Cilia-deficient renal tubule cells are primed for injury with mitochondrial defects and aberrant tryptophan metabolism.

The exocyst and Ift88 are necessary for primary ciliogenesis. Overexpression of Exoc5 (OE), a central exocyst component, resulted in longer cilia and enhanced injury recovery. Mitochondria are involved in acute kidney injury (AKI). To investigate cilia and mitochondria, basal respiration and mitochondrial maximal and spare respiratory capacity were measured in Exoc5 OE, Exoc5 knockdown (KD), Exoc5 ciliary targeting sequence mutant (CTS-mut), control Madin-Darby canine kidney (MDCK), Ift88 knockout (KO), and Ift88 rescue cells. In Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells, these parameters were decreased. In Exoc5 OE and Ift88 rescue cells they were increased. Reactive oxygen species were higher in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells compared with Exoc5 OE, control, and Ift88 rescue cells. By electron microscopy, mitochondria appeared abnormal in Exoc5 KD, Exoc5 CTS-mut, and Ift88 KO cells. A metabolomics screen of control, Exoc5 KD, Exoc5 CTS-mut, Exoc5 OE, Ift88 KO, and Ift88 rescue cells showed a marked increase in tryptophan levels in Exoc5 CTS-mut (113-fold) and Exoc5 KD (58-fold) compared with control cells. A 21% increase was seen in Ift88 KO compared with rescue cells. In Exoc5 OE compared with control cells, tryptophan was decreased 59%. To determine the effects of ciliary loss on AKI, we generated proximal tubule-specific Exoc5 and Ift88 KO mice. These mice had loss of primary cilia, decreased mitochondrial ATP synthase, and increased tryptophan in proximal tubules with greater injury following ischemia-reperfusion. These data indicate that cilia-deficient renal tubule cells are primed for injury with mitochondrial defects in tryptophan metabolism.NEW & NOTEWORTHY Mitochondria are centrally involved in acute kidney injury (AKI). Here, we show that cilia-deficient renal tubule cells both in vitro in cell culture and in vivo in mice are primed for injury with mitochondrial defects and aberrant tryptophan metabolism. These data suggest therapeutic strategies such as enhancing ciliogenesis or improving mitochondrial function to protect patients at risk for AKI.

Mitochondrial biogenesis induced by the ß2-adrenergic receptor agonist formoterol accelerates podocyte recovery from glomerular injury.

Podocytes have limited ability to recover from injury. Here, we demonstrate that increased mitochondrial biogenesis, to meet the metabolic and energy demand of a cell, accelerates podocyte recovery from injury. Analysis of events induced during podocyte injury and recovery showed marked upregulation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a transcriptional co-activator of mitochondrial biogenesis, and key components of the mitochondrial electron transport chain. To evaluate our hypothesis that increasing mitochondrial biogenesis enhanced podocyte recovery from injury, we treated injured podocytes with formoterol, a potent, specific, and long-acting ß2-adrenergic receptor agonist that induces mitochondrial biogenesis in vitro and in vivo. Formoterol increased mitochondrial biogenesis and restored mitochondrial morphology and the injury-induced changes to the organization of the actin cytoskeleton in podocytes. Importantly, ß2-adrenergic receptors were found to be present on podocyte membranes. Their knockdown attenuated formoterol-induced mitochondrial biogenesis. To determine the potential clinical relevance of these findings, mouse models of acute nephrotoxic serum nephritis and chronic (Adriamycin [doxorubicin]) glomerulopathy were used. Mice were treated with formoterol post-injury when glomerular dysfunction was established. Strikingly, formoterol accelerated the recovery of glomerular function by reducing proteinuria and ameliorating kidney pathology. Furthermore, formoterol treatment reduced cellular apoptosis and increased the expression of the mitochondrial biogenesis marker PGC-1α and multiple electron transport chain proteins. Thus, our results support ß2-adrenergic receptors as novel therapeutic targets and formoterol as a therapeutic compound for treating podocytopathies.

The motor protein Myo1c regulates transforming growth factor-ß-signaling and fibrosis in podocytes.

Transforming growth factor-ß (TGF-ß) is known to play a critical role in the pathogenesis of many progressive podocyte diseases. However, the molecular mechanisms regulating TGF-ß signaling in podocytes remain unclear. Using a podocyte-specific myosin (Myo)1c knockout, we demonstrate whether Myo1c is critical for TGF-ß-signaling in podocyte disease pathogenesis. Specifically, podocyte-specific Myo1c knockout mice were resistant to fibrotic injury induced by Adriamycin or nephrotoxic serum. Further, loss of Myo1c also protected from injury in the TGF-ß-dependent unilateral ureteral obstruction mouse model of renal interstitial fibrosis. Mechanistic analyses showed that loss of Myo1c significantly blunted TGF-ß signaling through downregulation of canonical and non-canonical TGF-ß pathways. Interestingly, nuclear rather than the cytoplasmic Myo1c was found to play a central role in controlling TGF-ß signaling through transcriptional regulation. Differential expression analysis of nuclear Myo1c-associated gene promoters showed that nuclear Myo1c targeted the TGF-ß responsive gene growth differentiation factor (GDF)-15 and directly bound to the GDF-15 promoter. Importantly, GDF15 was found to be involved in podocyte pathogenesis, where GDF15 was upregulated in glomeruli of patients with focal segmental glomerulosclerosis. Thus, Myo1c-mediated regulation of TGF-ß-responsive genes is central to the pathogenesis of podocyte injury. Hence, inhibiting this process may have clinical application in treating podocytopathies.

A Novel CLCN5 Mutation Associated With Focal Segmental Glomerulosclerosis and Podocyte Injury.

INTRODUCTION: Tubular dysfunction is characteristic of Dent's disease; however, focal segmental glomerulosclerosis (FSGS) can also be present. Glomerulosclerosis could be secondary to tubular injury, but it remains uncertain whether the CLCN5 gene, which encodes an endosomal chloride and/or hydrogen exchanger, plays a role in podocyte biology. Here, we implicate a role for CLCN5 in podocyte function and pathophysiology. METHODS: Whole exome capture and sequencing of the proband and 5 maternally-related family members was conducted to identify X-linked mutations associated with biopsy-proven FSGS. Human podocyte cultures were used to characterize the mutant phenotype on podocyte function. RESULTS: We identified a novel mutation (L521F) in CLCN5 in 2 members of a Hispanic family who presented with a histologic diagnosis of FSGS and low-molecular-weight proteinuria without hypercalciuria. Presence of CLCN5 was confirmed in cultured human podocytes. Podocytes transfected with the wild-type or the mutant (L521F) CLCN5 constructs showed differential localization. CLCN5 knockdown in podocytes resulted in defective transferrin endocytosis and was associated with decreased cell proliferation and increased cell migration, which are hallmarks of podocyte injury. CONCLUSIONS: The CLCN5 mutation, which causes Dent's disease, may be associated with FSGS without hyercalcuria and nepthrolithiasis. The present findings supported the hypothesis that CLCN5 participates in protein trafficking in podocytes and plays a critical role in organizing the components of the podocyte slit diaphragm to help maintain normal cell physiology and a functional filtration barrier. In addition to tubular dysfunction, mutations in CLCN5 may also lead to podocyte dysfunction, which results in a histologic picture of FSGS that may be a primary event and not a consequence of tubular damage.

Regulation of connective tissue growth factor expression in the aqueous humor outflow pathway.

PURPOSE: Connective Tissue Growth Factor (CTGF) is an inducible secretory protein known to regulate proliferation and extracellular matrix production in various cell types. We hypothesize that CTGF plays a critical role in the physiological regulation of aqueous humor outflow through the trabecular meshwork (TM) by influencing extracellular matrix synthesis and organization. METHODS: To determine the expression of CTGF in tissues of the aqueous outflow pathway, cells obtained from human TM and Schlemm's Canal (SC) were analyzed by PCR and western blot analysis. To understand the regulation of CTGF expression in TM cells, TM cells were either treated with various physiologic factors or subjected to cyclical stretch prior to analysis of CTGF expression by RT-PCR and western blot analysis. To study the effect of increased intraocular pressure on CTGF production, we perfused porcine eyes at high pressure (50 mm Hg) for 5 h, followed by analysis of CTGF expression by RT-PCR and western blotting. RESULTS: Treatment of human TM cells treated with either serum or transforming growth factor-beta 1 led to a robust stimulation, compared to thrombin, lysophosphatidic acid (LPA), and dexamethasone, which elicited a relatively moderate induction of CTGF expression. Both high pressure perfusion and mechanical stretch were associated with increases in the levels of CTGF at the protein and transcript levels. CONCLUSIONS: This study demonstrates that CTGF expression in TM cells is modulated by several physiological agonists and by increased ocular pressure and mechanical stretch. These results suggest that the regulation of CTGF expression within tissues of the outflow pathway may play a role in the homeostasis of intraocular pressure, possibly by modulation of ECM production in these tissues.

Effects of cholesterol-lowering statins on the aqueous humor outflow pathway.

PURPOSE: To investigate the effects of cholesterol-lowering statin drugs on trabecular meshwork cellular properties and aqueous humor outflow. METHODS: Primary cell cultures of porcine trabecular meshwork (PTM) and ciliary body (PCB) were treated with either lovastatin or compactin, to determine the effects of statins on cell shape, actin cytoskeletal organization, and cell-extracellular matrix interactions (focal adhesions) by immunofluorescence staining. Changes in myosin light-chain (MLC) phosphorylation were evaluated by Western blot analysis. Changes in Rho GTPase content of membrane fractions from lovastatin-treated PTM cells were assessed by Western blot analysis. A constant-flow, organ-culture perfusion system was used to measure the effects of statins on aqueous humor outflow facility in the anterior segments of porcine eyes. RESULTS: PTM and PCB cells treated with lovastatin or compactin exhibited dramatic changes in cell shape and cytoskeletal organization within 24 hours, consisting of cell rounding, actin depolymerization, and decreased focal adhesions. These effects were found to be reversible on supplementation with geranylgeranyl pyrophosphate. Both lovastatin and compactin decreased MLC phosphorylation in PTM and PCB cells. PTM cells treated with lovastatin exhibited marked decreases in membrane-bound Rho GTPase. In addition, perfusion of organ-cultured porcine eye anterior segments with 100 microM lovastatin for 96 hours caused a significant increase in aqueous humor outflow facility (110%) compared with control eyes, in a reversible manner. CONCLUSIONS: This study demonstrates that the statin drugs lovastatin and compactin induce changes in cell shape and actin cytoskeletal organization and decrease MLC phosphorylation in PTM and PCB cells, all of which are events that are likely to lead to cellular and tissue relaxation. In addition, these effects of the statins appear to be mediated by inhibition of isoprenylation of the small GTP-binding proteins such as Rho GTPase. An important finding is that statins exert an ocular hypotensive response in an organ-culture perfusion model, indicating the potential for this class of drugs in glaucoma therapy.

Expression of dominant negative Rho-binding domain of Rho-kinase in organ cultured human eye anterior segments increases aqueous humor outflow.

PURPOSE: Based on pharmacological inhibition of activity, a role has been proposed for Rho-kinase in the modulation of aqueous outflow and intraocular pressure (IOP). This study employed a molecular approach to specifically address the role of Rho-kinase in the modulation of aqueous humor outflow. METHODS: Adenoviral vectors expressing green fluorescent protein alone (Ad-GFP) or the dominant negative Rho-binding domain of Rho-kinase and GFP (Ad-DNRK-GFP) were utilized in these experiments. Human and porcine primary trabecular meshwork (TM) cells were infected with 30 MOI (multiplicity of infection) of Ad-GFP alone or with Ad-DNRK-GFP. Changes in cell shape, actomyosin cytoskeletal integrity, and the status of myosin light chain (MLC) phosphorylation were evaluated. The aqueous outflow facility was determined in organ cultured anterior segments of human cadaver eyes infected with 10(7) pfu adenoviral vectors (Ad-GFP or Ad-DNRK-GFP) using a constant flow perfusion system. RESULTS: Expression of DNRK resulted in changes in cell shape (cell rounding, cell-cell detachment) and decreased actin stress fiber and focal adhesion staining in TM cells. These cellular changes were associated with substantially reduced myosin light chain phosphorylation. Additionally, organ cultured human eye anterior segments infected with Ad-DNRK-GFP exhibited a significant increase in the outflow facility (80%, n=9) compared to control anterior segments infected with Ad-GFP (5%). CONCLUSIONS: This study demonstrated that specific inhibition of Rho-kinase activity in trabecular meshwork cells led to alterations in cell shape and presumed contractile properties, and we hypothesize that these morphological and contractile events underlie the observed effects of dominant negative Rho-kinase on the aqueous humor outflow facility. These data provide molecular evidence for the hypothesis of Rho-kinase being a potential cellular target involved in the regulation of aqueous humor outflow resistance, with implications for novel glaucoma therapy.

Role of lysophospholipid growth factors in the modulation of aqueous humor outflow facility.

PURPOSE: To investigate the role of lysophospholipid growth factors in the regulation of aqueous humor outflow in the trabecular meshwork (TM). METHODS: The expression profile of the endothelial differentiation gene (Edg) family of G-protein coupled receptors was determined by RT-PCR of human TM (HTM) cell-derived total RNA and by PCR amplification of HTM cell-derived and tissue-derived cDNA libraries. The effects of lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) on actin cytoskeleton and focal adhesions and on myosin light-chain (MLC) phosphorylation in HTM cells were evaluated by immunofluorescence microscopy and Western blot analysis, respectively. Activation of Rho GTPase in HTM cells was quantified by "pull-down" assays. Mobilization of intracellular calcium in HTM cells was determined using spectrofluorometric digital-imaging microscopy. The effects of LPA and S1P on aqueous humor outflow facility were evaluated by perfusion of enucleated porcine eyes. RESULTS: Each of the receptor isoforms Edg1, -2, -3, and -4 was readily detectable in three of four HTM cell-derived libraries, whereas Edg2 was detectable in the HTM tissue library. LPA (20 microM) and S1P (1 microM) stimulated actin stress fiber and focal adhesion formation, increased MLC phosphorylation, and induced marked activation of Rho GTPase in HTM cells. Both LPA (20 microM) and S1P (10 microM) also stimulated increases in intracellular calcium concentration in HTM cells. LPA- and S1P-induced effects on MLC phosphorylation in HTM cells were markedly inhibited by pretreatment with the Rho kinase-specific inhibitor Y-27632 (5 microM). Perfusion of LPA (50 microM) and S1P (5 microM) in enucleated porcine eyes produced a significant decrease in aqueous humor outflow facility from baseline of 37% (n = 6) and 31% (n = 5), respectively. CONCLUSIONS: These studies demonstrate that LPA and S1P, the physiological agonists of Edg receptors, decrease outflow facility in perfused porcine eyes in association with increased MLC phosphorylation and Rho guanosine triphosphatase (GTPase) activation. These data provide evidence for a novel mechanism for negative regulation of outflow facility, which may contribute to overall physiological homeostasis of aqueous humor outflow facility.

Regulation of myosin light chain phosphorylation in the trabecular meshwork: role in aqueous humour outflow facility.

Cellular contraction and relaxation and integrity of the actin cytoskeleton in trabecular meshwork (TM) tissue have been thought to influence aqueous humour outflow. However, the cellular pathways that regulate these events in TM cells are not well understood. In this study, we investigated physiological agonist-mediated regulation of myosin light chain (MLC) phosphorylation in the TM, and correlated such effects with alterations in aqueous outflow facility, since MLC phosphorylation is a critical biochemical determinant of cellular contraction in TM cells. Treatment of serum starved human TM cells with endothelin-1 (0.1 microM), thromboxane A2 mimetic U-46619 (1.0 microM), or angiotensin II (1 microM), all of which are agonists of G-protein coupled receptors, triggered activation of MLC phosphorylation, as determined by urea/glycerol-based Western blot analysis. Agonist-stimulated increase in MLC phosphorylation was associated with activation of Rho GTPase in TM cells, as determined in pull-down assays. In contrast, treatment of human TM cells with a novel Rho-kinase inhibitor H-1152 (0.1-2 microM), in the presence of serum reduced basal MLC phosphorylation. H-1152 also increased aqueous outflow facility significantly in a dose-dependent fashion, in perfusion studies with cadaver porcine eyes. This effect of H-1152 on outflow facility was associated with decreased MLC phosphorylation in TM tissue of drug-perfused eyes. Collectively, this study identifies potential physiological regulators of MLC phosphorylation in human TM cells and demonstrates the significance of Rho/Rho-kinase pathway-mediated MLC phosphorylation in modulation of aqueous outflow facility through TM.

The role of protein kinase C in modulation of aqueous humor outflow facility.

The elevated intraocular pressure that is commonly associated with glaucoma is believed to arise due to impairment of trabecular meshwork (TM) function. Although the TM and Schlemm's canal (SC) comprise the major route for aqueous humor outflow, little is known about the potential signaling mechanisms involved in the regulation of aqueous outflow. Based on knowledge regarding the role of protein kinase C (PKC) in vascular biology, we sought to understand the contribution of the PKC pathway towards outflow function by studying the modulation of contractile and morphological characteristics of TM and SC cells. We investigated the involvement of PKC in regulation of myosin light chain (MLC) phosphorylation, formation of actin stress fibers and integrin-ECM adhesions (focal adhesions) in human TM and SC cells and correlated these changes with aqueous outflow facility measured in an enucleated porcine whole eye perfusion model. Expression and distribution of PKC isoforms (alpha and epsilon ) in TM and SC cells and tissues was confirmed by Western blot and immunohistochemical analysis, respectively. Both, pharmacological activators (phorbol-12-myristate 13-acetate (PMA) and phorbol-12,13-dibutyrate (PDBu)) and inhibitors (staurosporine and GF109203X) of PKC were found to induce changes in cell shape (retraction and rounding up) and cytoskeletal organization in human TM and SC cells. While PMA and PDBu produced an increase in formation of actin stress fibers and focal adhesions and in MLC phosphorylation, PKC inhibitors were observed to induce contrasting effects in these cells. Intriguingly, both PDBU and GF109203X caused increases in aqueous outflow facility in the perfusion model. The PKC inhibitor (GF109203X) increased outflow by 46% while the PKC activator (PDBu) only increased outflow by 27%. These results suggest that PKC might play an important role in modulation of aqueous outflow facility by regulating MLC phosphorylation and thereby, the morphological and cytoskeletal characteristics of TM and SC cells.

Impaired cytoskeletal organization and membrane integrity in lens fibers of a Rho GTPase functional knockout transgenic mouse.

To investigate the effects of Rho GTPase inactivation on lens fiber cell cytoskeletal and morphological integrity, a transgenic mouse model expressing C3-exoenzyme (a bacterial toxin) in a lens-specific manner was utilized. Cryosections of whole eyes from C3 transgenic mice and littermate controls were stained for F-actin with rhodamine-phalloidin or immunostained for beta-catenin, aquaporin-0 or connexin-50, and confocal images were recorded. Lens fiber cell morphology was examined at both light and electron microscopic levels. To investigate the influence of Rho GTPase inactivation on the profiles of gene expression, cDNA libraries generated from transgenic and littermate control mouse lenses were screened by cDNA microarray analysis. In contrast to the wild-type lens, fiber cells of the transgenic lens were grossly swollen and disorganized, with abnormal membrane architecture. Staining of F-actin, beta-catenin, aquaporin-0 and connexin-50 was reduced dramatically in the C3 transgenic lens as compared to controls. Western blot analysis and cDNA microarray analysis did not reveal any noticeable decreases in actin, beta-catenin and aquaporin-0 protein levels or expression in C3 transgenic lenses, indicating that altered cytoskeletal organization in response to Rho GTPase inactivation might underlie the noted changes in staining for these proteins. Additionally, cDNA microarray analysis of C3 lens revealed altered expression (at least two-fold, compared to littermate controls) of 44 genes. These include genes encoding extracellular matrix and basement membrane proteins, cell survival and apoptotic pathways, and ion and protein transport. These data indicate that disruption of Rho GTPase function in the developing mouse lens results in abnormal cytoskeletal organization, fiber cell interactions, impaired lens fiber cell morphology and altered gene expression of cellular proteins involved in diverse functions. This work reveals that the morphological and cytoskeletal abnormalities triggered upon Rho GTPase inactivation in lens could be one of the important insults associated with cataract formation in C3 transgenic mouse lens.