Laminin-511 protects pancreatic β-cells from cytokine-induced death through integrin-mediated pro-survival signaling and modulation of protein kinase C δ

During the progression of type 1 diabetes (T1D), the extracellular matrix (ECM) surrounding pancreatic islets is degraded concurrent with infiltration of autoreactive immune cells and β-cell death. Among the lost ECM proteins, laminin-511 is known to be essential for islet survival under healthy and T1D associated conditions, including high levels of pro-inflammatory cytokines. However, the key β-cell signaling pathways regulated by laminin and the contributions to T1D pathogenesis when these cues are lost are poorly understood. This study utilizes a biomimetic reverse thermal gel (RTG) with laminin-511 to determine if laminin protects β-cells against cytokine-induced death and elucidate the signaling pathways involved. MIN6 cells, C57Bl/6 mouse islets and human islets were encapsulated in RTG scaffolds with laminin-511 and treated with a cytokine cocktail for 24 hours. Islet viability and the activities of several pro- and anti-apoptotic proteins were studied. Laminin-511 was shown to protect islets against cytokine-induced death by interacting with β1 integrins and activating pro-survival Akt signaling. Pro-survival signaling was mediated by reduced activity of protein kinase Cδ (PKCδ), a key mediator of cytokine-induced β-cell death, at the cell membrane in the presence of laminin via reduced levels of diacylglycerol (DAG), a canonical activator of PKCδ. Taken together, these results demonstrate that laminin-511 is an essential factor in protecting β-cells against cytokine-induced death by downregulation of membrane DAG, inhibiting activation of pro-apoptotic PKCδ. Our results suggest that loss of ECM in T1D may make β-cells more susceptible to cytokine-induced death by increasing activation of PKCδ.