FC 132: Deficiency of Proximal Tubular Cyclin-Dependent Kinase 12 Exacerbates Kidney Injury Through DNA-Damage Response

Abstract

Abstract BACKGROUND AND AIMS Acute kidney injury (AKI) is a frequent, serious condition characterized by acute tubular necrosis involving the destruction of tubular epithelial cells. Recent studies have shown that DNA damage contributes to renal tubular cell death during kidney injury. Cyclin-dependent kinase 12 (CDK12) is a member of the cyclin-dependent kinase family that phosphorylates the carboxy-terminal domain of RNA polymerase II and selectively regulates transcription of DNA-damage response (DDR) genes. CDK12 inhibitor was reported to play an important role in a variety of cancers. So far, the functions of CDK12 deficiency in the pathogenesis of AKI have not been studied. METHOD Here, we established a cisplatin-induced AKI mouse model with CDK12 knockdown mice and created stable in vitro models with CDK12 knockdown tubular epithelial cells. Cisplatin nephrotoxicity was induced by intraperitoneal injection of cisplatin (20 mg/kg). After 2 days following cisplatin treatment, blood and kidney tissues were harvested. Renal function and histology were evaluated. DDR, tubular apoptosis, cell proliferation were evaluated by immunofluorescence assays, real-time PCR, flow cytometer and western blot analysis. RESULTS Here we found that CDK12 was downregulated in the renal tubular epithelial cells of AKI patients and murine AKI models and associated with kidney functions. RNA-sequencing of kidney cortex demonstrated increased transcripts involved in DDR and tubular apoptosis signaling pathways and decreased transcripts cell proliferation pathways, in knockout versus control mice. Moreover, more severe AKI occurred in tubular cell-specific knock-down of CDK12 mice (CDK12RTEC+/–) than age- and sex-matched wild type mice, as evidenced by increased levels of serum creatinine (Scr), blood urea nitrogen (BUN) and tubular injury score. Mechanistically, CDK12 deficiency accelerated cisplatin-induced DDR, mitochondrial apoptosis and abrogates cell proliferation of renal tubular cells in these mice. Similar results were observed after the human renal tubular epithelial cell line HK-2 cells exposure to CDK12 siRNA stimulation. In contrast, lentivirus-mediated CDK12 overexpression protected against DDR and mitochondrial apoptosis while attenuating renal dysfunction, morphological damage and renal tubular cell death in cisplatin-induced AKI models. Moreover, representative Integrative Genomics Viewer (IGV) profiles demonstrated a minimal impact of gene length-dependent elongation defects, a substantial proportion of which participate in the DDR and cell proliferation. CONCLUSION Thus, proximal tubule-specific deficiency of CDK12 exacerbates acute kidney injury and tubular apoptosis, likely due to affecting the expression of genes involved in the DDR and mRNA processing.