Lactogens Prevent ER Stress-Induced ß-Cell Death and Diabetes

ER stress is highly relevant in the context of diabetes, as inducers of β cell death and dysfunction implicated in the disease - including proinflammatory cytokines and glucolipotoxicity - are known to impair ER function. Previous work has shown that prolactin (Prl) and placental lactogen (PL), which bind to the same receptor (Prl-R), are important for β cell function and proliferation, and enhance survival against cytokines and glucolipotoxicity. Here, we examine the effect of Prl/PL directly on ER stress and the associated unfolded protein response (UPR) in the β cell. ER stress was induced in vitro via tunicamycin in INS1, primary mouse, and primary human β cells, concurrent with Prl/veh treatment. Expression of ER stress and UPR associated genes was measured via qRT-PCR and preliminarily via WB, and insulin-TUNEL co-staining was used to assay for β cell death. As an in vivo model, heterozygous Akita mice - a well-established β cell ER stress model which becomes diabetic by 4 weeks of age - were bred to single-transgenic mice overexpressing PL in the β cell. Prl increases survival of INS1, primary mouse and human β cells against ER stress-mediated cell death in vitro (2.34±0.19% TM vs. 0.73±0.19% TM+Prl, human). Differences in mRNA expression point towards modulation of the PERK/IRE1 UPR arms. Non-Tg Akita mice quickly become and remain hyperglycemic/diabetic, while overexpression of PL in the β cells of these mice significantly improves glycemia in males (663±29mg/dL non-Tg vs. 327±37mg/dL Tg, 12 weeks) and results in normoglycemia in females. In vivo GSIS at 12 weeks shows a trend towards restoration of β cell function in Tg compared to non-Tg Akita mice. Males at this age exhibit improved β cell mass (0.28±0.12mg non-Tg vs. 2.29±0.44mg Tg), with similar trends in β cell proliferation. Taken together, these data demonstrate that Prl/PL can prevent and protect against ER stress in the β cell, in vitro and in vivo. As ER stress is highly relevant to diabetes, modulation of the lactogenic pathway could present a novel therapy for this disease.