Streptozotocin induces renal proximal tubular injury through p53 signaling activation.

Streptozotocin (STZ), an anti-cancer drug that is primarily used to treat neuroendocrine tumors (NETs) in clinical settings, is incorporated into pancreatic ß-cells or proximal tubular epithelial cells through the glucose transporter, GLUT2. However, its cytotoxic effects on kidney cells have been underestimated and the underlying mechanisms remain unclear. We herein demonstrated that DNA damage and subsequent p53 signaling were responsible for the development of STZ-induced tubular epithelial injury. We detected tubular epithelial DNA damage in NET patients treated with STZ. Unbiased transcriptomics of STZ-treated tubular epithelial cells in vitro showed the activation of the p53 signaling pathway. STZ induced DNA damage and activated p53 signaling in vivo in a dose-dependent manner, resulting in reduced membrane transporters. The pharmacological inhibition of p53 and sodium-glucose transporter 2 (SGLT2) mitigated STZ-induced epithelial injury. However, the cytotoxic effects of STZ on pancreatic ß-cells were preserved in SGLT2 inhibitor-treated mice. The present results demonstrate the proximal tubular-specific cytotoxicity of STZ and the underlying mechanisms in vivo. Since the cytotoxic effects of STZ against ß-cells were not impaired by dapagliflozin, pretreatment with an SGLT2 inhibitor has potential as a preventative remedy for kidney injury in NET patients treated with STZ.

Direct evidence of proximal tubular proliferation in early diabetic nephropathy.

Kidney hypertrophy is a common clinical feature in patients with diabetes and is associated with poor renal outcomes. Initial cell proliferation followed by cellular hypertrophy are considered the responsible mechanisms for diabetic kidney hypertrophy. However, whether similar responses against hyperglycemia continue in the chronic phase in diabetes is unclear. We performed lineage tracing analysis of proximal tubular epithelia using novel type 2 diabetic mice with a tamoxifen-inducible proximal tubule-specific fluorescent reporter. Clonal analysis of proximal tubular epithelia demonstrated that the labeled epithelia proliferated in type 2 diabetic mice. Based on the histological analysis and protein/DNA ratio of sorted labeled tubular epithelia, there was no evidence of cellular hypertrophy in type 2 diabetic mice. Lineage tracing and histological analyses of streptozocin-induced type 1 diabetes also revealed that cellular proliferation occurs in the chronic phase of type 1 diabetes induction. According to our study, epithelial proliferation accompanied by SGLT2 upregulation, rather than cellular hypertrophy, predominantly occurs in the hypertrophic kidney in both type 1 and type 2 diabetes. An increased number of SGLT2+ tubular epithelia may be an adaptive response against hyperglycemia, and linked to the hyper-reabsorption of sodium and glucose observed in type 2 diabetes patients.