Glucose and Endoplasmic Reticulum Calcium Channels Regulate HIF-1β via Presenilin in Pancreatic β-Cells

Abstract

Pancreatic ␤-cell death is a critical event in type 1 diabetes, type 2 diabetes, and clinical islet transplantation. We have previously shown that prolonged block of ryanodine receptor (RyR)-gated release from intracellular Ca 2؉ stores activates calpain-10-dependent apoptosis in ␤-cells. In the present study, we further characterized intracellular Ca 2؉ channel expression and function in human islets and the MIN6 ␤-cell line. All three RyR isoforms were identified in human islets and MIN6 cells, and these endoplasmic reticulum channels were observed in close proximity to mitochondria. Blocking RyR channels, but not sarco/endoplasmic reticulum ATPase (SERCA) pumps, reduced the ATP/ADP ratio. Blocking Ca 2؉ flux through RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of hypoxia-inducible factor (HIF-1␤). Moreover, inhibition of RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of presenilin-1. Both HIF-1␤ and presenilin-1 expression were also induced by low glucose. Overexpression of presenilin-1 increased HIF-1␤, suggesting that HIF is downstream of presenilin. Our results provide the first evidence of a presenilin-HIF signaling network in ␤-cells. We demonstrate that this pathway is controlled by Ca 2؉ flux through intracellular channels, likely via changes in mitochondrial metabolism and ATP. These findings provide a mechanistic understanding of the signaling pathways activated when intracellular Ca 2؉ homeostasis and metabolic activity are suppressed in diabetes and islet transplantation.

Roles of IP3R and RyR Ca2+ Channels in Endoplasmic Reticulum Stress and β-Cell Death

“…We have previously shown that longterm inhibition of RyR2 in low glucose leads to programmed ␤-cell death involving calpain-10, but not caspase-3; conversely, RyR inhibition protected islets under conditions of chronic hyperglycemia (17). We have also shown that RyR inhibition significantly reduces the ratio of ATP to ADP in MIN6 ␤-cells (23), an event that could conceivably activate ER stress (24,25). Furthermore, studies of other cells types have suggested that ER stressassociated damage can be affected by inhibitors of RyRs (26) or IP 3 Rs (27).…”

“…MIN6 cells were cultured and transfected as described previously (23). Cells were imaged 48 -72 h after transfection.…”

Roles of Hypoxia-Inducible Factor-1α (Hif-1α) Versus Hif-2α in the Survival of Hepatocellular Tumor Spheroids

“…Furthermore, HIF-1b expression was enhanced in perinecrotic areas of spheroids, presumably as a result of glucose deficiency, which accompanies hypoxia in spheroids and is known to induce HIF-1b expression. 18 Importantly, the knockdown of one a-subunit increased the expression of the other a-subunit. Spheroids lacking one a-subunit displayed growth and survival advantages as compared to both WT and b-knockdown spheroids.…”

Ca2+-induced Ca2+Release from Internal Stores in INS-1 Rat Insulinoma Cells

“…In fact, the presence of RyRs in insulin secreting β-cells is well-accepted at the present time, although the expression of each type of RyRs is variable, depending on the species studied. The mRNAs for the three types of RyRs have been detected in human β-cells, whereas mRNA for RyR2 but not RyR1 was detected in INS-1 cells and rat islets using RT-PCR methods [18][19][20]. Since there is still no clear consensus on the role of RyR in stimulus-secretion coupling in β-cells, we determined, using in-sulin secreting rat pancreatic β-cells (INS-1 …”