Mitotic cell cycle proteins increase in podocytes despite lack of proliferation

BACKGROUND

Podocyte proliferation is an uncommon response to glomerular injury and its lack may underlie the development of glomerulosclerosis. However, whether podocytes have the capacity to enter and finish mitosis and cytokinesis is not known.

METHODS

The expression of mitotic cell cycle proteins (phosphorylated Histone 3, Cdc2, cyclin B1 and B2) was examined by immunohistochemistry in kidneys of embryonal mice, transgenic HIV-mice, and rats with experimental membranous nephropathy (passive Heymann nephritis, PHN). Mitotic proteins also were measured by Western blot in glomerular protein from PHN-rats and the activity of mitotic cyclins was quantified by histone kinase assay.

RESULTS

Mitotic proteins were increased in embryonal mouse glomeruli during the S- and comma-shaped stages and were absent at the capillary loop stage and in mature rodent glomeruli. There was an increase in podocyte expression of Cdc2, cyclin B1 and B2 and phosphorylated histone 3 in PHN rats, and in HIV transgenic mice.

CONCLUSIONS

Podocytes have the ability to increase cell cycle proteins required for mitosis. Without obvious differences in the expression of the major mitotic proteins in PHN- and HIV-nephropathy, a regulatory disturbance in cytokinesis might be responsible for the development of polynucleated cells and a lack of podocyte proliferation in experimental glomerular disease.

Lytic JC virus infection in the kidneys of AIDS subjects

Our objective was to investigate the role of the human polyomavirus JC virus as a possible cause of renal damage in AIDS subjects. Histology, immunohistochemistry, and molecular biology were used to evaluate the frequency of viral infection, genotypes, viral status, and the presence of rearrangements or point mutations in specific genomic regions of strains isolated from renal tissue. Formalin-fixed, paraffin-embedded sections of postmortem renal specimens obtained from 111 unselected AIDS patients were stained for routine histology and with anti-SV40 antibody. The immunohistochemically positive specimens were further investigated by means of nested polymerase chain reaction for different polyomavirus genomic regions (large T, transcriptional control region, and viral protein 1). Furthermore, the sequences of transcriptional control region and viral protein 1 were also analyzed. Immunohistochemistry was positive in seven cases (6.3%), four of which showed morphological evidence of viral replication (intranuclear inclusion bodies and/or intratubular cellular casts): in all seven cases, only epithelial tubular cells (with and without inclusion bodies) and cellular casts were stained. The JC virus genome was identified by polymerase chain reaction in five of the seven immunohistochemically positive cases; transcriptional control region and viral protein 1 were amplified in, respectively, three and four cases. Transcriptional control region sequence analysis revealed major rearrangements in all three cases, with duplications of all the transcriptional factor-binding sites, whereas no point mutations were found in the viral protein 1 region, which was characterized as Type 1A in all cases. For the first time in AIDS subjects, this study shows that although rarely, JC virus can replicate in renal tissue. Molecular biology revealed major rearrangements in the transcriptional control region that, together with other unknown factors, could justify the increased pathogenicity of this human polyomavirus.

HIV-1 expression induces cyclin D1 expression and pRb phosphorylation in infected podocytes: cell-cycle mechanisms contributing to the proliferative phenotype in HIV-associated nephropathy

Background

The aberrant cell-cycle progression of HIV-1-infected kidney cells plays a major role in the pathogenesis of HIV-associated nephropathy, however the mechanisms whereby HIV-1 induces infected glomerular podocytes or infected tubular epithelium to exit quiescence are largely unknown. Here, we ask whether the expression of HIV-1 genes in infected podocytes induces cyclin D₁ and phospho-pRb (Ser780) expression, hallmarks of cyclin D1-mediated G₁ → S phase progression.

Results

We assessed cyclin D₁ and phospho-pRb (Ser780) expression in two well-characterized models of HIV-associated nephropathy pathogenesis: HIV-1 infection of cultured podocytes and HIV-1 transgenic mice (Tg26). Compared to controls, cultured podocytes expressing HIV-1 genes, and podocytes and tubular epithelium from hyperplastic nephrons in Tg26 kidneys, had increased levels of phospho-pRb (Ser780), a target of active cyclin D₁/cyclin-dependent kinase-4/6 known to promote G₁ → S phase progression. HIV-1-infected podocytes showed markedly elevated cyclin D₁ mRNA and cyclin D₁ protein, the latter of which did not down-regulate during cell-cell contact or differentiation, suggesting post-transcriptional stabilization of cyclin D₁ protein levels by HIV-1. The selective suppression of HIV-1 transcription by the cyclin-dependent kinase inhibitor, flavopiridol, abrogated cyclin D₁ expression, underlying the requirement for HIV-1 encoded products to induce cyclin D₁. Indeed, HIV-1 virus deleted of nef failed to induce cyclin D₁ mRNA to the level of other single gene mutant viruses.

Conclusions

HIV-1 expression induces cyclin D₁ and phospho-pRb (Ser780) expression in infected podocytes, suggesting that HIV-1 activates cyclin D1-dependent cell-cycle mechanisms to promote proliferation of infected renal epithelium.

Virus-related glomerular diseases: histological and clinical aspects

Viral infections can be the causative agent in many glomerular diseases, and diagnostic criteria include clinical and laboratory data and tissue molecular analysis. Hepatitis B virus (HBV) is a well known cause of membranous glomerulonephritis (MGN), membranoproliferative GN (MPGN) and IgA nephropathy (IgAN), frequently in Asian populations. Hepatitis C virus (HCV), besides cryoglobulinemia-mediated glomerulonephritis (GN), is reported to cause other forms of GN. Human immunodeficiency virus (HIV) infection is closely related to a collapsing focal segmental glomerulosclerosis (FSGS), a distinct disease that affects mainly Africans and African-Americans. In the course of HIV infection other immune complex (IC) GN can occur, most frequently in whites. Nephrotic syndrome and progression to renal insufficiency are the main clinical manifestations. HIV-HCV co-infection is related to an IC glomerular disease, sometimes with immunotactoid deposits. Recent reports emphasize the role of parvovirus B19 (PV B19) for "idiopathic" collapsing FSGS and ICGN, and of Coxsackie B virus for IgAN. Renal biopsy is useful for defining virus-related glomerular lesions and a guide for prognostic and therapeutic evaluation.

Collapsing glomerulopathy--a new pattern of renal injury

Collapsing glomerulopathy is a pattern of renal injury that has emerged along with the epidemic of HIV infection. The disease process is now increasingly recognized in non-HIV patients. In HIV and non-HIV patients the disease shares many clinical and pathologic features, and, we presume, pathogenetic factors. The disease entity is characterized by very heavy proteinuria frequently combined with rapidly progressive renal failure, poor outcome, glomerular collapse with hyperplasia and other degenerative changes of the visceral epithelial cells, and prominent tubulointerstitial injury with frequent microcystic changes. HIV-associated nephropathy has a higher prevalence in blacks, high frequency of intra-endothelial tubuloreticular inclusions, and prominent microcystic tubular changes. These differences, however, are not sufficient to predict the patient's HIV status from the biopsy findings alone. Collapsing glomerulopathy can also develop in association with lymphoproliferative disorders, systemic lupus erythematosus-like and other autoimmune diseases, other immune deficiency syndromes and viral infections, and in the context of immunosuppressive therapy.

Glomerular injury associated with hepatitis C infection: a correlation with blood and tissue HCV-PCR

Membranoproliferative glomerulonephritis, with or without cryoglobulinemia, and membranous glomerulonephritis are the best characterized glomerulonephropathies associated with hepatitis C virus (HCV) infection. Other more unusual patterns of glomerular injury, including IgA nephropathy, focal segmental glomerulosclerosis, crescentic glomerulonephritis, fibrillary glomerulonephritis, immunotactoid glomerulopathy, and thrombotic microangiopathy, have also been associated with HCV infection, but primarily on an anecdotal basis. It remains uncertain whether the patterns of glomerular injury seen in HCV infected patients, particularly the unusual patterns, represent a disease process specifically related to HCV infection or whether they represent nonspecific patterns of injury due to other causes that happen to occur in HCV-infected patients. We examine this issue by reviewing the epidemiological and pathological evidence in the literature that either supports or refutes a specific relationship between HCV and the pattern of glomerular injury. We also include our experience with 31 HCV-infected patients. In addition, the pathogenesis of HCV-associated glomerulonephropathies is discussed with an emphasis on the significance of detecting HCV in renal biopsies by reverse transcriptase-polymerase chain reaction.

Dysregulation of podocyte phenotype in idiopathic collapsing glomerulopathy and HIV-associated nephropathy

BACKGROUND

Idiopathic collapsing glomerulopathy (ICG) and HIV-associated nephropathy (HIV-AN) are characterized by severe nephrotic syndrome, collapse and sclerosis of the glomerular tuft with prominent podocyte alterations and extensive tubulointerstitial lesions. We previously showed phenotypic changes in podocytes from patients with diffuse mesangial sclerosis, a severe glomerulopathy sharing several morphological features with collapsing glomerulopathy. The aim of this study was to analyze the podocyte phenotype in ICG and HIV-AN.

METHODS

Using immunohistochemical techniques, we studied the podocyte expression of the transcription factor WT1 and its target PAX2, GLEPP1, synaptopodin and vimentin as markers of podocyte maturity and of proliferating cell nuclear antigen (PCNA) as a marker of proliferation. Apoptosis was analyzed by the TUNEL method. Results from renal biopsies of ICG and HIV-AN were compared with those obtained from normal kidney, minimal change nephrotic syndrome (MCNS), focal and segmental glomerulosclerosis (FSGS) and membranous glomerulonephritis (MGN).

RESULTS

Abnormal distribution of WT1 and PAX2 and extensive loss of podocyte markers were observed in ICG and HIV-AN; this dysregulation was associated with podocyte proliferation without detectable apoptosis. In contrast, no podocyte changes were detected in MCNS or MGN. In FSGS, phenotypic changes, without proliferation, were restricted to podocytes surrounding focal and segmental glomerular lesions. Increased PCNA expression and apoptosis were observed in ICG and HIV-AN tubular cells.

CONCLUSION

Dysregulation of podocyte phenotype and proliferation are present in both ICG and HIV-AN. This suggests that, whatever their etiology, both types of collapsing glomerulopathy share a common pathogenic pathway. Upregulation of cell proliferation and apoptosis observed in tubular epithelial cells is probably involved in the occurrence of severe tubulointerstitial lesions in collapsing glomerulonephritis.

HIV-1 Nef induces proliferation and anchorage-independent growth in podocytes

HIV-associated nephropathy (HIVAN) is now the third leading cause of end-stage renal disease in the African American population. HIV-1 infects renal tubular and glomerular epithelial cells or podocytes, cells that are a critical part of the filtration barrier. HIV-1 infection induces the loss of podocyte differentiation markers and increases podocyte proliferation. It has been previously shown that HIV-infection induces loss of contact inhibition. Here, the HIV-1 gene responsible for proliferative changes is identified by using cultured podocytes in vitro. The HIV-1 proviral construct, pNL4-3 was rendered noninfectious by replacing the HIV-1 gag/pol sequences with an EGFP reporter gene (pNL4-3: DeltaG/P-EGFP). This construct was then pseudotyped with VSV.G envelope to infect podocytes that were conditionally immortalized with SV-40 T antigen. In addition, mutated constructs were engineered with premature stop codons in the HIV-1 env, vif, vpr, vpu, nef, or rev genes. The parental construct and all the other mutated constructs, with the exception of nef, induced proliferation under nonpermissive conditions and anchorage-independent growth (colony formation in soft agar) under permissive conditions. In contrast, deletion of nef markedly reduced proliferation and colony formation. Although tat alone, or tat plus rev induced marginal levels of anchorage-independent growth, coexpression with nef significantly increased colony formation. Finally, stable expression of Nef in a retroviral vector, pBabe-puro, was sufficient to induce increased proliferation and colony formation. Moreover, nef induced saturation density and loss of contact inhibition. These data indicate that Nef induces multiple proliferative effects in podocytes in culture and that nef may therefore be an important gene in the pathogenesis of HIVAN in vivo.

Resolution of renal failure after initiation of HAART: 3 cases and a discussion of the literature

Renal failure is a known complication of HIV infection. The most common form is HIV-associated nephropathy, or HIVAN. It is characterized by high-grade proteinuria with rapid progression to end-stage renal disease. The kidneys of affected patients appear enlarged on ultrasonography. Histopathologically, there is focal segmental glomerulosclerosis with glomerular collapse. Before the era of HAART, patients with HIVAN had limited survival, although in some cases this was prolonged if dialysis was instituted. Over the past few years, isolated case reports have shown that patients with HIVAN will recover renal function following initiation of HAART. We report 3 patients believed to have HIVAN who exhibited marked improvement in renal function after treatment with a regimen comprising 2 nucleoside reverse transcriptase inhibitors and a protease inhibitor.

Type I membranoproliferative glomerulonephritis in an HIV-infected individual without hepatitis C co-infection

Type I membranoproliferative glomerulonephritis (MPGN) is an uncommon manifestation of human immunodeficiency virus (HIV)-associated renal disease in patients co-infected with hepatitis C virus (HCV). We describe a case of Type I MPGN in an HIV-positive diabetic man with nephrotic-range proteinuria and renal insufficiency who was not co-infected with HCV. Tubuloreticular inclusions were present but there was no evidence for either cryoglobulinemia or cryoglobulin deposits in the kidney. This finding suggests that Type I MPGN may represent a reaction of the kidney to HIV independent of the effects of HCV co-infection. Clinical suspicion must be maintained for Type I MPGN in all HIV infected patients presenting with significant proteinuria regardless of HCV infection status.

Microcyst formation and HIV-1 gene expression occur in multiple nephron segments in HIV-associated nephropathy

Tubular microcyst formation is a prominent histopathologic feature of HIV-associated nephropathy (HIVAN), but its pathogenesis is unknown. HIV-1 has recently been shown to infect renal tubular epithelial cells in patients with HIVAN. In addition, HIV-1 gene expression in renal epithelial cells has been shown to cause a renal disease that is identical to HIVAN in HIV-1 transgenic mice. In these studies, immunohistochemistry for tubular segment-specific markers and mRNA in situ hybridization for HIV-1 was used to determine which tubular segments develop microcysts and which segments express HIV-1 in the kidneys of transgenic mice and patients with HIVAN. It was found that microcysts involve multiple nephron segments in both patients with HIVAN and HIV-1 transgenic mice. Furthermore, HIV-1 infection in HIVAN and HIV-1 transgene expression also occurs in multiple segments of the nephron. These data support a direct role for HIV-1 infection of renal epithelial cells in the pathogenesis of microcyst formation in patients with HIVAN.

HIV nephropathy and the Duffy antigen/receptor for Chemokines in African Americans

BACKGROUND AND OBJECTIVES

HIV nephropathy (HIVAN) is markedly racially biased in its distribution, occurring in about 10% of HIV infected African Americans according to some studies. Based upon previous laboratory and epidemiological studies, the Duffy promoter polymorphism, which occurs almost exclusively in individuals of African descent, has been postulated to be the predisposing factor. We aimed to explore that relationship by directly genotyping individuals with HIV nephropathy to determine the proportion homozygous for this mutation to test the hypothesis it was responsible for the genetic component of this disease. We anticipated that if the polymorphism was associated with HIV nephropathy all individuals would be homozygous for this mutation.

METHOD

Individuals with HIVAN proven on biopsy were identified from previous studies and a pre-existing clinical database. This diagnosis was confirmed by an experienced pathologist examining the biopsies in a blinded fashion. PCR and RFLP strategies were used on the biopsy samples to genotype for the Duffy promoter polymorphism. The cases were compared to a control population of HIV seronegative African Americans.

RESULTS

Twenty African American individuals with HIV nephropathy were successfully genotyped. Only nine were homozygous for the promoter mutation. Nine were heterozygous and two homozygous wild type. Furthermore, the frequency of the polymorphism did not differ from the background rate in the African American population (OR = 0.788 95% confidence intervals 0.378-1.64).

CONCLUSION

The Duffy promoter polymorphism was not disproportionately represented in persons with HIVAN calling into question any significant role in the pathogenesis of HIVAN.

Human immunodeficiency virus-associated nephropathy

Human immunodeficiency virus-associated nephropathy (HIVAN) is a clinicopathological entity characterised by proteinuria, rapidly developing azotemia and histologically by collapsig variant of focal and segmental glomerulosclerosis with acute tubular necrosis and mild interstitial inflammation. Untreated, it may result in end stage renal disease (ESRD) in as little as four months. The incidence of HIVAN continues to increase and is the single most common cause of chronic renal disease in HIV-1 seropositive patients. It affects predominantly black individuals. Exact pathogenesis is still not clear but a great deal of progress has been made in the recent past by studies on transgenic mouse model, renal cell cultures and from study of human biopsy material. Current considerations revolve around the role of HIV or protein in renal epithelium and the effects of cytokines, including transforming growth factor-beta and basic fibroblast growth factor on renal structures. Different modalities of treatment with corticosteroids, zidovudine or angiotensin converting enzyme inhibitors have been tried with modest success.

Renal pathology and premortem clinical presentation of Caucasian patients with AIDS: an autopsy study from the era prior to antiretroviral therapy

PRINCIPLES

Renal disease in patients with HIV infection is becoming increasingly frequent. A particular form of HIV-associated nephropathy (HIVAN) has been found in patients of predominantly African-American and Hispanic origin. However, only limited data are available on renal pathology and premortem clinical presentation of kidney disease in Caucasian patients with AIDS.

METHODS

To determine the prevalence, clinical presentation and aetiology of renal disease in Caucasian patients with AIDS at the time of death we have performed a prospective autopsy study with 239 patients who died of AIDS between 1981 and 1989. None of these patients had received HIV-specific antiretroviral therapy. Autopsies and histological analyses were performed on the basis of a standardised protocol. Clinical and laboratory data were gathered according to a uniform questionnaire.

RESULTS

95% of patients were of Caucasian race. 75% of all patients had extended AIDS (stage IV). Clinical signs of nephropathy prior to death were found in 36% of patients, including proteinuria (18%), abnormal urinary sediment (19.5%), and renal insufficiency (11%). Histopathological lesions were present in 43% of the autopsies, with two or more distinct structural lesions in 12.5% of patients. Of the pathological findings 28% were glomerular or vascular, 33% were non-glomerular, and 29% were combined lesions. The remaining 10% were renal infiltrations of infectious agents or neoplastic tissue. The most common findings were ischaemic changes and vascular scars (18% of patients), as well as pyelo- and interstitial nephritides (12.2%). Importantly, FSGS was present in only 1.7% of patients, and only a single African patient had classical HIVAN.

CONCLUSIONS

Renal involvement in HIV disease is very common at the time of death among patients of Caucasian origin. However, classical HIV-associated nephropathy is absent in this population. These findings suggest that kidney disease affects all races and supports the hypothesis that HIVAN is specifically related to non-Caucasian ethnicity. The results reflect renal disease unaffected by HIV-specific antiretroviral therapy.

Treatment of HIV-associated nephropathy

HIV-associated nephropathy (HIVAN) is the most common cause of renal failure in patients infected with type 1 human immunodeficiency virus (HIV-1). The renal prognosis for HIVAN is poor and is typically associated with rapid progression to renal death. We report a patient with biopsy-proven HIVAN who was successfully treated with corticosteroids and review the currently available evidence supporting the specific treatments of this condition. A 34-year-old African-American male with a 2-year history of uncomplicated HIV disease developed progressive azotemia despite treatment with highly active antiretroviral therapy (HAART). He was treated with an uncomplicated 4-month course of prednisone, which improved his serum creatinine from 2.9 to 1.9 mg/dl and decreased his degree of proteinuria from 8 to 2.1 g/day. Two years post-steroid treatment his renal function remains stable. Increasing evidence supports that both ACE inhibitors and HAART are effective in preventing and in some cases of reversing HIVAN induced renal failure. In selected patients who progress despite these measures, a limited course of corticosteroid may achieve long-standing disease remissions. In general, with adequate supervision, corticosteroid therapy appears to be well tolerated and has an acceptable side effect profile. Although persuasive in view of the abysmal natural history of HIVAN, the currently available studies are subject to major methodological limitations. Appropriate randomized controlled trials are urgently required in order to further examine the efficacy, optimal timing, and potential side effects of these treatments.

Nephrotic syndrome due to thrombotic microangiopathy (TMA) as the first manifestation of human immunodeficiency virus infection: recovery before antiretroviral therapy without specific treatment against TMA

BACKGROUND

Among the possible renal complications that can develop a human immunodeficiency virus- (HIV) infected patient, thrombotic microangiopathy (TMA) is one of them. This is a type of vascular lesion more common in HIV patients than in normal population, and sometimes it can be the first manifestation of the HIV infection.

METHODS

We present a patient with TMA in whom the subsequent investigation to find the cause of TMA revealed HIV infection and Giardia Lamblia in stool.

RESULTS

Before antiretroviral therapy was started the patient began to show recovery of the hemolytic anemia, recovery of the nephrotic syndrome and partial remission of the proteinuria, so that he did not receive specific therapy for TMA.

CONCLUSIONS

HIV infection should be suspected in patients presenting with TMA, and a HIV test should be routinely performed as part of the initial clinical evaluation of TMA. If the patients have not developed acquired immunodeficiency syndrome, the prognosis of TMA is equal to non-infected ones.

Hiv-associated nephropathy occurring before HIV antibody seroconversion

It currently is thought that human immunodeficiency virus-associated nephropathy (HIVAN) occurs late in the course of HIV infection. Although HIVAN may be the presenting manifestation of acquired immunodeficiency syndrome (AIDS), it usually occurs after a prolonged period of viral infection often associated with high levels of HIV viremia. The patient described here developed HIVAN as a manifestation of acute retroviral syndrome. A 41-year-old black man presented with nephrotic range proteinuria, renal insufficiency, and acute gastrointestinal and pulmonary symptoms. He recently had been treated for primary syphilis. Two HIV serologic tests, performed 3 months apart, were negative. Renal biopsy was consistent with HIVAN. After the biopsy, the patient was discovered to have more than 700,000 viral copies per mL in his blood. CD4(+) count was greater than 500/mm(3). Six weeks later, enzyme-linked immunosorbent assay and Western blot analyses for HIV antibody became positive. HIVAN can occur early in the course of HIV infection, even during acute infection before seroconversion, and prolonged exposure to virus is not necessary for this renal involvement to occur in the susceptible host.

Lupus nephritis in a child with AIDS

Concomitant acquired immunodeficiency syndrome (AIDS) and lupus nephritis is an exceptional feature in white patients. A white boy with maternofetal human immunodeficiency virus (HIV) infection had no medical follow-up until he presented at 12 years of age with a nephrotic syndrome, macrohematuria, renal failure, pancytopenia, and low CD4(+) cell count. A renal biopsy revealed severe lupus nephritis (World Health Organization class IV) with specific immune deposits in the absence of any clinical sign of systemic lupus erythematosus or specific autoantibodies at the time of diagnosis. The treatment consisted of methylprednisolone pulses followed by oral prednisone; antiretroviral triple therapy was started a few weeks later, which contributed to clinical and biologic improvement. To our knowledge, this is the first case report of lupus-like nephritis in a white child with AIDS, whose outcome might be improved significantly by a combination of steroids and antiretroviral therapy.

[Collapsing glomerulopathy and cytomegalovirus, what are the links?]

BACKGROUND

Collapsing glomerulopathy is a form of focal and segmental glomerulosclerosis which occurs preferentially in black people. It causes severe nephrotic syndrome and quickly progresses towards end-stage renal failure.

CASE REPORT

We report the case of a 16-year-old black girl from Guadeloupe who was admitted for tetanus and edema in 1996. She had hypoparathyroidism, renal failure and a nephrotic syndrome as well as cytomegalovirus infection. Renal biopsy showed collapsing glomerulopathy. The renal function improved on glucocorticoid and ganciclovir therapy and her serum creatinine stabilized around 250 mumol/l for two years.

DISCUSSION

Collapsing nephropathy is the cellular type of focal and segmental glomerulosclerosis. The main etiology is the human immunodeficiency virus. A viral infection may be involved in its pathogenesis. Other viruses could be linked with this nephropathy. This case report relates a case associated with a cytomegalovirus viruria. The clinical course might be related with the antiviral treatment.

[HIV nephropathy and other kidney diseases in patients with human immunodeficiency virus infections]

Kidney diseases are a quite frequent complication of HIV infection. They may be caused by HIV infection itself, secondary infections or administered drugs. The most often causes of acute renal failure and main glomerular diseases in this group of patients are discussed. Special attention was paid to HIV associated nephropathy as a specific disease for the HIV infection. Epidemiology, clinical presentation, histological changes, pathogenesis and treatment options are presented.

Glomerulosclerosis and viral gene expression in HIV-transgenic mice: role of nef

BACKGROUND

Human immunodeficiency virus (HIV)-associated nephropathy is characterized by focal segmental glomerulosclerosis and microcystic tubular dilation. We have previously described a mouse transgenic for a Deltagag-pol HIV-1 genome, which develops glomerulosclerosis, cutaneous papillomas, and cataracts.

METHODS

We developed mice transgenic for a Deltagag-pol-nef HIV genome in order to investigate the role of the nef gene in these phenotypes.

RESULTS

One transgenic line, X5, expressed HIV mRNA in kidney and consistently manifested focal segmental glomerulosclerosis and tubular dilation by six weeks of age. Northern analysis indicated that renal transgene expression was higher in the Deltagag-pol-nef mice compared with the Deltagag-pol mice. In situ hybridization and immunostaining demonstrated HIV RNA and protein expression within the glomerular epithelial cells and tubular epithelial cells. These cell types showed histologic evidence of toxicity, including vacuolation and detachment from basement membrane, and exhibited increased rates of apoptosis. These data suggest that the renal disease seen in the Deltagag-pol-nef transgenic mouse may be caused by the expression of HIV genes within renal epithelial cells, that this expression may induce cellular toxicity, including apoptosis, and that nef is not required for the induction of renal disease. We have previously described mice bearing the nef gene, which do not manifest renal disease. In further experiments, Deltagag-pol-nef mice were bred with nef mice; these dual-transgenic mice developed renal disease that generally resembled that seen in Deltagag-pol-nef mice, but with somewhat more severe glomerulosclerosis and less severe tubulointerstitial injury.

RESULTS

The results of these transgenic studies suggest that the role of nef is complex and may act both to reduce transgene expression and to potentiate glomerular injury induced by other HIV-1 gene products.

Differential expression of cyclin-dependent kinase inhibitors in human glomerular disease: role in podocyte proliferation and maturation

BACKGROUND

Normal human podocytes are terminally differentiated and quiescent cells. It is not known why podocytes fail to proliferate in response to most forms of injury. Proliferation is regulated by cell cycle proteins and their inhibitors. The Cip/Kip family of cyclin-dependent kinase (CDK) inhibitors (p21, p27, p57) in general prevent proliferation by inhibiting cyclin-CDK complexes. In the current study, we determined the expression and possible role of specific CDK inhibitors in podocyte proliferation in human disease characterized by podocyte injury.

METHODS

Immunostaining was performed for the CDK inhibitors p21, p27, and p57 and the proliferation marker Ki-67 on renal biopsies from patients with minimal change disease (MCD; N = 6), membranous glomerulopathy (MGN; N = 19), cellular variant of focal segmental glomerulosclerosis (FSGS; N = 12), collapsing glomerulopathy (CG; N = 9), and HIV-associated nephropathy (HIVAN; N = 16). Adult nephrectomy specimens without evidence of glomerular disease served as controls (N = 9).

RESULTS

Normal quiescent podocytes express p27 and p57, but not p21. In diseases without podocyte proliferation (MCD, MGN), p21, p27, and p57 expression did not change. In contrast, there was a uniform decrease in p27 and p57 immunostaining in diseases with podocyte proliferation (cellular FSGS, CG, and HIVAN). This was accompanied by the de novo expression of p21 in podocytes.

CONCLUSIONS

Our results show that podocyte quiescence may require the presence of the CDK inhibitors p27 and p57. In human glomerular diseases, a decrease in p27 and p57 may be permissive for the altered proliferative podocyte phenotype. p21 may have a multifactorial role in podocyte cell cycle regulation.

HIV-1 induces renal epithelial dedifferentiation in a transgenic model of HIV-associated nephropathy

BACKGROUND

Human immunodeficiency virus-associated nephropathy (HIVAN) is the most common cause of renal failure in HIV-1-seropositive patients. Recent studies using an HIV-1 transgenic mouse model have demonstrated that expression of HIV-1 in the kidney is required for the development of HIVAN. What has remained unclear, however, is the renal cell type responsible for pathogenesis and the essential pathological process.

METHODS

To address these issues, we used a transgenic murine model of HIVAN. We identified the cell types in kidney in which HIV transgene expression occurs using in situ hybridization. We evaluated evidence of proliferation by immunocytochemical analysis using an antibody to Ki-67 and cell type-specific markers, including WT-1, synaptopodin, Na+,K+-ATPase, adducin, and desmin. TUNEL assay was used to evaluate apoptosis.

RESULTS

We found that glomerular and tubular epithelial cells express the HIV-1 transgene early in the disease process when renal architecture is well preserved. Transgene expression is lost, however, in tubular epithelial cells when they lose their differentiated cuboidal phenotype. In glomerular epithelial cells, dedifferentiation occurs with reduced expression of WT-1 and synaptopodin, in association with activation of desmin expression. Tubular microcysts also form with mislocalization of Na+,K+-ATPase expression to the lateral and apical cellular membranes.

CONCLUSIONS

These studies support the hypothesis that the glomerular and renal epithelial cells are the primary targets of HIV-1 pathogenesis in the kidney. The essential pathologic process is dysregulation of the epithelial cell cycle with increased proliferation, apoptosis, cellular dedifferentiation, and altered cellular polarity.

Podocyte cell cycle regulation and proliferation in collapsing glomerulopathies

BACKGROUND

Mature podocytes are growth-arrested because of the expression of cyclin-dependent kinase inhibitors. Under pathological conditions, podocytes may undergo mitosis, but not cell division. Exceptions to this rule are collapsing glomerulopathies (CGs), including HIV-associated nephropathy (HIVAN) and idiopathic CG, where podocytes undergo a dysregulation of their differentiated phenotype and proliferate.

METHODS

To shed light on the mechanism underlying podocyte proliferation in CG, we analyzed the expression of the proliferation marker Ki-67, cyclins (A, D1), cyclin-dependent kinase inhibitors (p27, p57), and podocyte differentiation marker synaptopodin in eight cases of HIVAN and two cases of idiopathic CG. Normal fetal and adult kidneys served as controls.

RESULTS

Both HIVAN and idiopathic CG showed a marked reduction in the expression of p27, p57, and cyclin D1 (absent in 69, 62, and 80% of all glomeruli, respectively). Cyclin A and Ki-67 were expressed in 11 and 29% of all glomeruli. Moreover, there was partial loss of synaptopodin and cyclin D1 expression in nonaffected glomeruli.

CONCLUSIONS

The loss of p27 and p57 leading to expression of cyclin A may account for the activation of podocyte proliferation in CG. Furthermore, the loss of cyclin D1 from histologically normal glomeruli suggests a possible role of cyclin D1 in mediating the dysregulation of the podocyte cell cycle in CG. These novel findings offer insight into the molecular regulation of mature podocyte differentiation. Podocyte proliferation in CG provides evidence in support of a previously underestimated plasticity of mature podocytes.