Significance of mesangial expression of alpha-smooth muscle actin in the progression of IgA nephropathy

The role of perirenal adipose tissue deposition in chronic kidney disease progression: Mechanisms and therapeutic implications

Chronic kidney disease (CKD) represents a significant and escalating global health challenge, with morbidity and mortality rates rising steadily. Evidence increasingly implicates perirenal adipose tissue (PRAT) deposition as a contributing factor in the pathogenesis of CKD. This review explores how PRAT deposition may exert deleterious effects on renal structure and function. The anatomical proximity of PRAT to the kidneys not only potentially causes mechanical compression but also leads to the dysregulated secretion of adipokines and inflammatory mediators, such as adiponectin, leptin, visfatin, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and exosomes. Additionally, PRAT deposition may contribute to renal lipotoxicity through elevated levels of free fatty acids (FFA), triglycerides (TAG), diacylglycerol (DAG), and ceramides (Cer). PRAT deposition is also linked to the hyperactivation of the renin-angiotensin-aldosterone system (RAAS), which further exacerbates CKD progression. Recognizing PRAT deposition as an independent risk factor for CKD underscores the potential of targeting PRAT as a novel strategy for the prevention and management of CKD. This review further discusses interventions that could include measuring PRAT thickness to establish a baseline, managing metabolic risk factors that promote its deposition, and inhibiting key PRAT-induced signaling pathways.

Immunohistochemical and Ultrastructural Characterization of Telocytes in Normal and Diabetic Human Kidneys

Background: Telocytes are interstitial stromal cells identified in various human organs, including the kidney. Their presence and role in human diabetic kidney disease remain unknown. Methods: To identify and localize telocytes in glomerular and tubule-interstitial compartments, both normal and diabetic human renal tissues were examined using immunohistochemistry, immunofluorescence, and transmission electron microscopy. Results: Renal telocytes are elongated interstitial cells with long, thin telopodes, showing alternating thin and thick segments. They expressed CD34, Nestin, α-SMA, and Vimentin markers. Occasionally, c-Kit expression was observed in some rounded and spindle cells, while no positivity was detected for PDGFR-β and NG2. Telocytes were identified around Bowman's capsule, tubules, and peritubular capillaries in both normal and diabetic conditions. In diabetic renal samples, there was a significant increase in α-SMA expressing telocytes, leading to periglomerular fibrosis. These telocytes also exhibited a synthetic phenotype with proteoglycan deposition in the extracellular matrix and, in some cases, showed pre-adipocytic differentiation. Conclusions: Telocytes were identified in normal and diabetic human kidneys. These cells form an elastic mechanical scaffold in the interstitium and are present in all renal cortical compartments. In diabetic samples, their increased α-SMA expression and synthetic phenotype suggest their potential role in the pathogenesis of diabetic nephropathy.

The role of mononuclear phagocyte system in IgA nephropathy: pathogenesis and prognosis

Although the "multiple hits" theory is a widely accepted pathogenesis in IgA nephropathy (IgAN), increasing evidence suggests that the mononuclear/macrophage system plays important roles in the progression of IgAN; however, the exact mechanism is unclear. In the present study, we explored 1,067 patients in 15 studies and found that the number of macrophages per glomerulus was positively related with the degree of hematuria, and the macrophages in the glomeruli were mainly related to mesangial proliferation (M) in renal biopsy. In the tubulointerstitium, macrophages were significantly paralleled to tubulointerstitial α-SMA and NF-kB expression, tubulointerstitial lesion, tubule atrophy/interstitial fibrosis (T), and segmental glomerulosclerosis (S). In the glomeruli and tubulointerstitium, M1 accounted for 85.41% in the M classification according to the Oxford MEST-C, while in the blood, M1 accounted for 100%, and the patients with low CD89⁺ monocyte mean fluorescence intensity displayed more severe pathological characteristics (S1 and T1-2) and clinical symptoms. M1 (CD80⁺) macrophages were associated with proinflammation in the acute phase; however, M2 (CD163⁺) macrophages participated in tissue repair and remodeling, which correlated with chronic inflammation. In the glomeruli, M2 macrophages activated glomerular matrix expansion by secreting cytokines such as IL-10 and tumor necrosis factor-β (TGF-β), and M0 (CD68⁺) macrophages stimulated glomerular hypercellularity. In the tubulointerstitium, M2 macrophages played pivotal roles in renal fibrosis and sclerosis. It is assumed that macrophages acted as antigen-presenting cells to activate T cells and released diverse cytokines to stimulate an inflammatory response. Macrophages infiltrating glomeruli destroy the integrity of podocytes through the mesangio-podocytic-tubular crosstalk as well as the injury of the tubule.

Glucosamine inhibits extracellular matrix accumulation in experimental diabetic nephropathy

INTRODUCTION

Glucosamine, the intermediate metabolite of the hexosamine biosynthesis pathway (HBP), is widely used as a supplementary drug in patients with osteoarthritis. However, its consequences in such patients concomitantly suffering from diabetic nephropathy is unknown.

METHODS

The aim of the study was to investigate the effect of exogenous administration of glucosamine in the diabetic kidney. A mouse model of streptozotocin-induced diabetic nephropathy in vivo and cultured endothelial cells in vitro were used in the study. The mice were treated with glucosamine for 6 months. Renal function was evaluated by metabolic cage, and histology of the kidney was estimated by periodic acid-schiff (PAS) staining. The expression of related genes was assessed by real-time PCR, immunofluorescence staining, immunoblotting and ELISA.

RESULTS

There was no significant difference in urinary albumin secretion, relative kidney weight, or creatinine clearance between the groups treated with glucosamine and controls. Assessment of the kidney demonstrated reduction in mesangial expansion and fibronectin expression in the diabetic glomeruli treated with glucosamine. Glucosamine treatment significantly decreased α-smooth muscle actin (α-SMA) protein expression in both diabetic and control kidneys, whereas the expression of other fibrosis-related genes and inflammatory factors was unaltered. Moreover, α-SMA colocalized with the endothelial marker CD31 in the diabetic and control kidneys, and glucosamine reduced α-SMA+ ECs in the diabetic glomeruli. In addition, glucosamine suppressed α-SMA expression in endothelial cells treated with or without high glucose.

DISCUSSION

In summary, this is the first report to show that glucosamine reduces mesangial expansion and inhibits endothelial-mesenchymal transition in diabetic nephropathy. The underlying mechanisms need to be further investigated.

Treatment strategy with multidrug therapy and tonsillectomy pulse therapy for childhood-onset severe IgA nephropathy

BACKGROUND

IgA nephropathy is a typical chronic glomerulonephritis that tends to occur in childhood.

METHOD

We reviewed the report on pathogenesis, treatment strategy with multidrug therapy and tonsillectomy pulse therapy for childhood-onset severe IgA nephropathy to clarify the pathophysiology and treatment of IgA nephropathy in childhood.

RESULTS

In recent years, it has been found that the pathogenesis at onset is associated with aberrant glycosylation at the IgA1 hinge. Given this genetic background, the aberrantly glycosylated IgA1immune complex produced by antigen-stimulated T cells and B cells is deposited in the glomeruli. Inflammation is induced via activation of the complement, macrophages and mesangial cells, and glomerular damage progresses thereafter. Treatment is selected according to the severity of IgA nephropathy. In order to prevent the development of renal damage, it is important to control the associated immune responses. For severe IgA nephropathy, in particular, multidrug therapy with prednisolone, immunosuppressants, and angiotensin enzyme synthesis inhibitors and tonsillectomy methylprednisolone pulse therapy are now performed- and, as a result, the number of renal deaths has decreased and the long-term prognosis has improved.

CONCLUSION

The prognosis of IgA nephropathy is improving. In the future, it will be important to develop a treatment method that takes into consideration the fact that children are in their growth and development stage and, therefore, seeks to minimizes side effects.

Clinical and Pathological Characteristics of Elderly Japanese Patients with IgA Vasculitis with Nephritis: A Case Series

Objective This case series aimed to identify the clinical and pathological characteristics of elderly patients (≥60 years) with biopsy-proven IgA vasculitis with nephritis (IgAVN). Methods The clinical and pathological presentation and treatment outcomes were compared between two groups. Patients Patients with IgAVN who were ≥19 years old at the time of their renal biopsy were divided into elderly (≥60 years) and adult (19-59 years) groups. Results Of the 23 patients in our study, 13 were elderly. In the elderly group, the median age at the diagnosis was 68 years (range, 60-85 years), with a median follow-up period of 15 months (range, 3-80 months). Twelve elderly patients had comorbidities, including hypertension, diabetes mellitus, chronic kidney disease, cardiovascular disease, and malignancies. A decrease in the estimated glomerular filtration rate, as well as massive proteinuria and rapidly progressive nephritic syndrome, were more frequent in the elderly group than in the adult group. Furthermore, renal pathological changes, including cellular or fibrocellular crescents, interstitial fibrosis, tubular atrophy, and arteriosclerosis, were more severe among elderly patients than adult patients. All elderly patients were treated with glucocorticoids and had no incidence of end-stage renal disease at the final follow-up; in addition, nine elderly patients had reduced proteinuria with a preserved renal function. Adverse events, including infection, diabetes mellitus, and vascular disorders, were identified in nine patients. Three elderly patients died from severe infections. Conclusion IgAVN in elderly patients is characterized by severe renal involvement. Elderly patients are at higher risk than adults for treatment-related adverse events.

Tensin Is Expressed in Glomerular Mesangial Cells and Is Related to Their Attachment to Surrounding Extracellular Matrix

Glomerular expression of tensin was immunohistochemically studied in normal and diseased rat kidneys to determine whether tensin might be related to specific binding in individual glomerular cells. Normal rat kidneys displayed an intense immunofluorescence reaction for tensin along the basal aspects of proximal and distal tubule cells and parietal epithelial cells of Bowman's capsules. In glomeruli, a positive reaction for tensin was detected only in the mesangial areas. Immunoelectron microscopy revealed a positive reaction in the mesangial cell (MC) processes. RT-PCR and immunoprecipitation demonstrated mRNA and protein levels of tensin in cultured rat MCs. Mesangial tensin expression was decreased when the mesangium was injured by Habu snake venom. During the regenerative process after mesangiolysis, tensin expression was not detected in early-phase proliferating MCs that did not have extracellular matrix (ECM). The expression of tensin recovered in late-phase proliferating MCs, which became attached to regenerated ECM. It appears that tensin is related to MC attachment to surrounding ECM, which suggests that signal transduction regulated by tensin may be related to a specific mechanism of MC matrix regeneration. Furthermore, tensin can act as a marker for rat MCs because the expression of tensin was detected only in MCs in glomeruli.

Smoking-Related Renal Histologic Injury in IgA Nephropathy Patients

PURPOSE

Smoking reportedly exerts deleterious effects on renal function; however, its effects on histology have not been clarified in patients with IgA nephropathy (IgAN).

MATERIALS AND METHODS

Renal histology was evaluated in a cohort of 397 patients diagnosed with IgAN according to smoking status and dose in relation to renal function.

RESULTS

Among the study cohort, which was predominantly male (88.5%), 52 patients (13%) were current smokers. These current smokers demonstrated more frequent hypertension and higher serum creatinine levels than non/ex-smokers at the time of diagnosis, which was apparent with increased smoking dose. The percentages of global glomerulosclerosis and arteriolar hyalinosis increased with increased smoking dose, whereas tubulointerstitial fibrosis or arterial intimal thickening did not. Glomerular mesangial alpha-smooth muscle actin expression were similar between current and non/ex-smokers matched for age, gender, hypertension, and histologic severity, although the number of glomerular CD68+ cells was significantly fewer in smokers. Initial serum creatinine level, estimated glomerular filtration rate (eGFR), and global glomerulosclerosis were found to be risk factors of serum creatinine doubling in both smokers and non/ex-smokers by univariate analysis during a mean follow-up of 3.8 years.

CONCLUSION

In addition to dose dependent renal functional decline and hypertension, smoking contributes to renal disease progression by eliciting microvascular injury in IgAN patients.

Clinicopathological characteristics of patients with immunoglobulin A nephropathy showing acute exacerbations after favorable long-term clinical courses

BACKGROUND

Sometimes, acute and progressive proteinuria increases occur in patients with IgA nephropathy (IgAN) after favorable long-term clinical courses of >10 years, but their clinical and histological characteristics are not well understood.

METHODS

We retrospectively selected 20 IgAN patients who had been followed for >10 years after their initial biopsies ((1st)Bx) and underwent second biopsies ((2nd)Bx), because their proteinuria increased to >1 g/day. Eight patients with acute exacerbations (Group A) showed acute proteinuria increases after long periods of mild proteinuria. Their clinicopathological characteristics were analyzed as a case series and were compared with those in Group B that comprised 12 patients with persistent proteinuria.

RESULTS

Group A experienced acute proteinuria increases and significant hematuria increases compared with the -1-year (P = 0.006) and -3-year (P = 0.010) time points before the (2nd)Bx, which contrasted to the clinical course in Group B. In Group A, glomerulosclerosis (GS) and the arteriosclerosis score did not differ between the (2nd)Bx and the (1st)Bx, and most patients (88 %) showed cellular and/or fibrocellular crescents within the (2nd)Bx. Compared with Group B, the (2nd)Bx revealed that the percentage of cellular and/or fibrocellular crescents (P = 0.001) was significantly higher, whereas the percentage of GS (P = 0.012) and the arteriosclerosis score (P = 0.020) were significantly lower in Group A.

CONCLUSION

Rapid proteinuria and hematuria increases, and acute histological lesions characterize acute exacerbations in IgAN after favorable long-term clinical courses.

Proregenerative Microenvironment Triggered by Donor Mesenchymal Stem Cells Preserves Renal Function and Structure in Mice with Severe Diabetes Mellitus

The aim of our work was to evaluate, in an animal model of severe diabetes mellitus, the effect of mesenchymal stem cells (MSCs) administration on diabetic nephropathy (DN) progression. After diabetes induction, one group of mice received the vehicle (DM) and other group received a single dose of MSCs (DM + MSCs). DM + MSCs mice showed a significant improvement in functional parameters of the kidney compared with untreated mice. While DM mice presented marked histopathological changes characteristics of advanced stages of DN (fibrosis, glomerulosclerosis, glomerular basement membrane thickening, capillary occlusion, decreased podocyte density, and effacement of foot processes), DM + MSCs mice showed only slight tubular dilatation. The renoprotection was not associated with an improvement in diabetic condition and very low number of donor cells was found in the kidney of DM + MSCs mice, suggesting that renoprotection could be mediated by paracrine effects. Indeed, DM + MSC mice presented increased renal proliferation index, decreased renal apoptotic index and the restoration of proregenerative factors, and anti-inflammatory cytokines levels. Moreover, macrophage infiltration and oxidative stress damage were also reduced in DM + MSCs mice. Our data demonstrate that MSC administration triggers a proregenerative microenvironment in DN kidney, which allows the preservation of the renal function even if diabetes was uncorrected.

Latent mesangial immunoglobulin A deposition in long-term functioning kidney does not correlate with disease progression and may exhibit fluctuating patterns

BACKGROUND

Latent mesangial immunoglobulin (Ig)A deposition in long-term functioning kidney does not correlate with disease progression and may exhibit fluctuating patterns Mesangial IgA deposition without urinary abnormalities (latent mesangial IgA deposition) is occasionally observed in non-episode biopsies of kidney allografts. However, the histologic features of latent IgA deposition have not been fully characterized.

METHODS

To better identify the clinicopathologic background of subclinical mesangial IgA deposition, we compared the clinical and histologic characteristics of long-term functioning kidney allografts with and without latent IgA deposition.

RESULTS

Among 29 patients with a posttransplant duration of >10 years, 37.9% exhibited latent mesangial IgA deposition. Biopsies indicated that renal function at the time of and 5 years before subclinical mesangial IgA deposition was generally similar. HLA-DR4 and HLA-Bw51 showed a nonsignificant trend to be more frequent in the IgA-positive group. Histologic investigation demonstrated no changes in disease scores based on the Banff 2009 classification between groups. Immunofluorescence revealed co-deposition of C3 at >1+ intensity in 72% IgA-positive patients. Immunohistochemical analysis revealed that IgA deposition per se did not cause notable increases in intraglomerular α-smooth muscle actin (SMA)-positive cells. One patient with subclinical IgA deposition demonstrated a waxing and waning pattern in the amount of IgA deposition.

CONCLUSION

This study suggests that subclinical IgA deposition in long-term functioning kidney allografts is not associated with progressive course in clinical and pathologic findings. Furthermore, the amount of subclinical IgA deposition may exhibit fluctuating patterns in some cases.

The interstitial expression of alpha-smooth muscle actin in glomerulonephritis is associated with renal function

BACKGROUND

In a healthy kidney, contractile protein alpha-smooth muscle actin (ASMA) is immunohistochemically strongly expressed only in the blood vessels, while in pathological conditions it can be visualized in glomerular mesangial cells and interstitial myofibroblasts. The aim of this study was to explore the possible correlation between expression of ASMA in glomerulonephritis (GN) and indicators of renal function.

MATERIAL/METHODS

We analyzed expression of ASMA in percutaneous renal biopsy of 142 adult and pediatric patients with GN and its correlation with blood pressure, serum creatinine, creatinine clearance and 24-hour urine protein at the time of biopsy. Immunoexpression of ASMA was analyzed quantitatively using computer-assisted morphometric analysis. Relative surface of ASMA expression in all glomeruli and interstitium was calculated for each patient.

RESULTS

In adults and children, greater expression of ASMA in interstitium was associated with higher serum creatinine and reduced creatinine clearance. Conversely, greater ASMA expression in glomeruli was associated with normal or decreased serum creatinine in adults and increased creatinine clearance in children. In children, correlation was found between high blood pressure and ASMA expression in interstitium.

CONCLUSIONS

We confirmed that interstitial expression of ASMA is associated with reduced renal function at time of biopsy. The connection of ASMA expression in glomeruli with lower serum creatinine and normal or increased creatinine clearance suggests a favorable role of this phenotypic change in glomerular filtration rate; further investigation is needed.

Changes in protein profiles during course of experimental glomerulonephritis

Better characterization of the molecular mechanisms underlying glomerular cell proliferation may improve our understanding of the pathogenesis of glomerulonephritis and yield disease-specific markers. We used two-dimensional gel electrophoresis (2DE) and mass spectrometry (MS) to generate expression profiles of glomerular proteins in the course of anti-Thy-1 nephritis. Glomeruli were isolated from Wistar rats by sieving, and proteins were separated by 2DE. In preliminary studies using normal rats, we identified known glomerular proteins from microfilaments [tropomyosin (Tm)] and intermediate filaments (vimentin and lamin A), proteins involved in assembly (α-actinin-4, F-actin capping protein) and membrane cytoskeletal linking (ezrin), as well as several enzymes (protein disulfide isomerase, ATP synthase, and aldehyde dehydrogenase). Comparison of glomerular protein abundance between normal rats and rats in the early phase of anti-Thy-1 nephritis yielded 28 differentially expressed protein spots. MS analysis identified 16 differentially expressed proteins including Tm. Altered Tm abundance in the course of anti-Thy-1 nephritis was confirmed, and specific isoforms were characterized by Western blotting. We demonstrated a complex change in Tm isoform abundance in the course of anti-Thy-1 nephritis. The early mesangiolytic phase of the disease was characterized by decreased abundance of low-molecular-weight isoforms Tm5a/5b and increased abundance of high-molecular-weight isoforms Tm6, Tm1, Tm2, and Tm3. The late proliferative phase of the disease was associated with increased abundance of isoforms Tm5a/5b, Tm6, and Tm1 and decreased abundance of Tm3. Isoforms Tm4 and Tm5 remained unchanged in the course of this model of experimental glomerulonephritis. Characterization of Tm isoform abundance in the course of clinical glomerulonephritis may identify disease-specific markers.

Renal expression of alpha-smooth muscle actin and c-Met in children with Henoch-Schönlein purpura nephritis

Alpha-smooth muscle actin (alpha-SMA) is the actin isoform that predominates within vascular smooth-muscle cells and plays an important role in fibrogenesis. On the other hand, c-Met is the receptor for hepatocyte growth factor (HGF), which plays a role in protection from injury and has anti-fibrogenetic effects. To clarify whether alpha-SMA and HGF are associated with the progression of renal injury in Henoch-Schönlein purpura nephritis (HSPN), we evaluated the renal expression of alpha-SMA and c-Met in HSPN patients. Patients were divided into three groups. Group 1 consisted of eight patients (male:female 4:4) with stage II or less in the classification of the International Study of Kidney Disease in Children (ISKDC), Group 2 consisted of 20 patients (male:female 11:9) with ISKDC stage III or greater and a good prognosis, and group 3 consisted of seven patients (male:female 3:4) with ISKDC stage III or greater and poor prognosis. Renal biopsy findings, including c-Met and alpha-SMA staining, were investigated for each group. At first biopsy, the mean scores for renal alpha-SMA and glomerular c-Met in groups 2 and 3 were higher than those in group 1, while mean scores for neither renal alpha-SMA nor glomerular c-Met differed between groups 2 and 3. At second biopsy, the mean scores for renal alpha-SMA staining in group 3 were higher than those in group 2, and mean score for glomerular c-Met staining in group 3 was lower than that in group 2. In groups 2 and 3, the mean scores for glomerular and interstitial alpha-SMA staining at first biopsy were correlated with the chronicity index (CI) at second biopsy, but the mean score for glomerular c-Met staining at first biopsy correlated with neither the activity index (AI) nor CI in the first or second biopsies in all groups. Our findings suggest that the expression of renal alpha-SMA may be associated with progression of renal injury in HSPN.

SM22α: The Novel Phenotype Marker of Injured Glomerular Epithelial Cells in Anti-Glomerular Basement Membrane Nephritis

BACKGROUND/AIMS

Our previous comprehensive analysis of the genes expressed in kidneys with anti-glomerular basement membrane (GBM) nephritis using DNA microarrays showed that SM22alpha was one of the highly expressed genes. SM22alpha is a 22-kDa cytoskeletal protein that is exclusively expressed in smooth muscle cells. We investigated the localization of SM22alpha at mRNA and protein levels, and its pathological significance in anti-GBM nephritis kidneys.

METHODS

Northern blot analysis, in situ hybridization, immunohistochemistry and double immunofluorescence studies were performed. The specific antibody (Ab) against SM22alpha was obtained by immunization of rabbits with recombinant rat SM22alpha protein.

RESULTS

SM22alpha mRNA expression was upregulated in kidneys and inducibly expressed in the parietal and visceral glomerular epithelial cells in anti-GBM nephritis kidneys. Immunohistochemistry with anti-SM22alpha Ab showed that SM22alpha protein was localized in the same series of cells. Double immunofluorescence with anti-SM22alpha and anti-glomerular cell markers demonstrated that SM22alpha might be expressed in epithelial cells of injured glomeruli. In visceral epithelial cells, SM22alpha might be expressed in cells in which podocyte specific markers, podocalyxin and nephrin were lost.

CONCLUSION

The injured glomerular epithelial cells in anti-GBM nephritis might undergo structural and functional alterations, including the expression of a smooth muscle marker, SM22alpha.

Role of peritubular capillary loss and hypoxia in progressive tubulointerstitial fibrosis in a rat model of aristolochic acid nephropathy

BACKGROUND/AIMS

To investigate the effects of peritubular capillary (PTC) loss and hypoxia on the progression of tubulointerstitial fibrosis in a rat model of aristolochic acid nephropathy (AAN).

METHODS

Female Wistar rats received Caulis aristolochiae manshuriensis (CAM) decoction by gavage for 8 weeks, and were sacrificed at 8, 12 and 16 weeks, respectively, after administration. Blood urea nitrogen (BUN), serum creatinine (Scr) and urinary protein were monitored prior to sacrifice. PTC loss and tubulointerstitial hypoxia were assessed by CD34 immunostaining and hypoxia-inducible factor-alpha subunit 1 (HIF-1alpha) expression, respectively. Myofibroblasts were assessed by alpha-smooth muscle actin (alpha-SMA) expression. The expression of angiogenic factor was assessed by vascular endothelial growth factor (VEGF).

RESULTS

AAN rats differed from controls by increased BUN, Scr and 24-hour urinary protein excretion rates. There was a progressive loss of PTCs in the AAN model, which was associated with the decreased expression of VEGF. A significant increase in nuclear localization of HIF-1alpha was seen 16 weeks after treatment with CAM decoction in the context of severe tubulointerstitial damage. Multifocal tubulointerstitial fibrosis was seen in AAN rats at weeks 12 and 16, predominantly in the area of the outer stripe and outer medulla. No significant pathologic changes were found in control rats.

CONCLUSION

Following the reduction of PTCs density and up-regulation of HIF-1alpha, the tubulointerstitial fibrosis area increased. Ischemia and hypoxia are the important causes of severe tubulointerstitial fibrosis in AAN rats.

Post-inflammatory glomerular remodeling is influenced by transformed mesangial cells

To identify the role of transformed mesangial cells (MC) during glomerular remodeling, anti-thymocyte-1 (Thy1) nephritis; modified Thy1 nephritis (injections of anti-Thy1 antibody four times, weekly); and Thy1 nephritis treated with signal transduction inhibitor 571 (Thy1 + STI); were analyzed. At week 1 the index of MC proliferation in modified Thy1 nephritis and in mesangiolysis in Thy1 + STI nephritis was highest among the three models. From week 4, the index of alpha-smooth muscle actin (alpha-SMA) was significantly higher in modified Thy1 nephritis than the other two models. Production of the mesangial matrix including type IV collagen was increased in modified Thy1 but inhibited in Thy1 + STI nephritis. In contrast to modified Thy1 nephritis, the capillary numbers in glomeruli recovered to normal at week 4 in Thy1, and at week 8 in Thy1 + STI nephritis. At week 12, both the adhesive and sclerotic index was significantly higher in modified Thy1 than in the other two models. Data suggest that a moderate amount of mesangial matrix results in a complete repair of capillary loops. Overproduction of the mesangial matrix retards capillary remodeling and finally induces glomerulosclerosis. Insufficient mesangial matrix delays the repair of capillary loops. In conclusion, transformed MC may influence glomerular remodeling by changing the amount of mesangial matrix.

Oxidative stress in the pathogenesis of experimental mesangial proliferative glomerulonephritis

Reactive oxygen species (ROS) are increasingly believed to be important intracellular signaling molecules in mitogenic pathways involved in the pathogenesis of glomerulonephritis (GN). We explored the effects of the antioxidants α-lipoic acid and N-acetyl-l-cysteine on ERK activation in cultured mesangial cells and the role of ERK activation in the severity of glomerular injury in a rat model of anti-Thy 1 GN. In cultured mesangial cells, growth factors stimulated ERK phosphorylation by 150–450%. Antioxidants reduced this increase by 50–60%. Induction of anti-Thy 1 nephritis in rats led to a 210% increase in glomerular ERK phosphorylation. This increase in phosphorylated ERK was reduced by 50% in animals treated with α-lipoic acid. Treatment with α-lipoic acid resulted in significant improvement of glomerular injury. Cellular proliferation was reduced by 100%, and the number of proliferating cell nuclear antigen-positive cells was reduced by 64%. The increased expression of glomerular transforming growth factor-β1 protein and mRNA in rats with anti-Thy 1 nephritis was significantly attenuated and mesangial cell transformation into myofibroblasts was completely prevented by treatment with α-lipoic acid. The effects of α-lipoic acid were at least partially due to inhibition of oxidative stress. In rats with anti-Thy 1 nephritis, ROS production was increased 400–500%, and this increase was inhibited by 55% by treatment with α-lipoic acid. We suggest that ROS may mediate glomerular injury by inducing ERK phosphorylation. α-Lipoic acid should be considered a potential therapeutic agent in certain types of human GN.

Predicting the prognosis of renal dysfunction by renal expression of α-smooth muscle actin in children with MPGN type 1

BACKGROUND

To clarify whether renal alpha-smooth muscle actin (alpha-SMA)-positive cell and macrophage accumulation can predict the prognosis of renal dysfunction, we evaluated them by means of multivariate analysis and compared them with other clinical predictors in patients with membranoproliferative glomerulonephritis (MPGN) type 1 with normal renal function.

METHODS

We enrolled 35 patients with MPGN type 1 who had normal creatinine clearance at the time of renal biopsy. These patients were divided into 2 groups based on clinical status at the last examination. Group 1 consisted of 12 patients with normal urine and 12 patients with minor urinary abnormalities at the latest observation, whereas group 2 consisted of 7 patients with persistent nephropathy and 4 patients with renal insufficiency. The first and second renal biopsy findings, including alpha-SMA and CD68-positive staining, were investigated for both groups.

RESULTS

Mean scores for glomerular and interstitial alpha-SMA staining in group 2 were significantly higher than those in group 1. At the second biopsy, mean scores for interstitial CD68-positive staining in group 2 were higher than those in group 1. Mean scores for glomerular and interstitial alpha-SMA at the first biopsy correlated with the chronicity index at the second biopsy in both groups.

CONCLUSION

Our results suggest that glomerular and interstitial alpha-SMA expression at the first biopsy can predict the prognosis of children with MPGN type 1.

Cytoskeletal rearrangement and signal transduction in TGF-beta1-stimulated mesangial cell collagen accumulation

TGF-beta1 has been implicated in glomerular extracellular matrix accumulation, although the precise cellular mechanism(s) by which this occurs is not fully understood. The authors have previously shown that the Smad signaling pathway is present and functional in human glomerular mesangial cells and plays a role in activating type I collagen gene expression. It also was determined that TGF-beta1 activates ERK mitogen-activated protein kinase in mesangial cells to enhance Smad activation and collagen expression. Here, it was shown that TGF-beta1 rapidly induces cytoskeletal rearrangement in human mesangial cells, stimulating smooth muscle alpha-actin detection in stress fibers and promoting focal adhesion complex assembly and redistribution. Disrupting the actin cytoskeleton with cytochalasin D (Cyto D) selectively decreased basal and TGF-beta1-induced cell-layer collagen I and IV accumulation. The balance of matrix metalloproteinases (MMP) and inhibitors was altered by Cyto D or TGF-beta1 alone, increasing MMP activity, increasing MMP-1 expression, and decreasing tissue inhibitor of matrix metalloproteinase-2 expression. Cyto D also decreased basal and TGF-beta1-stimulated alpha1(I) collagen mRNA but did not inhibit TGF-beta-stimulated alpha1(IV) mRNA expression. A similar decrease in alpha1(I) mRNA expression caused by the actin polymerization inhibitor latrunculin B was partially blocked by the addition of jasplakinolide, which promotes actin assembly. The Rho-family GTPase inhibitor C. difficile toxin B or the Rho-associated kinase inhibitor Y-27632 also blocked TGF-beta1-stimulated alpha1(I) mRNA expression. Cytoskeletal disruption reduced Smad2 phosphorylation but had little effect on mRNA stability, TGF-beta receptor number, or receptor affinity. Thus, TGF-beta1-mediated collagen I accumulation is associated with cytoskeletal rearrangement and Rho-GTPase signaling.

Glomerulosclerosis develops in Thy-1 nephritis under persistent accumulation of macrophages

To clarify the relationship between macrophages and development of glomerulosclerosis, the authors developed a new experimental nephritis model with macrophages persisting in Thy-1 nephritis. Methyl-cellulose was administered intraperitoneally in addition to the intravenous injection of the anti-Thy-1 antibody to Wistar rats. Foamy macrophages influxed into the lytic mesangium and stayed to form nodular aggregates. Mesangial cells proliferated with the formation of extracellular matrices around these nodular aggregates of macrophages. Immunohistochemical analyses revealed that alpha-smooth muscle actin (alpha-SMA) was expressed in the proliferative area around these nodules of foamy macrophages from day 7. Type I collagen and type IV collagen were also expressed around the foamy macrophages in correspondence with alpha-SMA expression from day 7. The electron microscopic study revealed that collagen fibrils were formed around the transformed mesangial cells. The expression of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31), a marker of glomerular vasculature endothelial cells, was not found in the area occupied by the foamy macrophages, suggesting the impairment of glomerular reconstruction. Macrophages may participate in the progression of glomerulosclerosis in Thy-1 nephritis by enhancing the production of the extracellular matrix through transformed mesangial cells and preventing reconstruction of the capillary network.

Urate transport via human PAH transporter hOAT1 and its gene structure

BACKGROUND

We recently cloned the human organic anion transporter 1 (hOAT1) as a p-aminohippurate (PAH) transporter. Whether urate is transported by the PAH transporter in humans remains unclear. Familial juvenile gouty nephropathy (FJGN) is thought to develop as a result of an abnormality in the urate transporter.

METHODS

To determine if hOAT1 transported urate, the cellular uptakes of PAH and urate were determined, as were the inhibition profiles of inorganic anions, and uricosuric and antiuricosuric agents using a mouse S2 cell line expressing hOAT1. The hOAT1 gene was cloned from a genomic library using full-length hOAT1-1 cDNA as a probe. The coding regions of the hOAT1 genes of two sisters with FJGN were sequenced. Also, immunohistochemical fluorescence analysis of hOAT1 in the kidney of the younger sister with FJGN was performed.

RESULTS

The Km and Vmax values of urate transport via hOAT1 were 943 +/- 84 micromol/L and 1286 +/- 162 pmol/mg protein/min, respectively. The order of the IC50 of urate transport via hOAT1 was benzbromarone < probenecid < salicylate or pyrazine carboxylic acid. The 10.9 kb hOAT1 gene was found to be interrupted by nine introns. Mutations in the coding region of the hOAT1 gene from the two sisters with FJGN were undetectable. Immunohistochemical fluorescent staining showed that hOAT1 in the kidney of the younger sister was similar to that of control individuals.

CONCLUSIONS

Our data show that hOAT1 transports urate, and the inhibition profiles of uricosuric and antiuricosuric agents are defined. hOAT1 is not responsible for FJGN in the two sisters examined in this study.

Adoptive transfer studies demonstrate that macrophages can induce proteinuria and mesangial cell proliferation

BACKGROUND

Glomerular macrophage accumulation is a feature of proliferative human and experimental glomerulonephritis. However, our understanding of the role of macrophages in the induction of renal injury is based upon indirect evidence from depletion studies, most of which lack specificity for this cell type. Therefore, an adoptive transfer approach was used to directly assess the potential of macrophages to induce renal injury.

METHODS

Accelerated anti-glomerular basement membrane (anti-GBM) disease was induced in rats by immunization with sheep IgG (day -5), followed by administration of sheep anti-rat GBM serum (day 0), with animals killed on day 2. To facilitate the adoptive transfer studies, immunized animals were made leukopenic by cyclophosphamide (CyPh) given on day -2. Bone marrow-derived (BM) or NR8383 macrophages were transferred by tail vein injection 24 hours after injection of anti-GBM serum, with animals killed 3 or 24 hours after transfer.

RESULTS

Pretreatment with CyPh prevented glomerular leukocyte accumulation and completely inhibited proteinuria, glomerular cell proliferation and hypercellularity in accelerated anti-GBM disease. Adoptive transfer led to significant glomerular accumulation of BM or NR8383 macrophages within 3 hours of injection, and this was still evident 24 hours later. Adoptive transfer of BM or NR8383 macrophages induced proteinuria (63 +/- 16 BM vs. 5 +/- 2 mg/24 h CyPh control; P < 0.001), glomerular cell proliferation (5.1 +/- 1.2 BM vs. 0.5 +/- 0.1 PCNA+ cells/gcs CyPh; P < 0.001) and glomerular hypercellularity (51.2 +/- 2.0 BM vs. 41.9 +/- 0.9 nuclei/gcs CyPh; P < 0.001). The degree of renal injury correlated with the number of transferred glomerular macrophages. Two-color immunostaining demonstrated that most glomerular proliferative cell nuclear antigen+ (PCNA+) proliferating cells were OX-7+ mesangial cells. CyPh treatment did not prevent up-regulation of glomerular intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule (VCAM-1) expression or an increase in urinary monocyte chemoattractant protein-1 (MCP-1) excretion.

CONCLUSION

This study provides the first direct evidence that macrophages can induce renal injury in terms of proteinuria and mesangial cell proliferation.

Y-27632 prevents tubulointerstitial fibrosis in mouse kidneys with unilateral ureteral obstruction

BACKGROUND

The small GTPase Rho is involved in cell-to-substratum adhesion and cell contraction. These actions of Rho mediated by downstream Rho effectors such as Rho-associated coiled-coil forming protein kinase (ROCK) may be partly responsible for the progression of renal interstitial fibrosis.

METHODS

The anti-fibrosis effects of Y-27632, a specific ROCK inhibitor, were studied both in vivo (unilateral ureteral obstruction; UUO) and in vitro. To investigate the therapeutic efficacy of Y-27632 in UUO kidneys, smooth muscle alpha actin (SMalphaA) expression, macrophage infiltration and fibrosis in the obstructed kidneys were studied. SMalphaA, transforming growth factor beta (TGF-beta), alpha1 (I) collagen, osteopontin, macrophage chemoattractant peptide-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) gene expression were examined by Northern blotting. To elucidate the mechanism linking the Rho-ROCK pathway with renal fibrosis, the effects of Y-27632 on in vitro cell proliferation and cell migration were studied.

RESULTS

In vivo analysis showed that Y-27632 suppressed SMalphaA expression, macrophage infiltration and interstitial fibrosis, and that Y-27632 suppressed SMalphaA, TGF-beta and alpha1 (I) collagen mRNA expression. In vitro analysis showed that Y-27632 did not suppress proliferation of renal fibroblasts but suppressed migration of macrophages.

CONCLUSIONS

The Rho-ROCK system may play an important role in the development of tissue fibrosis, and the Rho-ROCK signaling pathway may be a new therapeutic target for preventing interstitial fibrosis in progressive renal disease.

CD44 expression in IgA nephropathy

Immunoglobulin A (IgA) nephropathy is a frequent, chronic renal disease characterized by a broad spectrum of clinical presentations and pathologic findings. CD44, a family of type I transmembrane glycoproteins involved in cell-cell and cell-matrix interactions, may orchestrate partially the cascade of inflammation, accumulation of myofibroblasts, and fibrosis leading to end-stage renal disease. To clarify the possible role of CD44 in the progression of IgA nephropathy, the expression of CD44 in glomeruli and the tubulointerstitial compartment was analyzed in 25 renal biopsy specimens of patients with IgA nephropathy and was correlated to histopathologic, serologic, and urinary parameters. The expression of CD44 correlated significantly with the degree of glomerular and interstitial damage, even better than the accumulation of alpha-smooth muscle actin-positive myofibroblasts, which is recognized as a reliable marker for the progression of IgA nephropathy. A positive correlation also was found between proteinuria and the expression of CD44 in the tubulointerstitial compartment. The glomerular and tubulointerstitial expression of CD44 correlated with the degree of renal damage in IgA nephropathy and could be a reliable marker of the progression of IgA nephropathy. CD44 may have a pivotal role in the cascade of renal inflammation and fibrosis.

Glomerular expression of alpha-smooth muscle actin reflects disease activity of IgA nephropathy

To elucidate the relationship between histological disease states and clinicopathological features in immunoglobulin A nephropathy (IgAN), 90 needle-biopsy specimens diagnosed as IgAN were analyzed. The specimens were divided into four groups according to histological grade and stage index. Immunohistochemical features of alpha-smooth muscle actin (alpha-SMA), macrophages positive for myeloid/histiocyte antigen (MAC387), and expression of type I, III and IV collagens were all examined. Glomerular expression scores of alpha-SMA and the degree of intraglomerular macrophage infiltration were highest in the active and non-sclerotic groups. Type I and IV collagens were significantly more abundant in the sclerotic groups than in the active groups. Type III collagen was strongly expressed in both the active and sclerotic groups. Double immunolabeling of alpha-SMA and intercellular adhesion molecule (ICAM)-1 revealed that ICAM-1 was expressed around the alpha-SMA-positive mesangial area. In multivariate analysis, the glomerular expression score of alpha-SMA was mostly correlated with histological grading in the 10 clinicopathological parameters. Type IV collagen score was mostly correlated with histological staging. These results suggest that glomerular alpha-SMA expression reflects the histological activity of IgAN. Immunohistological staining of alpha-SMA is valuable to estimate the degree of disease activity in IgAN.

Fluvastatin suppresses oxidative stress and fibrosis in the interstitium of mouse kidneys with unilateral ureteral obstruction

BACKGROUND

Recently, we demonstrated increased oxidative stress in the interstitium of ureteral obstructed kidneys based on the increased expression of heme oxygenase-1 and immunohistochemical detection of advanced glycation end products (AGE) in the interstitium. Antioxidant therapy may have a therapeutic potential toward interstitial fibrosis of unilateral ureteral obstruction (UUO) kidneys. Fluvastatin is an HMG-CoA reductase inhibitor and has been demonstrated to have an antioxidant activity in vitro.

METHODS

The effects of fluvastatin on UUO kidneys from the viewpoints of antioxidant action in vivo and antifibrosis action were studied. To investigate the antioxidant action and its therapeutic efficacy of fluvastatin in UUO kidneys, AGE accumulation and fibrosis in the obstructed kidneys was compared among vehicle-, pravastatin-, or fluvastatin-treated (10 or 40 mg/kg/day) groups.

RESULTS

Tubulointerstitial fibrosis was significantly attenuated in fluvastatin-treated animals. Fluvastatin significantly suppressed the degree of immunostaining of AGE in UUO kidneys.

CONCLUSIONS

These results provide evidence for the antioxidant action of fluvastatin in vivo. The decreased interstitial fibrosis along with a decreased oxidative stress marker in the interstitial lesion strongly suggests the existence of a causal relationship between them. Fluvastatin may have therapeutic value in slowing or preventing interstitial fibrosis in progressive renal disease.

Participation of endothelial cells and transformed mesangial cells in remodeling of glomerular capillary loops in Thy-1 nephritis

The relationship between mesangial cells (MC) and endothelial cells (EC) in the remodeling of glomerular capillary loops was investigated in a rat model of anti-Thy-1 antibody (Ab)-induced glomerulonephritis. Immunohistochemical analysis showed that cells positive for alpha-smooth muscle actin (alpha-SMA) appeared in the mesangial stalks at day three, and had increased in number at day seven, after injection of Thy-1 Ab. Double staining for alpha-SMA and proliferating cell nuclear antigen (PCNA) showed that some MC expressing PCNA were negative for alpha-SMA at day three, but by day seven almost all PCNA-positive MC expressed alpha-SMA. Western blotting for alpha-SMA from isolated glomeruli was negative at day one after injection of Thy-1 Ab, but positive at day seven. Type III collagen appeared at day seven, followed by an increase of EC in the capillary loops, as determined by double immunofluorescent staining for rat endothelial cell antigen-1 (RECA-1) and type III collagen. RECA-1-positive cells increased rapidly in number after day seven and eventually showed the same distribution pattern as that in control rats. Both type I and type III collagens were expressed in the mesangial and the ballooning area of the glomerulus at day seven. Electron microscopy revealed that immature MC and EC forming small capillary lumina appeared in the enlarged mesangial area at day seven. In accordance with the increase of capillaries and the enlargement of the lumina, the number of MC and the amount of mesangial matrix decreased gradually, and most of the glomeruli returned to a normal structure by week 4. These data show that type I and type III collagen produced by transformed MC may be of benefit to proliferation of EC and remodeling of the capillary in Thy-1-induced nephritis.