Involvement of the CDKL5-SOX9 signaling axis in rhabdomyolysis-associated acute kidney injury

Abstract

Acute kidney injury (AKI) is a common clinical syndrome associated with adverse short and long-term sequelae. Renal tubular epithelial cell (RTECs) dysfunction and cell death are among the key pathological features of AKI. Diverse systemic and localized stress conditions such as sepsis, rhabdomyolysis, cardiac surgery, and nephrotoxic drugs can trigger RTEC dysfunction. Through an unbiased RNAi screen, we recently identified cyclin-dependent kinase-like 5 (Cdkl5) also known as serine/threonine kinase 9 as a critical regulator of RTEC dysfunction associated with nephrotoxic and ischemia-associated AKI. In the current study, we have examined the role of Cdkl5 in rhabdomyolysis-associated AKI. Using activation-specific antibodies and kinase assays, we found that Cdkl5 is activated in RTECs, early during the development of rhabdomyolysis-associated AKI. Furthermore, we found that RTEC-specific Cdkl5 gene ablation mitigates rhabdomyolysis-associated renal impairment. In addition, a small molecule kinase inhibitor AST-487 alleviated rhabdomyolysis-associated AKI in a Cdkl5-dependent manner. Mechanistically, we demonstrate that Cdkl5 phosphorylates the transcriptional regulator Sox9 and suppresses its protective function under stress conditions. Based on these studies we propose that by suppressing the protective Sox9-directed transcriptional program, Cdkl5 contributes to rhabdomyolysis-associated renal impairment. Together, these studies have identified Cdkl5 as a critical stress-induced kinase that drives RTEC dysfunction and kidney injury linked with distinct etiologies.

CDKL5: a promising new therapeutic target for acute kidney injury?

“…These genes are notable in that they have been shown to regulate several prosurvival pathways on nonrenal epithelia. Furthermore, they showed that this prosurvival, Sox-9-dependent transcriptional signature was activated and inhibited, respectively, in the kidneys of PTEC-specific Cdkl5 and Sox9-null mice after IRI-, cisplatin-, and rhabdomyolysis-induced AKI (5,6). These findings are consistent with the authors' conclusion that Sox9 acts downstream of Cdkl5 to mediate the cytoprotective effects of Cdkl5 inhibition after AKI.…”

“…Certainly, the two papers from the Pabla laboratory provide strong genetic and pharmacological data that Cdkl5 is a druggable candidate target for therapeutic intervention in AKI. The fact that this has been shown in at least three different models of AKI (5,6), and that there is genetic evidence that CDKL5 gene polymorphisms are risk factors for CKD progression (4), suggest that CDKL5 is likely to be involved in the heterogeneous pathobiology of injury in patients with AKI. However, in my opinion, a number of important questions remain to be answered before these findings are translated from the bench to the bedside:…”

“…In a kinome-wide siRNA screen, Kim et al (6) identified Cdkl5 as a kinase that when knocked down, increased viability of a cultured mouse proximal tubular epithelial cell (PTEC) line treated with cisplatin. Using phospho-specific Cdkl5 antibodies (pT169 Cdkl5) and in vitro kinase assays, they demonstrated that Cdkl5 is activated in PTECs from mice after AKI induced by ischemia-reperfusion injury (IRI-AKI), cisplatin (6), and, now, in article published in this issue of the American Journal of Physiology-Renal Physiology, rhabdomyolysis induced by intramuscular glycerol injection (5). They showed that conditional deletion of Cdkl5 in PTECs completely inhibits injury-induced activation of Cdkl5 and markedly ameliorates the severity of AKI 48À72 h after severe IRI, cisplatin, and rhabdomyolysis-induced AKI.…”

“…However, aside from its role in stem cell maintenance, Sox9 has not previously been shown to protect cells against injury. To address this, Kim et al demonstrated that overexpression of a stable S199A Sox9 mutant increased survival of cultured PTECs exposed to cisplatin and that there was a marked increase in the severity of AKI within 48À72 h of IRI-, cisplatin-, and rhabdomyolysisinduced AKI in mice with conditional deletion of Sox9 in PTECs (5,6). Importantly, the authors also showed that the protection afforded by AST-487 and PTEC-specific Cdkl5 mutation to IRI-and cisplatin-induced AKI is reduced (but not completely lost) in PTEC Sox9 mutant mice, suggesting that Sox9 plays a role in mediating the protective effects of Cdkl5 inhibition in AKI.…”

“…In part, this can be attributed to two common failures: 1) preclinical studies rarely evaluate their targets in models of AKI that reflect the heterogeneous nature of AKI syndrome in patients and 2) because concerns about the risks of renal biopsies in patients with AKI have limited our ability to examine renal tissues, there is often a failure to establish whether the therapeutic target is also involved in human disease (3). Two recent publications from the laboratory of Navjot Pabla have described the discovery of cyclin-dependent kinase-like 5 (Cdkl5) as a promising new therapeutic target that regulates the severity of acute tubular injury in models of AKI that reflect the diversity of injuries in human AKI (5,6). In addition, a genetic variant at the CDKL5 locus was recently identified as a kidney-specific expression quantitative trait locus that is predictive of CKD progression in a genome-wide association study involving two large CKD cohorts (4), suggesting that the CDKL5 pathway may also be involved in pathogenesis of human kidney disease.…”