Hepatocyte growth factor (HGF) has been shown to reduce renal injury in a variety of animal models of chronic renal disease. Suggested mechanisms to explain this action include prevention of tubular ...cell apoptosis, blocking epithelial-to-mesenchymal transition, and promotion of extracellular matrix degradation. Inflammation is another common finding in kidneys that progress to end-stage renal failure; however, the effect of HGF on inflammation has hardly been investigated. For examining this issue, beginning 2 wk after subtotal nephrectomy, rats received a continuous infusion of recombinant HGF, neutralization of endogenous HGF by daily injection of an anti-HGF antibody, or preimmune IgG for an additional 2 wk. HGF infusion halted the progression of proteinuria and decreased renal collagen accumulation. Renal inflammation in both glomeruli and tubulointerstitium was significantly attenuated, associated with reductions in the tubular expression of the chemokines macrophage chemoattractant protein-1 (MCP-1) and RANTES (regulated upon expression normal T cell expressed and secreted). In contrast, HGF neutralization worsened renal fibrosis, aggravated renal inflammation, and enhanced tubular expression of MCP-1 and RANTES. In vitro, HGF suppressed basal and TNF-alpha-induced expression of these chemokines at both the mRNA and protein levels in a time- and dose-dependent manner in proximal tubular epithelial cells. HGF also blunted TNF-alpha-induced nuclear translocation and activation of NF-kappaB, a pivotal transcription factor that regulates chemokine expression. Immunohistochemistry showed that activated NF-kappaB was evident in tubules in remnant kidneys and increased remarkably with anti-HGF treatment. HGF infusion markedly suppressed expression of activated NF-kappaB in remnant kidneys. These findings suggest that the beneficial effect of HGF in chronic renal disease is attributable, at least in part, to a direct anti-inflammatory action, likely via NF-kappaB, on tubular epithelial cells.
Our recent studies showed that transglutaminase-1 (TGase-1) is uniquely expressed in mouse renal proximal tubular cells (RPTC) and mediates cell proliferation. In this study, we investigated the role ...of TGase-1 in cell survival and the survival signaling pathways regulated by TGase-1 in RPTC following oxidant injury. Exposure of RPTC to hydrogen peroxide (H2O2) resulted in apoptosis and an increase in TGase activity. Inhibition of TGase activity with monodansylcadervine (MDC), a TGase inhibitor, or knockdown of TGase-1 with small interference (si)RNA enhanced apoptosis and decreased cell survival in H2O2-treated RPTC. Conversely, overexpression of TGase-1 rendered RPTC more resistant to H2O2 toxicity and MDC treatment blocked this response. Concurrent with RPTC apoptosis, phosphorylation of AKT, signal transducer and activator of transcription-3 (STAT3), and glucogen synthase kinase-3beta (GSK-3beta) were observed. Pretreatment of cells with MDC or TGase-1 siRNA inhibited phosphorylation of all these molecules. Inhibition of either the AKT or STAT3 pathway potentiated H2O2-induced cell death and increased GSK-3beta activity by dephosphorylation at serine 9. Furthermore, treatment with GSK-3beta inhibitors reduced H2O2-induced apoptosis and abolished the death-promoting effect of AKT and STAT3 inhibition. Therefore, we have identified TGase-1 as a novel survival factor in renal epithelial cells and it contributes to cell survival through activation of the AKT and STAT3 signaling pathways following oxidant injury.
Glycogen synthase kinase (GSK)3 is a ubiquitously expressed serine/threonine kinase existing in two isoforms, namely GSK3α and GSK3β. Aside from the long-recognized role in insulin signal ...transduction and glycogen biosynthesis, GSK3β has been recently coined as a master control molecule in nuclear factor-κB activation and inflammatory kidney injury. Nevertheless, previous studies are less conclusive because they relied greatly on small molecule inhibitors, which lack selectivity and barely distinguish between the GSK3 isoforms. In addition, early embryonic lethality after global knockout of GSK3β precludes interrogation of the biological role of GSK3β in the adult kidney. To circumvent these issues, the Cre/loxP system was used to generate a conditional knockout mouse model in which the GSK3β gene was specifically deleted in kidney cortical tubules at postnatal mature stage. Kidney-specific ablation of GSK3β resulted in a phenotype no different from control littermates. Knockout mice (KO) were viable and exhibited normal development and normal kidney physiology in terms of kidney function, urine albumin excretion, and urine-concentrating ability. It is noteworthy that apart from normal glomerular and tubulointerstitial morphology, the kidneys from KO demonstrated more glycogen accumulation in the renal cortical tubules as assessed by both periodic acid-Schiff staining for light microscopy and direct biochemical assay, consistent with an elevated glycogen synthetic activity as evidenced by diminished inhibitory phosphorylation of glycogen synthase that occurred subsequent to GSK3β ablation. This finding was further validated by electron microscopic observations of increased deposition of glycogen particles in the renal tubules of KO, suggesting that GSK3α could not fully compensate for the loss of GSK3β in regulating glycogen metabolism in the kidney. Collectively, our study suggests that kidney-specific ablation of GSK3β barely affects kidney function and histology under normal circumstances. Extended examinations of these KO under diseased conditions are merited to understand the role of GSK3β in renal pathophysiology.
Vascular tissue expresses two isoforms of the enzyme 11β-Hydroxysteroid dehydrogenase, 11β-HSD1 and 11β-HSD2. These enzymes are responsible for the local metabolism of endogenous glucocorticoids ...(GCs). 11β-HSD1 deactivates GCs to their 11
keto metabolites or transforms inert 11
keto metabolites back to active GCs. Although, bi-directional, vascular 11β-HSD1 favors reactivation (reductase) over the deactivation (dehydrogenase) reaction, 11β-HSD2 only functions as a dehydrogenase. GC deactivation by enhanced 11β-HSD2 dehydrogenase activity or by impaired 11β-HSD1 reductase activity correlates with lower vascular resistance. These studies were designed to demonstrate the existence and regulation of these isoforms in vascular endothelial cells and to determine whether the expression varied by species and locale. Western blots were prepared from pre-confluent and confluent cultures of human umbilical vein endothelial cells (HUVEC). 11β-HSD1 was clearly expressed while 11β-HSD2 was much less prominent. Cultured rat aortic and bovine glomerular endothelial cells showed a similar pattern. Using immunohistochemistry, endothelial cells from human and mouse artery preparations clearly demonstrated 11β-HSD1. In separate experiments, pre-confluent growing HUVEC expressed more 11β-HSD1 compared to confluent cells. Serum-deprived growth-retarded HUVEC expressed significantly less 11β-HSD1. The enhanced expression of 11β-HSD1 was also observed 24
h following a scratch “injury” to the culture plates. Changes in 11β-HSD1 with growth and during repair occurred at the transcription level. Thus, 11β-HSD1 protein expression predominates in endothelial cells and varies during periods of growth.
Diabetic kidney disease (DKD) is one of the most common complications of diabetes and is clinically featured by progressive albuminuria, consequent to glomerular destruction that involves podocyte ...senescence. Burgeoning evidence suggests that ketosis, in particular β-hydroxybutyrate, exerts a beneficial effect on aging and on myriad metabolic or chronic diseases, including obesity, diabetes and chronic kidney diseases. Its effect on DKD is largely unknown. In vitro in podocytes exposed to a diabetic milieu, β-hydroxybutyrate treatment substantially mitigated cellular senescence and injury, as evidenced by reduced formation of γH2AX foci, reduced staining for senescence-associated-β-galactosidase activity, diminished expression of key mediators of senescence signaling like p16INK4A and p21, and preserved expression of synaptopodin. This beneficial action of β-hydroxybutyrate coincided with a reinforced transcription factor Nrf2 antioxidant response. Mechanistically, β-hydroxybutyrate inhibition of glycogen synthase kinase 3β (GSK3β), a convergent point for myriad signaling pathways regulating Nrf2 activity, seems to contribute. Indeed, trigonelline, a selective inhibitor of Nrf2, or ectopic expression of constitutively active mutant GSK3β abolished, whereas selective activation of Nrf2 was sufficient for the anti-senescent and podocyte protective effects of β-hydroxybutyrate. Moreover, molecular modeling and docking analysis revealed that β-hydroxybutyrate is able to directly target the ATP-binding pocket of GSK3β and thereby block its kinase activity. In murine models of streptozotocin-elicited DKD, β-hydroxybutyrate therapy inhibited GSK3β and reinforced Nrf2 activation in glomerular podocytes, resulting in lessened podocyte senescence and injury and improved diabetic glomerulopathy and albuminuria. Thus, our findings may pave the way for developing a β-hydroxybutyrate-based novel approach of therapeutic ketosis for treating DKD.
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Evidence suggests that hepatocyte growth factor (HGF) ameliorates renal fibrosis in animal models of chronic renal disease by promoting extracellular matrix catabolism. This study examined the ...molecular mechanisms of HGF-induced alterations in matrix degradation both in vitro and in vivo. In vitro, HGF increased the collagen catabolizing activity of human proximal tubular epithelial cells (HKC) that were treated with TGF-beta1. Increased collagen catabolism was associated with enhanced activity of both matrix metalloproteinases (MMP) and plasminogen activators (PA)/plasmin proteolytic pathways. HGF abrogated TGF-beta1-induced production of the profibrotic tissue inhibitor of metalloproteinase-2 (TIMP-2) and plasminogen activator inhibitor-1 (PAI-1). In addition, HGF induced the production of MMP-9. In vivo, continuous infusion of HGF in the rat remnant kidney model ameliorated renal fibrosis and tubulointerstitial collagen deposition. This was associated with increased tubular expression of MMP-9, enhanced in situ gelatinolytic activity, partially restored plasmin activity and decreased expression of TIMP-2 and PAI-1 in tubular cells, and upregulation of renal TIMP-3 expression. Conversely, blocking of endogenous HGF by an anti-HGF neutralizing antibody increased renal fibrosis and interstitial collagen. This was accompanied by decreased tubular expression of MMP-9, less in situ proteolytic activity, and elevated expression of TIMP-2 and PAI-1 in tubular cells. Collectively, these findings demonstrate that HGF ameliorates renal fibrosis by enhancing extracellular matrix catabolism via both MMP and the PA/plasmin proteolytic pathways.
Nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) is regulated by a myriad of signaling cascades including glycogen synthase kinase (GSK) 3β and plays a Janus role in podocyte ...injury. In vitro, lipopolysaccharide (LPS) or adriamycin (ADR) elicited podocyte injury and cytoskeletal disruption, associated with NFκB activation and induced expression of NFκB target molecules, including pro-survival Bcl-xL and podocytopathic mediators like MCP-1, cathepsin L, and B7-1. Broad-range inhibition of NFκB diminished the expression of all NFκB target genes, restored cytoskeleton integrity, but potentiated apoptosis. In contrast, blockade of GSK3β by lithium or 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) mitigated the expression of podocytopathic mediators, ameliorated podocyte injury, but barely affected Bcl-xL expression or sensitized apoptosis. Mechanistically, GSK3β was sufficient and essential for RelA/p65 phosphorylation, specifically at serine 467, which specifies the expression of selective NFκB target molecules, including podocytopathic mediators, but not Bcl-xL. In vivo, lithium or TDZD-8 therapy improved podocyte injury and proteinuria in mice treated with LPS or ADR, concomitant with the suppression of podocytopathic mediators, but retained Bcl-xL in glomerulus. Broad-range inhibition of NFκB conferred similar but much weakened antiproteinuric and podoprotective effects accompanied with a blunted glomerular expression of Bcl-xL and marked podocyte apoptosis. Thus, the GSK3β-dictated fine-tuning of NFκB may serve as a novel therapeutic target for podocytopathy.
•As life expectancy continues to improve, kidney ageing has become an imminent challenge to clinical practice.•Age-related renal impairment is featured by functional decline and histological ...degeneration and predisposes to renal and other diseases.•Senescence of renal parenchymal cells plays a key role in kidney ageing.•Actionable targets have been identified for improving kidney ageing and maintaining lifelong kidney health.
As human life expectancy keeps increasing, ageing populations present a growing challenge for clinical practices. Human ageing is associated with molecular, structural, and functional changes in a variety of organ systems, including the kidney. During the ageing process, the kidney experiences progressive functional decline as well as macroscopic and microscopic histological alterations, which are accentuated by systemic comorbidities like hypertension and diabetes mellitus, or by preexisting or underlying kidney diseases. Although ageing per se does not cause kidney injury, physiologic changes associated with normal ageing processes are likely to impair the reparative capacity of the kidney and thus predispose older people to acute kidney disease, chronic kidney disease and other renal diseases. Mechanistically, cell senescence plays a key role in renal ageing, involving a number of cellular signaling mechanisms, many of which may be harnessed as international targets for slowing or even reversing kidney ageing. This review summarizes the clinical characteristics of renal ageing, highlights the latest progresses in deciphering the role of cell senescence in renal ageing, and envisages potential interventional strategies and novel therapeutic targets for preventing or improving renal ageing in the hope of maintaining long-term kidney health and function across the life course.
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