IFI16 Is Indispensable for Promoting HIF-1α-Mediated APOL1 Expression in Human Podocytes under Hypoxic Conditions.

Genetic variants in the protein-coding regions of APOL1 are associated with an increased risk and progression of chronic kidney disease (CKD) in African Americans. Hypoxia exacerbates CKD progression by stabilizing HIF-1α, which induces APOL1 transcription in kidney podocytes. However, the contribution of additional mediators to regulating APOL1 expression under hypoxia in podocytes is unknown. Here, we report that a transient accumulation of HIF-1α in hypoxia is sufficient to upregulate APOL1 expression in podocytes through a cGAS/STING/IRF3-independent pathway. Notably, IFI16 ablation impedes hypoxia-driven APOL1 expression despite the nuclear accumulation of HIF-1α. Co-immunoprecipitation assays indicate no direct interaction between IFI16 and HIF-1α. Our studies identify hypoxia response elements (HREs) in the APOL1 gene enhancer/promoter region, showing increased HIF-1α binding to HREs located in the APOL1 gene enhancer. Luciferase reporter assays confirm the role of these HREs in transcriptional activation. Chromatin immunoprecipitation (ChIP)-qPCR assays demonstrate that IFI16 is not recruited to HREs, and IFI16 deletion reduces HIF-1α binding to APOL1 HREs. RT-qPCR analysis indicates that IFI16 selectively affects APOL1 expression, with a negligible impact on other hypoxia-responsive genes in podocytes. These findings highlight the unique contribution of IFI16 to hypoxia-driven APOL1 gene expression and suggest alternative IFI16-dependent mechanisms regulating APOL1 gene expression under hypoxic conditions.

Rac1 promotes kidney collecting duct integrity by limiting actomyosin activity.

A polarized collecting duct (CD), formed from the branching ureteric bud (UB), is a prerequisite for an intact kidney. The small Rho GTPase Rac1 is critical for actin cytoskeletal regulation. We investigated the role of Rac1 in the kidney collecting system by selectively deleting it in mice at the initiation of UB development. The mice exhibited only a mild developmental phenotype; however, with aging, the CD developed a disruption of epithelial integrity and function. Despite intact integrin signaling, Rac1-null CD cells had profound adhesion and polarity abnormalities that were independent of the major downstream Rac1 effector, Pak1. These cells did however have a defect in the WAVE2-Arp2/3 actin nucleation and polymerization apparatus, resulting in actomyosin hyperactivity. The epithelial defects were reversible with direct myosin II inhibition. Furthermore, Rac1 controlled lateral membrane height and overall epithelial morphology by maintaining lateral F-actin and restricting actomyosin. Thus, Rac1 promotes CD epithelial integrity and morphology by restricting actomyosin via Arp2/3-dependent cytoskeletal branching.

Metformin attenuates cardiovascular and renal injury in uninephrectomized rats on DOCA-salt: Involvement of AMPK and miRNAs in cardioprotection.

Hypertension is associated with major cardiovascular (CV) and renal complications. The molecular intricacy by which hypertension leads to end organ damage is not known. To address this, we aimed to determine the effect of deoxycorticosterone acetate (DOCA) -salt (sodium chloride)-induced hypertension on the alterations in renin-angiotensin system, leading to CV and renal dysfunction in uninephrectomized male Sprague Dawley rats. MicroRNAs involved in this were also not yet explored. Metformin was used to delineate the role of AMPK in mitigating the hypertension-induced CV and renal dysfunction. Administering DOCA and offering saline to uninephrectomized rats, induced hypertension and associated abnormalities of diastolic dysfunction, CV and renal hypertrophy and fibrosis via activating local renin angiotensin system. Western blotting and RT-qPCR analysis of diseased heart revealed decreased SERCA2, p-AMPK, miR-146a, miR-99b and increased miR-155 and metformin administered, at dose of 300 mg/kg/day, for a period of 8 weeks prevented CV and renal damage. To our knowledge, we are the first to show that involvement of epigenetic alterations at microRNA level might be responsible for hypertension-induced cardiac dysfunction and metformin reverses these alterations.

Dysregulation of microRNAs and renin-angiotensin system in high salt diet-induced cardiac dysfunction in uninephrectomized rats.

Uninephrectomy is not associated with major adverse events in cardiovascular and renal functions of live kidney donors. The effect of high salt diet on the quality of life of live kidney donors is largely unknown. Hence in this study, we aimed to determine the effect of high salt diet on the alterations of renin-angiotensin system and microRNAs leading to CV and renal dysfunction in uninephrectomized rats. In order to mimic clinical scenario, uninephrectomized male Sprague Dawley rats were fed initially with normal pellet diet for 12 weeks and then for 20 weeks with high salt (10% w/w NaCl) diet. At the end of the study, biochemical, functional, histological and molecular parameters were measured. High salt diet feeding resulted in renal dysfunction & fibrosis, decreased baroreflex sensitivity, increased in vivo cardiovascular reactivity to angiotensin II owing to upregulation of angiotensin II type 1 receptors and L-type calcium channels leading to cardiovascular dysfunction in uninephrectomized rats (UNX+HSD) worse than that of normal (binephric) rats fed with high salt diet (HSD). Protein expression of functional and hypertrophic protein markers revealed decreased SERCA, p-AMPK and increased p-AKT. Interestingly, levels of miR-25, miR-451 and miR-155 increased and miR-99 decreased in heart of uninephrectomized rats fed with high salt. However, circulating miR-25 and miR-451 levels decreased and miR-99b increased in these animals. Our study points out that since tissue and circulating levels of miRNAs are not similar, caution must be exercised during the usage of miRs as diagnostic or prognostic biomarkers. To our knowledge, we are the first to show that epigenetic alterations result in cardiac dysfunction in uninephrectomized rats fed with high salt diet.

Metformin Improves Metabolic Memory in High Fat Diet (HFD)-induced Renal Dysfunction.

Recently, we have shown that high fat diet (HFD) in vivo and in vitro generates metabolic memory by altering H3K36me2 and H3K27me3 on the promoter of FOXO1 (transcription factor of gluconeogenic genes) (Kumar, S., Pamulapati, H., and Tikoo, K. (2016) Mol. Cell. Endocrinol. 422, 233-242). Here we checked the hypothesis whether concomitant diet reversal and metformin could overcome HFD-induced metabolic memory and renal damage. Male adult Sprague-Dawley rats were rendered insulin-resistant by feeding high fat diet for 16 weeks. Then the rats were subjected to diet reversal alone and along with metformin for 8 weeks. Biochemical and histological markers of insulin resistance and kidney function were measured. Blood pressure and in vivo vascular reactivity to angiotensin II (200 ng kg-1) were also checked. Diet reversal could improve lipid profile but could not prevent renal complications induced by HFD. Interestingly, metformin along with diet reversal restored the levels of blood glucose, triglycerides, cholesterol, blood urea nitrogen, and creatinine. In kidney, metformin increased the activation of AMP-activated protein kinase (AMPK) and decreased inflammatory markers (COX-2 and IL-1ß) and apoptotic markers (poly(ADP-ribose) polymerase (PARP) and caspase 3). Metformin was effective in lowering elevated basal blood pressure and acute change in mean arterial pressure in response to angiotensin II (Ang II). It also attenuated tubulointerstitial fibrosis and glomerulosclerosis induced by HFD feeding in kidney. Here we report, for the first time, that metformin treatment overcomes metabolic memory and prevents HFD-induced renal damage.

Activation of angiotensin-converting enzyme 2 (ACE2) attenuates allergic airway inflammation in rat asthma model.

Angiotensin-I converting enzyme (ACE) is positively correlated to asthma, chronic obstructive pulmonary disease (COPD), acute respiratory distress syndrome (ARDS) and is highly expressed in lungs. ACE2, the counteracting enzyme of ACE, was proven to be protective in pulmonary, cardiovascular diseases. In the present study we checked the effect of ACE2 activation in animal model of asthma. Asthma was induced in male wistar rats by sensitization and challenge with ovalbumin and then treated with ACE2 activator, diminazene aceturate (DIZE) for 2weeks. 48h after last allergen challenge, animals were anesthetized, blood, BALF, femoral bone marrow lavage were collected for leucocyte count; trachea for measuring airway responsiveness to carbachol; lungs and heart were isolated for histological studies and western blotting. In our animal model, the characteristic features of asthma such as altered airway responsiveness to carbachol, eosinophilia and neutrophilia were observed. Western blotting revealed the increased pulmonary expression of ACE1, IL-1ß, IL-4, NF-κB, BCL2, p-AKT, p-p38 and decreased expression of ACE2 and IκB. DIZE treatment prevented these alterations. Intraalveolar interstitial thickening, inflammatory cell infiltration, interstitial fibrosis, oxidative stress and right ventricular hypertrophy in asthma control animals were also reversed by DIZE treatment. Activation of ACE2 by DIZE conferred protection against asthma as evident from biochemical, functional, histological and molecular parameters. To the best of our knowledge, we report for the first time that activation of ACE2 by DIZE prevents asthma progression by altering AKT, p38, NF-κB and other inflammatory markers.