cAMP signaling prevents podocyte apoptosis via activation of protein kinase A and mitochondrial fusion

Biofactors regulating mitochondrial function and dynamics in podocytes and podocytopathies

Podocytes are terminally differentiated kidney cells acting as the main gatekeepers of the glomerular filtration barrier; hence, inhibiting proteinuria. Podocytopathies are classified as kidney diseases caused by podocyte damage. Different genetic and environmental risk factors can cause podocyte damage and death. Recent evidence shows that mitochondrial dysfunction also contributes to podocyte damage. Understanding alterations in mitochondrial metabolism and function in podocytopathies and whether altered mitochondrial homeostasis/dynamics is a cause or effect of podocyte damage are issues that need in-depth studies. This review highlights the roles of mitochondria and their bioenergetics in podocytes. Then, factors/signalings that regulate mitochondria in podocytes are discussed. After that, the role of mitochondrial dysfunction is reviewed in podocyte injury and the development of different podocytopathies. Finally, the mitochondrial therapeutic targets are considered.

Therapeutic Potential Targeting Podocyte Mitochondrial Dysfunction in Focal Segmental Glomerulosclerosis

Background

Podocytes are essential components of the glomerular filtration barrier and essential for the proper filtration function of the glomerulus. Podocyte injury under various stress conditions is the primary pathogenesis and key determinant of focal segmental glomerulosclerosis (FSGS) with prominent clinical manifestations of proteinuria or nephrotic syndrome.

Summary

Under physiological conditions, a highly coordinated mitochondrial quality control system, including antioxidant defenses, mitochondrial dynamics (fusion, fission, and mitophagy), and mitochondrial biogenesis, guarantees the sophisticated structure and various functions of podocytes. However, under FSGS pathological conditions, mitochondria encounter oxidative stress, dynamics disturbances, and defective mitochondrial biogenesis. Moreover, mutations in mitochondrial DNA and mitochondria-related genes are also strongly associated with FSGS. Based on these pieces of evidence, bioactive agents that function to relieve mitochondrial oxidative stress and promote mitochondrial biogenesis have been proven effective in preclinical FSGS models. Targeting the mitochondrial network is expected to provide new therapeutic strategies for the treatment of FSGS and delay its progression to end-stage renal disease.

Key Messages

Mitochondrial dysfunction plays a key role in podocyte injury and FSGS progression. This review summarized recent advances in the study of mitochondrial homeostatic imbalance and dysfunction in FSGS and discussed the potential of mitochondria-targeted therapeutics in improving FSGS and retarding its progression to end-stage renal disease.

Therapeutic treatment with phosphodiesterase-4 inhibitors alleviates kidney injury and renal fibrosis by increasing MMP-9 in a doxorubicin-induced nephrotoxicity mouse model

Nephrotic syndrome (NS) is associated with kidney dysfunction and is an important cause of morbidity and mortality in industrialized countries. Here, we evaluated the effects of the phosphodiesterase-4 (PDE-4) inhibitors rolipram and roflumilast on a doxorubicin-induced NS model. Early-stage rolipram treatment preserved glomerular filtration barrier function, as indicated by reduced serum protein and albumin loss and the prevention of hypercholesterolemia. These effects were associated with reduced glomerular and tubular lesions and abrogated renal cell apoptosis. In addition, rolipram treatment reduced inflammation, which was characterized by a decrease in macrophage accumulation and reduced levels of CCL2 and TNF in the kidneys. Rolipram also reduced renal fibrosis, which was associated with decreased α-smooth muscle actin (α-SMA) area and increased metalloproteinase 9 (MMP9) activity in renal tissue. Late-stage rolipram or roflumilast treatment preserved glomerular filtration barrier function, as characterized by reduced serum albumin loss, decreased proteinuria, and the prevention of hypercholesterolemia. Importantly, only roflumilast treatment was associated with a reduction in glomerular and tubular lesions at this time point. In addition, both rolipram and roflumilast reduced renal tissue fibrosis and MMP9 activity in renal tissue.

Nicorandil protects podocytes via modulation of antioxidative capacity in acute puromycin aminonucleoside-induced nephrosis in rats

Nephrotic syndrome, characterized by proteinuria and hypoalbuminemia, results from the dysregulation of glomerular podocytes and is a significant cause of end-stage kidney disease. Patients with idiopathic nephrotic syndrome are generally treated with immunosuppressive agents; however, these agents produce various adverse effects. Previously, we reported the renoprotective effects of a stimulator of the mitochondrial ATP-dependent K⁺ channel (MitK_ATP), nicorandil, in a remnant kidney model. Nonetheless, the cellular targets of these effects remain unknown. Here, we examined the effect of nicorandil on puromycin aminonucleoside-induced nephrosis (PAN) rats, a well-established model of podocyte injury and human nephrotic syndrome. PAN was induced using a single intraperitoneal injection. Nicorandil was administered orally at 30 mg/kg/day. We found that proteinuria and hypoalbuminemia in PAN rats were significantly ameliorated following nicorandil treatment. Immunostaining and ultrastructural analysis under electron microscopy demonstrated that podocyte injury in PAN rats showed a significant partial attenuation following nicorandil treatment. Nicorandil ameliorated the increase in the oxidative stress markers nitrotyrosine and 8-hydroxy-2-deoxyguanosine in glomeruli. Conversely, nicorandil prevented the decrease in levels of the antioxidant enzyme manganese superoxide dismutase in PAN rats. We found that mitochondrial Ca²⁺ uniporter levels in glomeruli were higher in PAN rats than in control rats, and this increase was significantly attenuated by nicorandil. We conclude that stimulation of MitK_ATP by nicorandil reduces proteinuria by attenuating podocyte injury in PAN nephrosis, which restores mitochondrial antioxidative capacity, possibly through mitochondrial Ca²⁺ uniporter modulation. These data indicate that MitK_ATP may represent a novel target for podocyte injury and nephrotic syndrome.NEW & NOTEWORTHY Our findings suggest that the mitochondrial Ca²⁺ uniporter may be an upstream regulator of manganese superoxide dismutase and indicate a biochemical basis for the interaction between the ATP-sensitive K⁺ channel and Ca²⁺ signaling. We believe that our study makes a significant contribution to the literature because our results indicate that the ATP-sensitive K⁺ channel may be a potential therapeutic target for podocyte injury and nephrotic syndrome.

Anti-ANGPTL3-FLD monoclonal antibody treatment ameliorates podocyte lesions through attenuating mitochondrial damage

Proteinuria, an indication of kidney disease, is caused by the malfunction of podocytes, which play a key role in maintaining glomerular filtration. Angiopoietin-like 3 (ANGPTL3) has been documented to have a cell-autonomous involvement in podocytes, and deletion of Angptl3 in podocytes reduced proteinuria in adriamycin-induced nephropathy. Here, we developed a monoclonal antibody (mAb) against ANGPTL3 to investigate its effects on podocyte injury in an ADR nephropathy mouse model and puromycin (PAN) induced podocyte damage in vitro. The mAb against the human ANGPTL3-FLD sequence (5E5F6) inhibited the binding of ANGPTL3-FLD to integrin β3. Treatment with the 5E5F6 mAb in ADR nephropathy mice mitigated proteinuria and led to a significant decline in podocyte apoptosis, reactive oxygen species (ROS) generation and mitochondrial fragmentation. In PAN-induced podocyte damage in vitro, the 5E5F6 mAb blocked the ANPGPLT3-mediated activation of integrin αvβ3 and Rac1, which regulated the mitochondrial homeostasis. Altogether, anti-ANGPLT3-FLD mAb attenuates proteinuria and podocyte lesions in ADR mice models, as well as PAN-induced podocyte damage, in part through regulating mitochondrial functions. Our study provides a therapeutic approach for targeting ANGPTL3 in proteinuric kidney disease.

Mechanisms of podocyte injury and implications for diabetic nephropathy

Albuminuria is the hallmark of both primary and secondary proteinuric glomerulopathies, including focal segmental glomerulosclerosis (FSGS), obesity-related nephropathy, and diabetic nephropathy (DN). Moreover, albuminuria is an important feature of all chronic kidney diseases (CKDs). Podocytes play a key role in maintaining the permselectivity of the glomerular filtration barrier (GFB) and injury of the podocyte, leading to foot process (FP) effacement and podocyte loss, the unifying underlying mechanism of proteinuric glomerulopathies. The metabolic insult of hyperglycemia is of paramount importance in the pathogenesis of DN, while insults leading to podocyte damage are poorly defined in other proteinuric glomerulopathies. However, shared mechanisms of podocyte damage have been identified. Herein, we will review the role of haemodynamic and oxidative stress, inflammation, lipotoxicity, endocannabinoid (EC) hypertone, and both mitochondrial and autophagic dysfunction in the pathogenesis of the podocyte damage, focussing particularly on their role in the pathogenesis of DN. Gaining a better insight into the mechanisms of podocyte injury may provide novel targets for treatment. Moreover, novel strategies for boosting podocyte repair may open the way to podocyte regenerative medicine.

Deiodinase-3 is a thyrostat to regulate podocyte homeostasis

BACKGROUND

Nephrotic syndrome (NS) is associated with kidney podocyte injury and may occur as part of thyroid autoimmunity such as Graves' disease. Therefore, the present study was designed to ascertain if and how podocytes respond to and regulate the input of biologically active thyroid hormone (TH), 3,5,3'-triiodothyronine (T3); and also to decipher the pathophysiological role of type 3 deiodinase (D3), a membrane-bound selenoenzyme that inactivates TH, in kidney disease.

METHODS

To study D3 function in healthy and injured (PAN, puromycin aminonucleoside and LPS, Lipopolysaccharide-mediated) podocytes, immunofluorescence, qPCR and podocyte-specific D3 knockout mouse were used. Surface plasmon resonance (SPR), co-immunoprecipitation and Proximity Ligation Assay (PLA) were used for the interaction studies.

FINDINGS

Healthy podocytes expressed D3 as the predominant deiodinase isoform. Upon podocyte injury, levels of Dio3 transcript and D3 protein were dramatically reduced both in vitro and in the LPS mouse model of podocyte damage. D3 was no longer directed to the cell membrane, it accumulated in the Golgi and nucleus instead. Further, depleting D3 from the mouse podocytes resulted in foot process effacement and proteinuria. Treatment of mouse podocytes with T3 phenocopied the absence of D3 and elicited activation of αvβ3 integrin signaling, which led to podocyte injury. We also confirmed presence of an active thyroid stimulating hormone receptor (TSH-R) on mouse podocytes, engagement and activation of which resulted in podocyte injury.

INTERPRETATION

The study provided a mechanistic insight into how D3-αvβ3 integrin interaction can minimize T3-dependent integrin activation, illustrating how D3 could act as a renoprotective thyrostat in podocytes. Further, injury caused by binding of TSH-R with TSH-R antibody, as found in patients with Graves' disease, explained a plausible link between thyroid disorder and NS.

FUNDING

This work was supported by American Thyroid Association (ATA-2018-050.R1).

High glucose induces Nox4 expression and podocyte apoptosis through the Smad3/ezrin/PKA pathway

Podocytes are the major target in proteinuric kidney diseases such as diabetic nephropathy. The underlying molecular mechanisms by which high glucose (HG) results in podocyte damage remain unclear. This study investigated the regulatory role of Smad3, ezrin, and protein kinase A (PKA) in NADPH oxidase (Nox4) expression, reactive oxidative species (ROS) production, and apoptosis in HG-treated podocytes. A human podocyte cell line was cultured and differentiated, then treated with 30 mM HG. Apoptosis and intracellular ROS levels were assessed using TUNEL and DCF assays, respectively. Expressions of Nox4, phospho-Smad3^Ser423/425, phospho-PKA^Thr197, and phospho-ezrin^Thr567 were evaluated using western blotting. ELISA was used to quantify intracellular cAMP concentration and PKA activity. Knockdown assay was used to inhibit the expressions of Smad3, Nox4, and ezrin by lentiviral shRNA. In HG-treated podocytes, the level of phospho-Smad3^Ser423/425 and phospho-ezrin^Thr567 was increased significantly, which was accompanied by the reduction of cAMP and phospho-PKA^Thr197. HG-induced apoptosis was significantly prevented by the Smad3-inhibitor SIS3 or shRNA-Smad3. In podocytes expressing shRNA-ezrin or shRNA-Nox4, apoptosis was remarkably mitigated following HG treatment. HG-induced upregulation of phospho-ezrin^Thr567 and downregulation of phospho-PKA^Thr197 was significantly prevented by SIS3, shRNA-ezrin or shRNA-Smad3. Forskolin, a PKA activator, significantly inhibited HG-mediated upregulation of Nox4 expression, ROS generation, and apoptosis. Additionally, an increase in the ROS level was prohibited in HG-treated podocytes with the knockdown of Nox4, Smad3, or ezrin. Taken together, our findings provided evidence that Smad3-mediated ezrin activation upregulates Nox4 expression and ROS production, by suppressing PKA activity, which may at least in part contribute to HG-induced podocyte apoptosis.

Summary: The actin-membrane linker protein ezrin-related signaling plays a critical role in podocyte apoptosis through regulation of Nox4 expression and ROS production.

β2-Adrenergic receptor agonism as a therapeutic strategy for kidney disease

Approximately 14% of the general population suffer from chronic kidney disease that can lead to acute kidney injury (AKI), a condition with up to 50% mortality for which there is no effective treatment. Hypertension, diabetes, and cardiovascular disease are the main comorbidities, and more than 660,000 Americans have kidney failure. β₂-Adrenergic receptors (β₂ARs) have been extensively studied in association with lung and cardiovascular disease, but with limited scope in kidney and renal diseases. β₂ARs are expressed in multiple parts of the kidney including proximal and distal convoluted tubules, glomeruli, and podocytes. Classical and noncanonical β₂AR signaling pathways interface with other intracellular mechanisms in the kidney to regulate important cellular functions including renal blood flow, electrolyte balance and salt handling, and tubular function that in turn exert control over critical physiology and pathology such as blood pressure and inflammatory responses. Nephroprotection through activation of β₂ARs has surfaced as a promising field of investigation; however, there is limited data on the pharmacology and potential side effects of renal β₂AR modulation. Here, we provide updates on some of the major areas of preclinical kidney research involving β₂AR signaling that have advanced to describe molecular pathways and identify potential drug targets some of which are currently under clinical development for the treatment of kidney-related diseases.

The complicated role of mitochondria in the podocyte

Mitochondria play a complex role in maintaining cellular function including ATP generation, generation of biosynthetic precursors for macromolecules, maintenance of redox homeostasis, and metabolic waste management. Although the contribution of mitochondrial function in various kidney diseases has been studied, there are still avenues that need to be explored under healthy and diseased conditions. Mitochondrial damage and dysfunction have been implicated in experimental models of podocytopathy as well as in humans with glomerular diseases resulting from podocyte dysfunction. Specifically, in the podocyte, metabolism is largely driven by oxidative phosphorylation or glycolysis depending on the metabolic needs. These metabolic needs may change drastically in the presence of podocyte injury in glomerular diseases such as diabetic kidney disease or focal segmental glomerulosclerosis. Here, we review the role of mitochondria in the podocyte and the factors regulating its function at baseline and in a variety of podocytopathies to identify potential targets for therapy.

C3a receptor blockade protects podocytes from injury in diabetic nephropathy

Renal activation of the complement system has been described in patients with diabetic nephropathy (DN), although its pathological relevance is still ill-defined. Here, we studied whether glomerular C3a, generated by uncontrolled complement activation, promotes podocyte damage, leading to proteinuria and renal injury in mice with type 2 diabetes. BTBR ob/ob mice exhibited podocyte loss, albuminuria, and glomerular injury accompanied by C3 deposits and increased C3a and C3a receptor (C3aR) levels. Decreased glomerular nephrin and α-actinin4 expression, coupled with integrin-linked kinase induction, were also observed. Treatment of DN mice with a C3aR antagonist enhanced podocyte density and preserved their phenotype, limiting proteinuria and glomerular injury. Mechanistically, ultrastructural and functional mitochondrial alterations, accompanied by downregulation of antioxidant superoxide dismutase 2 (SOD2) and increased protein oxidation, occurred in podocytes and were normalized by C3aR blockade. In cultured podocytes, C3a induced cAMP-dependent mitochondrial fragmentation. Alterations of mitochondrial membrane potential, SOD2 expression, and energetic metabolism were also found in response to C3a. Notably, C3a-induced podocyte motility was inhibited by SS-31, a peptide with mitochondrial protective effects. These data indicate that C3a blockade represents a potentially novel therapeutic strategy in DN for preserving podocyte integrity through the maintenance of mitochondrial functions.

Bucladesine Attenuates Spatial Learning and Hippocampal Mitochondrial Impairments Induced by 3, 4-Methylenedioxymethamphetamine (MDMA)

Neurotoxic effects of systemic administration of 3, 4- methylenedioxymethamphetamine (MDMA) has been attributed to MDMA and its metabolites. However, the role of the parent compound in MDMA-induced mitochondrial and memory impairment has not yet been investigated. Moreover, it is not yet studied that analogs of 3', 5'-cyclic adenosine monophosphate (cAMP) could decrease these neurotoxic effects of MDMA. We wished to investigate the effects of the central administration of MDMA on spatial memory and mitochondrial function as well as the effects of bucladesine, a membrane-permeable analog of cAMP, on these effects of MDMA. We assessed the effects of pre-training bilateral intrahippocampal infusion of MDMA (0.01, 0.1, 0.5, and 1 μg/side), bucladesine (10 and 100 μM) or combination of them on spatial memory, and different parameters of hippocampal mitochondrial function including the level of reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP), mitochondrial swelling, mitochondrial outer membrane damage, the amount of cytochrome c release as well as hippocampal ADP/ATP ratio. The results showed that MDMA caused spatial memory impairments as well as mitochondrial dysfunction as evidenced by the marked increase in hippocampal ADP/ATP ratio, ROS level, the collapse of MMP, mitochondrial swelling, and mitochondrial outer membrane damage leading to cytochrome c release from the mitochondria. The current study also found that bucladesine markedly reduced the destructive effects of MDMA. These results provide evidence of the role of the parent compound (MDMA) in MDMA-induced memory impairments through mitochondrial dysfunction. This study highlights the role of cAMP/PKA signaling in MDMA-induced memory and mitochondrial defects.

Efficacy of a mitochondrion-targeting agent for reducing the level of urinary protein in rats with puromycin aminonucleoside-induced minimal-change nephrotic syndrome

Background

Oxidative stress is a major factor responsible for minimal-change nephrotic syndrome (MCNS), which occurs most commonly in children. However, the influence of oxidative stress localized to mitochondria remains unclear. We examined the effect of a mitochondrion-targeting antioxidant, MitoTEMPO, in rats with puromycin aminonucleoside (PAN)-induced MCNS to clarify the degree to which mitochondrial oxidative stress affects MCNS.

Materials and methods

Thirty Wistar rats were divided into three groups: normal saline group (n = 7), PAN group (n = 12), and PAN + MitoTEMPO group (n = 11). Rats in the PAN and PAN + MitoTEMPO groups received PAN on day 1, and those in the PAN + MitoTEMPO group received MitoTEMPO on days 0 to 9. Whole-day urine samples were collected on days 3 and 9, and samples of glomeruli and blood were taken for measurement of lipid peroxidation products. We also estimated the mitochondrial damage score in podocytes in all 3 groups using electron microscopy.

Results

Urinary protein excretion on day 9 and the levels of lipid peroxidation products in urine, glomeruli, and blood were significantly lower in the PAN　+　MitoTEMPO group than in the PAN group (p = 0.0019, p = 0.011, p = 0.039, p = 0.030). The mitochondrial damage score in podocytes was significantly lower in the PAN　+　MitoTEMPO group than in the PAN group (p <0.0001).

Conclusions

This mitochondrion-targeting agent was shown to reduce oxidative stress and mitochondrial damage in a MCNS model. A radical scavenger targeting mitochondria could be a promising drug for treatment of MCNS.

Morphological control of mitochondria as the novel mechanism of Gastrodia elata in attenuating mutant huntingtin-induced protein aggregations

BACKGROUND

According to Compendium of Materia Medica, Gastrodia elata (GE) Blume as a top grade and frequently prescribed herbal medicine has been used in treating dizziness, headaches, and epilepsy, indicating a neuroprotective effect. Because GE is capable of suppressing a hyperactive liver and thus calming endogenous wind, and because Huntington's disease (HD) can be classified as a phenomenon of disturbed liver wind, it is suggested that GE might be beneficial in treating HD. However, although current studies support GE for the prevention of diverse neurodegenerations such as HD, its detailed mechanisms remain elusive.

PURPOSE

To investigate the molecular mechanism of GE in preventing HD by focusing on mitochondrial morphology, which is highly associated with HD etiology and thus proposed as a therapeutic target of neurodegenerations.

STUDY DESIGN/METHODS

The overexpression of the mutant huntingtin (mHTT) gene in rat pheochromocytoma (PC12) cells was used as an in vitro cell model of HD. A filter retardation assay was applied to measure protein aggregations during HTT expression. Cotransfection with mitochondrial fusion and fission genes was used to test their relationships with HTT aggregates by monitoring with a confocal laser scanning microscope and filter retardation assay. Western blot analysis was used to estimate protein expression under different drug treatments or cotransfections with other related genes.

RESULTS

The overexpression of mutant but not normal HTT genes significantly resulted in protein aggregations in PC12 cells. GE dose-dependently attenuated mHTT-induced protein aggregations and free radical formations. GE significantly reversed mHTT-induced mitochondrial fragmentation and dysregulation of mitochondrial fusion and fission molecules. The overexpression of mitochondrial fusion genes attenuated mHTT-induced protein aggregations. Further, Mdivi-1, a DRP1 fission molecule inhibitor, significantly reversed mHTT-induced protein aggregations and mitochondrial fragmentation.

CONCLUSION

GE attenuated mHTT aggregations through the control of mitochondrial fusion and the fission pathway.

Epigenetic regulation of RCAN1 expression in kidney disease and its role in podocyte injury

Mounting evidence suggests that epigenetic modification is important in kidney disease pathogenesis. To determine whether epigenetic regulation is involved in HIV-induced kidney injury, we performed genome-wide methylation profiling and transcriptomic profiling of human primary podocytes infected with HIV-1. Comparison of DNA methylation and RNA sequencing profiles identified several genes that were hypomethylated with corresponding upregulated RNA expression in HIV-infected podocytes. Notably, we found only one hypermethylated gene with corresponding downregulated RNA expression, namely regulator of calcineurin 1 (RCAN1). Further, we found that RCAN1 RNA expression was suppressed in glomeruli in human diabetic nephropathy, IgA nephropathy, and lupus nephritis, and in mouse models of HIV-associated nephropathy and diabetic nephropathy. We confirmed that HIV infection or high glucose conditions suppressed RCAN1 expression in cultured podocytes. This suppression was alleviated upon pretreatment with DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine, suggesting that RCAN1 expression is epigenetically suppressed in the context of HIV infection and diabetic conditions. Mechanistically, increased expression of RCAN1 decreased HIV- or high glucose-induced nuclear factor of activated T cells (NFAT) transcriptional activity. Increased RCAN1 expression also stabilized actin cytoskeleton organization, consistent with the inhibition of the calcineurin pathway. In vivo, knockout of RCAN1 aggravated albuminuria and podocyte injury in mice with Adriamycin-induced nephropathy. Our findings suggest that epigenetic suppression of RCAN1 aggravates podocyte injury in the setting of HIV infection and diabetic nephropathy.

TGR5 signalling promotes mitochondrial fission and beige remodelling of white adipose tissue

Remodelling of energy storing white fat into energy expending beige fat could be a promising strategy to reduce adiposity. Here, we show that the bile acid-responsive membrane receptor TGR5 mediates beiging of the subcutaneous white adipose tissue (scWAT) under multiple environmental cues including cold exposure and prolonged high-fat diet feeding. Moreover, administration of TGR5-selective bile acid mimetics to thermoneutral housed mice leads to the appearance of beige adipocyte markers and increases mitochondrial content in the scWAT of Tgr5^+/+ mice but not in their Tgr5^−/− littermates. This phenotype is recapitulated in vitro in differentiated adipocytes, in which TGR5 activation increases free fatty acid availability through lipolysis, hence fuelling β-oxidation and thermogenic activity. TGR5 signalling also induces mitochondrial fission through the ERK/DRP1 pathway, further improving mitochondrial respiration. Taken together, these data identify TGR5 as a druggable target to promote beiging with potential applications in the management of metabolic disorders.

White adipose tissue can undergo a process of beiging and acquire functional characteristics similar to brown adipose tissue, including the ability to dissipate energy via uncoupled respiration. Here, Velazquez-Villegas et al. show that activation of the bile acid membrane receptor, TGR5, leads to white adipocyte beiging by promoting mitochondrial fission.

YiQiFuMai Powder Injection Protects against Ischemic Stroke via Inhibiting Neuronal Apoptosis and PKCδ/Drp1-Mediated Excessive Mitochondrial Fission

YiQiFuMai (YQFM) powder injection has been reported to be used in cardiovascular and nervous system diseases with marked efficacy. However, as a treatment against diseases characterized by hypoxia, lassitude, and asthenia, the effects and underlying mechanisms of YQFM in neuronal mitochondrial function and dynamics have not been fully elucidated. Here, we demonstrated that YQFM inhibited mitochondrial apoptosis and activation of dynamin-related protein 1 (Drp1) in cerebral ischemia-injured rats, producing a significant improvement in cerebral infarction and neurological score. YQFM also attenuated oxidative stress-induced mitochondrial dysfunction and apoptosis through increasing ATP level and mitochondria membrane potential (Δψm), inhibiting ROS production, and regulating Bcl-2 family protein levels in primary cultured neurons. Moreover, YQFM inhibited excessive mitochondrial fission, Drp1 phosphorylation, and translocation from cytoplasm to mitochondria induced by oxidative stress. We provided the first evidence that YQFM inhibited the activation, association, and translocation of PKCδ and Drp1 upon oxidative stress. Taken together, we demonstrate that YQFM ameliorates ischemic stroke-induced neuronal apoptosis through inhibiting mitochondrial dysfunction and PKCδ/Drp1-mediated excessive mitochondrial fission. These findings not only put new insights into the unique neuroprotective properties of YQFM associated with the regulation of mitochondrial function but also expand our understanding of the underlying mechanisms of ischemic stroke.

GDC-0879, a BRAFV600E Inhibitor, Protects Kidney Podocytes from Death

Progressive kidney diseases affect approximately 500 million people worldwide. Podocytes are terminally differentiated cells of the kidney filter, the loss of which leads to disease progression and kidney failure. To date, there are no therapies to promote podocyte survival. Drug repurposing may therefore help accelerate the development of cures in an area of tremendous unmet need. In a newly developed high-throughput screening assay of podocyte viability, we identified the BRAF^V600E inhibitor GDC-0879 and the adenylate cyclase agonist forskolin as podocyte-survival-promoting compounds. GDC-0879 protects podocytes from injury through paradoxical activation of the MEK/ERK pathway. Forskolin promotes podocyte survival by attenuating protein biosynthesis. Importantly, GDC-0879 and forskolin are shown to promote podocyte survival against an array of cellular stressors. This work reveals new therapeutic targets for much needed podocyte-protective therapies and provides insights into the use of GDC-0879-like molecules for the treatment of progressive kidney diseases.

Protein Kinase A/CREB Signaling Prevents Adriamycin-Induced Podocyte Apoptosis via Upregulation of Mitochondrial Respiratory Chain Complexes

Previous work showed that the activation of protein kinase A (PKA) signaling promoted mitochondrial fusion and prevented podocyte apoptosis. The cAMP response element binding protein (CREB) is the main downstream transcription factor of PKA signaling. Here we show that the PKA agonist 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate-cyclic AMP (pCPT-cAMP) prevented the production of adriamycin (ADR)-induced reactive oxygen species and apoptosis in podocytes, which were inhibited by CREB RNA interference (RNAi). The activation of PKA enhanced mitochondrial function and prevented the ADR-induced decrease of mitochondrial respiratory chain complex I subunits, NADH-ubiquinone oxidoreductase complex (ND) 1/3/4 genes, and protein expression. Inhibition of CREB expression alleviated pCPT-cAMP-induced ND3, but not the recovery of ND1/4 protein, in ADR-treated podocytes. In addition, CREB RNAi blocked the pCPT-cAMP-induced increase in ATP and the expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1-α). The chromatin immunoprecipitation assay showed enrichment of CREB on PGC1-α and ND3 promoters, suggesting that these promoters are CREB targets. In vivo, both an endogenous cAMP activator (isoproterenol) and pCPT-cAMP decreased the albumin/creatinine ratio in mice with ADR nephropathy, reduced glomerular oxidative stress, and retained Wilm's tumor suppressor gene 1 (WT-1)-positive cells in glomeruli. We conclude that the upregulation of mitochondrial respiratory chain proteins played a partial role in the protection of PKA/CREB signaling.

p53/Drp1-dependent mitochondrial fission mediates aldosterone-induced podocyte injury and mitochondrial dysfunction

Mitochondrial dysfunction is increasingly recognized as an important factor in glomerular diseases. Previous study has shown that mitochondrial fission contributed to mitochondrial dysfunction. However, the mechanism of mitochondrial fission on mitochondrial dysfunction in aldosterone-induced podocyte injury remains ambiguous. This study aimed to investigate the pathogenic effect of mitochondrial fission both in vivo and in vitro. In an animal model of aldosterone-induced nephropathy, inhibition of the mitochondrial fission protein dynamin-related protein 1 (Drp1) suppressed aldosterone-induced podocyte injury. In cultured podocytes, aldosterone dose dependently induced Drp1 expression. Knockdown of Drp1 inhibited aldosterone-induced mitochondrial fission, mitochondrial dysfunction, and podocyte apoptosis. Furthermore, aldosterone dose dependently induced p53 expression. Knockdown of p53 inhibited aldosterone-induced Drp1 expression, mitochondrial dysfunction, and podocyte apoptosis. These findings implicated that aldosterone induced mitochondrial dysfunction and podocyte injury mediated by p53/Drp1-dependent mitochondrial fission, which may provide opportunities for therapeutic intervention for podocyte injury.

Antioxidative Stress Effects of Salvia przewalskii Extract in Experimentally Injured Podocytes

BACKGROUND

Oxidative stress is a leading cause of puromycin aminonucleoside (PAN)-induced nephrosis. As the inhibition of oxidative stress may improve injury of podocyte, we aimed at examining the effect of total phenolic acid extract of Salvia przewalskii (SPE) on PAN-induced oxidative stress in vivo and in vitro.

METHODS

Seventy-two male Sprague-Dawley rats were randomly assigned into 6 groups (n = 12), PAN alone, tacrolimus (TAC), SPE (50, 100 and 200 mg/kg) and normal control group. Salvianolic acid B (SalB, 5.52%) and rosmarinic acid (RA, 31.58%) were isolated from SPE. The intensities of 8-oxo-2'-deoxyguanosine (8-OHdG) were evaluated by immunofluorescence. In vitro, the podocytes were assigned into groups of control, PAN alone, TAC (1 μg/ml), SPE (158, 316 μg/ml), SalB (8.5, 17 μg/ml) and RA (25, 50 μg/ml). The intracellular reactive oxygen species (ROS) production and cell apoptosis rate were measured by flow cytometry. Form factor and aspect ratio were calculated to assess mitochondrial morphology.

RESULTS

In vivo, PAN increased the intensity of 8-OHdG in the renal tissue in the PAN group (p < 0.05). The high-dose SPE reduced 8-OHdG significantly at levels comparable to TAC alone (p > 0.05) on day 15. The intracellular ROS production, podocytes apoptosis rate and mitochondrial fragmentation increased significantly following PAN exposure in podocytes (p < 0.05). Treatment with high-dose SalB significantly ameliorated the increase in the expression of ROS and revised the structure of mitochondria. The percentage of apoptotic cells was decreased compared with the PAN group after SPE, SalB, RA, and TAC treatment for 24 h (p < 0.05).

CONCLUSION

These findings suggest that high-dose SPE significantly attenuated 8-OHdG in PAN nephrosis. Antioxidative stress effects of high-dose SPE, SalB against PAN-stimulated cultured podocyte via mechanisms include suppression of ROS expression and mitochondria fission. In addition, SPE, SalB and RA can suppress PAN-induced apoptosis.

Mitochondrial Dynamics Is Linked to Longevity and Protects from End-Organ Injury: The Emerging Role of Sirtuin 3

SIGNIFICANCE

Mitochondrial integrity is instrumental in protecting against damage associated with aging and a variety of chronic disease conditions. Mitochondrial silent information regulator 3 (Sirt3) plays pivotal roles in maintaining mitochondrial homeostasis by regulating different aspects of the organelle processes.

RECENT ADVANCES

Mitochondria are highly dynamic organelles that constantly fuse and divide to maintain normal cell function, and perturbation in mitochondrial dynamics is responsible for mitochondrial dysfunction. Improved knowledge of mitochondrial physiology has disclosed the pleiotropic role of Sirt3 in mitochondria and shows how alterations in protein expression and/or activity may have an important impact on aging-associated organ dysfunction.

CRITICAL ISSUES

This review describes updated experimental evidence on the role of mitochondrial dysfunction during aging and renal diseases and highlights the emerging role of Sirt3 as a crucial regulator of mitochondrial dynamics.

FUTURE DIRECTIONS

Strategies that activate Sirt3 may offer attractive therapies to achieve healthy longevity and preserve functional integrity of multiple organs. Antioxid. Redox Signal. 25, 185-199.

Melanocortin 1 receptor agonist protects podocytes through catalase and RhoA activation

Drugs containing adrenocorticotropic hormone have been used as therapy for patients with nephrotic syndrome. We have previously shown that adrenocorticotropic hormone and a selective agonist for the melanocortin 1 receptor (MC1R) exert beneficial actions in experimental membranous nephropathy with reduced proteinuria, reduced oxidative stress, and improved glomerular morphology and function. Our hypothesis is that MC1R activation in podocytes elicits beneficial effects by promoting stress fibers and maintaining podocyte viability. To test the hypothesis, we cultured podocytes and used highly specific agonists for MC1R. Podocytes were subjected to the nephrotic-inducing agent puromycin aminonucleoside, and downstream effects of MC1R activation on podocyte survival, antioxidant defense, and cytoskeleton dynamics were studied. To increase the response and enhance intracellular signals, podocytes were transduced to overexpress MC1R. We showed that puromycin promotes MC1R expression in podocytes and that activation of MC1R promotes an increase of catalase activity and reduces oxidative stress, which results in the dephosphorylation of p190RhoGAP and formation of stress fibers through RhoA. In addition, MC1R agonists protect against apoptosis. Together, these mechanisms protect the podocyte against puromycin. Our findings strongly support the hypothesis that selective MC1R-activating agonists protect podocytes and may therefore be useful to treat patients with nephrotic syndromes commonly considered as podocytopathies.

Comparison of Glomerular Transcriptome Profiles of Adult-Onset Steroid Sensitive Focal Segmental Glomerulosclerosis and Minimal Change Disease

Objective

To search for biomarkers to differentiate primary focal segmental glomerulosclerosis (FSGS) and minimal change disease (MCD).

Methods

We isolated glomeruli from kidney biopsies of 6 patients with adult-onset steroid sensitiveFSGS and 5 patients with MCD, and compared the profiles of glomerular transcriptomes between the two groups of patients using microarray analysis.

Results

Analysis of differential expressed genes (DEGs) revealed that up-regulated DEGs in FSGS patients compared with MCD patients were primarily involved in spermatogenesis, gamete generation, regulation of muscle contraction, response to unfolded protein, cell proliferation and skeletal system development. The down-regulated DEGs were primarily related to metabolic process, intracellular transport, oxidation/reduction andestablishment of intracellular localization. We validated the expression of the top 6 up-regulated and top 6 down-regulated DEGs using real-time PCR. Membrane metallo-endopeptidase (MME) is a down-regulated gene that was previously identified as a key gene for kidney development. Immunostaining confirmed that the protein expression of MME decreased significantly in FSGS kidneys compared with MCD kidneys.

Conclusions

This report was the first study to examine transcriptomes in Chinese patients with various glomerular diseases. Expressions of MME both in RNA and protein level decreased significantly in glomeruli of FSGS kidneys compared with MCD kidneys. Our data suggested that MME might play a role in the normal physiological function of podocytes and a decrease in MME expression might be related to podocyte injury. We also identified genes and pathways specific for FSGS versus MCD, and our data could help identify potential new biomarkers for the differential diagnosis between these two diseases.

Cyclic adenosine monophosphate protects renal cell lines against amphotericin B toxicity in a PKA-independent manner

Amphotericin B is the "gold standard" agent in the management of serious systemic fungal infections. However, this drug can cause nephrotoxicity, which contributes up to 25% of all acute kidney injuries in critically ill patients. Cyclic adenosine monophosphate can protect kidney cells from death due to injury or drug exposure in some cases. Hence, the objective of this work was to evaluate if cAMP could prevent cell death that occurs in renal cell lines subjected to AmB treatment and, if so, to assess the involvement of PKA in the transduction of this signal. Two different renal cell lines (LLC-PK1 and MDCK) were used in this study. MTT and flow cytometry assays showed increased cell survival when cells were exposed to cAMP in a PKA-independent manner, which was confirmed by western blot. This finding suggests that cAMP (db-cAMP) may prevent cell death caused by exposure to AmB. This is the first time this effect has been identified when renal cells are exposed to AmB's nephrotoxic potential.

Caspase-9 as a therapeutic target for treating cancer

INTRODUCTION

Caspase-9 is the apoptotic initiator protease of the intrinsic or mitochondrial apoptotic pathway, which is activated at multi-protein activation platforms. Its activation is believed to involve homo-dimerization of the monomeric zymogens. It binds to the apoptosome to retain substantial catalytic activity. Variety of apoptotic stimuli can regulate caspase-9. However, the mechanism of action of various regulators of caspase-9 has not been summarized and compared yet. In this article, we elucidate the regulators of caspase-9 including microRNAs, natural compounds that are related to caspase-9 and ongoing clinical trials with caspase-9 to better understand the caspase-9 in suppressing cancer.

AREAS COVERED

In this study, the basic mechanism of apoptosis pathways, regulators of caspase-9 and the development of drugs to regulate caspase-9 are reviewed. Also, ongoing clinical trials for caspase-9 are discussed.

EXPERT OPINION

Apoptosis has crucial role in cancer, brain disease, aging and heart disease to name a few. Since caspase-9 is an initiator caspase of apoptosis, it is an important therapeutic target of various diseases related to apoptosis. Therefore, a deep understanding on the roles as well as regulators of caspase-9 is required to find more effective ways to conquer apoptosis-related diseases especially cancer.