Inhibition of p66ShcA longevity gene rescues podocytes from HIV-1-induced oxidative stress and apoptosis

Novel insights into NOD-like receptors in renal diseases

Nucleotide-binding oligomerization domain-like receptors (NLRs), including NLRAs, NLRBs (also known as NAIPs), NLRCs, and NLRPs, are a major subfamily of pattern recognition receptors (PRRs). Owing to a recent surge in research, NLRs have gained considerable attention due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, which is a central phenomenon in the pathogenesis of multiple diseases, including renal diseases. NLRs are expressed in different renal tissues during pathological conditions, which suggest that these receptors play roles in acute kidney injury, obstructive nephropathy, diabetic nephropathy, IgA nephropathy, lupus nephritis, crystal nephropathy, uric acid nephropathy, and renal cell carcinoma, among others. This review summarises recent progress on the functions of NLRs and their mechanisms in the pathophysiological processes of different types of renal diseases to help us better understand the role of NLRs in the kidney and provide a theoretical basis for NLR-targeted therapy for renal diseases.

Sirtuins as Interesting Players in the Course of HIV Infection and Comorbidities

The sirtuins (SIRTs) are a family of enzymes from the group of NAD⁺-dependent deacetylases. Through the reaction of splitting the acetyl group of various transcription factors and histones they regulate many processes in the organism. The activity of sirtuins is linked to metabolic control, oxidative stress, inflammation and apoptosis, and they also affect the course of viral infections. For this reason, they may participate in the pathogenesis and development of many diseases, but little is known about their role in the course of human immunodeficiency virus (HIV) infection, which is the subject of this review. In the course of HIV infection, comorbidities such as: neurodegenerative disorders, obesity, insulin resistance and diabetes, lipid disorders and cardiovascular diseases, renal and bone diseases developed more frequently and faster compared to the general population. The role of sirtuins in the development of accompanying diseases in the course of HIV infection may also be interesting. There is still a lack of detailed information on this subject. The role of sirtuins, especially SIRT1, SIRT3, SIRT6, are indicated to be of great importance in the course of HIV infection and the development of the abovementioned comorbidities.

APOL1 and kidney cell function

The apolipoprotein L1 (APOL1) gene is unique to humans and gorillas and appeared ~33 million years ago. Since the majority of the mammals do not carry APOL1, it seems to be dispensable for kidney function. APOL1 renal risk variants (RRVs; G1 and G2) are associated with the development as well as progression of chronic kidney diseases (CKDs) at higher rates in populations with African ancestry. Cellular expression of two APOL1 RRVs has been demonstrated to induce cytotoxicity, including necrosis, apoptosis, and pyroptosis, in several cell types including podocytes; mechanistically, these toxicities were attributed to lysosomal swelling, K⁺ depletion, mitochondrial dysfunction, autophagy blockade, protein kinase receptor activation, ubiquitin D degradation, and endoplasmic reticulum stress; notably, these effects were found to be dose dependent and occurred only in overtly APOL1 RRV-expressing cells. However, cellular protein expressions as well as circulating blood levels of APOL1 RRVs were not elevated in patients suffering from APOL1 RRV-associated CKDs. Therefore, the question arises as to whether it is gain or loss of function on the part of APOL1 RRVs contributing to kidney cell injury. The question seems to be more pertinent after the recognition of the role of APOL1 nonrisk (G0) in the transition of parietal epithelial cells and preservation of the podocyte molecular phenotype through modulation of the APOL1-miR-193a axis. With this background, the present review analyzed the available literature in terms of the known function of APOL1 nonrisk and how the loss of these functions could have contributed to two APOL1 RRV-associated CKDs.

Role of Apolipoprotein L1 in Human Parietal Epithelial Cell Transition

Human parietal epithelial cells (PECs) are progenitor cells that sustain podocyte homeostasis. We hypothesized that the lack of apolipoprotein (APO) L1 ensures the PEC phenotype, but its induction initiates PEC transition (expression of podocyte markers). APOL1 expression and down-regulation of miR193a coincided with the expression of podocyte markers during the transition. The induction of APOL1 also stimulated transition markers in human embryonic kidney cells (cells with undetectable APOL1 protein expression). APOL1 silencing in PECs up-regulated miR193a expression, suggesting the possibility of a reciprocal feedback relationship between APOL1 and miR193a. HIV, interferon-γ, and vitamin D receptor agonist down-regulated miR193a expression and induced APOL1 expression along with transition markers in PECs. Luciferase assay suggested a putative interaction between miR193a and APOL1. Since silencing of APOL1 attenuated HIV-, vitamin D receptor agonist-, miR193a inhibitor-, and interferon-γ-induced expression of transition markers, APOL1 appears to be a critical functional constituent of the miR193a- APOL1 axis in PECs. This notion was confirmed by further enhanced expression of PEC markers in APOL1 mRNA-silenced PECs. In vivo studies, glomeruli in patients with HIV, and HIV/APOL1 transgenic mice had foci of PECs expressing synaptopodin, a transition marker. APOL1 likely regulates PEC molecular phenotype through modulation of miR193a expression, and APOL1 and miR193a share a reciprocal feedback relationship.

Molecular Mechanisms of Injury in HIV-Associated Nephropathy

HIV-associated nephropathy (HIVAN) is an important cause of secondary focal glomerulosclerosis that occurs primarily in persons of African ancestry with advanced HIV disease. Although HIVAN is characterized by severe proteinuria and rapid progression to end stage renal disease without treatment, the phenotype is markedly attenuated by treatment with antiretroviral medications. HIV infection of glomerular and tubular epithelial cells and subsequent viral gene expression is a key contributor to HIVAN pathogenesis and the kidney can serve as reservoir for HIV strains that differ those in blood. HIV gene expression in renal epithelial cells leads to dysregulation of cellular pathways including cell cycle, inflammation, cell death, and cytoskeletal homeostasis. Polymorphisms in the APOL1 gene explain the marked predilection of HIVAN to occur in persons of African descent and HIVAN. Since HIVAN has the strongest association with APOL1 genotype of any of the APOL1-associated nephropathies, studies to determine the mechanisms by which HIV and APOL1 risk variants together promote kidney injury hold great promise to improve our understanding of the pathogenesis of APOL1-mediated kidney diseases.

Modulation of apolipoprotein L1-microRNA-193a axis prevents podocyte dedifferentiation in high-glucose milieu

The loss of podocyte (PD) molecular phenotype is an important feature of diabetic podocytopathy. We hypothesized that high glucose (HG) induces dedifferentiation in differentiated podocytes (DPDs) through alterations in the apolipoprotein (APO) L1-microRNA (miR) 193a axis. HG-induced DPD dedifferentiation manifested in the form of downregulation of Wilms' tumor 1 (WT1) and upregulation of paired box 2 (PAX2) expression. WT1-silenced DPDs displayed enhanced expression of PAX2. Immunoprecipitation of DPD cellular lysates with anti-WT1 antibody revealed formation of WT1 repressor complexes containing Polycomb group proteins, enhancer of zeste homolog 2, menin, and DNA methyltransferase (DNMT1), whereas silencing of either WT1 or DNMT1 disrupted this complex with enhanced expression of PAX2. HG-induced DPD dedifferentiation was associated with a higher expression of miR193a, whereas inhibition of miR193a prevented DPD dedifferentiation in HG milieu. HG downregulated DPD expression of APOL1. miR193a-overexpressing DPDs displayed downregulation of APOL1 and enhanced expression of dedifferentiating markers; conversely, silencing of miR193a enhanced the expression of APOL1 and preserved DPD phenotype. Moreover, stably APOL1G0-overexpressing DPDs displayed the enhanced expression of WT1 but attenuated expression of miR193a; nonetheless, silencing of APOL1 reversed these effects. Since silencing of APOL1 enhanced miR193a expression as well as dedifferentiation in DPDs, it appears that downregulation of APOL1 contributed to dedifferentiation of DPDs through enhanced miR193a expression in HG milieu. Vitamin D receptor agonist downregulated miR193a, upregulated APOL1 expression, and prevented dedifferentiation of DPDs in HG milieu. These findings suggest that modulation of the APOL1-miR193a axis carries a potential to preserve DPD molecular phenotype in HG milieu.

Glomerular mitochondrial changes in HIV associated renal injury

HIV-associated nephropathy (HIVAN) is an AIDs-related disease of the kidney. HIVAN is characterized by severe proteinuria, podocyte hyperplasia, collapse, glomerular, and tubulointerstitial damage. HIV-1 transgenic (Tg26) mouse is the most popular model to study the HIV manifestations that develop similar renal presentations as HIVAN. Viral proteins, including Tat, Nef, and Vpr play a significant role in renal cell damage. It has been shown that mitochondrial changes are involved in several kidney diseases, and therefore, mitochondrial dysfunction may be implicated in the pathology of HIVAN. In the present study, we investigated the changes of mitochondrial homeostasis, biogenesis, dynamics, mitophagy, and examined the role of reactive oxygen species (ROS) generation and apoptosis in the Tg26 mouse model. The Tg26 mice showed significant impairment of kidney function, which was accompanied by increased blood urea nitrogen (BUN), creatinine and protein urea level. In addition, histological, western blot and PCR analysis of the Tg26 mice kidneys showed a downregulation of NAMPT, SIRT1, and SIRT3 expressions levels. Furthermore, the kidney of the Tg26 mice showed a downregulation of PGC1α, MFN2, and PARKIN, which are coupled with decrease of mitochondrial biogenesis, imbalance of mitochondrial dynamics, and downregulation of mitophagy, respectively. Furthermore, our results indicate that mitochondrial dysfunction were associated with ER stress, ROS generation and apoptosis. These results strongly suggest that the impaired mitochondrial morphology, homeostasis, and function associated with HIVAN. These findings indicated that a new insight on pathological mechanism associated with mitochondrial changes in HIVAN and a potential therapeutic target.

Hedgehog pathway plays a vital role in HIV-induced epithelial-mesenchymal transition of podocyte

HIV-associated nephropathy (HIVAN) is characterized by heavy proteinuria, rapidly progressive renal failure, and distinct morphological features in the kidney. HIV-induced epithelial-mesenchymal transition (EMT) is critically important for the progression of kidney injury. In this study, we tested the role of hedgehog pathway in the HIV-induced EMT and fibrosis of kidney. We used the Tg26 mice, the abundantly used HIVAN mouse model, to investigate the activation of hedgehog pathway by HIV. Western blotting and real time PCR results showed that renal tissue expression of hedgehog pathway related molecules, including hedgehog homologous (Shh, Ihh, Dhh), PTCH, and Gli1, were increased in HIVAN (Tg26) mice; while immunofluorescent staining displayed localization PTCH expression in podocytes. For in vitro studies, we used recombinant sonic hedgehog (Shh) and HIV for their expression by podocytes. Both the methods activated the hedgehog pathway, enhanced the expression of EMT markers, and decreased impermeability. Overexpression of Gli1 by human podocytes also augmented their expression of EMT markers. On the other hand, the blockade of hedgehog pathway with Gant 58, a specific blocker for Gli1-induced transcription, dramatically decreased HIV-induced podocyte EMT and permeability. These results indicate that hedgehog pathway plays an important role in HIV-induced podocyte injury. The present study provides mechanistical insight into a new target for therapeutic strategy.

Neuronal Cell Death and Degeneration through Increased Nitroxidative Stress and Tau Phosphorylation in HIV-1 Transgenic Rats

The underlying mechanisms for increased neurodegeneration and neurocognitive deficits in HIV-infected people are unclear. Therefore, this study was aimed to investigate the mechanisms of increased neurodegeneration in 5-month old male HIV-1 Transgenic (Tg) rats compared to the age- and gender-matched wild-type (WT) by evaluating histological changes and biochemical parameters of the key proteins involved in the cell death signaling and apoptosis. Histological and immunohistochemical analyses revealed decreased neuronal cells with elevated astrogliosis in HIV-1 Tg rats compared to WT. Mechanistic studies revealed that increased levels of nitroxidative stress marker proteins such as NADPH-oxidase, cytochrome P450-2E1 (CYP2E1), inducible nitric oxide synthase (iNOS), the stress-activated mitogen-activated protein kinases such as JNK and p38K, activated cell-cycle dependent CDK5, hypoxia-inducible protein-1α, nitrated proteins, hyperphosphorylated tau, and amyloid plaques in HIV-Tg rats were consistently observed in HIV-1 Tg rats. Confocal microscopy and cell viability analyses showed that treatment with an antioxidant N-acetylcysteine or a specific inhibitor of iNOS 1400W significantly prevented the increased apoptosis of neuro-2A cells by HIV-1 Tat or gp120 protein, demonstrating the causal role of HIV-1 mediated nitroxidative stress and protein nitration in promoting neuronal cell death. Immunoprecipitation and immunoblot analysis confirmed nitration of Hsp90, evaluated as an example of nitrated proteins, suggesting possible involvement of nitrated proteins in neuronal damage. Further, activated p-JNK directly binds tau and phosphorylates multiple amino acids, suggesting an important role of p-JNK in tau hyperphosphorylation and tauopathy. These changes were accompanied with elevated levels of many apoptosis-related proteins Bax and cleaved (activated) caspase-3 as well as proinflammatory cytokines including TNF-α, IL-6 and MCP-1. Collectively, these results indicate that raised nitroxidative stress accompanied by elevated inflammation, cell death signaling pathway including activated p-JNK, C-terminal C99 amyloid fragment formation and tau hyperphosphorylation are responsible for increased apoptosis of neuronal cells and neurodegeneration in 5-month old HIV-Tg rats.

Impact of APOL1 polymorphism and IL-1β priming in the entry and persistence of HIV-1 in human podocytes

BACKGROUND

Patients of African ancestry with untreated HIV-1 infection and carrying the G1 or G2 kidney disease risk variants (Vs) at the APOL1 gene have a tenfold higher risk of developing HIV-associated nephropathy (HIVAN) compared to those with the non-risk wild type (WT) G0 variant. However, the mechanistic contribution of the APOL1 allelic state to kidney injury in HIV-1 infection remains to be elucidated.

RESULTS

Non-risk WT APOL1 is associated with lower intracellular levels of HIV-1 in conditionally immortalized human podocytes, while the over expression of G1 or G2 risk Vs significantly increases viral accumulation. The priming of podocytes with exogenous IL-1β facilitates HIV-1 entry, via the up-regulation of DC-SIGN. The over expression of APOL1 G1 and G2 risk Vs in combination with an increase in IL-1β levels causes a greater increase in viral concentration than either condition alone. In turn, HIV-1 and exogenous IL-1β together induce a de novo secretion of endogenous IL-1β and an increase of APOL1 gene expression.

CONCLUSIONS

Our findings indicate that the presence of risk Vs of APOL1 is permissive of HIV-1 persistence in human podocytes in synergy with IL-1β, a cytokine that characterizes the inflammatory milieu of acute and chronic phases of HIV-1 infection. The elucidation of these molecular mechanisms explains, at least in part, the higher frequency of HIVAN in populations carrying the risk polymorphic genetic variant of APOL1 gene.

HIV Promotes NLRP3 Inflammasome Complex Activation in Murine HIV-Associated Nephropathy

Dysregulated growth and loss of podocytes are important features of HIV-associated nephropathy. Recently, HIV was reported to induce a new type of programed cell death, pyroptosis, in T lymphocytes through induction of Nod-like receptor protein 3 (NLRP3) inflammasome complexes. We evaluated the role of HIV in podocyte NLRP3 inflammasome formation both in vivo and in vitro. Renal cortical sections of HIV-transgenic mice (Tg26) displayed increased expression of NLRP3, ASC (a CARD protein), caspase-1, and IL-1β proteins, confirming NLRP3 inflammasome complex formation in podocytes of Tg26 mice. Renal tissues of Tg26 mice also displayed enhanced mRNA levels and protein expressions of inflammasome markers (NLRP3, ASC, and caspase-1, and IL-1β). Serum of Tg26 mice also showed elevated concentrations of IL-1β cytokine compared with FVBN mice. HIV induced pyroptosis in a dose- and time-dependent manner within podocytes, a phenotype of inflammasome activation. Caspase-1 inhibitor not only attenuated podocyte expression of caspase-1 and IL-1β but also provided protection against pyroptosis, suggesting that HIV-induced podocyte injury was mediated by caspase-1 activation. Interestingly, HIV-induced podocyte pyroptosis could be partially inhibited by Tempol (a superoxide dismutase-mimetic agent) and by glyburide (an inhibitor of potassium efflux). These findings suggest that generation of reactive oxygen species and potassium efflux contribute to HIV-induced pyroptosis and NLRP3 inflammasome activation in podocytes.

Epigenetic Modulation of Human Podocyte Vitamin D Receptor in HIV Milieu

HIV (human immunodeficiency virus) has been reported to induce podocyte injury through down regulation of vitamin D receptor (VDR) and activation of renin angiotensin system; however, the involved mechanism is not clear. Since HIV has been reported to modulate gene expression via epigenetic phenomena, we asked whether epigenetic factors contribute to down regulation of VDR. Kidney cells in HIV transgenic mice and HIV-infected podocytes (HIV/HPs) displayed enhanced expression of SNAIL, a repressor of VDR. To elucidate the mechanism, we studied the effect of HIV on expression of molecules involved in SNAIL repressor complex formation and demonstrated that HIV enhances expression of the histone deacetylase HDAC1 and DNA methyl transferases DNMT3b and DNMT1. 293T cells, when stably transfected with SNAIL (SNAIL/293T), displayed suppressed transcription and translation of VDR. In SNAIL/293T cells, co-immunoprecipitation studies revealed the association of HDAC1, DNMT3b, DNMT1, and mSin3A with SNAIL. Chromatin immunoprecipitation experiments confirmed the presence of the SNAIL repressor complex at the VDR promoter. Consistent with the enhanced DNA methyl transferase expression in HIV/HPs, there was an increased CpG methylation at the VDR promoter. Chromatin immunoprecipitation assay confirmed occurrence of H3K4 trimethylation on SNAIL promoter. Neither a VDR agonist (VDA) nor an HDAC inhibitor (HDACI) nor a demethylating agent (DAC) individually could optimally up regulate VDR in HIV milieu. However, VDA and HDACI when combined were successful in de-repressing VDR expression. Our findings demonstrate that SNAIL recruits multiple chromatin enzymes to form a repressor complex in HIV milieu that down regulates VDR expression.

AT1R blockade in adverse milieus: role of SMRT and corepressor complexes

ANG II type 1 receptor blockade (AT1R-BLK) is used extensively to slow down the progression of proteinuric kidney diseases. We hypothesized that AT1R-BLK provides podocyte protection through regulation of silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and vitamin D receptor (VDR) expression under adverse milieus such as high glucose and human immunodeficiency virus infection. Both AT1R-BLK and VDR agonists (VDAs) stimulated VDR complex formation that differed not only in their composition but also in their functionality. AT1R-BLK-induced VDR complexes contained predominantly unliganded VDR, SMRT, and phosphorylated histone deacetylase 3, whereas VDA-VDR complexes were constituted by liganded VDR and CREB-binding protein/p300. AT1R-BLK-induced complexes attenuated podocyte acetyl-histone 3 levels as well as cytochrome P-450 family 24A1 expression, thus indicating their deacetylating and repressive properties. On the other hand, VDA-VDR complexes not only increased podocyte acetyl-histone 3 levels but also enhanced cytochrome P-450 family 24A1 expression, thus suggesting their acetylating and gene activation properties. AT1R-BLK- induced podocyte SMRT inhibited expression of the proapoptotic gene BAX through downregulation of Wip1 and phosphorylation of checkpoint kinase 2 in high-glucose milieu. Since SMRT-depleted podocytes lacked AT1R-BLK-mediated protection against DNA damage, it appears that SMRT is necessary for DNA repairs during AT1R-BLK. We conclude that AT1R-BLK provides podocyte protection in adverse milieus predominantly through SMRT expression and partly through unliganded VDR expression in 1,25(OH)2D-deficient states; on the other hand, AT1R-BLK contributes to liganded VDR expression in 1,25(OH)2D-sufficient states.

Vascular smooth muscle cells contribute to APOL1-induced podocyte injury in HIV milieu

Clinical reports have demonstrated that higher rates of non-diabetic glomerulosclerosis in African Americans can be attributed to two coding sequence variants (G1 and G2) in the APOL1 gene; however, the underlying mechanism is still unknown. Kidney biopsy data suggest enhanced expression of APOL1/APOL1 variants (Vs) in smooth muscle cells (SMCs) of renal vasculature. Since APOL1 is a secretory protein of relatively low molecular weight (41kDa), SMCs may be a contributory endocrine/paracrine source of APOL1 wild type (WT)/APOL1Vs in the glomerular capillary perfusate percolating podocytes. In the present study, we tested the hypothesis that an HIV milieu stimulated secretion of APOL1 and its risk variants by arterial SMCs contributes to podocyte injury. Human umbilical artery smooth muscle cells (HSMCs)-treated with conditioned media (CM) of HIV-infected peripheral mononuclear cells (PBMC/HIV-CM), CM of HIV-infected U939 cells, or recombinant IFN-γ displayed enhanced expression of APOL1. Podocytes co-cultured in trans-wells with HSMCs-over expressing APOL1WT showed induction of injury; however, podocytes co-cultured with HSMC-over expressing either APOL1G1 or APOL1G2 showed several folds greater injury when compared to HSMC-over expressing APOL1WT. Conditioned media collected from HSMC-over-expressing APOL1G1/APOL1G2 (HSMC/APOL1G1-CM or HSMC/APOL1G2-CM) also displayed higher percentages of injured podocytes in the form of swollen cells, leaky lysosomes, loss of viability, and enhanced sensitivity to adverse host factors when compared to HSMC/APOL1WT-CM. Notably, HSMC/APOL1WT-CM promoted podocyte injury only at a significantly higher concentrations compared to HSMC/APOL1G1/G2-CM. We conclude that HSMCs could serve as an endocrine/paracrine source of APOL1Vs, which mediate accelerated podocyte injury in HIV milieu.

Krüppel-like factor 6 regulates mitochondrial function in the kidney

Maintenance of mitochondrial structure and function is critical for preventing podocyte apoptosis and eventual glomerulosclerosis in the kidney; however, the transcription factors that regulate mitochondrial function in podocyte injury remain to be identified. Here, we identified Krüppel-like factor 6 (KLF6), a zinc finger domain transcription factor, as an essential regulator of mitochondrial function in podocyte apoptosis. We observed that podocyte-specific deletion of Klf6 increased the susceptibility of a resistant mouse strain to adriamycin-induced (ADR-induced) focal segmental glomerulosclerosis (FSGS). KLF6 expression was induced early in response to ADR in mice and cultured human podocytes, and prevented mitochondrial dysfunction and activation of intrinsic apoptotic pathways in these podocytes. Promoter analysis and chromatin immunoprecipitation studies revealed that putative KLF6 transcriptional binding sites are present in the promoter of the mitochondrial cytochrome c oxidase assembly gene (SCO2), which is critical for preventing cytochrome c release and activation of the intrinsic apoptotic pathway. Additionally, KLF6 expression was reduced in podocytes from HIV-1 transgenic mice as well as in renal biopsies from patients with HIV-associated nephropathy (HIVAN) and FSGS. Together, these findings indicate that KLF6-dependent regulation of the cytochrome c oxidase assembly gene is critical for maintaining mitochondrial function and preventing podocyte apoptosis.

Altered expression pattern of Nrf2/HO-1 axis during accelerated-senescence in HIV-1 transgenic rat

Chronic oxidative stress plays a central role in the pathogenesis of many diseases, including HIV-1 associated disorders. Concomitantly with the decline of endogenous antioxidant systems, it was reported that HIV-1-related proteins increase the production of radical species in cells and tissues that are not directly infected by the virus. In the context of HIV-1 infection, the role of Nrf2, a key transcription factor that contributes to the maintenance of cellular redox homeostasis, remains largely uncharacterized. One of the major stress-responsive player regulated by Nrf2 is the antioxidant enzyme HO-1. The Nrf2/HO-1 axis constitutes a crucial cell survival mechanism to counteract oxidative stress and inflammation. The present study aims to investigate the age-related patterns of Nrf2 and HO-1 in different brain regions and tissues of HIV-1 transgenic rat. Since HIV-1 induces an accelerated aging and the redox imbalance may actively promote senescence, we also evaluated the senescence phenotype-switching by quantifying levels of β-galactosidase activity. Our results showed changes in gene expression, with different trends depending on the brain regions and tissues examined. However, compared to age-matched controls, we observed in HIV-1 transgenic rats a significant reduction in the protein levels of Nrf2 and HO-1, suggesting a weakening in the protection exerted by Nrf2/HO-1 system. Moreover, we show that senescence occurs more rapidly in HIV-1 transgenic rats than in control animals. To our knowledge this is the first in vivo report showing the involvement of Nrf2/HO-1 pathway in a rat model of HIV-1.

APOL1 risk variants enhance podocyte necrosis through compromising lysosomal membrane permeability

Development of higher rates of nondiabetic glomerulosclerosis (GS) in African Americans has been attributed to two coding sequence variants (G1 and G2) in the APOL1 gene. To date, the cellular function and the role of APOL1 variants (Vs) in GS are still unknown. In this study, we examined the effects of overexpressing wild-type (G0) and kidney disease risk variants (G1 and G2) of APOL1 in human podocytes using a lentivirus expression system. Interestingly, G0 inflicted podocyte injury only at a higher concentration; however, G1 and G2 promoted moderate podocyte injury at lower and higher concentrations. APOL1Vs expressing podocytes displayed diffuse distribution of both Lucifer yellow dye and cathepsin L as manifestations of enhanced lysosomal membrane permeability (LMP). Chloroquine attenuated the APOL1Vs-induced increase in podocyte injury, consistent with targeting lysosomes. The chloride channel blocker DIDS prevented APOL1Vs- induced injury, indicating a role for chloride influx in osmotic swelling of lysosomes. Direct exposure of noninfected podocytes with conditioned media from G1- and G2-expressing podocytes also induced injury, suggesting a contributory role of the secreted component of G1 and G2 as well. Adverse host factors (AHFs) such as hydrogen peroxide, hypoxia, TNF-α, and puromycin aminonucleoside augmented APOL1- and APOL1Vs-induced podocyte injury, while the effect of human immunodeficiency virus (HIV) on podocyte injury was overwhelming under conditions of APOLVs expression. We conclude that G0 and G1 and G2 APOL1 variants have the potential to induce podocyte injury in a manner which is further augmented by AHFs, with HIV infection being especially prominent.

mTOR plays a critical role in p53-induced oxidative kidney cell injury in HIVAN

Oxidative stress has been implicated to contribute to HIV-induced kidney cell injury; however, the role of p53, a modulator of oxidative stress, has not been evaluated in the development of HIV-associated nephropathy (HIVAN). We hypothesized that mammalian target of rapamycin (mTOR) may be critical for the induction of p53-mediated oxidative kidney cell injury in HIVAN. To test our hypothesis, we evaluated the effect of an mTOR inhibitor, rapamycin, on kidney cell p53 expression, downstream signaling, and kidney cell injury in both in vivo and in vitro studies. Inhibition of the mTOR pathway resulted in downregulation of renal tissue p53 expression, associated downstream signaling, and decreased number of sclerosed glomeruli, tubular microcysts, and apoptosed and 8-hydroxy deoxyguanosine (8-OHdG)-positive (+ve) cells in Tg26 mice. mTOR inhibition not only attenuated kidney cell expression of p66ShcA and phospho-p66ShcA but also reactivated the redox-sensitive stress response program in the form of enhanced expression of manganese superoxide dismutase (MnSOD) and catalase. In in vitro studies, the mTOR inhibitor also provided protection against HIV-induced podocyte apoptosis. Moreover, mTOR inhibition downregulated HIV-induced podocyte (HP/HIV) p53 expression. Since HP/HIV silenced for mTOR displayed a lack of expression of p53 as well as attenuated podocyte apoptosis, this suggests that mTOR is critical for kidney cell p53 activation and associated oxidative kidney cell injury in the HIV milieu.

Morphine induces albuminuria by compromising podocyte integrity

Morphine has been reported to accelerate the progression of chronic kidney disease. However, whether morphine affects slit diaphragm (SD), the major constituent of glomerular filtration barrier, is still unclear. In the present study, we examined the effect of morphine on glomerular filtration barrier in general and podocyte integrity in particular. Mice were administered either normal saline or morphine for 72 h, then urine samples were collected and kidneys were subsequently isolated for immunohistochemical studies and Western blot. For in vitro studies, human podocytes were treated with morphine and then probed for the molecular markers of slit diaphragm. Morphine-receiving mice displayed a significant increase in albuminuria and showed effacement of podocyte foot processes. In both in vivo and in vitro studies, the expression of synaptopodin, a molecular marker for podocyte integrity, and the slit diaphragm constituting molecules (SDCM), such as nephrin, podocin, and CD2-associated protein (CD2AP), were decreased in morphine-treated podocytes. In vitro studies indicated that morphine modulated podocyte expression of SDCM through opiate mu (MOR) and kappa (KOR) receptors. Since morphine also enhanced podocyte oxidative stress, the latter seems to contribute to decreased SDCM expression. In addition, AKT, p38, and JNK pathways were involved in morphine-induced down regulation of SDCM in human podocytes. These findings demonstrate that morphine has the potential to alter the glomerular filtration barrier by compromising the integrity of podocytes.

HIV compromises integrity of the podocyte actin cytoskeleton through downregulation of the vitamin D receptor

Alterations in the podocyte actin cytoskeleton have been implicated in the development of proteinuric kidney diseases. In the present study, we evaluated the effect of HIV on the podocyte actin cytoskeleton and the mechanism involved. We hypothesized that HIV may be compromising the actin cytoskeleton via downregulation of the vitamin D receptor (VDR) of conditionally immortalized differentiated human podocytes (CIDHPs). HIV-transduced podocytes (HIV/CIDHPs) not only displayed downregulation of VDR but also showed activation of the renin-angiotensin system (RAS) in the form of enhanced expression of renin and increased production of ANG II. Moreover, CIDHPs lacking VDR displayed enhanced ANG II production, and treatment of HIV/CIDHPs with EB1089 (vitamin D3; VD) attenuated ANG II production. HIV/CIDHPs as well as ANG II-treated CIDHPs exhibited enhanced expression of cathepsin (CTS) L. Additionally, losartan (an ANG II type I receptor blocker) inhibited both HIV- and ANG II-induced podocyte cathepsin L expression. Furthermore, VD downregulated HIV-induced podocyte CTSL expression. Both losartan and free radical scavengers attenuated HIV- and ANG II-induced podocyte reactive oxygen species (ROS) generation. HIV also led to cytosolic CTSL accumulation through enhancement of podocyte lysosomal membrane permeabilization; on the other hand, VD, losartan, and superoxide dismutase (SOD) attenuated HIV-induced enhanced podocyte cytosolic CTSL accumulation. Morphological evaluation of HIV/CIDHPs revealed sparse actin filaments and attenuated expression of dynamin. Interestingly, podocytes lacking CTSL displayed enhanced dynamin expression, and HIV/CIDHPs expressing CTSL exhibited downregulation of dynamin. These findings indicate that HIV-induced downregulation of podocyte VDR and associated RAS activation and cytosolic CTSL accumulation compromised the actin cytoskeleton.

Activated protein C ameliorates diabetic nephropathy by epigenetically inhibiting the redox enzyme p66Shc

The coagulation protease activated protein C (aPC) confers cytoprotective effects in various in vitro and in vivo disease models, including diabetic nephropathy. The nephroprotective effect may be related to antioxidant effects of aPC. However, the mechanism through which aPC may convey these antioxidant effects and the functional relevance of these properties remain unknown. Here, we show that endogenous and exogenous aPC prevents glomerular accumulation of oxidative stress markers and of the redox-regulating protein p66(Shc) in experimental diabetic nephropathy. These effects were predominately observed in podocytes. In vitro, aPC inhibited glucose-induced expression of p66(Shc) mRNA and protein in podocytes (via PAR-1 and PAR-3) and various endothelial cell lines, but not in glomerular endothelial cells. Treatment with aPC reversed glucose-induced hypomethylation and hyperacetylation of the p66(Shc) promoter in podocytes. The hyperacetylating agent sodium butyrate abolished the suppressive effect of aPC on p66(Shc) expression both in vitro and in vivo. Moreover, sodium butyrate abolished the beneficial effects of aPC in experimental diabetic nephropathy. Inhibition of p66(Shc) expression and mitochondrial translocation by aPC normalized mitochondrial ROS production and the mitochondrial membrane potential in glucose-treated podocytes. Genetic ablation of p66(Shc) compensated for the loss of protein C activation in vivo, normalizing markers of diabetic nephropathy and oxidative stress. These studies identify a unique mechanism underlying the cytoprotective effect of aPC. Activated PC epigenetically controls expression of the redox-regulating protein p66(Shc), thus linking the extracellular protease aPC to mitochondrial function in diabetic nephropathy.

Null mutations at the p66 and bradykinin 2 receptor loci induce divergent phenotypes in the diabetic kidney

Candidate genes have been identified that confer increased risk for diabetic glomerulosclerosis (DG). Mice heterozygous for the Akita (Ins2(+/C96Y)) diabetogenic mutation with a second mutation introduced at the bradykinin 2 receptor (B2R(-/-)) locus express a disease phenotype that approximates human DG. Src homology 2 domain transforming protein 1 (p66) controls mitochondrial metabolism and cellular responses to oxidative stress, aging, and apoptosis. We generated p66-null Akita mice to test whether inactivating mutations at the p66 locus will rescue kidneys of Akita mice from disease-causing mutations at the Ins2 and B2R loci. Here we show null mutations at the p66 and B2R loci interact with the Akita (Ins2(+/C96Y)) mutation, independently and in combination, inducing divergent phenotypes in the kidney. The B2R(-/-) mutation induces detrimental phenotypes, as judged by increased systemic and renal levels of oxidative stress, histology, and urine albumin excretion, whereas the p66-null mutation confers a powerful protection phenotype. To elucidate the mechanism(s) of the protection phenotype, we turned to our in vitro system. Experiments with cultured podocytes revealed previously unrecognized cross talk between p66 and the redox-sensitive transcription factor p53 that controls hyperglycemia-induced ROS metabolism, transcription of p53 target genes (angiotensinogen, angiotensin II type-1 receptor, and bax), angiotensin II generation, and apoptosis. RNA-interference targeting p66 inhibits all of the above. Finally, protein levels of p53 target genes were upregulated in kidneys of Akita mice but unchanged in p66-null Akita mice. Taken together, p66 is a potential molecular target for therapeutic intervention in DG.

MicroRNAs in HIV-associated nephropathy (HIVAN)

MicroRNAs (miRNAs) play a critical role in multiple biological and metabolic processes. Recent studies suggested that miRNAs are critical in the maintenance of glomerular homeostasis in both physiological and pathological states. However, the role of miRNAs in the pathogenesis of HIV-associated nephropathy (HIVAN) has not been studied. In the present study, we have used a microarray-based approach in combination with real-time PCR to profile the miRNA expression patterns in HIV-1 transgenic mice (Tg26). Our results showed that 13 miRNAs, which belong to 11 miRNA families, were downregulated in HIVAN when compared with control mice. These miRNAs were classified into 20 functional categories. In in vitro studies, we examined the expression of specific miRNAs in HIV-1 transduced human podocytes. Our results showed that HIV-1 downregulated miRNA expression, specifically of miR-200 and miR-33. These studies suggest that miRNAs contributed to the development of the proliferative phenotype of HIVAN. Further functional analysis of these miRNAs in HIVAN animal model will not only enhance understanding of the pathogenesis but would also lead to the development of therapeutic strategies for HIVAN patients.

Ethanol and vitamin D receptor in T cell apoptosis

Ethanol has been demonstrated to cause T cell apoptosis. In the present study, we evaluated the role of VDR and the renin angiotensin system (RAS) in oxidative stress-induced T cell apoptosis. Ethanol-treated human T cells displayed down regulation of vitamin D receptor (VDR) and the activation of the RAS in the form of enhanced T cell renin expression and angiotensin II (Ang II) production. The silencing of VDR with siRNA displayed the activation of the RAS, and activation of the VDR resulted in the down regulation of the RAS. It suggested that ethanol-induced T cell RAS activation was dependent on the VDR status. T cell ROS generation by ethanol was found to be dose dependent. Conversely, ethanol-induced ROS generation was inhibited if VDR was activated or Ang II was blocked by an angiotensin II type 1 (AT1) receptor blocker (Losartan). Furthermore, it was observed that ethanol not only induced double strand breaks in T cells but also attenuated DNA repair response, whereas, VDR activation inhibited ethanol-induced double strand breaks and also enhanced DNA repairs. Since free radical scavengers inhibited ethanol-induced DNA damage, it would indicate that ethanol-induced DNA damage was mediated through ROS generation. These findings indicated that ethanol-induced T cell apoptosis was mediated through ROS generation in response to ethanol-induced down regulation of VDR and associated activation of the RAS.

Deletion of the ageing gene p66(Shc) reduces early stroke size following ischaemia/reperfusion brain injury

AIMS

Stroke is a leading cause of morbidity and mortality, and its incidence increases with age. Both in animals and in humans, oxidative stress appears to play an important role in ischaemic stroke, with or without reperfusion. The adaptor protein p66(Shc) is a key regulator of reactive oxygen species (ROS) production and a mediator of ischaemia/reperfusion damage in ex vivo hearts. Hence, we hypothesized that p66(Shc) may be involved in ischaemia/reperfusion brain damage. To this end, we investigated whether genetic deletion of p66(Shc) protects from ischaemia/reperfusion brain injury.

METHODS AND RESULTS

Transient middle cerebral artery occlusion (MCAO) was performed to induce ischaemia/reperfusion brain injury in wild-type (Wt) and p66(Shc) knockout mice (p66(Shc-/-)), followed by 24 h of reperfusion. Cerebral blood flow and blood pressure measurements revealed comparable haemodynamics in both experimental groups. Neuronal nuclear antigen immunohistochemical staining showed a significantly reduced stroke size in p66(Shc-/-) when compared with Wt mice (P < 0.05, n = 7-8). In line with this, p66(Shc-/-) mice exhibited a less impaired neurological function and a decreased production of free radicals locally and systemically (P < 0.05, n = 4-5). Following MCAO, protein levels of gp91phox nicotinamide adenine dinucleotide phosphate oxidase subunit were increased in brain homogenates of Wt (P < 0.05, n = 4), but not of p66(Shc-/-) mice. Further, reperfusion injury in Wt mice induced p66(Shc) protein in the basilar and middle cerebral artery, but not in brain tissue, suggesting a predominant involvement of vascular p66(Shc).

CONCLUSION

In the present study, we show that the deletion of the ageing gene p66(Shc) protects mice from ischaemia/reperfusion brain injury through a blunted production of free radicals. The ROS mediator p66(Shc) may represent a novel therapeutical target for the treatment of ischaemic stroke.

Vitamin D receptor activation and downregulation of renin-angiotensin system attenuate morphine-induced T cell apoptosis

Opiates have been reported to induce T cell loss. We evaluated the role of vitamin D receptor (VDR) and the activation of the renin-angiotensin system (RAS) in morphine-induced T cell loss. Morphine-treated human T cells displayed downregulation of VDR and the activation of the RAS. On the other hand, a VDR agonist (EB1089) enhanced T cell VDR expression both under basal and morphine-stimulated states. Since T cells with silenced VDR displayed the activation of the RAS, whereas activation of the VDR was associated with downregulation of the RAS, it appears that morphine-induced T cell RAS activation was dependent on the VDR status. Morphine enhanced reactive oxygen species (ROS) generation in a dose-dependent manner. Naltrexone (an opiate receptor antagonist) inhibited morphine-induced ROS generation and thus, suggested the role of opiate receptors in T cell ROS generation. The activation of VDR as well as blockade of ANG II (by losartan, an AT(1) receptor blocker) also inhibited morphine-induced T cell ROS generation. Morphine not only induced double-strand breaks (DSBs) in T cells but also attenuated DNA repair response, whereas activation of VDR not only inhibited morphine-induced DSBs but also enhanced DNA repair. Morphine promoted T cell apoptosis; however, this effect of morphine was inhibited by blockade of opiate receptors, activation of the VDR, and blockade of the RAS. These findings indicate that morphine-induced T cell apoptosis is mediated through ROS generation in response to morphine-induced downregulation of VDR and associated activation of the RAS.

HIV-induced kidney cell injury: role of ROS-induced downregulated vitamin D receptor

Reactive oxygen species (ROS) have been demonstrated to contribute to HIV-induced tubular cell injury. We hypothesized that HIV-induced ROS generation may be causing tubular cell injury through downregulation of vitamin D receptor (VDR) and associated downstream effects. In the present study, HIV not only downregulated tubular cell VDR expression but also inflicted DNA injury. On the other hand, EB-1089, a VDR agonist (VD), inhibited both downregulation of VDR and tubular cell DNA injury in the HIV milieu. H(2)O(2) (an O(-) donor) directly downregulated tubular cell VDR, whereas catalase, a free radical scavenger, inhibited HIV-induced downregulation of tubular cell VDR expression. HIV also stimulated the tubular cell renin-angiotensin system (RAS) through downregulation of VDR. Because losartan (an ANG II blolcker) partially inhibited HIV-induced tubular cell ROS generation while ANG II directly stimulated tubular cell ROS generation, it appears that HIV-induced ROS production was partly contributed by the RAS activation. VD not only inhibited HIV-induced RAS activation but also attenuated tubular cell ROS generation. Tubular cells displayed double jeopardy in the HIV milieu induction of double-strand breaks and attenuated DNA repair; additionally, in the HIV milieu, tubular cells exhibited enhanced expression of phospho-p53 and associated downstream signaling. A VDR agonist and an ANG II blocker not only preserved expression of tubular cell DNA repair proteins but also inhibited induction of double-strand breaks. In in vivo studies, renal cortical sections of Tg26 mice displayed attenuated expression of VDR both in podocytes and tubular cells. In addition, renal cortical sections of Tg26 mice displayed enhanced oxidative stress-induced kidney cell DNA damage. These findings indicated that HIV-induced tubular cell downregulation of VDR contributed to the RAS activation and associated tubular cell DNA damage. However, both VD and RAS blockade provided protection against these effects of HIV.

HIV-1, reactive oxygen species, and vascular complications

Over 1 million people in the United States and 33 million individuals worldwide suffer from HIV/AIDS. Since its discovery, HIV/AIDS has been associated with an increased susceptibility to opportunistic infection due to immune dysfunction. Highly active antiretroviral therapies restore immune function and, as a result, people infected with HIV-1 are living longer. This improved survival of HIV-1 patients has revealed a previously unrecognized risk of developing vascular complications, such as atherosclerosis and pulmonary hypertension. The mechanisms underlying these HIV-associated vascular disorders are poorly understood. However, HIV-induced elevations in reactive oxygen species (ROS), including superoxide and hydrogen peroxide, may contribute to vascular disease development and progression by altering cell function and redox-sensitive signaling pathways. In this review, we summarize the clinical and experimental evidence demonstrating HIV- and HIV antiretroviral therapy-induced alterations in reactive oxygen species and how these effects are likely to contribute to vascular dysfunction and disease.

A systems approach identifies HIPK2 as a key regulator of kidney fibrosis

Kidney fibrosis is a common process that leads to the progression of various types of kidney disease. We used an integrated computational and experimental systems biology approach to identify protein kinases that regulate gene expression changes in the kidneys of human immunodeficiency virus (HIV) transgenic mice (Tg26 mice), which have both tubulointerstitial fibrosis and glomerulosclerosis. We identified homeo-domain interacting protein kinase 2 (HIPK2) as a key regulator of kidney fibrosis. HIPK2 was upregulated in the kidneys of Tg26 mice and in those of patients with various kidney diseases. HIV infection increased the protein concentrations of HIPK2 by promoting oxidative stress, which inhibited the seven in absentia homolog 1 (SIAH1)-mediated proteasomal degradation of HIPK2. HIPK2 induced apoptosis and the expression of epithelial-to-mesenchymal transition markers in kidney epithelial cells by activating the p53, transforming growth factor β (TGF-β)-SMAD family member 3 (Smad3) and Wnt-Notch pathways. Knockout of HIPK2 improved renal function and attenuated proteinuria and kidney fibrosis in Tg26 mice, as well as in other murine models of kidney fibrosis. We therefore conclude that HIPK2 is a potential target for anti-fibrosis therapy.

HIV-1 promotes renal tubular epithelial cell protein synthesis: role of mTOR pathway

Tubular cell HIV-infection has been reported to manifest in the form of cellular hypertrophy and apoptosis. In the present study, we evaluated the role of mammalian target of rapamycin (mTOR) pathway in the HIV induction of tubular cell protein synthesis. Mouse proximal tubular epithelial cells (MPTECs) were transduced with either gag/pol-deleted NL4-3 (HIV/MPTEC) or empty vector (Vector/MPTEC). HIV/MPTEC showed enhanced DNA synthesis when compared with Vector/MPTECs by BRDU labeling studies. HIV/MPTECs also showed enhanced production of β-laminin and fibronection in addition to increased protein content per cell. In in vivo studies, renal cortical sections from HIV transgenic mice and HIVAN patients showed enhanced tubular cell phosphorylation of mTOR. Analysis of mTOR revealed increased expression of phospho (p)-mTOR in HIV/MPTECs when compared to vector/MPTECs. Further downstream analysis of mTOR pathway revealed enhanced phosphorylation of p70S6 kinase and associated diminished phosphorylation of eEF2 (eukaryotic translation elongation factor 2) in HIV/MPTECs; moreover, HIV/MPTECs displayed enhanced phosphorylation of eIF4B (eukaryotic translation initiation factor 4B) and 4EBP-1 (eukaryotic 4E binding protein). To confirm our hypothesis, we evaluated the effect of rapamycin on HIV-induced tubular cell downstream signaling. Rapamycin not only attenuated phosphorylation of p70S6 kinase and associated down stream signaling in HIV/MPTECs but also inhibited HIV-1 induced tubular cell protein synthesis. These findings suggest that mTOR pathway is activated in HIV-induced enhanced tubular cell protein synthesis and contributes to tubular cell hypertrophy.

HIV gene expression deactivates redox-sensitive stress response program in mouse tubular cells both in vitro and in vivo

Human immunodeficiency virus (HIV)-1 has been reported to cause tubular cell injury both in in vivo and in vitro studies. In the present study, we evaluated the role of oxidative stress in the induction of apoptosis in HIV gene expressing mouse tubular cells in in vivo (Tg26, a transgenic mouse model of HIV-associated nephropathy) and in vitro (tubular cells were transduced with pNL4-3: ΔG/P-GFP, VSV.G psueudo typed virus) studies. Although Tg26 mice showed enhanced tubular cell reactive oxygen species (ROS) generation and apoptosis, renal tissue did not display a robust antioxidant response in the form of enhanced free radical scavenger (MnSOD/catalase) expression. Tg26 mice not only showed enhanced tubular cell expression of phospho-p66ShcA but also displayed nuclear Foxo3a translocation to the cytoplasm. These findings indicated deactivation of tubular cell Foxo3A-dependent redox-sensitive stress response program (RSSRP) in Tg26 mice. In in vitro studies, NL4-3 (pNL4-3: ΔG/P-GFP, VSV.G pseudotyped virus)-transduced mouse proximal tubular cells (NL4-3/MPTEC) displayed enhanced phosphorylation of p66ShcA. NL4-3/MPTECs also displayed greater (P < 0.01) ROS generation when compared with empty vector-transduced tubular cells; however, both diminution of p66ShcA and N-acetyl cysteine attenuated NL4-3-induced tubular cell ROS generation as well as apoptosis. In addition, both antioxidants and free radical scavengers partially inhibited HIV-induced tubular cell apoptosis. NL4-3/MPTEC displayed deactivation of RSSRP in the form of enhanced phosphorylation of Foxo3A and attenuated expression of superoxide dismutase (SOD) and catalase. Since both SOD and catalase were able to provide protection against HIV-1-induced tubular cell apoptosis, it suggests that HIV-1-induced proapoptotic effect may be a consequence of the deactivated RSSRP.

Recent progress in HIV-associated nephropathy

The classic kidney disease of HIV infection, HIV-associated nephropathy (HIVAN), is an aggressive form of collapsing focal segmental glomerulosclerosis with accompanying tubular and interstitial lesions. HIVAN was first described among African-Americans and Haitian immigrants with advanced HIV disease, an early suggestion of a strong genetic association. This genetic susceptibility was recently linked to polymorphisms on chromosome 22 in individuals of African descent. The association with advanced HIV infection and evidence from HIV-transgenic mice suggested the possibility that HIV directly infects the kidney and that specific HIV gene expression induces host cellular pathways that are responsible for HIVAN pathogenesis. Although combination antiretroviral therapy has substantially reduced the impact of HIVAN in the United States, continued growth of the HIV epidemic in susceptible African populations may have important public health implications. This article reviews recent progress in the pathogenesis and treatment of HIVAN and describes the changing epidemiology of HIV-related kidney disease.

HIV-associated nephropathy: pathogenesis

PURPOSE OF REVIEW

HIV-associated nephropathy (HIVAN) is characterized histologically by a collapsing form of focal segmental glomerulosclerosis (FSGS), microcystic tubular dilation, interstitial inflammation and fibrosis. In this review, we provide a summary of the current state of knowledge about the mechanisms involved in the pathogenesis of HIVAN.

RECENT FINDINGS

Two variants in the ApoL1 gene have been identified as the susceptibility alleles that account for a majority of the increased risk of FSGS and nondiabetic end-stage renal disease in blacks. HIVAN1 and HIVAN2 are the other host susceptibility genes that have been identified in animal models for HIVAN. HIV infects renal tubular epithelial cells likely through direct cell-cell transmission. Both in-vivo and in-vitro evidence suggests that Nef and Vpr are the key viral genes mediating HIVAN. Nef induces podocyte dysfunction, whereas Vpr induces renal tubular epithelial cell apoptosis.

SUMMARY

HIVAN results from direct infection by HIV-1 and expression of viral genes, especially Nef and Vpr, in renal epithelial cells in a genetically susceptible host. The infected renal epithelium acts as a separate viral compartment from the blood and facilitates evolution of strains distant from blood. Dysregulation of several host cellular pathways, including those involved in cell cycle and apoptosis, ultimately results in the unique histopathological syndrome of HIVAN.

Insulin-like growth factor-I-forkhead box O transcription factor 3a counteracts high glucose/tumor necrosis factor-α-mediated neuronal damage: implications for human immunodeficiency virus encephalitis

In HIV patients, antiretroviral medications trigger metabolic abnormalities, including insulin resistance. In addition, the inflammatory cytokine tumor necrosis factor-α (TNFα), which is elevated in human immunodeficiency virus encephalitis (HIVE), also induces insulin resistance and inflicts neuronal damage in vitro. In differentiated PC12 cells and rat cortical neurons, high glucose (HG; 25 mM) triggers reactive oxygen species (ROS) accumulation, contributing to the retraction of neuronal processes, with only a minimal involvement of neuronal apoptosis. In the presence of TNFα, HG-treated neurons undergo massive apoptosis. Because mammalian homolog of the Forkhead family of transcription factors, Forkhead box O transcription factor 3a (FOXO3a), controls ROS metabolism, we asked whether FOXO3a could affect the fate of differentiated neurons in the paradigm of HIVE. We observed FOXO3a nuclear translocation in HG-treated neuronal cultures, accompanied by partial loss of mitochondrial potential and gradual retraction of neuronal processes. Addition of TNFα to HG-treated neurons increased expression of the FOXO-dependent proapoptotic gene Bim, which resulted in extensive apoptotic death. Insulin-like growth factor-I (IGF-I) significantly lowered intracellular ROS, which was accompanied by IGF-I-mediated FOXO3a nuclear export and decrease in its transcriptional activity. The clinical relevance of these findings is supported by detection of nuclear FOXO3a in TUNEL-positive cortical neurons from HIVE, especially in brain areas characterized by elevated TNFα.

p66Shc mediates high-glucose and angiotensin II-induced oxidative stress renal tubular injury via mitochondrial-dependent apoptotic pathway

p66Shc, a promoter of apoptosis, modulates oxidative stress response and cellular survival, but its role in the progression of diabetic nephropathy is relatively unknown. In this study, mechanisms by which p66Shc modulates high-glucose (HG)- or angiotensin (ANG) II-induced mitochondrial dysfunction were investigated in renal proximal tubular cells (HK-2 cells). Expression of p66Shc and its phosphorylated form (p-p66Shc, serine residue 36) and apoptosis were notably increased in renal tubules of diabetic mice, suggesting an increased reactive oxygen species production. In vitro, HG and ANG II led to an increased expression of total and p-p66Shc in HK-2 cells. These changes were accompanied with increased production of mitochondrial H(2)O(2), reduced mitochondrial membrane potential, increased translocation of mitochondrial cytochrome c from mitochondria into cytosol, upregulation of the expression of caspase-9, and ultimately reduced cell survival. Overexpression of a dominant-negative Ser36 mutant p66Shc (p66ShcS36A) or treatment of p66Shc- or PKC-β-short interfering RNAs partially reversed these changes. Treatment of HK-2 cells with HG and ANG II also increased the protein-protein association between p-p66Shc and Pin1, an isomerase, in the cytosol, and with cytochrome c in the mitochondria. These interactions were partially disrupted with the treatment of PKC-β inhibitor or Pin1-short interfering RNA. These data suggest that p66Shc mediates HG- and ANG II-induced mitochondrial dysfunctions via PKC-β and Pin1-dependent pathways in renal tubular cells.

ROS accumulation and IGF-IR inhibition contribute to fenofibrate/PPARalpha -mediated inhibition of glioma cell motility in vitro

BACKGROUND

Glioblastomas are characterized by rapid cell growth, aggressive CNS infiltration, and are resistant to all known anticancer regimens. Recent studies indicate that fibrates and statins possess anticancer potential. Fenofibrate is a potent agonist of peroxisome proliferator activated receptor alpha (PPARalpha) that can switch energy metabolism from glycolysis to fatty acid beta-oxidation, and has low systemic toxicity. Fenofibrate also attenuates IGF-I-mediated cellular responses, which could be relevant in the process of glioblastoma cell dispersal.

METHODS

The effects of fenofibrate on Glioma cell motility, IGF-I receptor (IGF-IR) signaling, PPARalpha activity, reactive oxygen species (ROS) metabolism, mitochondrial potential, and ATP production were analyzed in human glioma cell lines.

RESULTS

Fenofibrate treatment attenuated IGF-I signaling responses and repressed cell motility of LN-229 and T98G Glioma cell lines. In the absence of fenofibrate, specific inhibition of the IGF-IR had only modest effects on Glioma cell motility. Further experiments revealed that PPARalpha-dependent accumulation of ROS is a strong contributing factor in Glioma cell lines responses to fenofibrate. The ROS scavenger, N-acetyl-cysteine (NAC), restored cell motility, improved mitochondrial potential, and increased ATP levels in fenofibrate treated Glioma cell lines.

CONCLUSIONS

Our results indicate that although fenofibrate-mediated inhibition of the IGF-IR may not be sufficient in counteracting Glioma cell dispersal, PPARalpha-dependent metabolic switch and the resulting ROS accumulation strongly contribute to the inhibition of these devastating brain tumor cells.

ANG II promotes autophagy in podocytes

Podocytes are an integral and important constituent of the glomerular filtration barrier (GFB) and are exposed to a higher concentrations of ANG II in diseased states; consequently, podocytes may accumulate oxidized proteins and damaged mitochondria. In the present study, we evaluated the effect of ANG II on the podocyte autophagic process, which is likely to be triggered in order to degrade unwanted proteins and damaged organelles. To quantitate the occurrence of autophagy, electron microscopic studies were carried out on control and ANG II-treated conditionally immortalized mouse podocytes (CIMPs). ANG II-treated cells showed a fivefold greater number of autophagosomes/field compared with control cells. This proautophagic effect of ANG II was inhibited by pretreatment with 3-methyladenine, an inhibitor of autophagy. ANG II also enhanced podocyte expression of autophagic genes such as LC3-2 and beclin-1. Since oxidative stress is often associated with the induction of autophagy, we examined the effect of ANG II on podocyte reactive oxygen species (ROS) generation. ANG II enhanced podocyte ROS generation in a time-dependent manner. To determine whether there is a causal relationship between ANG II-induced oxidative stress and induction of autophagy, we evaluated the effect of antioxidants on ANG II-induced autophagy. As expected, the proautophagic effect of ANG II was inhibited by antioxidants. We conclude that ANG II promotes podocyte autophagy through the generation of ROS.

HIV-1 and kidney cells: better understanding of viral interaction

HIV-associated nephropathy (HIVAN) is the most common disease affecting untreated seropositive patients of African descent. Besides genetic (African descent) and HIV-1 infection (environmental), specific host factors such as activation of renin-angiotensin-aldosterone system (RAAS) have also been demonstrated to play a role in the manifestation of HIVAN. The recent identification of MYH9 as susceptible allele is a key step forward in our understanding for the pathogenesis of focal glomerulosclerosis in people of African-American descent. HIV-1 transgenic models have significantly advanced our knowledge base in terms of role of HIV-1 genes in general and individual gene in particular in the development of renal lesions mimicking HIVAN. These studies suggest that viral replication is not needed for the development of renal lesions. Renal biopsy data from HIVAN patients suggest that renal epithelial cells express HIV-1 genes and thus it may be sufficient to invoke HIVAN phenotype in the presence of specific host and genetic factors. On the other hand, immune response to infection may be required to induce HIV-1 associated immune complex kidney disease (HIVICK). Since renal cell lack conventional HIV-1 receptors, HIV-1 entry into renal cells has been a mystery. Recently, non-conventional pathways have been demonstrated to facilitate HIV-1 entry into renal cells in in vitro studies. These include presence of DEC-205 receptors in renal tubular cells and lipid rafts in podocytes. However, HIV-1 entry through these pathways only allows non-productive infection. It appears that the presence of specific genetic and host factors in in vivo conditions may be facilitating the development of the productive HIV-1 infection in kidney cells.

The Role of p66shc in Oxidative Stress and Apoptosis

p66shcis a gene that regulates the level of reactive oxygen species (ROS), apoptosis induction, and lifespan in mammals. Miceknocked out forp66shchave a lifespan~30% longeranddemonstrate an enhanced resistance to oxidative stress and age-related pathologies such as hypercholesterolemia, ischemia, and hyperglycemia. In this respect, p66shc is a promising pharmacological target for the treatment of age-related diseases. In this review, an attempt has been made to survey and put to a critical analysis data concerning the involvement of p66shс in the different signaling pathways that regulate oxidative stress and apoptosis.

Reactive oxygen species and age-related genes p66shc, Sirtuin, FOX03 and Klotho in senescence

Reactive oxygen species (ROS) superoxide and hydrogen peroxide perform important signaling functions in many physiological and pathophysiological processes. Cell senescence and organismal age are not exemptions.Aging-regulating genes p66shc, Sirtuin, FOXO3a and Klotho are new important factors which are stimulated by ROS signaling. It has been shown that ROS participate in initiation and prolongation of gene-dependent aging development.ROS also participate in the activation of protein kinases Akt/PKB and extracellular signal-regulated kinase ERK, which by themselves or through gene activation stimulates or retards cell senescence.Different retarding/stimulating effects of ROS might depend on the nature of signaling species-superoxide or hydrogen peroxide. Importance of radical anion superoxide as a signaling molecule with"super-nucleophilic" properties points to the possibility of the use of superoxide scavengers (SOD mimetics, ubiquinones and flavonoids) for retarding the development of aging.

The pathogenesis of HIV-associated nephropathy

HIV-associated nephropathy (HIVAN) is one of the leading causes of ESRD in HIV-1-seropositive patients. Patients typically present with heavy proteinuria and chronic renal failure with pathologic findings of collapsing focal segmental glomerulosclerosis (FSGS). The disease is caused by direct infection of renal epithelial cells by HIV-1 in a genetically susceptible host. The genetic factors responsible for the susceptibility to HIVAN among blacks include a noncoding variant in the podocyte-expressed gene nonmuscle myosin, heavy chain 9 (MYH9) as well as other genes yet to be identified. Podocyte and tubular dysfunction results from the expression of viral genes, in particular nef and vpr, and the subsequent dysregulation of numerous host factors, including critical signaling pathways, inflammatory mediators, and others. The identification of these factors has the potential to provide novel therapeutic targets to prevent and treat this important disease.

HIVAN phenotype: consequence of epithelial mesenchymal transdifferentiation

Human immunodeficiency virus (HIV)-1-associated nephropathy (HIVAN) is characterized by proliferation of glomerular and tubular epithelial cells. We studied the role of epithelial mesenchymal transdifferentiation (EMT) in the development of HIVAN phenotype. Renal cortical sections from six FVB/N (control) and six Tg26 (HIVAN) mice were immunolabeled for PCNA, alpha-smooth muscle actin (alpha-SMA), fibroblast-specific protein-1 (FSP1), CD3, and F4/80. Since periglomerular cells (PGCs) and peritubular cells (PTCs) did not show any labeling for CD3 and F4/80 but showed labeling for alpha-SMA or FSP1, it appears that these were myofibroblasts that migrated from either glomerular or tubular sites, respectively. Occurrence of EMT was also supported by diminished expression of E-cadherin by renal epithelial cells in Tg26 mice. Interestingly, Tg26 mice also showed enhanced renal tissue expression of ZEB2; henceforth, it appears that transcription of molecules required for maintenance of de novo renal epithelial cell phenotype was suppressed. To evaluate the role of ANG II, Tg26 mice in groups of three were administered either normal saline or telmisartan (an AT1 receptor blocker) for 2 wk, followed by evaluation for renal cell EMT. Renal cortical section of Tg26 mice showed a sevenfold increase (P < 0.001) in parietal epithelial cell (PEC)-PGC and a threefold increase (P < 0.01) in tubular cell (TC)-PTC proliferation (PCNA-positive cells). Similarly, both PECs-PGCs and TCs-PTCs in Tg26 mice showed enhanced expression of alpha-SMA and FSP1. Both PECs and podocytes contributed to the glomerular proliferative phenotype, but the contribution of PECs was much greater. Telmisartan-receiving Tg26 mice (TRM) showed attenuated number of proliferating PECs-PGCs and TCs-PTCs compared with saline-receiving Tg26 mice (SRM). Similarly, TRM showed diminished expression of alpha-SMA and FSP1 by both PECs-PGCs and TCs-PTCs compared with SRM. We conclude that EMT contributes to the manifestation of the proliferative phenotype in HIVAN mice.