Phosphodiesterase 5 inhibition ameliorates angiontensin II-induced podocyte dysmotility via the protein kinase G-mediated downregulation of TRPC6 activity

The roles of TRPC6 in renal tubular disorders: a narrative review

The transient receptor potential canonical 6 (TRPC6) channel, a nonselective cation channel that allows the passage of Ca2+, plays an important role in renal diseases. TRPC6 is activated by Ca2+ influx, oxidative stress, and mechanical stress. Studies have shown that in addition to glomerular diseases, TRPC6 can contribute to renal tubular disorders, such as acute kidney injury, renal interstitial fibrosis, and renal cell carcinoma (RCC). However, the tubule-specific physiological functions of TRPC6 have not yet been elucidated. Its pathophysiological role in ischemia/reperfusion (I/R) injury is debatable. Thus, TRPC6 may have dual roles in I/R injury. TRPC6 induces renal fibrosis and immune cell infiltration in a unilateral ureteral obstruction (UUO) mouse model. Additionally, TRPC6 overexpression may modify G2 phase transition, thus altering the DNA damage checkpoint, which can cause genomic instability and RCC tumorigenesis and can control the proliferation of RCC cells. This review highlights the importance of TRPC6 in various conditions of the renal tubular system. To better understand certain renal disorders and ultimately identify new therapeutic targets to improve patient care, the pathophysiology of TRPC6 must be clarified.

β-Arrestin pathway activation by selective ATR1 agonism promotes calcium influx in podocytes, leading to glomerular damage

Angiotensin receptor blockers (ARBs) are the first-line treatment for hypertension; they act by inhibiting signaling through the angiotensin 1 receptor (AT1R). Recently, a novel biased AT1R agonist, TRV120027 (TRV), which selectively activates the β-arrestin cascade and blocks the G-protein-coupled receptor pathway has been proposed as a potential blood pressure medication. Here, we explored the effects of TRV and associated β-arrestin signaling in podocytes, essential cells of the kidney filter. We used human podocyte cell lines to determine β-arrestin's involvement in calcium signaling and cytoskeletal reorganization and Dahl SS rats to investigate the chronic effects of TRV administration on glomerular health. Our experiments indicate that the TRV-activated β-arrestin pathway promotes the rapid elevation of intracellular Ca2+ in a dose-dependent manner. Interestingly, the amplitude of β-arrestin-mediated Ca2+ influx was significantly higher than the response to similar Ang II concentrations. Single-channel analyses show rapid activation of transient receptor potential canonical (TRPC) channels following acute TRV application. Furthermore, the pharmacological blockade of TRPC6 significantly attenuated the β-arrestin-mediated Ca2+ influx. Additionally, prolonged activation of the β-arrestin pathway in podocytes resulted in pathological actin cytoskeleton rearrangements, higher apoptotic cell markers, and augmented glomerular damage. TRV-activated β-arrestin signaling in podocytes may promote TRPC6 channel-mediated Ca2+ influx, foot process effacement, and apoptosis, possibly leading to severe defects in glomerular filtration barrier integrity and kidney health. Under these circumstances, the potential therapeutic application of TRV for hypertension treatment requires further investigation to assess the balance of the benefits versus possible deleterious effects and off-target damage.

Cingulate cGMP-dependent protein kinase I facilitates chronic pain and pain-related anxiety and depression

ABSTRACT

Patients with chronic pain often experience exaggerated pain response and aversive emotion, such as anxiety and depression. Central plasticity in the anterior cingulate cortex (ACC) is assumed to be a critical interface for pain perception and emotion, which has been reported to involve activation of NMDA receptors. Numerous studies have documented the key significance of cGMP-dependent protein kinase I (PKG-I) as a crucial downstream target for the NMDA receptor-NO-cGMP signaling cascade in regulating neuronal plasticity and pain hypersensitivity in specific regions of pain pathway, ie, dorsal root ganglion or spinal dorsal horn. Despite this, whether and how PKG-I in the ACC contributes to cingulate plasticity and comorbidity of chronic pain and aversive emotion has remained elusive. Here, we uncovered a crucial role of cingulate PKG-I in chronic pain and comorbid anxiety and depression. Chronic pain caused by tissue inflammation or nerve injury led to upregulation of PKG-I expression at both mRNA and protein levels in the ACC. Knockdown of ACC-PKG-I relieved pain hypersensitivity as well as pain-associated anxiety and depression. Further mechanistic analysis revealed that PKG-I might act to phosphorylate TRPC3 and TRPC6, leading to enhancement of calcium influx and neuronal hyperexcitability as well as synaptic potentiation, which results in the exaggerated pain response and comorbid anxiety and depression. We believe this study sheds new light on the functional capability of ACC-PKG-I in modulating chronic pain as well as pain-associated anxiety and depression. Hence, cingulate PKG-I may represent a new therapeutic target against chronic pain and pain-related anxiety and depression.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Repurposing Riociguat to Target a Novel Paracrine Nitric Oxide-TRPC6 Pathway to Prevent Podocyte Injury

Increased expression and activity of the Ca²⁺ channel transient receptor potential channel 6 (TRPC6) is associated with focal segmental glomerulosclerosis, but therapeutic strategies to target TRPC6 are currently lacking. Nitric oxide (NO) is crucial for normal glomerular function and plays a protective role in preventing glomerular diseases. We investigated if NO prevents podocyte injury by inhibiting injurious TRPC6-mediated signaling in a soluble guanylate cyclase (sGC)-dependent manner and studied the therapeutic potential of the sGC stimulator Riociguat. Experiments were performed using human glomerular endothelial cells and podocytes. Podocyte injury was induced by Adriamycin incubation for 24 h, with or without the NO-donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP), the sGC stimulator Riociguat or the TRPC6 inhibitor Larixyl Acetate (LA). NO and Riociguat stimulated cGMP synthesis in podocytes, decreased Adriamycin-induced TRPC6 expression, inhibited the Adriamycin-induced TRPC6-mediated Ca²⁺ influx and reduced podocyte injury. The protective effects of Riociguat and NO were blocked when sGC activity was inhibited with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or when TRPC6 activity was inhibited by LA. Our data demonstrate a glomerular (e)NOS-NO-sGC-cGMP-TRPC6 pathway that prevents podocyte injury, which can be translated to future clinical use by, e.g., repurposing the market-approved drug Riociguat.

Urine-Derived Epithelial Cells as Models for Genetic Kidney Diseases

Epithelial cells exfoliated in human urine can include cells anywhere from the urinary tract and kidneys; however, podocytes and proximal tubular epithelial cells (PTECs) are by far the most relevant cell types for the study of genetic kidney diseases. When maintained in vitro, they have been proven extremely valuable for discovering disease mechanisms and for the development of new therapies. Furthermore, cultured patient cells can individually represent their human sources and their specific variants for personalized medicine studies, which are recently gaining much interest. In this review, we summarize the methodology for establishing human podocyte and PTEC cell lines from urine and highlight their importance as kidney disease cell models. We explore the well-established and recent techniques of cell isolation, quantification, immortalization and characterization, and we describe their current and future applications.

Established and emerging therapeutic uses of PDE type 5 inhibitors in cardiovascular disease

PDE type 5 inhibitors (PDE5Is), such as sildenafil, tadalafil and vardenafil, are a class of drugs used to prolong the physiological effects of NO/cGMP signalling in tissues through the inhibition of cGMP degradation. Although these agents were originally developed for the treatment of hypertension and angina, unanticipated side effects led to advances in the treatment of erectile dysfunction and, later, pulmonary arterial hypertension. In the last decade, accumulating evidence suggests that PDE5Is may confer a wider range of clinical benefits than was previously recognised. This has led to a broader interest in the cardiovascular therapeutic potential of PDE5Is, in conditions such as hypertension, myocardial infarction, stroke, peripheral arterial disease, chronic kidney disease and diabetes mellitus. Here, we review the pharmacological properties and established licensed uses of this class of drug, along with emerging therapeutic developments and possible future indications.

Post-Translational Modification and Natural Mutation of TRPC Channels

Transient Receptor Potential Canonical (TRPC) channels are homologues of Drosophila TRP channel first cloned in mammalian cells. TRPC family consists of seven members which are nonselective cation channels with a high Ca²⁺ permeability and are activated by a wide spectrum of stimuli. These channels are ubiquitously expressed in different tissues and organs in mammals and exert a variety of physiological functions. Post-translational modifications (PTMs) including phosphorylation, N-glycosylation, disulfide bond formation, ubiquitination, S-nitrosylation, S-glutathionylation, and acetylation play important roles in the modulation of channel gating, subcellular trafficking, protein-protein interaction, recycling, and protein architecture. PTMs also contribute to the polymodal activation of TRPCs and their subtle regulation in diverse physiological contexts and in pathological situations. Owing to their roles in the motor coordination and regulation of kidney podocyte structure, mutations of TRPCs have been implicated in diseases like cerebellar ataxia (moonwalker mice) and focal and segmental glomerulosclerosis (FSGS). The aim of this review is to comprehensively integrate all reported PTMs of TRPCs, to discuss their physiological/pathophysiological roles if available, and to summarize diseases linked to the natural mutations of TRPCs.

TRPC Channels in Proteinuric Kidney Diseases

Over a decade ago, mutations in the gene encoding TRPC6 (transient receptor potential cation channel, subfamily C, member 6) were linked to development of familial forms of nephrosis. Since this discovery, TRPC6 has been implicated in the pathophysiology of non-genetic forms of kidney disease including focal segmental glomerulosclerosis (FSGS), diabetic nephropathy, immune-mediated kidney diseases, and renal fibrosis. On the basis of these findings, TRPC6 has become an important target for the development of therapeutic agents to treat diverse kidney diseases. Although TRPC6 has been a major focus for drug discovery, more recent studies suggest that other TRPC family members play a role in the pathogenesis of glomerular disease processes and chronic kidney disease (CKD). This review highlights the data implicating TRPC6 and other TRPC family members in both genetic and non-genetic forms of kidney disease, focusing on TRPC3, TRPC5, and TRPC6 in a cell type (glomerular podocytes) that plays a key role in proteinuric kidney diseases.

TRPC6 Binds to and Activates Calpain, Independent of Its Channel Activity, and Regulates Podocyte Cytoskeleton, Cell Adhesion, and Motility

BACKGROUND

Mutations in the transient receptor potential channel 6 (TRPC6) gene are associated with an inherited form of FSGS. Despite widespread expression, patients with TRPC6 mutations do not present with any other pathologic phenotype, suggesting that this protein has a unique yet unidentified role within the target cell for FSGS, the kidney podocyte.

METHODS

We generated a stable TRPC6 knockout podocyte cell line from TRPC6 knockout mice. These cells were engineered to express wild-type TRPC6, a dominant negative TRPC6 mutation, or either of two disease-causing mutations of TRPC6, G109S or K874*. We extensively characterized these cells using motility, detachment, and calpain activity assays; immunofluorescence; confocal or total internal reflection fluorescence microscopy; and western blotting.

RESULTS

Compared with wild-type cells, TRPC6^-/- podocytes are less motile and more adhesive, with an altered actin cytoskeleton. We found that TRPC6 binds to ERK1/2 and the actin regulatory proteins, caldesmon (a calmodulin- and actin-binding protein) and calpain 1 and 2 (calcium-dependent cysteine proteases that control the podocyte cytoskeleton, cell adhesion, and motility via cleavage of paxillin, focal adhesion kinase, and talin). Knockdown or expression of the truncated K874* mutation (but not expression of the gain-of-function G019S mutation or dominant negative mutant of TRPC6) results in the mislocalization of calpain 1 and 2 and significant downregulation of calpain activity; this leads to altered podocyte cytoskeleton, motility, and adhesion-characteristics of TRPC6 ^-/- podocytes.

CONCLUSIONS

Our data demonstrate that independent of TRPC6 channel activity, the physical interaction between TRPC6 and calpain in the podocyte is important for cell motility and detachment and demonstrates a scaffolding role of the TRPC6 protein in disease.

TRPC channels: Regulation, dysregulation and contributions to chronic kidney disease

Mutations in the gene encoding canonical transient receptor potential-6 (TRPC6) channels result in severe nephrotic syndromes that typically lead to end-stage renal disease. Many but not all of these mutations result in a gain in the function of the resulting channel protein. Since those observations were first made, substantial work has supported the hypothesis that TRPC6 channels can also contribute to progression of acquired (non-genetic) glomerular diseases, including primary and secondary FSGS, glomerulosclerosis during autoimmune glomerulonephritis, and possibly in type-1 diabetes. Their regulation has been extensively studied, especially in podocytes, but also in mesangial cells and other cell types present in the kidney. More recent evidence has implicated TRPC6 in renal fibrosis and tubulointerstitial disease caused by urinary obstruction. Consequently TRPC6 is being extensively investigated as a target for drug discovery. Other TRPC family members are present in kidney. TRPC6 can form a functional heteromultimer with TRPC3, and it has been suggested that TRPC5 may also play a role in glomerular disease progression, although the evidence on this is contradictory. Here we review literature on the expression and regulation of TRPC6, TRPC3 and TRPC5 in various cell types of the vertebrate kidney, the evidence that these channels are dysregulated in disease models, and research showing that knock-out or pharmacological inhibition of these channels can reduce the severity of kidney disease. We also summarize several areas that remain controversial, and some of the large gaps of knowledge concerning the fundamental role of these proteins in regulation of renal function.

Regulation of cofilin phosphorylation in glomerular podocytes by testis specific kinase 1 (TESK1)

Expression of a constitutively active Rho A (V14Rho) in podocytes in vivo induces albuminuria and foot process (FP) effacement. These effects may be mediated by the Rho A effector Rho kinase (ROK); but inhibition of ROK with Y27632 failed to attenuate albuminuria or FP effacement in V14Rho mice. ROK activates LIM kinases (LIMKs), which phosphorylate and inhibit the actin depolymerizing factor cofilin 1 (CFL1). Sustained phosphorylation of CFL1 is implicated in human nephrotic diseases, but Y27632 did not inhibit phosphorylation of CFL1 in vivo, despite effective ROK inhibition. CFL1 is also phosphorylated by testis-specific kinase 1 (TESK1) on the same serine residue. TESK1 was expressed in podocytes, and, similar to the in vivo situation, Y27632 had little effect on phospho-CFL1 (pCFL1) levels in cultured podocytes. In contrast, Y27632 reduced pCFL1 levels in TESK1 knockout (KO) cells. ROK inhibition enhanced podocyte motility but, the motility promoting effect of Y27632 was absent in TESK1 KO podocytes. Thus, TESK1 regulates podocyte cytoskeletal dynamics in glomerular podocytes and may play an important role in regulating glomerular filtration barrier integrity in glomerular disease processes.

The Impact of the Nitric Oxide (NO)/Soluble Guanylyl Cyclase (sGC) Signaling Cascade on Kidney Health and Disease: A Preclinical Perspective

Chronic Kidney Disease (CKD) is a highly prevalent disease with a substantial medical need for new and more efficacious treatments. The Nitric Oxide (NO), soluble guanylyl cyclase (sGC), cyclic guanosine monophosphate (cGMP) signaling cascade regulates various kidney functions. cGMP directly influences renal blood flow, renin secretion, glomerular function, and tubular exchange processes. Downregulation of NO/sGC/cGMP signaling results in severe kidney pathologies such as CKD. Therefore, treatment strategies aiming to maintain or increase cGMP might have beneficial effects for the treatment of progressive kidney diseases. Within this article, we review the NO/sGC/cGMP signaling cascade and its major pharmacological intervention sites. We specifically focus on the currently known effects of cGMP on kidney function parameters. Finally, we summarize the preclinical evidence for kidney protective effects of NO-donors, PDE inhibitors, sGC stimulators, and sGC activators.

The mechanism of attenuation of epithelial-mesenchymal transition by a phosphodiesterase 5 inhibitor via renal klotho expression

Phosphodiesterase-5 (PDE-5) inhibitors induces vasodilation in several organs by blocking cyclic GMP (guanosine monophosphate) degradation. However, the existence of alternative mechanism of action in case of an impaired nitric oxide (NO) system remains controversial. Previous studies suggested that decreased NO bioavailability may result in the downregulation of klotho expression, but the relationship between klotho and NO remains obscure. Therefore, we investigated whether a PDE-5 inhibitor could preserve epithelial-mesenchymal transition (EMT) and relationship exists between the NO and renal klotho expression. Ten-week-old SD rats (N = 24, 200 g, male) were divided (N = 6) into four groups, which received: A LSD, L-NAME 1 mg/mL in drinking water, Udenafil 5 mg/kg subcutaneously and both for 4 weeks. Urine nitrate/nitrite, NGAL (Neutrophil gelatinase-associated lipocalin), and cGMP were measured using ELISA. Kidney was subjected to evaluate PCNA (proliferative cell nuclear antigen), α-SMA (smooth muscle cell antigen), E-cadherin, and klotho expression. Urine cGMP decreased after treatment of PDE-5 inhibitor compared with control due to blocking degradation of cGMP (P < .05, control vs Udenafil and L-NAME with Udenafil groups). Urine NGAL increased after treating of L-NAME and attenuated after using PDE-5 inhibitor (P < .05, control vs L-NAME and L-NAME with Udenafil). PCNA, α-SMA, and E-cadherin (EMT markers) increased after L-NAME treatment and normalized after using PDE-5 inhibitor. Klotho expression showed trend to increase in the L-NAME with PDE-5 inhibitor group compared with the L-NAME group, however, eNOS expression did not change after treatment of L-NAME or PDE-5 inhibitor compared with control. PDE-5 inhibitor alleviates EMT in the kidney via klotho modulation independent of the NO system.

Precision Medicine for Heart Failure with Preserved Ejection Fraction: An Overview

There are few proven therapies for heart failure with preserved ejection fraction (HFpEF). The lack of therapies, along with increased recognition of the disorder and its underlying pathophysiology, has led to the acknowledgement that HFpEF is heterogeneous and is not likely to respond to a one-size-fits-all approach. Thus, HFpEF is a prime candidate to benefit from a precision medicine approach. For this reason, we have assembled a compendium of papers on the topic of precision medicine in HFpEF in the Journal of Cardiovascular Translational Research. These papers cover a variety of topics relevant to precision medicine in HFpEF, including automated identification of HFpEF patients; machine learning, novel molecular approaches, genomics, and deep phenotyping of HFpEF; and clinical trial designs that can be used to advance precision medicine in HFpEF. In this introductory article, we provide an overview of precision medicine in HFpEF with the hope that the work described here and in the other papers in this special theme issue will stimulate investigators and clinicians to advance a more targeted approach to HFpEF classification and treatment.

Sildenafil Prevents Podocyte Injury via PPAR-γ-Mediated TRPC6 Inhibition

Transient receptor potential channel C6 (TRPC6) gain-of-function mutations and increased TRPC6 expression in podocytes induce glomerular injury and proteinuria. Sildenafil reduces TRPC6 expression and activity in nonrenal cell types, although the mechanism is unknown. Peroxisome proliferator-activated receptor γ (PPAR-γ) is a downstream target of sildenafil in the cyclic guanosine monophosphate (cGMP)-activated protein kinase G (PKG) axis. PPAR-γ agonists, like pioglitazone, appear antiproteinuric. We hypothesized that sildenafil inhibits TRPC6 expression in podocytes through PPAR-γ-dependent mechanisms, thereby counteracting podocyte injury and proteinuria. Treatment with sildenafil, the cGMP derivative 8-bromoguanosine 3',5'-cyclic monophosphate sodium salt (8-Br-cGMP), or pioglitazone dose-dependently downregulated podocyte injury-induced TRPC6 expression in vitro Knockdown or application of antagonists of PKG or PPAR-γ enhanced TRPC6 expression in podocytes and counteracted effects of sildenafil and 8-Br-cGMP. We observed similar effects on TRPC6 promoter activity and TRPC6-dependent calcium influx. Chromatin immunoprecipitation showed PPAR-γ binding to the TRPC6 promoter. Sildenafil or pioglitazone treatment prevented proteinuria and the increased TRPC6 expression in rats with adriamycin-induced nephropathy and mice with hyperglycemia-induced renal injury. Rats receiving PPAR-γ antagonists displayed proteinuria and increased podocyte TRPC6 expression, as did podocyte-specific PPAR-γ knockout mice, which were more sensitive to adriamycin and not protected by sildenafil. Thus, sildenafil ameliorates podocyte injury and prevents proteinuria through cGMP- and PKG-dependent binding of PPAR-γ to the TRPC6 promoter, which inhibits TRPC6 promoter activity, expression, and activity. Because sildenafil is approved for clinical use, our results suggest that additional clinical study of its antiproteinuric effect in glomerular disease is warranted.

Emerging therapeutics for the treatment of diabetic nephropathy

Diabetic nephropathy (DN) is the most common pathology contributing to the development of chronic kidney disease (CKD). DN caused by hypertension and unmitigated inflammation in diabetics, renders the kidneys unable to perform normally, and leads to renal fibrosis and organ failure. The increasing global prevalence of DN has been directly attributed to rising incidences of Type II diabetes, and is now the largest non-communicable cause of death worldwide. Despite the high morbidity, successful new treatments for DN are lacking. This review seeks to provide new insight on emerging clinical candidates under investigation for the treatment of DN.

Old dog, new tricks: novel cardiac targets and stress regulation by protein kinase G

The second messenger cyclic guanosine 3'5' monophosphate (cGMP) and its downstream effector protein kinase G (PKG) have been discovered more than 40 years ago. In vessels, PKG1 induces smooth muscle relaxation in response to nitric oxide signalling and thus lowers systemic and pulmonary blood pressure. In platelets, PKG1 stimulation by cGMP inhibits activation and aggregation, and in experimental models of heart failure (HF), PKG1 activation by inhibiting cGMP degradation is protective. The net effect of the above-mentioned signalling is cardiovascular protection. Yet, while modulation of cGMP-PKG has entered clinical practice for treating pulmonary hypertension or erectile dysfunction, translation of promising studies in experimental HF to clinical success has failed thus far. With the advent of new technologies, novel mechanisms of PKG regulation, including mechanosensing, redox regulation, protein quality control, and cGMP degradation, have been discovered. These novel, non-canonical roles of PKG1 may help understand why clinical translation has disappointed thus far. Addressing them appears to be a requisite for future, successful translation of experimental studies to the clinical arena.

Drug discovery in focal and segmental glomerulosclerosis

Despite the high medical burden experienced by patients with focal segmental glomerulosclerosis, the etiology of the condition remains largely unknown. Focal segmental glomerulosclerosis is highly heterogeneous in clinical and morphologic manifestations. While this presents challenges for the development of new treatments, research investments over the last 2 decades have yielded a surfeit of potential avenues for therapeutic intervention. The development of many of those ideas and concepts into new therapies, however, has been very disappointing. Here, we describe some of the factors that have potentially contributed to the poor translational performance from this research investment, including the confidence we ascribe to a target, the conduct of experimental studies, and the availability of selective reagents to test hypotheses. We will discuss the significance of genetic and systems traits as well as other methods for reducing bias. We will analyze the limitations of a successful drug development. We will use specific examples hoping that these will guide a consensus for investment and drive greater translational quality. We hope that this substrate will serve to exemplify the tremendous opportunity for intervention as well as facilitate greater collaborative effort between industry, academia, and private foundations in promoting appropriate validation of these targets. Only then will we have achieved our goal for curative therapies for this devastating disease.

Treatment with irbesatan may improve slit diaphragm alterations in rats with adriamycin-induced nephropathy

Objective:

The study aimed to evaluate the effects of oral administration of irbesartan in adriamycin-induced nephropathy considering laboratory changes, kidney histology, and expression of proteins related to slit diaphragm and cytoskeleton of the podocyte.

Methods:

The animals were divided into control, model, methylprednisolone (MP), and irbesartan groups. The 24-hour urinary protein and biochemical indicators were determined, and renal pathological changes were observed. The mRNA and protein expression of nephrin, podocin, CD2-associated protein (CD2AP), and desmin in the kidney tissue were analyzed.

Results:

The urinary protein excretion levels in the MP and irbesartan groups were lower than those in the model group (p<0.01). Electron microscopy showed that fusion of the glomerular foot processes of the rats in the irbesartan group was significantly reduced. The mRNA and protein expression levels of nephrin and podocin in the renal tissue in the MP and irbesartan groups were up-regulated compared with the model group (p<0.05), whereas the mRNA and protein expression levels of CD2AP and desmin were significantly down-regulated (p<0.01).

Conclusions:

For rats with adriamycin-induced nephropathy, irbesartan could significantly reduce proteinuria. As a possible mechanism, irbesartan may improve the slit diaphragm protein of the glomerular podocyte and stabilize the cytoskeleton of the podocyte.

Natriuretic Peptide Receptor Guanylyl Cyclase-A in Podocytes is Renoprotective but Dispensable for Physiologic Renal Function

The cardiac natriuretic peptides (NPs), atrial NP and B-type NP, regulate fluid homeostasis and arterial BP through renal actions involving increased GFR and vascular and tubular effects. Guanylyl cyclase-A (GC-A), the transmembrane cGMP-producing receptor shared by these peptides, is expressed in different renal cell types, including podocytes, where its function is unclear. To study the effects of NPs on podocytes, we generated mice with a podocyte-specific knockout of GC-A (Podo-GC-A KO). Despite the marked reduction of GC-A mRNA in GC-A KO podocytes to 1% of the control level, Podo-GC-A KO mice and control littermates did not differ in BP, GFR, or natriuresis under baseline conditions. Moreover, infusion of synthetic NPs similarly increased the GFR and renal perfusion in both genotypes. Administration of the mineralocorticoid deoxycorticosterone-acetate (DOCA) in combination with high salt intake induced arterial hypertension of similar magnitude in Podo-GC-A KO mice and controls. However, only Podo-GC-A KO mice developed massive albuminuria (controls: 35-fold; KO: 5400-fold versus baseline), hypoalbuminemia, reduced GFR, and marked glomerular damage. Furthermore, DOCA treatment led to decreased expression of the slit diaphragm-associated proteins podocin, nephrin, and synaptopodin and to enhanced transient receptor potential canonical 6 (TRPC6) channel expression and ATP-induced calcium influx in podocytes of Podo-GC-A KO mice. Concomitant treatment of Podo-GC-A KO mice with the TRPC channel blocker SKF96365 markedly ameliorated albuminuria and glomerular damage in response to DOCA. In conclusion, the physiologic effects of NPs on GFR and natriuresis do not involve podocytes. However, NP/GC-A/cGMP signaling protects podocyte integrity under pathologic conditions, most likely by suppression of TRPC channels.

Phosphodiesterase Type 5 Inhibition Reduces Albuminuria in Subjects with Overt Diabetic Nephropathy

Diabetic nephropathy (DN) is the leading cause of ESRD worldwide. Reduced bioavailability or uncoupling of nitric oxide in the kidney, leading to decreased intracellular levels of the nitric oxide pathway effector molecule cyclic guanosine monophosphate (cGMP), has been implicated in the progression of DN. Preclinical studies suggest that elevating the cGMP intracellular pool through inhibition of the cGMP-hydrolyzing enzyme phosphodiesterase type 5 (PDE5) might exert renoprotective effects in DN. To test this hypothesis, the novel, highly specific, and long-acting PDE5 inhibitor, PF-00489791, was assessed in a multinational, multicenter, randomized, double-blind, placebo-controlled, parallel group trial of subjects with type 2 diabetes mellitus and overt nephropathy receiving angiotensin converting enzyme inhibitor or angiotensin receptor blocker background therapy. In total, 256 subjects with an eGFR between 25 and 60 ml/min per 1.73 m² and macroalbuminuria defined by a urinary albumin-to-creatinine ratio >300 mg/g, were randomly assigned 3:1, respectively, to receive PF-00489791 (20 mg) or placebo orally, once daily for 12 weeks. Using the predefined primary assessment of efficacy (Bayesian analysis with informative prior), we observed a significant reduction in urinary albumin-to-creatinine ratio of 15.7% (ratio 0.843; 95% credible interval 0.73 to 0.98) in response to the 12-week treatment with PF-00489791 compared with placebo. PF-00489791 was safe and generally well tolerated in this patient population. Most common adverse events were mild in severity and included headache and upper gastrointestinal events. In conclusion, the safety and efficacy profile of PDE5 inhibitor PF-00489791 supports further investigation as a novel therapy to improve renal outcomes in DN.

Prevention of PKG1α oxidation augments cardioprotection in the stressed heart

The cGMP-dependent protein kinase-1α (PKG1α) transduces NO and natriuretic peptide signaling; therefore, PKG1α activation can benefit the failing heart. Disease modifiers such as oxidative stress may depress the efficacy of PKG1α pathway activation and underlie variable clinical results. PKG1α can also be directly oxidized, forming a disulfide bond between homodimer subunits at cysteine 42 to enhance oxidant-stimulated vasorelaxation; however, the impact of PKG1α oxidation on myocardial regulation is unknown. Here, we demonstrated that PKG1α is oxidized in both patients with heart disease and in rodent disease models. Moreover, this oxidation contributed to adverse heart remodeling following sustained pressure overload or Gq agonist stimulation. Compared with control hearts and myocytes, those expressing a redox-dead protein (PKG1α(C42S)) better adapted to cardiac stresses at functional, histological, and molecular levels. Redox-dependent changes in PKG1α altered intracellular translocation, with the activated, oxidized form solely located in the cytosol, whereas reduced PKG1α(C42S) translocated to and remained at the outer plasma membrane. This altered PKG1α localization enhanced suppression of transient receptor potential channel 6 (TRPC6), thereby potentiating antihypertrophic signaling. Together, these results demonstrate that myocardial PKG1α oxidation prevents a beneficial response to pathological stress, may explain variable responses to PKG1α pathway stimulation in heart disease, and indicate that maintaining PKG1α in its reduced form may optimize its intrinsic cardioprotective properties.

Gq signaling causes glomerular injury by activating TRPC6

Familial forms of focal segmental glomerulosclerosis (FSGS) have been linked to gain-of-function mutations in the gene encoding the transient receptor potential channel C6 (TRPC6). GPCRs coupled to Gq signaling activate TRPC6, suggesting that Gq-dependent TRPC6 activation underlies glomerular diseases. Here, we developed a murine model in which a constitutively active Gq α subunit (Gq(Q209L), referred to herein as GqQ>L) is specifically expressed in podocytes and examined the effects of this mutation in response to puromycin aminonucleoside (PAN) nephrosis. We found that compared with control animals, animals expressing GqQ>L exhibited robust albuminuria, structural features of FSGS, and reduced numbers of glomerular podocytes. Gq activation stimulated calcineurin (CN) activity, resulting in CN-dependent upregulation of TRPC6 in murine kidneys. Deletion of TRPC6 in GqQ>L-expressing mice prevented FSGS development and inhibited both tubular damage and podocyte loss induced by PAN nephrosis. Similarly, administration of the CN inhibitor FK506 reduced proteinuria and tubular injury but had more modest effects on glomerular pathology and podocyte numbers in animals with constitutive Gq activation. Moreover, these Gq-dependent effects on podocyte injury were generalizable to diabetic kidney disease, as expression of GqQ>L promoted albuminuria, mesangial expansion, and increased glomerular basement membrane width in diabetic mice. Together, these results suggest that targeting Gq/TRPC6 signaling may have therapeutic benefits for the treatment of glomerular diseases.

Translating genetic findings in hereditary nephrotic syndrome: the missing loops

Nephrotic syndrome (NS) is a clinicopathological entity characterized by proteinuria, hypoalbuminemia, peripheral edema, and hyperlipidemia. It is the most common cause of glomerular disease in children and adults. Although the molecular pathogenesis of NS is not completely understood, data from the study of familial NS suggest that it is a "podocytopathy." Virtually all of the genes mutated in hereditary NS localize to the podocyte or its secreted products and the slit diaphragm. Since the completion of human genome sequence and the advent of next generation sequencing, at least 29 causes of single-gene NS have been identified. However, these findings have not been matched by therapeutic advances owing to suboptimal in vitro and in vivo models for the study of human glomerular disease and podocyte injury phenotypes. Multidisciplinary collaboration between clinicians, geneticists, cell biologists, and molecular physiologists has the potential to overcome this barrier and thereby speed up the translation of genetic findings into improved patient care.