Islets are surrounded by a specialized extracellular matrix (ECM). Interactions with the peri-islet ECM, specifically laminin, promote islet viability and function. In T1D during immune infiltration the peri-islet ECM is broken down and β-cell death occurs in part through production of high levels of Th1 cytokines. Recent work has shown that cytokines alter islet function via protein kinase C Δ (PKCΔ) dependent mechanisms and that islet interactions with laminin reduce PKCΔ activity. We hypothesize that laminin-islet interactions protect against cytokine-mediated β-cell death via downregulation of PKCΔ. To test our hypothesis, we used a 3D reverse thermal gel (RTG) scaffold with either laminin-10 (RTG-Lam) or lysine (RTG-Lys) as a control. Islets were isolated from WT or mice with an inducible β-cell specific PKCΔ knockout (PKCΔ-βKO) and encapsulated in RTG-Lam and RTG-Lys for 24hrs with or without cytokines (10ng/mL TNF-α, 5ng/mL IL-1β, 100ng/mL IFN-γ). Viability, PKCΔ translocation, and PKCΔ activity were measured in encapsulated islets in situ using fluorescent biosensors or by western blot. PKCΔ-βKO islets were protected against cytokine-induced death compared to controls (p=0.003). Cytokines increased β-cell death in RTG-Lys (p<0.001), while islets encapsulated in RTG-Lam were protected against cytokine-mediated death (p<0.04). Islets encapsulated in RTG-Lam had reduced PKCΔ activity at the cell membrane compared to RTG-Lys and were also protected against cytokine-mediated increases in PKCΔ activity at the cell membrane.
In summary, islet interactions with laminin protect against cytokine-induced β-cell death via downregulation of PKCΔ activity at the cell membrane. Our results suggest that loss of islet interactions with laminin, as occurs in T1D, may make islets more susceptible to cytokine-mediated death. This mechanism of β-cell death provides a novel therapeutic target to prevent β-cell death and halt the progression of T1D.
N.L. Farnsworth: None. R.A. Piscopio: None. R.K. Benninger: None.
JDRF (3-APF-2019-749-A-N, 1-FAC-2020-891-A-N); Colorado Clinical and Translational Sciences Institute (CO-M-19-133)