarity. It is unclear whether these cells present a functional asymmetry related to their spatial organization. Here, we identify murine β cell edges, the sites at which adjacent cell faces meet at a sharp angle, as surface microdomains of cell-cell adhesion and signaling. The edges are marked by enrichment of F-actin and E-cadherin and are aligned between neighboring cells. The edge organization is E-cadherin contact dependent and correlates with insulin secretion capacity. Edges display elevated levels of glucose transporters and SNAP25 and extend numerous F-actin-rich filopodia. A similar β cell edge organization was observed in human islets. When stimulated, β cell edges exhibit high calcium levels. In view of the functional importance of intra-islet communication, the spatial architecture of their edges may prove fundamental for coordinating physiological insulin secretion

Serine Phosphorylation Proximal to Its Phosphotyrosine Binding Domain Inhibits Insulin Receptor Substrate 1 Function and Promotes Insulin Resistance

Ser/Thr phosphorylation of insulin receptor substrate (IRS) proteins negatively modulates insulin signaling. Therefore, the identification of serine sites whose phosphorylation inhibit IRS protein functions is of physiological importance. Here we mutated seven Ser sites located proximal to the phosphotyrosine binding domain of insulin receptor substrate 1 (IRS-1) (S265, S302, S325, S336, S358, S407, and S408) into Ala. When overexpressed in rat hepatoma Fao or CHO cells, the mutated IRS-1 protein in which the seven Ser sites were mutated to Ala (IRS-1(7A)), unlike wild-type IRS-1 (IRS-1(WT)), maintained its Tyr-phosphorylated active conformation after prolonged insulin treatment or when the cells were challenged with inducers of insulin resistance prior to acute insulin treatment. This was due to the ability of IRS-1(7A) to remain complexed with the insulin receptor (IR), unlike IRS-1(WT), which underwent Ser phosphorylation, resulting in its dissociation from IR. Studies of truncated forms of IRS-1 revealed that the region between amino acids 365 to 430 is a main insulin-stimulated Ser phosphorylation domain. Indeed, IRS-1 mutated only at S408, which undergoes phosphorylation in vivo, partially maintained the properties of IRS-1(7A) and conferred protection against selected inducers of insulin resistance. These findings suggest that S408 and additional Ser sites among the seven mutated Ser sites are targets for IRS-1 kinases that play a key negative regulatory role in IRS-1 function and insulin action. These sites presumably serve as points of convergence, where physiological feedback control mechanisms, which are triggered by insulin-stimulated IRS kinases, overlap with IRS kinases triggered by inducers of insulin resistance to terminate insulin signaling

Cognate microglia-T cell interactions shape the functional regulatory T cell pool in experimental autoimmune encephalomyelitis pathology

Microglia, the parenchymal brain macrophages of the central nervous system, have emerged as critical players in brain development and homeostasis. The immune functions of these cells, however, remain less well defined. We investigated contributions of microglia in a relapsing-remitting multiple sclerosis paradigm, experimental autoimmune encephalitis in C57BL/6 x SJL F1 mice. Fate mapping-assisted translatome profiling during the relapsing-remitting disease course revealed the potential of microglia to interact with T cells through antigen presentation, costimulation and coinhibition. Abundant microglia-T cell aggregates, as observed by histology and flow cytometry, supported the idea of functional interactions of microglia and T cells during remission, with a bias towards regulatory T cells. Finally, microglia-restricted interferon-γ receptor and major histocompatibility complex mutagenesis significantly affected the functionality of the regulatory T cell compartment in the diseased central nervous system and remission. Collectively, our data establish critical non-redundant cognate and cytokine-mediated interactions of microglia with CD4+ T cells during autoimmune neuroinflammation