Glucose Level Fluctuations Induce Apoptosis of Human Mesangial Cells via PERK/CHOP Endoplasmic Reticulum Stress Pathway

Background Diabetic nephropathy (DN) is a major microvascular complication of diabetes and a leading precursor to end‐stage renal disease. Accumulating evidence suggests that blood glucose fluctuations exert a more profound pathogenic effect on diabetes‐related complications than sustained hyperglycemia. This study aimed to investigate the impact of different glucose conditions (low, high, and fluctuating glucose [FG]) on the apoptosis in human mesangial cells (HMCs) and explore the underlying role of the PERK/CHOP endoplasmic reticulum (ER) stress pathway. Methods HMCs were divided into five groups: normal glucose (NC, 11.11 mmol/L), hypertonic control (HOS, 11.11 mmol/L glucose + 18.89 mmol/L mannitol), continuous low‐glucose (LG, 3.3 mmol/L), continuous high‐glucose (HG, 30 mmol/L), and FG (alternating 3.3 mmol/L and 30 mmol/L every 12 h). After 48 h of intervention, Annexin V/PI double staining combined with flow cytometry and TUNEL staining was used to detect cell apoptosis. Western blot analysis was performed to quantify the expression levels of ER stress‐related proteins (PERK, phospho‐PERK, eIF‐2α, phospho‐eIF‐2α, and CHOP) and the pro‐apoptotic protein BAX. Results There was no significant difference in the apoptosis rate between the HOS group (8.11 ± 0.49%) and the NC group (7.55 ± 0.97%, p = 0.382). In contrast, the LG (14.64 ± 0.84%), HG (15.89 ± 1.22%), and FG (20.55 ± 0.94%) groups exhibited significantly increased apoptosis rates compared with the NC group (all p < 0.05). Notably, the apoptosis rate of the FG group was significantly higher than that of the LG group ( p = 0.027) and the HG groups ( p = 0.038). TUNEL staining confirmed similar results: the apoptotic index of the FG group (21.83 ± 1.15%) was significantly higher than that of the NC (7.85 ± 0.89%, p < 0.001), LG (15.17 ± 1.03%, p = 0.021), and HG (16.45 ± 1.32%, p = 0.032) groups. Western blot results revealed that compared with the NC group, the LG, HG, and FG groups had significantly upregulated expression of phospho‐PERK and phospho‐eIF‐2α (all p < 0.05). The relative expression level of phospho‐PERK in the FG group (1.42 ± 0.11) was significantly higher than that in the LG group (1.08 ± 0.09, p = 0.023) and the HG group (1.25 ± 0.10, p = 0.048). The relative expression level of phospho‐eIF‐2α in the FG group (1.56 ± 0.13) was significantly higher than that in the NC group (0.89 ± 0.07, p < 0.001), LG group (1.12 ± 0.08, p = 0.018), and HG group (1.28 ± 0.11, p = 0.022). CHOP expression in the FG group (1.38 ± 0.12) was significantly elevated compared with the NC (0.76 ± 0.06, p < 0.001), LG (0.83 ± 0.07, p = 0.031), and HG (0.91 ± 0.08, p = 0.027) groups. BAX expression was significantly increased in the HG group (1.19 ± 0.10, p = 0.021 vs. NC) and FG group (1.45 ± 0.12, p < 0.001 vs. NC) relative to the NC group (0.82 ± 0.06), with the FG group showing a more pronounced increase than the LG group (0.89 ± 0.07, p = 0.024) and HG group ( p = 0.037). Conclusion FG levels induce more severe ER stress and subsequent apoptosis in HMCs compared with sustained low or high glucose, which is mediated through the activation of the PERK/CHOP signaling pathway. These findings highlight the critical role of glucose variability in the pathogenesis of DN and provide a potential therapeutic target for the prevention and treatment of DN by targeting the PERK/CHOP ER stress pathway.