Approximately 1.25 million Americans have type 1 diabetes mellitus (T1DM), resulting from autoimmune β-cell destruction: there is no known way to prevent such destruction of β-cells. We have already reported that activation of cannabinoid 1 receptor (CB1R) contributes to the pathogenesis of pancreatic β-cell dysfunction during high fat feeding. To uncover if CB1R signaling might influence toxin-induced β-cell injury, we induced β-cell destruction in wild type mice (WT: n=8) and in mice in which CB1R was genetically nullified in β-cells only (β-CB1R-/-: n=8) in adulthood by five daily injections of streptozotocin (STZ; 50 mg/kg intraperitoneally [IP]), a toxin selective for β-cells. We found that β-CB1R-/- mice had random blood glucose (BG) levels in the range of 137-220 mg/dL throughout the study period (28 days following STZ) as well as preserved insulin secretion with superior glucose tolerance after a glucose challenge (2g/kg) at day 8, 15 or 27, relative to their WT littermates (random BG 500-600 mg/dL). CB1R-deficient β-cells exhibited significant increases in autophagy flux following STZ. We determined that mice or β-cells lacking CB1R had reduced mTOR activation and increased nuclear translocation of TFEB, a key prerequisite for lysosome biogenesis and autophagy. Importantly, we found that CB1R deletion protected against oxidative stress, endoplasmic reticulum stress, and prevented the induction of apoptosis by STZ. These anti-stress functions were accompanied by increased phosphorylation of AKT (ser) 473 and ERK1/2 in β-cells, which reveals a previously unrecognized route for mTOR/AKT axis to regulate autophagy that coordinately is permissive to β-cell survival. We conclude that CB1R nullification confers resistance to pancreatic β-cell dysfunction by upregulating autophagy and subsequently antagonizing the decline in lysosomal activity. Altogether, we propose that CB1R is a potential therapeutic target during the honeymoon phase of T1DM.
K. Aseer: None. J.F. O’Connell: None. J.M. Egan: None.
