Genome-Wide CRISPR Screen Identifies Phospholipid Scramblase 3 as the Biological Target of Mitoprotective Drug SS-31.

BACKGROUND: The synthetic tetra-peptide SS-31 shows promise in alleviating mitochondrial dysfunction associated with common diseases. However, the precise pharmacological basis of its mitoprotective effects remains unknown. METHODS: To uncover the biological targets of SS-31, we performed a genome-scale CRISPR screen in HK-2 cells, a cell culture model where SS-31 mitigates cisplatin-associated cell death and mitochondrial dysfunction. The identified hit candidate gene was functionally validated using knockout cell lines, siRNA mediated downregulation, and tubular epithelial specific conditional knockout mice. Biochemical interaction studies were also performed to examine the interaction of SS-31 with the identified target protein. RESULTS: Our primary screen and validation studies in HK-2 and primary murine tubular epithelial cells showed that phospholipid scramblase 3 (PLSCR3), an understudied inner mitochondrial membrane protein, is essential for the protective effects of SS-31. For in vivo validation, we generated tubular epithelial-specific knockout mice and found that Plscr3 gene ablation did not influence kidney function under normal conditions or affect the severity of cisplatin and rhabdomyolysis-associated AKI. However, Plscr3 gene deletion completely abrogated the protective effects of SS-31 during cisplatin and rhabdomyolysis-associated AKI. Biochemical studies showed that SS-31 directly binds to a previously uncharacterized N-terminal domain and stimulates PLSCR3 scramblase activity. Finally, PLSCR3 protein expression was found to be increased in the kidneys of AKI patients. CONCLUSIONS: PLSCR3 is identified as the essential biological target that facilitates the mitoprotective effects of SS-31 in vitro and in vivo. PLSCR3 agonists can alleviate mitochondrial dysfunction linked to AKI.

IL-22 is secreted by proximal tubule cells and regulates DNA damage response and cell death in acute kidney injury.

Acute kidney injury (AKI) affects over 13 million people worldwide annually and is associated with a 4-fold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces cell death and worsens AKI. The factors that trigger DDR to switch from pro-repair to pro-cell death remain to be resolved. Here we investigated the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identified PTCs as a novel source of urinary IL-22. Functionally, IL-22 binding IL-22RA1 on PTCs amplified the DDR. Treating primary PTCs with IL-22 alone induced rapid activation of the DDR. The combination of IL-22 and either cisplatin- or AA-induced cell death in primary PTCs, while the same dose of cisplatin or AA alone did not. Global deletion of IL-22 protected against cisplatin- or AA-induced AKI, reduced expression of DDR components, and inhibited PTC cell death. To confirm PTC IL-22 signaling contributed to AKI, we knocked out IL-22RA1 specifically in kidney tubule cells. IL-22RA1ΔTub mice displayed reduced DDR activation, cell death, and kidney injury compared to controls. Thus, targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with repair of damaged DNA.

Tubular mitochondrial pyruvate carrier disruption elicits redox adaptations that protect from acute kidney injury.

OBJECTIVE: Energy-intensive kidney reabsorption processes essential for normal whole-body function are maintained by tubular epithelial cell metabolism. Although tubular metabolism changes markedly following acute kidney injury (AKI), it remains unclear which metabolic alterations are beneficial or detrimental. By analyzing large-scale, publicly available datasets, we observed that AKI consistently leads to downregulation of the mitochondrial pyruvate carrier (MPC). This investigation aimed to understand the contribution of the tubular MPC to kidney function, metabolism, and acute injury severity. METHODS: We generated tubular epithelial cell-specific Mpc1 knockout (MPC TubKO) mice and employed renal function tests, in vivo renal 13C-glucose tracing, mechanistic enzyme activity assays, and tests of injury and survival in an established rhabdomyolysis model of AKI. RESULTS: MPC TubKO mice retained normal kidney function, displayed unchanged markers of kidney injury, but exhibited coordinately increased enzyme activities of the pentose phosphate pathway and the glutathione and thioredoxin oxidant defense systems. Following rhabdomyolysis-induced AKI, compared to WT control mice, MPC TubKO mice showed increased glycolysis, decreased kidney injury and oxidative stress markers, and strikingly increased survival. CONCLUSIONS: Our findings suggest that decreased renal tubular mitochondrial pyruvate uptake hormetically upregulates oxidant defense systems before AKI and is a beneficial adaptive response after rhabdomyolysis-induced AKI. This raises the possibility of therapeutically modulating the MPC to attenuate AKI severity.

Sex-specific lung inflammation and mitochondrial damage in a model of electronic cigarette exposure in asthma.

The prevalence of electronic cigarette (EC) use among adult with asthma has continued to increase over time, in part due to the belief of being less harmful than smoking. However, the extent of their toxicity and the involved mechanisms contributing to the deleterious impact of EC exposure on patients with preexisting asthma have not been delineated. In the present project, we tested the hypothesis that EC use contributes to respiratory damage and worsening inflammation in the lungs of patients with asthma. To define the consequences of EC exposure in established asthma, we used a mouse model with/without preexisting asthma for short-term exposure to EC aerosols. C57/BL6J mice were sensitized and challenged with a DRA (dust mite, ragweed, Aspergillus fumigates, 200 µg/mL) mixture and exposed daily to EC with nicotine (2% nicotine in 30:70 propylene glycol: vegetable glycerin) or filtered air for 2 wk. The mice were evaluated at 24 h after the final EC exposure. After EC exposure in asthmatic mice, lung inflammatory cell infiltration and goblet cell hyperplasia were increased, whereas EC alone did not cause airway inflammation. Our data also show that mitochondrial DNA (mtDNA) content and a key mtDNA regulator, mitochondrial transcription factor A (TFAM), are reduced in asthmatic EC-exposed mice in a sex-dependent manner. Together, these results indicate that TFAM loss in lung epithelium following EC contributes to male-predominant sex pathological differences, including mitochondrial damage, inflammation, and remodeling in asthmatic airways.NEW & NOTEWORTHY Respiratory immunity is dysregulated in preexisting asthma, and further perturbations by EC use could exacerbate asthma severity. However, the extent of their toxicity and the involved mechanisms contributing to the deleterious impact of EC exposure on patients with preexisting asthma have not been delineated. We found that EC has unique biological impacts in lungs and potential sex differences with loss of TFAM, a key mtDNA regulator, in lung epithelial region from our animal EC study.

IL-22 promotes acute kidney injury through activation of the DNA damage response and cell death in proximal tubule cells.

Acute kidney injury (AKI) affects over 13 million people world-wide annually and is associated with a fourfold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces to cell death and worsens AKI. The factors that trigger the switch from pro-reparative to pro-cell death DDR remain to be resolved. Here we investigate the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identify PTCs as a novel source of urinary IL-22, making PTCs the only epithelial cells known to secret IL-22, to our knowledge. Functionally, IL-22 binding its receptor (IL-22RA1) on PTCs amplifies the DDR. Treating primary PTCs with IL-22 alone induces rapid activation of the DDR in vitro. The combination of IL-22 + cisplatin or AA treatment on primary PTCs induces cell death, while the same dose of cisplatin or AA alone does not. Global deletion of IL-22 protects against cisplatin or AA induced AKI. IL-22 deletion reduces expression of components of the DDR and inhibits PTC cell death. To confirm PTC IL-22 signaling contributes to AKI, we knocked out IL-22RA1 in renal epithelial cells by crossing IL-22RA1floxed mice with Six2-Cre mice. IL-22RA1 KO reduced DDR activation, cell death, and kidney injury. These data demonstrate that IL-22 promotes DDR activation in PTCs, switching pro-recovery DDR responses to a pro-cell death response and worsening AKI. Targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with the processes necessary for repair of damaged DNA.

CDK4/6 and autophagy inhibitors synergize to suppress the growth of human head and neck squamous cell carcinomas.

Head and neck squamous cell carcinoma (HNSCC) accounts for over 10,000 deaths in the United States annually. Approximately 80% of HNSCC are human papillomavirus (HPV)-negative which have an overall poorer prognosis compared to the HPV-positive disease. Treatment options are mainly nontargeted chemotherapy, radiation, and surgery. The cyclin-d-CDK4/6-RB pathway, which regulates cell cycle progression, is often deregulated in HNSCC, making it an attractive therapeutic target. In the current study, we investigated the therapeutic effects of cyclin-dependent kinase 4/6 (CDK4/6) inhibitors in preclinical models of HNSCCs. Our results show that the specific CDK4/6 inhibitor, abemaciclib, inhibited cell growth, and induced apoptosis in HNSCC cell lines. We also demonstrated that both the pro-survival autophagy pathway and the ERK pathway in HNSCC cells were activated with abemaciclib treatment through the generation of reactive oxygen species (ROS). Coinhibition of CDK4/6 and autophagy synergistically decreased cell viability, induced apoptosis, and inhibited tumor growth in both in vitro and in vivo preclinical HNSCC models. These results reveal a potential therapeutic strategy that supports the rationale for further clinical development of a combination of CDK4/6 and autophagy inhibitors in HNSCC.

Discovery of a Potent and Selective CDKL5/GSK3 Chemical Probe That Is Neuroprotective.

Despite mediating several essential processes in the brain, including during development, cyclin-dependent kinase-like 5 (CDKL5) remains a poorly characterized human protein kinase. Accordingly, its substrates, functions, and regulatory mechanisms have not been fully described. We realized that availability of a potent and selective small molecule probe targeting CDKL5 could enable illumination of its roles in normal development as well as in diseases where it has become aberrant due to mutation. We prepared analogs of AT-7519, a compound that has advanced to phase II clinical trials and is a known inhibitor of several cyclin-dependent kinases (CDKs) and cyclin-dependent kinase-like kinases (CDKLs). We identified analog 2 as a highly potent and cell-active chemical probe for CDKL5/GSK3 (glycogen synthase kinase 3). Evaluation of its kinome-wide selectivity confirmed that analog 2 demonstrates excellent selectivity and only retains GSK3α/ß affinity. We next demonstrated the inhibition of downstream CDKL5 and GSK3α/ß signaling and solved a co-crystal structure of analog 2 bound to human CDKL5. A structurally similar analog (4) proved to lack CDKL5 affinity and maintain potent and selective inhibition of GSK3α/ß, making it a suitable negative control. Finally, we used our chemical probe pair (2 and 4) to demonstrate that inhibition of CDKL5 and/or GSK3α/ß promotes the survival of human motor neurons exposed to endoplasmic reticulum stress. We have demonstrated a neuroprotective phenotype elicited by our chemical probe pair and exemplified the utility of our compounds to characterize the role of CDKL5/GSK3 in neurons and beyond.

Zinc finger protein 24-dependent transcription factor SOX9 up-regulation protects tubular epithelial cells during acute kidney injury.

Transcriptional profiling studies have identified several protective genes upregulated in tubular epithelial cells during acute kidney injury (AKI). Identifying upstream transcriptional regulators could lead to the development of therapeutic strategies augmenting the repair processes. SOX9 is a transcription factor controlling cell-fate during embryonic development and adult tissue homeostasis in multiple organs including the kidneys. SOX9 expression is low in adult kidneys; however, stress conditions can trigger its transcriptional upregulation in tubular epithelial cells. SOX9 plays a protective role during the early phase of AKI and facilitates repair during the recovery phase. To identify the upstream transcriptional regulators that drive SOX9 upregulation in tubular epithelial cells, we used an unbiased transcription factor screening approach. Preliminary screening and validation studies show that zinc finger protein 24 (ZFP24) governs SOX9 upregulation in tubular epithelial cells. ZFP24, a Cys2-His2 (C2H2) zinc finger protein, is essential for oligodendrocyte maturation and myelination; however, its role in the kidneys or in SOX9 regulation remains unknown. Here, we found that tubular epithelial ZFP24 gene ablation exacerbated ischemia, rhabdomyolysis, and cisplatin-associated AKI. Importantly, ZFP24 gene deletion resulted in suppression of SOX9 upregulation in injured tubular epithelial cells. Chromatin immunoprecipitation and promoter luciferase assays confirmed that ZFP24 bound to a specific site in both murine and human SOX9 promoters. Importantly, CRISPR/Cas9-mediated mutation in the ZFP24 binding site in the SOX9 promoter in vivo led to suppression of SOX9 upregulation during AKI. Thus, our findings identify ZFP24 as a critical stress-responsive transcription factor protecting tubular epithelial cells through SOX9 upregulation.

A Potent and Selective CDKL5/GSK3 Chemical Probe is Neuroprotective.

Despite mediating several essential processes in the brain, including during development, cyclin-dependent kinase-like 5 (CDKL5) remains a poorly characterized human protein kinase. Accordingly, its substrates, functions, and regulatory mechanisms have not been fully described. We realized that availability of a potent and selective small molecule probe targeting CDKL5 could enable illumination of its roles in normal development as well as in diseases where it has become aberrant due to mutation. We prepared analogs of AT-7519, a known inhibitor of several cyclin dependent and cyclin-dependent kinase-like kinases that has been advanced into Phase II clinical trials. We identified analog 2 as a highly potent and cell-active chemical probe for CDKL5/GSK3 (glycogen synthase kinase 3). Evaluation of its kinome-wide selectivity confirmed that analog 2 demonstrates excellent selectivity and only retains GSK3α/ß affinity. As confirmation that our chemical probe is a high-quality tool to use in directed biological studies, we demonstrated inhibition of downstream CDKL5 and GSK3α/ß signaling and solved a co-crystal structure of analog 2 bound to CDKL5. A structurally similar analog ( 4 ) proved to lack CDKL5 affinity and maintain potent and selective inhibition of GSK3α/ß. Finally, we used our chemical probe pair ( 2 and 4 ) to demonstrate that inhibition of CDKL5 and/or GSK3α/ß promotes the survival of human motor neurons exposed to endoplasmic reticulum (ER) stress. We have demonstrated a neuroprotective phenotype elicited by our chemical probe pair and exemplified the utility of our compounds to characterize the role of CDKL5/GSK3 in neurons and beyond.

Tubular Mitochondrial Pyruvate Carrier Disruption Elicits Redox Adaptations that Protect from Acute Kidney Injury.

Energy-intensive kidney reabsorption processes essential for normal whole-body function are maintained by tubular epithelial cell metabolism. Tubular metabolism changes markedly following acute kidney injury (AKI), but which changes are adaptive versus maladaptive remain poorly understood. In publicly available data sets, we noticed a consistent downregulation of the mitochondrial pyruvate carrier (MPC) after AKI, which we experimentally confirmed. To test the functional consequences of MPC downregulation, we generated novel tubular epithelial cell-specific Mpc1 knockout (MPC TubKO) mice. 13C-glucose tracing, steady-state metabolomic profiling, and enzymatic activity assays revealed that MPC TubKO coordinately increased activities of the pentose phosphate pathway and the glutathione and thioredoxin oxidant defense systems. Following rhabdomyolysis-induced AKI, MPC TubKO decreased markers of kidney injury and oxidative damage and strikingly increased survival. Our findings suggest that decreased mitochondrial pyruvate uptake is a central adaptive response following AKI and raise the possibility of therapeutically modulating the MPC to attenuate AKI severity.

Exogenous mitochondrial transfer increases energy expenditure and attenuates adiposity gains in mice with diet-induced obesity.

Obesity is associated with chronic multi-system bioenergetic stress that may be improved by increasing the number of healthy mitochondria available across organ systems. However, treatments capable of increasing mitochondrial content are generally limited to endurance exercise training paradigms, which are not always sustainable long-term, let alone feasible for many patients with obesity. Recent studies have shown that local transfer of exogenous mitochondria from healthy donor tissues can improve bioenergetic outcomes and alleviate the effects of tissue injury in recipients with organ specific disease. Thus, the aim of this project was to determine the feasibility of systemic mitochondrial transfer for improving energy balance regulation in the setting of diet-induced obesity. We found that transplantation of mitochondria from lean mice into mice with diet-induced obesity attenuated adiposity gains by increasing energy expenditure and promoting the mobilization and oxidation of lipids. Additionally, mice that received exogenous mitochondria demonstrated improved glucose uptake, greater insulin responsiveness, and complete reversal of hepatic steatosis. These changes were, in part, driven by adaptations occurring in white adipose tissue. Together, these findings are proof-of-principle that mitochondrial transplantation is an effective therapeutic strategy for limiting the deleterious metabolic effects of diet-induced obesity in mice.

Targeting ETosis by miR-155 inhibition mitigates mixed granulocytic asthmatic lung inflammation.

Asthma is phenotypically heterogeneous with several distinctive pathological mechanistic pathways. Previous studies indicate that neutrophilic asthma has a poor response to standard asthma treatments comprising inhaled corticosteroids. Therefore, it is important to identify critical factors that contribute to increased numbers of neutrophils in asthma patients whose symptoms are poorly controlled by conventional therapy. Leukocytes release chromatin fibers, referred to as extracellular traps (ETs) consisting of double-stranded (ds) DNA, histones, and granule contents. Excessive components of ETs contribute to the pathophysiology of asthma; however, it is unclear how ETs drive asthma phenotypes and whether they could be a potential therapeutic target. We employed a mouse model of severe asthma that recapitulates the intricate immune responses of neutrophilic and eosinophilic airway inflammation identified in patients with severe asthma. We used both a pharmacologic approach using miR-155 inhibitor-laden exosomes and genetic approaches using miR-155 knockout mice. Our data show that ETs are present in the bronchoalveolar lavage fluid of patients with mild asthma subjected to experimental subsegmental bronchoprovocation to an allergen and a severe asthma mouse model, which resembles the complex immune responses identified in severe human asthma. Furthermore, we show that miR-155 contributes to the extracellular release of dsDNA, which exacerbates allergic lung inflammation, and the inhibition of miR-155 results in therapeutic benefit in severe asthma mice. Our findings show that targeting dsDNA release represents an attractive therapeutic target for mitigating neutrophilic asthma phenotype, which is clinically refractory to standard care.

BMX kinase mediates gilteritinib resistance in FLT3-mutated AML through microenvironmental factors.

Despite the clinical benefit associated with gilteritinib in relapsed/refractory acute myeloid leukemia (AML), most patients eventually develop resistance through unknown mechanisms. To delineate the mechanistic basis of resistance to gilteritinib, we performed targeted sequencing and scRNASeq on primary FLT3-ITD-mutated AML samples. Co-occurring mutations in RAS pathway genes were the most common genetic abnormalities, and unresponsiveness to gilteritinib was associated with increased expression of bone marrow-derived hematopoietic cytokines and chemokines. In particular, we found elevated expression of the TEK-family kinase, BMX, in gilteritinib-unresponsive patients pre- and post-treatment. BMX contributed to gilteritinib resistance in FLT3-mutant cell lines in a hypoxia-dependent manner by promoting pSTAT5 signaling, and these phenotypes could be reversed with pharmacological inhibition and genetic knockout. We also observed that inhibition of BMX in primary FLT3-mutated AML samples decreased chemokine secretion and enhanced the activity of gilteritinib. Collectively, these findings indicate a crucial role for microenvironment-mediated factors modulated by BMX in the escape from targeted therapy and have implications for the development of novel therapeutic interventions to restore sensitivity to gilteritinib.

Role of Mitochondrial Therapy for Ischemic-Reperfusion Injury and Acute Kidney Injury.

Acute kidney injury (AKI) is a common clinical disorder associated with decline in renal function because of ischemic and nephrotoxic insults. The pathophysiology of AKI involves multiple cellular mechanisms, such as kidney parenchymal cell (epithelial and endothelial) dysfunction and immune-cell infiltration. Mitochondrial injury which causes ATP depletion and triggers apoptosis and necrosis is at the heart of ischemia reperfusion injury (IRI). Pharmacological (SS-31 or MitoQ), cellular (dendritic cells or mesenchymal stem cells), or genetic strategies that either directly or indirectly preserve mitochondrial integrity and function have been shown to mitigate IRI-linked AKI in preclinical models. Interestingly, isolated mitochondria have been recently shown to be taken up by various mammalian cells resulting in incorporation of transplanted mitochondria into the endogenous mitochondrial network of recipient cells and contributing to protection from ischemic injury in various preclinical models of ischemia including the heart, liver, and kidneys. The mini review summarizes the current available therapeutic strategies that improve kidney function by targeting mitochondria health.

Gilteritinib-induced upregulation of S100A9 is mediated through BCL6 in acute myeloid leukemia.

Drug resistance and relapse are common challenges in acute myeloid leukemia (AML), particularly in an aggressive subset bearing internal tandem duplications (ITDs) of the FLT3 receptor (FLT3-ITD+). The tyrosine kinase inhibitor gilteritinib is approved for the treatment of relapse/refractory AML with FLT3 mutations, yet resistance to gilteritinib remains a clinical concern, and the underlying mechanisms remain incompletely understood. Using transcriptomic analyses and functional validation studies, we identified the calcium-binding proteins S100A8 and S100A9 (S100A8/A9) as contributors to gilteritinib resistance in FLT3-ITD+ AML. Exposure of FLT3-ITD+ AML cells to gilteritinib increased S100A8/A9 expression in vivo and in vitro and decreased free calcium levels, and genetic manipulation of S100A9 was associated with altered sensitivity to gilteritinib. Using a transcription factor screen, we identified the transcriptional corepressor BCL6, as a regulator of S100A9 expression and found that gilteritinib decreased BCL6 binding to the S100A9 promoter, thereby increasing S100A9 expression. Furthermore, pharmacological inhibition of BCL6 accelerated the growth rate of gilteritinib-resistant FLT3-ITD+ AML cells, suggesting that S100A9 is a functional target of BCL6. These findings shed light on mechanisms of resistance to gilteritinib through regulation of a target that can be therapeutically exploited to enhance the antileukemic effects of gilteritinib.

Kidney toxicity of the BRAF-kinase inhibitor vemurafenib is driven by off-target ferrochelatase inhibition.

A multitude of disease and therapy related factors drive the frequent development of kidney disorders in cancer patients. Along with chemotherapy, the newer targeted therapeutics can also cause kidney dysfunction through on and off-target mechanisms. Interestingly, among the small molecule inhibitors approved for the treatment of cancers that harbor BRAF-kinase activating mutations, vemurafenib can trigger tubular damage and acute kidney injury. BRAF is a proto-oncogene involved in cell growth. To investigate the underlying mechanisms, we developed cell culture and mouse models of vemurafenib kidney toxicity. At clinically relevant concentrations vemurafenib induces cell-death in transformed and primary mouse and human kidney tubular epithelial cells. In mice, two weeks of daily vemurafenib treatment causes moderate acute kidney injury with histopathological characteristics of kidney tubular epithelial cells injury. Importantly, kidney tubular epithelial cell-specific BRAF gene deletion did not influence kidney function under normal conditions or alter the severity of vemurafenib-associated kidney impairment. Instead, we found that inhibition of ferrochelatase, an enzyme involved in heme biosynthesis contributes to vemurafenib kidney toxicity. Ferrochelatase overexpression protected kidney tubular epithelial cells and conversely ferrochelatase knockdown increased the sensitivity to vemurafenib-induced kidney toxicity. Thus, our studies suggest that vemurafenib-associated kidney tubular epithelial cell dysfunction and kidney toxicity is BRAF-independent and caused, in part, by off-target ferrochelatase inhibition.

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

Acute kidney injury (AKI) is a common clinical syndrome associated with adverse short- and long-term sequelae. Renal tubular epithelial cell (RTEC) 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 RNA inhibition 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 present study, we 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, the small-molecule kinase inhibitor AST-487 alleviated rhabdomyolysis-associated AKI in a Cdkl5-dependent manner. Mechanistically, we demonstrated that Cdkl5 phosphorylates the transcriptional regulator sex-determining region Y box 9 (Sox9) and suppresses its protective function under stress conditions. On the basis of these results, we propose that, by suppressing the protective Sox9-directed transcriptional program, Cdkl5 contributes to rhabdomyolysis-associated renal impairment. All together, the present study identified Cdkl5 as a critical stress-induced kinase that drives RTEC dysfunction and kidney injury linked with distinct etiologies.

SOX9 promotes stress-responsive transcription of VGF nerve growth factor inducible gene in renal tubular epithelial cells.

Acute kidney injury (AKI) is a common clinical condition associated with diverse etiologies and abrupt loss of renal function. In patients with sepsis, rhabdomyolysis, cancer, and cardiovascular disorders, the underlying disease or associated therapeutic interventions can cause hypoxia, cytotoxicity, and inflammatory insults to renal tubular epithelial cells (RTECs), resulting in the onset of AKI. To uncover stress-responsive disease-modifying genes, here we have carried out renal transcriptome profiling in three distinct murine models of AKI. We find that Vgf nerve growth factor inducible gene up-regulation is a common transcriptional stress response in RTECs to ischemia-, cisplatin-, and rhabdomyolysis-associated renal injury. The Vgf gene encodes a secretory peptide precursor protein that has critical neuroendocrine functions; however, its role in the kidneys remains unknown. Our functional studies show that RTEC-specific Vgf gene ablation exacerbates ischemia-, cisplatin-, and rhabdomyolysis-associated AKI in vivo and cisplatin-induced RTEC cell death in vitro Importantly, aggravation of cisplatin-induced renal injury caused by Vgf gene ablation is partly reversed by TLQP-21, a Vgf-derived peptide. Finally, in vitro and in vivo mechanistic studies showed that injury-induced Vgf up-regulation in RTECs is driven by the transcriptional regulator Sox9. These findings reveal a crucial downstream target of the Sox9-directed transcriptional program and identify Vgf as a stress-responsive protective gene in kidney tubular epithelial cells.

Neuronal uptake transporters contribute to oxaliplatin neurotoxicity in mice.

Peripheral neurotoxicity is a debilitating condition that afflicts up to 90% of patients with colorectal cancer receiving oxaliplatin-containing therapy. Although emerging evidence has highlighted the importance of various solute carriers to the toxicity of anticancer drugs, the contribution of these proteins to oxaliplatin-induced peripheral neurotoxicity remains controversial. Among candidate transporters investigated in genetically engineered mouse models, we provide evidence for a critical role of the organic cation transporter 2 (OCT2) in satellite glial cells in oxaliplatin-induced neurotoxicity, and demonstrate that targeting OCT2 using genetic and pharmacological approaches ameliorates acute and chronic forms of neurotoxicity. The relevance of this transport system was verified in transporter-deficient rats as a secondary model organism, and translational significance of preventive strategies was demonstrated in preclinical models of colorectal cancer. These studies suggest that pharmacological targeting of OCT2 could be exploited to afford neuroprotection in cancer patients requiring treatment with oxaliplatin.

A kinome-wide screen identifies a CDKL5-SOX9 regulatory axis in epithelial cell death and kidney injury.

Renal tubular epithelial cells (RTECs) perform the essential function of maintaining the constancy of body fluid composition and volume. Toxic, inflammatory, or hypoxic-insults to RTECs can cause systemic fluid imbalance, electrolyte abnormalities and metabolic waste accumulation- manifesting as acute kidney injury (AKI), a common disorder associated with adverse long-term sequelae and high mortality. Here we report the results of a kinome-wide RNAi screen for cellular pathways involved in AKI-associated RTEC-dysfunction and cell death. Our screen and validation studies reveal an essential role of Cdkl5-kinase in RTEC cell death. In mouse models, genetic or pharmacological Cdkl5 inhibition mitigates nephrotoxic and ischemia-associated AKI. We propose that Cdkl5 is a stress-responsive kinase that promotes renal injury in part through phosphorylation-dependent suppression of pro-survival transcription regulator Sox9. These findings reveal a surprising non-neuronal function of Cdkl5, identify a pathogenic Cdkl5-Sox9 axis in epithelial cell-death, and support CDKL5 antagonism as a therapeutic approach for AKI.