Sonic hedgehog connects podocyte injury to mesangial activation and glomerulosclerosis

Myofibroblast-derived exosomes enhance macrophages to myofibroblasts transition and kidney fibrosis

A critical event in the pathogenesis of kidney fibrosis is the transition of macrophages into myofibroblasts (MMT). Exosomes play an important role in crosstalk among cells in the kidney and the development of renal fibrosis. However, the role of myofibroblast-derived exosomes in the process of MMT and renal fibrosis progression remains unknown. Here, we examined the role of myofibroblast-derived exosomes in MMT and kidney fibrogenesis. In vitro, transforming growth factor-β1 stimulated the differentiation of kidney fibroblasts into myofibroblasts and promoted exosome release from myofibroblasts. RAW264.7 cells were treated with exosomes derived from myofibroblasts. We found purified exosomes from myofibroblasts trigger the MMT. By contrast, inhibition of exosome production with GW4869 or exosome depletion from the conditioned media abolished the ability of myofibroblasts to induce MMT. Mice treatment with myofibroblast-derived exosomes (Myo-Exo) exhibited severe fibrotic lesion and more abundant MMT cells in kidneys with folic acid (FA) injury, which was negated by TANK-banding kinase-1 inhibitor. Furthermore, suppression of exosome production reduced collagen deposition, extracellular matrix protein accumulation, and MMT in FA nephropathy. Collectively, Myo-Exo enhances the MMT and kidney fibrosis. Blockade of exosomes mediated myofibroblasts-macrophages communication may provide a novel therapeutic target for kidney fibrosis.

Proteome characterization of liver-kidney comorbidity after microbial sepsis

Sepsis is a life-threatening condition that occurs when the body responds to an infection but subsequently triggers widespread inflammation and impaired blood flow. These pathologic responses can rapidly cause multiple organ dysfunction or failure either one by one or simultaneously. The fundamental common mechanisms involved in sepsis-induced multiple organ dysfunction remain unclear. Here, employing quantitative global and phosphoproteomics, we examine the liver's temporal proteome and phosphoproteome changes after moderate sepsis induced by cecum ligation and puncture. In total, 4593 global proteins and 1186 phosphoproteins according to 3275 phosphosites were identified. To characterize the liver-kidney comorbidity after sepsis, we developed a mathematical model and performed cross-analyses of liver and kidney proteome data obtained from the same set of mice. Beyond immune response, we showed the commonly disturbed pathways and key regulators of the liver-kidney comorbidity are linked to energy metabolism and consumption. Our data provide open resources to understand the communication between the liver and kidney as they work to fight infection and maintain homeostasis.

Central role of podocytes in mediating cellular cross talk in glomerular health and disease

Podocytes are highly specialized epithelial cells that surround the capillaries of the glomeruli in the kidney. Together with the glomerular endothelial cells, these postmitotic cells are responsible for regulating filtrate from the circulating blood with their organized network of interdigitating foot processes that wrap around the glomerular basement membrane. Although podocyte injury and subsequent loss is the hallmark of many glomerular diseases, recent evidence suggests that the cell-cell communication between podocytes and other glomerular and nonglomerular cells is critical for the development and progression of kidney disease. In this review, we highlight these key cellular pathways of communication and how they might be a potential target for therapy in glomerular disease. We also postulate that podocytes might serve as a central hub for communication in the kidney under basal conditions and in response to cellular stress, which may have implications for the development and progression of glomerular diseases.

Nox4-SH3YL1 complex is involved in diabetic nephropathy

Nox4-derived H2O2 generation plays an important role in the pathogenesis of chronic kidney diseases (CKDs) such as diabetic nephropathy (DN). Here, we showed that SH3 domain-containing Ysc84-like 1 (SH3YL1), a Nox4 cytosolic activator, regulated DN. Streptozotocin (STZ)-induced type Ⅰ diabetic models in SH3YL1 whole-body knockout (KO) mice and podocyte-specific SH3YL1 conditional KO (Nphs2-Cre/SH3YL1fl/fl) mice were established to investigate the function of SH3YL1 in DN. The expression of fibrosis markers and inflammatory cytokines, the generation of oxidative stress, and the loss of podocytes were suppressed in diabetic SH3YL1 KO and Nphs2-Cre/SH3YL1fl/fl mice, compared to diabetic control mice. To extrapolate the observations derived from diabetic mice to clinical implication, we measured the protein level of SH3YL1 in patients DN. In fact, the SH3YL1 level was increased in patients DN. Overall, the SH3YL1-Nox4 complex was identified to play an important role in renal inflammation and fibrosis, resulting in the development of DN.

The CXCR4-AT1 axis plays a vital role in glomerular injury via mediating the crosstalk between podocyte and mesangial cell

Glomeruli stand at the center of nephrons to accomplish filtration and albumin interception. Podocytes and mesangial cells are the major constituents in the glomeruli. However, their interdependency in glomerular injury has rarely been reported. Herein, we investigated the role of C-X-C chemokine receptor type 4 (CXCR4) in mediating the crosstalk between podocytes and mesangial cells. We found CXCR4 and angiotensin II (AngII) increased primarily in injured podocytes. However, type-1 receptor of angiotensin II (AT1) and stromal cell-derived factor 1α (SDF-1α), a ligand of CXCR4, were evidently upregulated in mesangial cells following the progression of podocyte injury. Ectopic expression of CXCR4 in 5/6 nephrectomy mice increased the decline of renal function and glomerular injury, accelerated podocyte injury and mesangial cell activation, and initiated CXCR4-AT1 axis signals. Additionally, treatment with losartan, an AT1 blocker, interrupted the cycle of podocyte injury and mesangial matrix deposition triggered by CXCR4. Podocyte-specific ablation of CXCR4 gene blocked podocyte injury and mesangial cell activation. In vitro, CXCR4 overexpression induced oxidative stress and renin angiotensin system (RAS) activation in podocytes, and triggered the communication between podocytes and mesangial cells. In cultured mesangial cells, AngII treatment induced the expression of SDF-1α, which was secreted into the supernatant to further promote oxidative stress and cell injury in podocytes. Collectively, these results demonstrate that the CXCR4-AT1 axis plays a vital role in glomerular injury via mediating pathologic crosstalk between podocytes and mesangial cells. Our findings uncover a novel pathogenic mechanism by which the CXCR4-AT1 axis promotes glomerular injury.

Transcriptional regulation by the NSL complex enables diversification of IFT functions in ciliated versus nonciliated cells

Members of the NSL histone acetyltransferase complex are involved in multiorgan developmental syndromes. While the NSL complex is known for its importance in early development, its role in fully differentiated cells remains enigmatic. Using a kidney-specific model, we discovered that deletion of NSL complex members KANSL2 or KANSL3 in postmitotic podocytes led to catastrophic kidney dysfunction. Systematic comparison of two primary differentiated cell types reveals the NSL complex as a master regulator of intraciliary transport genes in both dividing and nondividing cells. NSL complex ablation led to loss of cilia and impaired sonic hedgehog pathway in ciliated fibroblasts. By contrast, nonciliated podocytes responded with altered microtubule dynamics and obliterated podocyte functions. Finally, overexpression of wild-type but not a double zinc finger (ZF-ZF) domain mutant of KANSL2 rescued the transcriptional defects, revealing a critical function of this domain in NSL complex assembly and function. Thus, the NSL complex exhibits bifurcation of functions to enable diversity of specialized outcomes in differentiated cells.

Smad3 Phospho-Isoform Signaling in Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis with insulin resistance, oxidative stress, lipotoxicity, adipokine secretion by fat cells, endotoxins (lipopolysaccharides) released by gut microbiota, and endoplasmic reticulum stress. Together, these factors promote NAFLD progression from steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, and eventually end-stage liver diseases in a proportion of cases. Hepatic fibrosis and carcinogenesis often progress together, sharing inflammatory pathways. However, NASH can lead to hepatocarcinogenesis with minimal inflammation or fibrosis. In such instances, insulin resistance, oxidative stress, and lipotoxicity can directly lead to liver carcinogenesis through genetic and epigenetic alterations. Transforming growth factor (TGF)-β signaling is implicated in hepatic fibrogenesis and carcinogenesis. TGF-β type I receptor (TβRI) and activated-Ras/c-Jun-N-terminal kinase (JNK) differentially phosphorylate the mediator Smad3 to create two phospho-isoforms: C-terminally phosphorylated Smad3 (pSmad3C) and linker-phosphorylated Smad3 (pSmad3L). TβRI/pSmad3C signaling terminates cell proliferation, while constitutive Ras activation and JNK-mediated pSmad3L promote hepatocyte proliferation and carcinogenesis. The pSmad3L signaling pathway also antagonizes cytostatic pSmad3C signaling. This review addresses TGF-β/Smad signaling in hepatic carcinogenesis complicating NASH. We also discuss Smad phospho-isoforms as biomarkers predicting HCC in NASH patients with or without cirrhosis.

Non-canonical Wnt/calcium signaling is protective against podocyte injury and glomerulosclerosis

Activation of canonical Wnt signaling has been implicated in podocyte injury and proteinuria. As Wnts are secreted proteins, whether Wnts derived from podocytes are obligatory for promoting proteinuria remains unknown. To address this, we generated conditional knockout mice where Wntless, a cargo receptor protein required for Wnt secretion, was specifically deleted in glomerular podocytes. Mice with podocyte-specific ablation of Wintless (Podo-Wntless-/-) were phenotypically normal. However, after inducing kidney damage with Adriamycin for six days, Podo-Wntless-/- mice developed more severe podocyte injury and albuminuria than their control littermates. Surprisingly, ablation of Wntless resulted in upregulation of β-catenin, accompanied by reduction of nephrin, podocin, podocalyxin, and Wilms tumor 1 proteins. In chronic injury induced by Adriamycin, increased albuminuria, aggravated podocyte lesions and extracellular matrix deposition were evident in Podo-Wntlessl-/- mice, compared to wild type mice. Mechanistically, specific ablation of Wintless in podocytes caused down-regulation of the nuclear factor of activated T cell 1 (NFAT1) and Nemo-like kinase (NLK), key downstream mediators of non-canonical Wnt/calcium signaling. In vitro, knockdown of either NFAT1 or NLK induced β-catenin activation while overexpression of NLK significantly repressed β-catenin induction and largely preserved nephrin in glomerular podocytes. Thus, our results indicate that podocyte-derived Wnts play an important role in protecting podocytes from injury by repressing β-catenin via activating non-canonical Wnt/calcium signaling.

Identification of matrix metalloproteinase-10 as a key mediator of podocyte injury and proteinuria

Podocyte injury or dysfunction plays an essential role in causing proteinuria and glomerulosclerosis in chronic kidney diseases. To search for new players involved in podocyte injury, we performed gene expression profiling in the glomeruli by RNA sequencing. This unbiased approach led us to discover matrix metalloproteinase-10 (MMP-10), a secreted zinc-dependent endopeptidase, as one of the most upregulated genes after glomerular injury. In animal models and patients with proteinuric chronic kidney diseases, MMP-10 was upregulated specifically in the podocytes of injured glomeruli. Patients with chronic kidney diseases also had elevated circulating levels of MMP-10, which correlated with the severity of kidney insufficiency. In transgenic mice with podocyte-specific expression of MMP-10, proteinuria was aggravated after injury induced by Adriamycin. This was accompanied by more severe podocytopathy and glomerulosclerotic lesions. In contrast, knockdown of MMP-10 in vivo protected mice from proteinuria, restored podocyte integrity and reduced kidney fibrosis. Interestingly, MMP-10 reduced podocyte tight junctional protein zonula occludens-1 (ZO-1) but did not affect its mRNA level. Incubation of purified ZO-1 with MMP-10 directly resulted in its proteolytic degradation in vitro, suggesting ZO-1 as a novel substrate of MMP-10. Thus, our findings illustrate that induction of MMP-10 could lead to podocyte injury by degrading ZO-1, thereby promoting proteinuria and glomerulosclerosis in chronic kidney diseases.

Cellular Senescence in Kidney Fibrosis: Pathologic Significance and Therapeutic Strategies

Age-related disorders such as chronic kidney disease (CKD) are increasingly prevalent globally and pose unprecedented challenges. In many aspects, CKD can be viewed as a state of accelerated and premature aging. Aging kidney and CKD share many common characteristic features with increased cellular senescence, a conserved program characterized by an irreversible cell cycle arrest with altered transcriptome and secretome. While developmental senescence and acute senescence may positively contribute to the fine-tuning of embryogenesis and injury repair, chronic senescence, when unresolved promptly, plays a crucial role in kidney fibrogenesis and CKD progression. Senescent cells elicit their fibrogenic actions primarily by secreting an assortment of inflammatory and profibrotic factors known as the senescence-associated secretory phenotype (SASP). Increasing evidence indicates that senescent cells could be a promising new target for therapeutic intervention known as senotherapy, which includes depleting senescent cells, modulating SASP and restoration of senescence inhibitors. In this review, we discuss current understanding of the role and mechanism of cellular senescence in kidney fibrosis. We also highlight potential options of targeting senescent cells for the treatment of CKD.

Global Proteome and Phosphoproteome Characterization of Sepsis-induced Kidney Injury

Sepsis-induced acute kidney injury (S-AKI) is the most common complication in hospitalized and critically ill patients, highlighted by a rapid decline of kidney function occurring a few hours or days after sepsis onset. Systemic inflammation elicited by microbial infections is believed to lead to kidney damage under immunocompromised conditions. However, although AKI has been recognized as a disease with long-term sequelae, partly because of the associated higher risk of chronic kidney disease (CKD), the understanding of kidney pathophysiology at the molecular level and the global view of dynamic regulations in situ after S-AKI, including the transition to CKD, remains limited. Existing studies of S-AKI mainly focus on deriving sepsis biomarkers from body fluids. In the present study, we constructed a mid-severity septic murine model using cecal ligation and puncture (CLP), and examined the temporal changes to the kidney proteome and phosphoproteome at day 2 and day 7 after CLP surgery, corresponding to S-AKI and the transition to CKD, respectively, by employing an ultrafast and economical filter-based sample processing method combined with the label-free quantitation approach. Collectively, we identified 2,119 proteins and 2950 phosphosites through multi-proteomics analyses. Among them, we identified an array of highly promising candidate marker proteins indicative of disease onset and progression accompanied by immunoblot validations, and further denoted the pathways that are specifically responsive to S-AKI and its transition to CKD, which include regulation of cell metabolism regulation, oxidative stress, and energy consumption in the diseased kidneys. Our data can serve as an enriched resource for the identification of mechanisms and biomarkers for sepsis-induced kidney diseases.

MicroRNA-466o-3p mediates β-catenin-induced podocyte injury by targeting Wilms tumor 1

Podocytes are highly specialized cells that play an essential role in maintaining the integrity and function of the glomerular filtration barrier. Wilms tumor 1 (WT1) and β-catenin are two master regulators that play opposing roles in podocyte biology and mutually antagonize each other. However, exactly how β-catenin inhibits WT1 remains incompletely understood. In this study, we demonstrated the role of miR-466o-3p in mediating β-catenin-triggered podocyte injury by targeting WT1. The expression of miR-466o-3p was upregulated in cultured podocytes after β-catenin activation and in glomerular podocytes in adriamycin (ADR) nephropathy, remnant kidney after 5/6 renal ablation, and diabetic kidney disease. Bioinformatics analysis and luciferase reporter assay confirmed that miR-466o-3p directly targeted WT1 mRNA. Furthermore, overexpression of miR-466o-3p downregulated WT1 protein and promoted podocyte injury in vitro. Conversely, inhibition of miR-466o-3p alleviated β-catenin-induced podocyte dysfunction. In mouse model of ADR nephropathy, overexpression of miR-466o-3p inhibited WT1, aggravated podocytes injury and deteriorated proteinuria. In contrast, inhibition of renal miR-466o-3p by antagomiR, either prior to or after ADR injection, substantially restored WT1, alleviated podocytes injury and reduced renal fibrosis. These studies reveal a critical role for miR-466o-3p, a novel microRNA that has not been characterized previously, in mediating β-catenin-triggered WT1 inhibition. Our findings also uncover a new pathogenic mechanism by which β-catenin promotes podocyte injury and proteinuria in glomerular diseases.

Tubule-derived exosomes play a central role in fibroblast activation and kidney fibrosis

Extracellular vesicles such as exosomes are involved in mediating cell-cell communication by shuttling an assortment of proteins and genetic information. Here, we tested whether renal tubule-derived exosomes play a central role in mediating kidney fibrosis. The production of exosomes was found to be increased in the early stage of unilateral ureteral obstruction, ischemia reperfusion injury or 5/6 nephrectomy models of kidney disease. Exosome production occurred primarily in renal proximal tubular epithelium and was accompanied by induction of sonic hedgehog (Shh). In vitro, upon stimulation with transforming growth factor-β1, kidney proximal tubular cells (HKC-8) increased exosome production. Purified exosomes from these cells were able to induce renal interstitial fibroblast (NRK-49F) activation. Conversely, pharmacologic inhibition of exosome secretion with dimethyl amiloride, depletion of exosome from the conditioned media or knockdown of Shh expression abolished the ability of transforming growth factor-β1-treated HKC-8 cells to induce NRK-49F activation. In vivo, injections of tubular cell-derived exosomes aggravated kidney injury and fibrosis, which was negated by an Shh signaling inhibitor. Blockade of exosome secretion in vivo ameliorated renal fibrosis after either ischemic or obstructive injury. Furthermore, knockdown of Rab27a, a protein that is essential for exosome formation, also preserved kidney function and attenuated renal fibrotic lesions in mice. Thus, our results suggest that tubule-derived exosomes play an essential role in renal fibrogenesis through shuttling Shh ligand. Hence, strategies targeting exosomes could be a new avenue in developing therapeutics against renal fibrosis.