Tg26 Mouse Research Articles

Abstract 52: HIV-derived Proteins Induce Neuroinflammation, Hypertension, and Sympatho-activation via T cell-dependent mechanisms in the Tg26 Mouse Model

Combination antiretroviral therapy (cART) has extended life expectancy in people living with HIV (PLWH), shifting the primary cause of death to cardiovascular disease (CVD). Hypertension affects over 65% of PLWH. However, the mechanisms underlying HIV-associated hypertension remain poorly understood. In PLWH on cART, T cells persist as viral reservoirs, secreting viral proteins that circulate and localize in the central nervous system (CNS). Here, we used theTg26 mouse model, clinically relevant to cART-controlled PLWH, to test the hypothesis that HIV-derived proteins elevate blood pressure (BP) and induce sympatho-activation through blood-brain barrier disruption, microglial activation, and neuroinflammation. Telemetry-based BP measurements revealed a hypertensive phenotype in male and female Tg26 mice (male: WT=112.3 ±1.3 vs. Tg26=121.9 ±4.0 mmHg; female: WT=110.6 ±3.01 vs. Tg26=120.3 ±6.9 mmHg). Tg26 mice displayed increased sympathetic contribution to BP, indicated by a larger BP decrease following ganglionic blockade compared to WT, with no changes in heart rate responses to muscarinic and β-adrenergic receptor blockade, suggesting increased neurogenic BP regulation. Tg26 mice also showed increased aortic vasoconstriction to phenylephrine (P<0.05). LC/MS analysis revealed no significant differences in circulating catecholamine and metabolites between WT and Tg26 mice (n=5). MRI-based brain perfusion measurements also showed no significant differences, indicating an alteration in brain perfusion is not responsible for increased sympathetic activation. Inhibiting T-cell activation using abatacept, a CTLA-4-Ig fusion protein, significantly reduced BP, sympatho-activation, and phenylephrine-induced vasoconstriction in Tg26 mice (n=5, p<0.05). We analyzed the brains of Tg26 mice to investigate how T cells promote hypertension and sympatho-activation. Quantitative PCR confirmed viral protein expression in brain tissues and microglia of Tg26 mice, associated with increased markers of neuroinflammation, microglia activation, and T-cell infiltration (fold change>1.5, n=6, p<0.05). Tg26 mice also showed increased expression of NADPH oxidases and matrix metalloproteinase. However, there were no changes in the expression of tight junction proteins. Our data suggest that the expression of HIV-derived proteins in Tg26 mice induces central inflammation and T cell infiltration, leading to sympatho-activation through T cell-dependent mechanisms.

NAD deficiency contributes to progressive kidney disease in HIV-nephropathy mice.

HIV disease remains prevalent in the United States and is particularly prevalent in sub-Saharan Africa. Recent investigations revealed that mitochondrial dysfunction in kidney contributes to HIV-associated nephropathy (HIVAN) in Tg26 transgenic mice. We hypothesized that nicotinamide adenine dinucleotide (NAD) deficiency contributes to energetic dysfunction and progressive tubular injury. We investigated metabolomic mechanisms of HIVAN tubulopathy. Tg26 and wild-type (WT) mice were treated with the farnesoid X receptor (FXR) agonist INT-747 or nicotinamide riboside (NR) from 6 to 12 wk of age. Multiomic approaches were used to characterize kidney tissue transcriptomes and metabolomes. Treatment with INT-747 or NR ameliorated kidney tubular injury, as shown by serum creatinine, the tubular injury marker urinary neutrophil-associated lipocalin, and tubular morphometry. Integrated analysis of metabolomic and transcriptomic measurements showed that NAD levels and production were globally downregulated in Tg26 mouse kidneys, especially nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD salvage pathway. Furthermore, NAD-dependent deacetylase sirtuin3 activity and mitochondrial oxidative phosphorylation activity were lower in ex vivo proximal tubules from Tg26 mouse kidneys compared with those of WT mice. Restoration of NAD levels in the kidney improved these abnormalities. These data suggest that NAD deficiency might be a treatable target for HIVAN.NEW & NOTEWORTHY The study describes a novel investigation that identified nicotinamide adenine dinucleotide (NAD) deficiency in a widely used HIV-associated nephropathy (HIVAN) transgenic mouse model. We show that INT-747, a farnesoid X receptor agonist, and nicotinamide riboside (NR), a precursor of nicotinamide, each ameliorated HIVAN tubulopathy. Multiomic analysis of mouse kidneys revealed that NAD deficiency was an upstream metabolomic mechanism contributing to HIVAN tubulopathy.

Investigating quantitative histological characteristics in renal pathology using HistoLens

HistoLens is an open-source graphical user interface developed using MATLAB AppDesigner for visual and quantitative analysis of histological datasets. HistoLens enables users to interrogate sets of digitally annotated whole slide images to efficiently characterize histological differences between disease and experimental groups. Users can dynamically visualize the distribution of 448 hand-engineered features quantifying color, texture, morphology, and distribution across microanatomic sub-compartments. Additionally, users can map differentially detected image features within the images by highlighting affected regions. We demonstrate the utility of HistoLens to identify hand-engineered features that correlate with pathognomonic renal glomerular characteristics distinguishing diabetic nephropathy and amyloid nephropathy from the histologically unremarkable glomeruli in minimal change disease. Additionally, we examine the use of HistoLens for glomerular feature discovery in the Tg26 mouse model of HIV-associated nephropathy. We identify numerous quantitative glomerular features distinguishing Tg26 transgenic mice from wild-type mice, corresponding to a progressive renal disease phenotype. Thus, we demonstrate an off-the-shelf and ready-to-use toolkit for quantitative renal pathology applications.

HIV-derived Proteins induce Hypertension, Sympatho-activation, and neuroinflammation via T cell-dependent mechanisms

Combination antiretroviral therapy (cART) has markedly increased life expectancy in people living with HIV (PLWH) and induced a switch in the cause of death from opportunistic diseases to cardiovascular disease (CVD). CVD is currently the leading cause of death in PLWH and hypertension, the primary risk factor for CVD, presents in more than 65% of them. However, the mechanisms whereby hypertension develops in PLWH remain unknown. In PLWH on cART, T lymphocytes (T cells) remain a viral reservoir for HIV and continue to secrete viral proteins. Viral proteins remain in circulation and are expressed in the central nervous system. Herein, we tested the hypothesis that expression of HIV-derived proteins increases blood pressure (BP), induces sympatho-activation and inflammation of the central nervous system. We utilized the Tg26 mouse model which expresses 7/9 viral proteins. Quantitative PCR analysis of viral protein expression showed that Tat, gp120, Nef, Vif, and Vpr are primarily expressed in spleen, lung, and brain tissues in Tg26 mice. Morphometric analysis revealed slight but significant increases and decreases in lean mass and fat weights respectively in Tg26. Flow cytometry analysis showed no reduction in CD4+ T cells in Tg26 mice indicating that this mouse model does not progress to AIDS and reproduce the conditions of virally suppressed PLWH. Blood pressure (BP) measurement via telemetry revealed a hypertensive phenotype in male and female Tg26 mice. Hypertension was associated with a larger drop in BP in response to ganglionic blockade but no alterations in heart rate responses to muscarinic and β-adrenergic receptor blockade in Tg26 mice, indicating that viral proteins expression increases neurogenic control of BP but did not alter cardiac autonomic control. β-adrenergic receptor blockade did not reduce BP in Tg26 mice. Tg26 mice also display increased aortic vasoconstriction to phenylephrine. To test the contribution of T cells in BP regulation and sympatho-activation, mice were subjected to a CTLA-4 inhibitor, abatacept, which inhibits T cell activation. Abatacept treatment significantly reduced BP, sympatho-activation, and phenylephrine constriction in Tg26 mice with no effects on wild-type mice. To determine whether the increase in sympatho-activation involves central inflammation, inflammatory cytokines and T cell markers levels were measured in the brain. Levels of pro-inflammatory cytokines including IL-1α, TNFα, IL-6, and CCL2 were increased in the brain of Tg26 mice as well as levels of the T-cell marker GATA3. Altogether, our data shows that the expression of HIV-derived proteins increases BP, sympatho-activation, and vascular adrenergic contractility via T cell-dependent mechanisms likely through central mechanisms involving neuro-inflammation. R01HL147639-01A1, R01HL15526501 and 19EIA34760167 (E.J.B). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Chronic Morphine Treatment and Antiretroviral Therapy Exacerbate HIV-Distal Sensory Peripheral Neuropathy and Induce Distinct Microbial Alterations in the HIV Tg26 Mouse Model.

Distal Sensory Peripheral Neuropathy (DSP) is a common complication in HIV-infected individuals, leading to chronic pain and reduced quality of life. Even with antiretroviral therapy (ART), DSP persists, often prompting the use of opioid analgesics, which can paradoxically worsen symptoms through opioid-induced microbial dysbiosis. This study employs the HIV Tg26 mouse model to investigate HIV-DSP development and assess gut microbiome changes in response to chronic morphine treatment and ART using 16S rRNA sequencing. Our results reveal that chronic morphine and ART exacerbate HIV-DSP in Tg26 mice, primarily through mechanical pain pathways. As the gut microbiome may be involved in chronic pain persistence, microbiome analysis indicated distinct bacterial community changes between WT and Tg26 mice as well as morphine- and ART-induced microbial changes in the Tg26 mice. This study reveals the Tg26 mouse model to be a relevant system that can help elucidate the pathogenic mechanisms of the opioid- and ART-induced exacerbation of HIV-associated pain. Our results shed light on the intricate interplay between HIV infection, ART, opioid use, and the gut microbiome in chronic pain development. They hold implications for understanding the mechanisms underlying HIV-associated pain and microbial dysbiosis, with potential for future research focused on prevention and treatment strategies.

Glomerular Parietal Epithelial Cell Expression of Cathepsin C Increases in Tg26 Mouse Model of HIV-Associated Nephropathy (HIVAN)

Glomerular Parietal Epithelial Cell Expression of Cathepsin C Increases in Tg26 Mouse Model of HIV-Associated Nephropathy (HIVAN)

Correlation of HIV-Induced Neuroinflammation and Synaptopathy with Impairment of Learning and Memory in Mice with HAND.

Over 38 million people worldwide are living with HIV/AIDS, and more than half of them are affected by HIV-associated neurocognitive disorders (HAND). Such disorders are characterized by chronic neuroinflammation, neurotoxicity, and central nervous system deterioration, which lead to short- or long-term memory loss, cognitive impairment, and motor skill deficits that may show gender disparities. However, the underlying mechanisms remain unclear. Our previous study suggested that HIV-1 infection and viral protein R (Vpr) upregulate the SUR1-TRPM4 channel associated with neuroinflammation, which may contribute to HAND. The present study aimed to explore this relationship in a mouse model of HAND. This study employed the HIV transgenic Tg26 mouse model, comparing Tg26 mice with wildtype mice in various cognitive behavioral and memory tests, including locomotor activity tests, recognition memory tests, and spatial learning and memory tests. The study found that Tg26 mice exhibited impaired cognitive skills and reduced learning abilities compared to wildtype mice, particularly in spatial memory. Interestingly, male Tg26 mice displayed significant differences in spatial memory losses (p < 0.001), while no significant differences were identified in female mice. Consistent with our early results, SUR1-TRPM4 channels were upregulated in Tg26 mice along with glial fibrillary acidic protein (GFAP) and aquaporin 4 (AQP4), consistent with reactive astrocytosis and neuroinflammation. Corresponding reductions in neurosynaptic responses, as indicated by downregulation of Synapsin-1 (SYN1) and Synaptophysin (SYP), suggested synaptopathy as a possible mechanism underlying cognitive and motor skill deficits. In conclusion, our study suggests a possible relationship between SUR1-TRPM4-mediated neuroinflammation and synaptopathy with impairments of learning and memory in mice with HAND. These findings could help to develop new therapeutic strategies for individuals living with HAND.

Neuromodulation of BAG co-chaperones by HIV-1 viral proteins and H2O2: implications for HIV-associated neurological disorders

Despite increasing numbers of aged individuals living with HIV, the mechanisms underlying HIV-associated neurological disorders (HANDs) remain elusive. As HIV-1 pathogenesis and aging are characterized by oxidative stress as well as altered protein quality control (PQC), reactive oxygen species (ROS) themselves might constitute a molecular mediator of neuronal PQC by modulating BCL-2 associated athanogene (BAG) family members. Present results reveal H2O2 replicated and exacerbated a reduction in neuronal BAG3 induced by the expression of HIV-1 viral proteins (i.e., Tat and Nef), while also causing an upregulation of BAG1. Such a reciprocal regulation of BAG3 and BAG1 levels was also indicated in two animal models of HIV, the doxycycline-inducible Tat (iTat) and the Tg26 mouse. Inhibiting oxidative stress via antioxidants in primary culture was capable of partially preserving neuronal BAG3 levels as well as electrophysiological functioning otherwise altered by HIV-1 viral proteins. Current findings indicate HIV-1 viral proteins and H2O2 may mediate neuronal PQC by exerting synergistic effects on complementary BAG family members, and suggest novel therapeutic targets for the aging HIV-1 population.

Glycogen synthase kinase-3 inhibition rescues sex-dependent contextual fear memory deficit in human immunodeficiency virus-1 transgenic mice.

A significant number of HIV-1 patients on antiretroviral therapy develop HIV-associated neurocognitive disorders (HAND). Evidence indicate that biological sex may regulate HAND pathogenesis, but the mechanisms remain unknown. We investigated synaptic mechanisms associated with sex differences in HAND, using the HIV-1-transgenic 26 (Tg26) mouse model. Contextual- and cue-dependent memories of male and female Tg26 mice and littermate wild type mice were assessed in a fear conditioning paradigm. Hippocampal electrophysiology, immunohistochemistry, western blot, qRT-PCR and ELISA techniques were used to investigate cellular, synaptic and molecular impairments. Cue-dependent memory was unaltered in male and female Tg26 mice, when compared to wild type mice. Male, but not female, Tg26 mice showed deficits in contextual fear memory. Consistently, only male Tg26 mice showed depressed hippocampal basal synaptic transmission and impaired LTP induction in area CA1. These deficits in male Tg26 mice were independent of hippocampal neuronal loss and microglial activation but were associated with increased HIV-1 long terminal repeat mRNA expression, reduced hippocampal synapsin-1 protein, reduced BDNF mRNA and protein, reduced AMPA glutamate receptor (GluA1) phosphorylation levels and increased glycogen synthase kinase 3 (GSK3) activity. Importantly, selective GSK3 inhibition using 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione increased levels of synapsin-1, BDNF and phosphorylated-GluA1 proteins, restored hippocampal basal synaptic transmission and LTP, and improved contextual fear memory in male Tg26 mice. Sex-dependent impairments in contextual fear memory and synaptic plasticity in Tg26 mice are associated with increased GSK3 activity. This implicates GSK3 inhibition as a potential therapeutic strategy to improve cognition in HIV-1 patients.

Adult neurogenic deficits in HIV-1 Tg26 transgenic mice

BackgroundEven in the antiretroviral treatment (ART) era, HIV-1-infected patients suffer from milder forms of HIV-1-associated neurocognitive disorders (HAND). While the viral proteins Tat and gp120 have been shown to individually inhibit the proliferation and neural differentiation of neural stem cells (NSCs), no studies have characterized the effects of all the combined viral proteins on adult neurogenesis.MethodsThe HIV-1 Tg26 transgenic mouse model was used due to its clinical relevance to ART-controlled HIV-1-infected patients who lack active viral replication but suffer from continuous stress from the viral proteins. Quantitative RT-PCR analysis was performed to validate the expression of viral genes in the neurogenic zones. In vitro stemness and lineage differentiation assays were performed in cultured NSCs from HIV-1 Tg26 transgenic mice and their wild-type littermates. Hippocampal neurogenic lineage analysis was performed to determine potential changes in initial and late differentiation of NSCs in the subgranular zone (SGZ). Finally, fluorescent retroviral labeling of mature dentate granule neurons was performed to assess dendritic complexity and dendritic spine densities.ResultsVarying copy numbers of partial gag (p17), tat (unspliced and spliced variants), env (gp120), vpu, and nef transcripts were detected in the neurogenic zones of Tg26 mice. Significantly fewer primary neurospheres and a higher percentage of larger sized primary neurospheres were generated from Tg26 NSCs than from littermated wild-type mouse NSCs, implying that Tg26 mouse NSCs exhibit deficits in initial differentiation. In vitro differentiation assays revealed that Tg26 mouse NSCs have reduced neuronal differentiation and increased astrocytic differentiation. In the SGZs of Tg26 mice, significantly higher amounts of quiescent NSCs, as well as significantly lower levels of active NSCs, proliferating neural progenitor cells, and neuroblasts, were observed. Finally, newborn mature granule neurons in the dentate gyri of Tg26 mice had deficiencies in dendritic arborization, dendritic length, and dendritic spine density.ConclusionsBoth in vitro and in vivo studies demonstrate that HIV-1 Tg26 mice have early- and late-stage neurogenesis deficits, which could possibly contribute to the progression of HAND. Future therapies should be targeting this process to ameliorate, if not eliminate HAND-like symptoms in HIV-1-infected patients.

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.

A Novel Inhibitor of Homeodomain Interacting Protein Kinase 2 Mitigates Kidney Fibrosis through Inhibition of the TGF-β1/Smad3 Pathway.

Homeodomain interacting protein kinase 2 (HIPK2) is a critical regulator of multiple profibrotic pathways, including that of TGF-β1/Smad3. Genetic ablation of HIPK2 was shown previously to significantly reduce renal fibrosis in the experimental unilateral ureteral obstruction model and Tg26 mice, a model of HIV-associated nephropathy. To develop specific pharmacologic inhibitors of HIPK2 for antifibrotic therapy, we designed and synthesized small molecule inhibitor compounds on the basis of the predicted structure of HIPK2. Among these compounds, we identified one, BT173, that strongly inhibited the ability of HIPK2 to potentiate the downstream transcriptional activity of Smad3 in kidney tubular cells. Notably, binding of BT173 to HIPK2 did not inhibit HIPK2 kinase activity but rather, interfered allosterically with the ability of HIPK2 to associate with Smad3. In vitro, treatment with BT173 inhibited TGF-β1-induced Smad3 phosphorylation and Smad3 target gene expression in human renal tubular epithelial cells. In vivo, administration of BT173 decreased Smad3 phosphorylation and mitigated renal fibrosis and deposition of extracellular matrix in unilateral ureteral obstruction and Tg26 mouse models of renal fibrosis. Our data indicate that BT173 is a novel HIPK2 inhibitor that attenuates renal fibrosis through suppression of the TGF-β1/Smad3 pathway and may be developed as an antifibrotic therapy in patients with kidney disease.

Expression of HIV-1 matrix protein p17 and association with B-cell lymphoma in HIV-1 transgenic mice

HIV-1 infection is associated with increased risk for B-cell lymphomas. How HIV infection promotes the development of lymphoma is unclear, but it may involve chronic B-cell activation, inflammation, and/or impaired immunity, possibly leading to a loss of control of oncogenic viruses and reduced tumor immunosurveillance. We hypothesized that HIV structural proteins may contribute to lymphomagenesis directly, because they can persist long term in lymph nodes in the absence of viral replication. The HIV-1 transgenic mouse Tg26 carries a noninfectious HIV-1 provirus lacking part of the gag-pol region, thus constituting a model for studying the effects of viral products in pathogenesis. Approximately 15% of Tg26 mice spontaneously develop leukemia/lymphoma. We investigated which viral proteins are associated with the development of leukemia/lymphoma in the Tg26 mouse model, and performed microarray analysis on RNA from spleen and lymph nodes to identify potential mechanisms of lymphomagenesis. Of the viral proteins examined, only expression of HIV-1 matrix protein p17 was associated with leukemia/lymphoma development and was highly expressed in bone marrow before disease. The tumor cells resembled pro-B cells, and were CD19+IgM-IgD-CD93+CD43+CD21-CD23-VpreB+CXCR4+ Consistent with the pro-B-cell stage of B-cell development, microarray analysis revealed enrichment of transcripts, including Rag1, Rag2, CD93, Vpreb1, Vpreb3, and Igll1 We confirmed RAG1 expression in Tg26 tumors, and hypothesized that HIV-1 matrix protein p17 may directly induce RAG1 in B cells. Stimulation of human activated B cells with p17 enhanced RAG1 expression in three of seven donors, suggesting that intracellular signaling by p17 may lead to genomic instability and transformation.

Cardiac Dysfunction in HIV-1 Transgenic Mouse: Role of Stress and BAG3.

Since highly active antiretroviral therapy improved long-term survival of acquired immunodeficiency syndrome (AIDS) patients, AIDS cardiomyopathy has become an increasingly relevant clinical problem. We used human immunodeficiency virus (HIV)-1 transgenic (Tg26) mouse to explore molecular mechanisms of AIDS cardiomyopathy. Tg26 mice had significantly lower left ventricular (LV) mass and smaller end-diastolic and end-systolic LV volumes. Under basal conditions, cardiac contractility and relaxation and single myocyte contraction dynamics were not different between wild-type (WT) and Tg26 mice. Ten days after open heart surgery, contractility and relaxation remained significantly depressed in Tg26 hearts, suggesting that Tg26 mice did not tolerate surgical stress well. To simulate heart failure in which expression of Bcl2-associated athanogene 3 (BAG3) is reduced, we down-regulated BAG3 by small hairpin ribonucleic acid in WT and Tg26 hearts. BAG3 down-regulation significantly reduced contractility in Tg26 hearts. BAG3 overexpression rescued contractile abnormalities in myocytes expressing the HIV-1 protein Tat. We conclude: (i) Tg26 mice exhibit normal contractile function at baseline; (ii) Tg26 mice do not tolerate surgical stress well; (iii) BAG3 down-regulation exacerbated cardiac dysfunction in Tg26 mice; (iv) BAG3 overexpression rescued contractile abnormalities in myocytes expressing HIV-1 protein Tat; and (v) BAG3 may occupy a role in pathogenesis of AIDS cardiomyopathy.

Inhibition of Notch pathway attenuates the progression of human immunodeficiency virus-associated nephropathy

The Notch pathway is an evolutionarily conserved signaling cascade that is critical in kidney development and has also been shown to play a pathogenetic role in a variety of kidney diseases. We have previously shown that the Notch signaling pathway is activated in human immunodeficiency virus-associated nephropathy (HIVAN) as well as in a rat model of the disease. In this study, we examined Notch signaling in the well established Tg26 mouse model of HIVAN. Notch signaling components were distinctly upregulated in the kidneys of these mice as well as in immortalized podocytes derived from these mice. Notch1 and Notch4 were upregulated in the Tg26 glomeruli, and Notch4 was also expressed in tubules. Notch ligands Jagged1, Jagged2, Delta-like1, and Delta-like 4 were all upregulated in the tubules of Tg26 mice, but glomeruli showed minimal expression of Notch ligands. To examine a potential pathogenetic role for Notch in HIVAN, Tg26 mice were treated with GSIXX, a gamma secretase inhibitor that blocks Notch signaling. Strikingly, GSIXX treatment resulted in significant improvement in both histological kidney injury scores and renal function. GSIXX-treated Tg26 mice also showed diminished podocyte proliferation and dedifferentiation, cellular hallmarks of the disease. Moreover, GSIXX blocked podocyte proliferation in vitro induced by HIV proteins Nef and Tat. These studies suggest that Notch signaling can promote HIVAN progression and that Notch inhibition may be a viable treatment strategy for HIVAN.

Roflumilast enhances the renal protective effects of retinoids in an HIV-1 transgenic mouse model of rapidly progressive renal failure

Retinoic acid decreases proteinuria and glomerulosclerosis in several animal models of kidney disease by protecting podocytes from injury. Our recent in vitro studies suggest that all-trans retinoic acid induces podocyte differentiation by activating the retinoic acid receptor-α (RARα)/cAMP/PKA/CREB pathway. When used in combination with all-trans retinoic acid, an inhibitor of phosphodiesterase 4 further enhanced podocyte differentiation by increasing intracellular cAMP. Additionally, we found that Am580, a specific RARα agonist, has similar renal protective effects as all-trans retinoic acid in a rederived colony of HIV-1 transgenic mice with rapidly progressive renal failure (HIV-Tg) that mimics human HIV-associated nephropathy. Treatment with either the inhibitor of phoshodiesterase 4, roflumilast, or Am580 significantly reduced proteinuria, attenuated kidney injury, and improved podocyte differentiation in these HIV-Tg mice. Additional renal protective effects were found when roflumilast was combined with Am580. Consistent with the in vitro data, glomeruli from HIV-Tg mice treated with both Am580 and roflumilast had more active phosphorylated CREB than with either agent alone. Thus, phosphodiesterase 4 inhibitors could be used in combination with RARα agonists to provide additional renal protection.

Human immunodeficiency virus downregulates podocyteapoEexpression

Apolipoprotein E (apoE) has been demonstrated to play an important role in providing protection against mesangial cell injury. In the present study, we evaluated the role of apoE and its associated downstream effects in human immunodeficiency virus (HIV)-associated nephropathy (HIVAN). Control (n = 6) and age- and sex-matched HIV-1 transgenic mice (Tg26, n = 6) were evaluated for their renal cortical expression of apoE. Renal tissue from Tg26 mice not only showed decreased apoE expression but also displayed downregulation of perlecan mRNA expression. In in vitro studies, conditionally immortalized human podocytes (CIHPs) were transduced with either NL4-3HIV (an HIV-1 construct lacking gag and pol, used for the development of Tg26 mouse model; NL4-3/CIHP) or empty vector (EV/CIHP); NL4-3/CIHPs and EV/CIHPs were studied for apoE mRNA expression. NL4-3/CIHPs showed reduction in apoE expression compared with EV/CIHPs. To evaluate the role of HIV-1 genes in the modulation of apoE expression, conditionally immortalized mouse podocytes (CIMPs) were transduced with individual HIV-1 gene constructs. Only nef-transduced CIMPs showed a decrease in apoE expression. To confirm this effect of nef in CIHPs, microarray analysis was performed in stable colonies of nef/CIHPs and EV/CIHPs. nef/CIHPs showed a 60% decrease in apoE and a 90% reduction in heparan sulfate mRNA expression. Moreover, nef transgenic mice showed a decrease in renal tissue expression of both apoE and perlecan. Both Tg26 and nef transgenic mice also showed areas of mesangial cell proliferation. These findings suggest that HIV-1-induced reduction in podocyte apoE expression and associated downregulation of podocyte perlecan might be contributing to mesangial cell (MC) phenotype in HIVAN.