Acute hypoxia induces apoptosis of pancreatic β-cell by activation of the unfolded protein response and upregulation of CHOP

Abstract

The success of pancreatic β-cells transplantation to treat type 1 diabetes has been hindered by massive β-cell dysfunction and loss of β-cells that follows the procedure. Hypoxia-mediated cell death has been considered one of the main difficulties that must be overcome for transplantation to be regarded as a reliable therapy. Here we have investigated the mechanisms underlying β-cell death in response to hypoxia (1% O2). Our studies show that mouse insulinoma cell line 6 (Min6) cells undergo apoptosis with caspase-3 activation occurring as early as 2 h following exposure to hypoxia. Hypoxia induces endoplasmic reticulum stress in Min6 cells leading to activation of the three branches of the unfolded protein response pathway. In response to hypoxia the pro-apoptotic transcription factor C/EBP homologous protein (CHOP) is upregulated. The important role of CHOP in the apoptotic process was highlighted by the rescue of Min6 cells from hypoxia-mediated apoptosis observed in CHOP-knockdown cells. Culturing isolated pancreatic mouse islets at normoxia showed intracellular hypoxia with accumulation of hypoxia-inducible factor-1α and upregulation of CHOP, the latter one occurring as early as 4 h after isolation. Finally, we observed that pancreatic islets of type 2 db/db diabetic mice were more hypoxic than their counterpart in normoglycemic animals. This finding indicates that hypoxia-mediated apoptosis may occur in type 2 diabetes.

Involvement of a proapoptotic gene (BBC3) in islet injury mediated by cold preservation and rewarming

“…6D). As others have reported previously, hypoxia induces Bbc3 in the mouse pancreatic ␤-cell line MIN6 (45). We found an increase in both BBC3 mRNA and BBC3 protein in human islets cultured under hypoxia for 48 h (4.1 Ϯ 1.3-and 4.4 Ϯ 1.0-fold increase compared with preculture, respectively) and a great decrease in viability.…”

“…Bbc3 is known to be induced by hypoxia and oxidative stress in cultured islets, contributing to ␤-cell apoptosis (11,42,45). Our study has shown that cold preservation of human islets under hypoxic conditions does not change BBC3 mRNA expression, but rather, the subsequent rewarming in culture increases BBC3 mRNA.…”

“…High BBC3 mRNA levels in human islets are associated with poor graft function after transplantation in streptozotocin-induced diabetic NOD Scid mice. Studies have shown that Bbc3-mediated ␤-cell death is also associated with exposure to high glucose, endoplasmic reticulum (ER) stress, oxidative stress, and hypoxia through another Bcl-2 family protein, Bim (11,24,42,45). Involvement of Bbc3 in ischemia-reperfusioninduced apoptosis was reported in intestinal cells, cardiomyocytes, and cerebral cells (2,23,43,44).…”

Hypoxia reduces ER-to-Golgi protein trafficking and increases cell death by inhibiting the adaptive unfolded protein response in mouse beta cells

“…Glucose stimulation of beta cell oxygen consumption generates intracellular hypoxia leading to activation of hypoxia-inducible factors (HIFs) and upregulation of HIF-target genes in rodent and human islets (reviewed in [1]). The presence of hypoxia in vivo in the islets of animal models of type 2 diabetes [3][4][5][6][7][8] supports a role for hypoxic stress in beta cell apoptosis. Moreover, severe hypoxia in islet grafts contributes to beta cell apoptosis in the early post-transplantation period [9,10].…”

miR-577 inhibits pancreatic β-cell function and survival by targeting fibroblast growth factor 21 (FGF-21) in pediatric diabetes

“…Glucose plays an essential role in the control of β-cell secretory activity. Glucose metabolism leads to an increase in the ATP/ADP ratio, membrane depolarization, Ca 2+ influx, and stimulated insulin secretion (Zheng et al, 2012;Schaap et al, 2013;Wang et al, 2013).…”