APOL1 risk variants in individuals of African genetic ancestry drive endothelial cell defects that exacerbate sepsis.

The incidence and severity of sepsis is higher among individuals of African versus European ancestry. We found that genetic risk variants (RVs) in the trypanolytic factor apolipoprotein L1 (APOL1), present only in individuals of African ancestry, were associated with increased sepsis incidence and severity. Serum APOL1 levels correlated with sepsis and COVID-19 severity, and single-cell sequencing in human kidneys revealed high expression of APOL1 in endothelial cells. Analysis of mice with endothelial-specific expression of RV APOL1 and in vitro studies demonstrated that RV APOL1 interfered with mitophagy, leading to cytosolic release of mitochondrial DNA and activation of the inflammasome (NLRP3) and the cytosolic nucleotide sensing pathways (STING). Genetic deletion or pharmacological inhibition of NLRP3 and STING protected mice from RV APOL1-induced permeability defects and proinflammatory endothelial changes in sepsis. Our studies identify the inflammasome and STING pathways as potential targets to reduce APOL1-associated health disparities in sepsis and COVID-19.

Expression of active B-Raf proto-oncogene in kidney collecting ducts induces cyst formation in normal mice and accelerates cyst growth in mice with polycystic kidney disease.

Polycystic kidney disease (PKD) is characterized by the formation and progressive enlargement of fluid-filled cysts due to abnormal cell proliferation. Cyclic AMP agonists, including arginine vasopressin, stimulate ERK-dependent proliferation of cystic cells, but not normal kidney cells. Previously, B-Raf proto-oncogene (BRAF), a MAPK kinase kinase that activates MEK-ERK signaling, was shown to be a central intermediate in the cAMP mitogenic response. However, the role of BRAF on cyst formation and enlargement in vivo had not been demonstrated. To determine if active BRAF induces kidney cyst formation, we generated transgenic mice that conditionally express BRAFV600E, a common activating mutation, and bred them with Pkhd1-Cre mice to express active BRAF in the collecting ducts, a predominant site for cyst formation. Collecting duct expression of BRAFV600E (BRafCD) caused kidney cyst formation as early as three weeks of age. There were increased levels of phosphorylated ERK (p-ERK) and proliferating cell nuclear antigen, a marker for cell proliferation. BRafCD mice developed extensive kidney fibrosis and elevated blood urea nitrogen, indicating a decline in kidney function, by ten weeks of age. BRAFV600E transgenic mice were also bred to Pkd1RC/RC and pcy/pcy mice, well-characterized slowly progressive PKD models. Collecting duct expression of active BRAF markedly increased kidney weight/body weight, cyst number and size, and total cystic area. There were increased p-ERK levels and proliferating cells, immune cell infiltration, interstitial fibrosis, and a decline in kidney function in both these models. Thus, our findings demonstrate that active BRAF is sufficient to induce kidney cyst formation in normal mice and accelerate cystic disease in PKD mice.

Overexpression of TGF-ß1 induces renal fibrosis and accelerates the decline in kidney function in polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the presence of numerous fluid-filled cysts, extensive fibrosis, and the progressive decline in kidney function. Transforming growth factor-ß1 (TGF-ß1), an important mediator for renal fibrosis and chronic kidney disease, is overexpressed by cystic cells compared with normal kidney cells; however, its role in PKD pathogenesis remains undefined. To investigate the effect of TGF-ß1 on cyst growth, fibrosis, and disease progression, we overexpressed active TGF-ß1 specifically in collecting ducts (CDs) of phenotypic normal (Pkd1RC/+) and Pkd1RC/RC mice. In normal mice, CD-specific TGF-ß1 overexpression caused tubule dilations by 5 wk of age that were accompanied by increased levels of phosphorylated SMAD3, α-smooth muscle actin, vimentin, and periostin; however, it did not induce overt cyst formation by 20 wk. In Pkd1RC/RC mice, CD overexpression of TGF-ß1 increased cyst epithelial cell proliferation. However, extensive fibrosis limited cyst enlargement and caused contraction of the kidneys, leading to a loss of renal function and a shortened lifespan of the mice. These data demonstrate that TGF-ß1-induced fibrosis constrains cyst growth and kidney enlargement and accelerates the decline of renal function, supporting the hypothesis that a combined therapy that inhibits renal cyst growth and fibrosis will be required to effectively treat ADPKD.

Periostin overexpression in collecting ducts accelerates renal cyst growth and fibrosis in polycystic kidney disease.

In polycystic kidney disease (PKD), persistent activation of cell proliferation and matrix production contributes to cyst growth and fibrosis, leading to progressive deterioration of renal function. Previously, we showed that periostin, a matricellular protein involved in tissue repair, is overexpressed by cystic epithelial cells of PKD kidneys. Periostin binds αVß3-integrins and activates integrin-linked kinase (ILK), leading to Akt/mammalian target of rapamycin (mTOR)-mediated proliferation of human PKD cells. By contrast, periostin does not stimulate the proliferation of normal human kidney cells. This difference in the response to periostin is due to elevated expression of αVß3-integrins by cystic cells. To determine whether periostin accelerates cyst growth and fibrosis, we generated mice with conditional overexpression of periostin in the collecting ducts (CDs). Ectopic CD expression of periostin was not sufficient to induce cyst formation or fibrosis in wild-type mice. However, periostin overexpression in pcy/pcy ( pcy) kidneys significantly increased mTOR activity, cell proliferation, cyst growth, and interstitial fibrosis; and accelerated the decline in renal function. Moreover, CD-specific overexpression of periostin caused a decrease in the survival of pcy mice. These pathological changes were accompanied by increased renal expression of vimentin, α-smooth muscle actin, and type I collagen. We also found that periostin increased gene expression of pathways involved in repair, including integrin and growth factor signaling and ECM production, and it stimulated focal adhesion kinase, Rho GTPase, cytoskeletal reorganization, and migration of PKD cells. These results suggest that periostin stimulates signaling pathways involved in an abnormal tissue repair process that contributes to cyst growth and fibrosis in PKD.

Integrin-Linked Kinase Signaling Promotes Cyst Growth and Fibrosis in Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by innumerous fluid-filled cysts and progressive deterioration of renal function. Previously, we showed that periostin, a matricellular protein involved in tissue repair, is markedly overexpressed by cyst epithelial cells. Periostin promotes cell proliferation, cyst growth, interstitial fibrosis, and the decline in renal function in PKD mice. Here, we investigated the regulation of these processes by the integrin-linked kinase (ILK), a scaffold protein that links the extracellular matrix to the actin cytoskeleton and is stimulated by periostin. Pharmacologic inhibition or shRNA knockdown of ILK prevented periostin-induced Akt/mammalian target of rapamycin (mTOR) signaling and ADPKD cell proliferation in vitro Homozygous deletion of ILK in renal collecting ducts (CD) of Ilkfl/fl ;Pkhd1-Cre mice caused tubule dilations, apoptosis, fibrosis, and organ failure by 10 weeks of age. By contrast, Ilkfl/+ ;Pkhd1-Cre mice had normal renal morphology and function and survived >1 year. Reduced expression of ILK in Pkd1fl/fl ;Pkhd1-Cre mice, a rapidly progressive model of ADPKD, decreased renal Akt/mTOR activity, cell proliferation, cyst growth, and interstitial fibrosis, and significantly improved renal function and animal survival. Additionally, CD-specific knockdown of ILK strikingly reduced renal cystic disease and fibrosis and extended the life of pcy/pcy mice, a slowly progressive PKD model. We conclude that ILK is critical for maintaining the CD epithelium and renal function and is a key intermediate for periostin activation of signaling pathways involved in cyst growth and fibrosis in PKD.

Phosphodiesterase Isoform Regulation of Cell Proliferation and Fluid Secretion in Autosomal Dominant Polycystic Kidney Disease.

cAMP stimulates cell proliferation and Cl(-)-dependent fluid secretion, promoting the progressive enlargement of renal cysts in autosomal dominant polycystic kidney disease (ADPKD). Intracellular cAMP levels are determined by the balance of cAMP synthesis by adenylyl cyclases and degradation by phosphodiesterases (PDEs). Therefore, PDE isoform expression and activity strongly influence global and compartmentalized cAMP levels. We report here that PDE3 and PDE4 expression levels are lower in human ADPKD tissue and cells compared with those of normal human kidneys (NHKs), whereas PDE1 levels are not significantly different. Inhibition of PDE4 caused a greater increase in basal and vasopressin (AVP)-stimulated cAMP levels and Cl(-) secretion by ADPKD cells than inhibition of PDE1, and inhibition of PDE4 induced cyst-like dilations in cultured mouse Pkd1(-/-) embryonic kidneys. In contrast, inhibition of PDE1 caused greater stimulation of extracellular signal-regulated kinase (ERK) and proliferation of ADPKD cells than inhibition of PDE4, and inhibition of PDE1 enhanced AVP-induced ERK activation. Notably, inhibition of PDE1, the only family of Ca(2+)-regulated PDEs, also induced a mitogenic response to AVP in NHK cells, similar to the effect of restricting intracellular Ca(2+). PDE1 coimmunoprecipitated with B-Raf and A-kinase anchoring protein 79, and AVP increased this interaction in ADPKD but not NHK cells. These data suggest that whereas PDE4 is the major PDE isoform involved in the regulation of global intracellular cAMP and Cl(-) secretion, PDE1 specifically affects the cAMP signal to the B-Raf/MEK/ERK pathway and regulates AVP-induced proliferation of ADPKD cells.

Periostin promotes renal cyst growth and interstitial fibrosis in polycystic kidney disease.

In renal cystic diseases, sustained enlargement of fluid-filled cysts is associated with severe interstitial fibrosis and progressive loss of functioning nephrons. Periostin, a matricellular protein, is highly overexpressed in cyst-lining epithelial cells of autosomal-dominant polycystic disease kidneys (ADPKD) compared with normal tubule cells. Periostin accumulates in situ within the matrix subjacent to ADPKD cysts, binds to αVß3 and αVß5 integrins, and stimulates the integrin-linked kinase to promote cell proliferation. We knocked out periostin (Postn) in pcy/pcy mice, an orthologous model of nephronophthisis type 3, to determine whether periostin loss reduces PKD progression in a slowly progressive model of renal cystic disease. At 20 weeks of age, pcy/pcy:Postn(-/-) mice had a 34% reduction in kidney weight/body weight, a reduction in cyst number and total cystic area, a 69% reduction in phosphorylated S6, a downstream component of the mTOR pathway, and fewer proliferating cells in the kidneys compared with pcy/pcy:Postn(+/+) mice. The pcy/pcy Postin knockout mice also had less interstitial fibrosis with improved renal function at 20 weeks and significantly longer survival (51.4 compared with 38.0 weeks). Thus, periostin adversely modifies the progression of renal cystic disease by promoting cyst epithelial cell proliferation, cyst enlargement, and interstitial fibrosis, all contributing to the decline in renal function and premature death.

The key role of NLRP3 and STING in APOL1-associated podocytopathy.

Coding variants in apolipoprotein L1 (APOL1), termed G1 and G2, can explain most excess kidney disease risk in African Americans; however, the molecular pathways of APOL1-induced kidney dysfunction remain poorly understood. Here, we report that expression of G2 APOL1 in the podocytes of Nphs1rtTA/TRE-G2APOL1 (G2APOL1) mice leads to early activation of the cytosolic nucleotide sensor, stimulator of interferon genes (STING), and the NLR family pyrin domain-containing 3 (NLRP3) inflammasome. STING and NLRP3 expression was increased in podocytes from patients with high-risk APOL1 genotypes, and expression of APOL1 correlated with caspase-1 and gasdermin D (GSDMD) levels. To demonstrate the role of NLRP3 and STING in APOL1-associated kidney disease, we generated transgenic mice with the G2 APOL1 risk variant and genetic deletion of Nlrp3 (G2APOL1/Nlrp3 KO), Gsdmd (G2APOL1/Gsdmd KO), and STING (G2APOL1/STING KO). Knockout mice displayed marked reduction in albuminuria, azotemia, and kidney fibrosis compared with G2APOL1 mice. To evaluate the therapeutic potential of targeting NLRP3, GSDMD, and STING, we treated mice with MCC950, disulfiram, and C176, potent and selective inhibitors of NLRP3, GSDMD, and STING, respectively. G2APOL1 mice treated with MCC950, disulfiram, and C176 showed lower albuminuria and improved kidney function even when inhibitor treatment was initiated after the development of albuminuria.

Going from acute to chronic kidney injury with FoxO3.

Acute kidney injury (AKI) is one of the most important risk factors for chronic and progressive kidney disease, leading to end-stage kidney failure. Tubule epithelial regeneration leads to the resolution of renal failure in AKI. Failure of tubule epithelial regeneration leads to concomitant hypoxia from loss of microcirculation, which serves as a critical factor leading to chronic kidney disease. In this issue of the JCI, Li et al. show that hypoxia activates the stress-responsive transcription factor FoxO3. Increased FoxO3 protein abundance leads to alterations in tubular epithelial autophagy and metabolism, highlighting an important mechanism causing permanent renal damage even after an acute injury.

Antioxidant effects of ethyl acetate extract of Desmodium gangeticum root on myocardial ischemia reperfusion injury in rat hearts.

BACKGROUND: This study aims to evaluate the antioxidant potential of the ethyl acetate extract of Desmodium gangeticum root for cardioprotection from ischemia reperfusion-induced oxidative stress. METHODS: The in vitro antioxidant potential of the extract was in terms of hydroxyl radical scavenging activity, lipid peroxide scavenging activity, nitric oxide scavenging activity and diphenylpicrylhydrazyl radical scavenging activity. The in vivo antioxidant potential of the extract was assessed in an isolated rat heart model. RESULTS: Free radicals were scavenged by the extract in a concentration-dependent manner within the range of the given concentrations in all models. Administration of the ethyl acetate extract of Desmodium gangeticum root (100 mg per kg body weight) before global ischemia caused a significant improvement of cardiac function and a decrease in the release of lactate dehydrogenase in coronary effluent, as well as the level of malondialdehyde in myocardial tissues. CONCLUSION: The ethyl acetate extract of Desmodium gangeticum root protects the myocardium against ischemia-reperfusion-induced damage in rats. The effects of the extract may be related to the inhibition of lipid peroxidation.