Type 2 Diabetes and Congenital Hyperinsulinism Cause DNA Double-Strand Breaks and p53 Activity in β Cells

Abstract

β cell failure in type 2 diabetes (T2D) is associated with hyperglycemia, but the mechanisms are not fully understood. Congenital hyperinsulinism caused by glucokinase mutations (GCK-CHI) is associated with β cell replication and apoptosis. Here, we show that genetic activation of β cell glucokinase, initially triggering replication, causes apoptosis associated with DNA double-strand breaks and activation of the tumor suppressor p53. ATP-sensitive potassium channels (KATP channels) and calcineurin mediate this toxic effect. Toxicity of long-term glucokinase overactivity was confirmed by finding late-onset diabetes in older members of a GCK-CHI family. Glucagon-like peptide-1 (GLP-1) mimetic treatment or p53 deletion rescues β cells from glucokinase-induced death, but only GLP-1 analog rescues β cell function. DNA damage and p53 activity in T2D suggest shared mechanisms of β cell failure in hyperglycemia and CHI. Our results reveal membrane depolarization via KATP channels, calcineurin signaling, DNA breaks, and p53 as determinants of β cell glucotoxicity and suggest pharmacological approaches to enhance β cell survival in diabetes.

β Cell–specific increased expression of calpastatin prevents diabetes induced by islet amyloid polypeptide toxicity

“…In the context of hIAPP toxicity in hTG mice, the Nrf2 pathway was suppressed by calpastatin in hTG:hCAST mice, implying that hIAPP-induced oxidative stress is overcome by suppression of calpain hyperactivation ( Figure 5A). These data were consistent with the presence of increased β cell DNA damage detected by histone H2AX phosphorylation (P-H2AX), a marker of double-strand break repair (37), in hTG mice compared with WT controls (0.94% ± 0.18% vs. 0.31% ± 0.05%, P < 0.001; Figure 5B). Calpastatin-mediated suppression of calpain hyperactivation suppressed the hIAPP-induced DNA damage (0.22% ± 0.06%, P < 0.001 vs. hTG; Figure 5, B and C), further supporting the importance of calpain hyperactivation in oxidative stress.…”

“…Mitochondrial network disruption and dysfunction with increased ROS generation and DNA damage are prominent in protein misfolding diseases and are characteristic of β cells in both humans with T2D and hIAPP transgenic models of T2D (27,37). This disruption might be mediated directly by the membrane-permeable toxic oligomers, by hyperactivated calpains (45,46), and by Ca 2+ overload as a result of dysregulated ER Ca 2+ leakage (47), particularly if the latter were to occur at the mitochondrial endoplasmic reticulum membrane interface.…”

Aurora Kinase A is critical for the Nkx6.1 mediated β-cell proliferation pathway

“…24,25 In addition, a recent study demonstrated that a gain of function mutation of glucokinase results in increased b-cell proliferation that corresponds with increased apoptosis rates. 26 To determine the effect of AURKA overexpression on b-cell apoptosis rates, we measured the percentage of phosphorylated histone gH2AX positive primary rat islet b-cells. Phosphorylated histone gH2AX staining is an indicator of DNA double-strand breaks that are observed during apoptosis.…”

Advances in β cell replacement and regeneration strategies for treating diabetes

“…Glucose metabolism is required for β cell proliferation, as lack of glucokinase, a key enzyme in glycolysis that converts glucose to glucose-6-phosphate, decreases β cell proliferation whereas treatment with a small-molecule glucokinase activator stimulates β cell proliferation (104). However, the pro-proliferative effect of glucose is only observed in the short term, while sustained exposure of β cells to high glucose can cause glucotoxicity, resulting in DNA damage and apoptosis, as also seen in β cells from T2D patients (105). Therefore, there is a need to better understand where the mitogenic and DNA damage pathways diverge before the glucose-induced mitogenic pathway can be considered for therapeutic intervention.…”