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Objective: To investigate the effects of losartan on Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 in glomeruli of diabetic rats., Methods: Sixty Wistar male rats were randomly divided into control group (n=20), diabetes group (n=20), and losartan treatment group (n=20). Diabetes was induced by intraperitoneal injection of streptozotocin (STZ, 65 mg/kg). Losartan (10 mg/kg) was administered daily by gavage from the day following the induction of diabetes. The animals were sacrificed in the weeks 2 and 4 after STZ injection. The renal cortical tissues were obtained and glomeruli were isolated. The protein expressions of JAK2, STAT3 and tyrosine phosphorylated STAT3 (p-STAT3) were assessed respectively by Western blot. Immunoprecipitation and Western blot analysis were used to determine tyrosine phosphorylated JAK2 (p-JAK2). JAK2 and STAT3 mRNA were assayed by reverse transcription-polymerase chain reaction (RT-PCR)., Results: Compared with the control group rats, the respective expression of JAK2, p-JAK2, STAT3, p-STAT3, JAK2 mRNA and STAT3 mRNA was significantly increased in the diabetic glomeruli without losartan treatment (all P<0.01). After treatment with losartan, the expression of p-JAK2 and p-STAT3 in the diabetic glomeruli was down-regulated (all P<0.05). However losartan had no effect on the expression of JAK2, STAT3, JAK2 mRNA and STAT3 mRNA in the diabetic glomeruli., Conclusion: JAK2 and STAT3 signal proteins may be involved in the kidney damage associated with diabetes. Regulation of phosphorylation of JAK2 and STAT3 may be responsible for the renal protective effects of losartan in diabetic rats.

Serum sickness nephritis was induced in male Fisher 344/JCL rats by injecting egg albumin into the foot pads and peritoneal cavity. The alteration of anionic sites in the glomerular basement membrane (GBM) of the rats with significant proteinuria was studied with a quick-freezing and deep-etching method using polyethyleneimine as a cationic probe. In control rats, anionic sites were located around the fibrils of the lamina rara externa, which radiated perpendicularly from the lamina densa to podocyte cell membranes. In the glomeruli of proteinuric rats, many electron-dense deposits were observed in the subepithelial side of the GBM, where the fibrils of the lamina rara externa were usually obscured and anionic sites around them could not be recognized. However, in some areas, a clear boundary could be observed between deposits and the lamina densa. Electron micrographs of freeze-fractured deposits showed that the fibrils radiated perpendicularly from the lamina densa and that anionic sites around them had been preserved. These results suggest that some of the deposits simply passed through the GBM and masked transiently the fibril structures of the GBM, but others probably destroyed these fibril structures, including anionic sites.

A morphometric study was undertaken to examine age-related changes in glomerular ultrastructure and anionic sites in ddY male mice at various ages. A progressive increase in glomerular extracellular matrices, including thickening of the glomerular basement membrane (GBM), formation of GBM nodules, and mesangial matrix increase, was found to be the primary age-related ultrastructural change in aging mice; there were also electron-dense deposits in mesangial and subepithelial regions. The extent of GBM thickening in mice was less than was reported in rats. Rather, the GBM nodules, which had the same electron density as the lamina densa (LD) and protruded on the subepithelial side of the GBM, were more striking. Quantitative evaluation showed that GBM thickness, number and size of GBM nodules, and the area of the mesangial matrix were significantly correlated with the age of the mice. The distribution of anionic sites in the glomeruli of aging animals was described for the first time. No statistically significant differences were noted between the number of glomerular anionic sites in the different age groups. These results indicate that the increase in glomerular extracellular matrices reported in aged rats was also present in aged mice, although the extent of various changes was different. The results also indicate that this increase in glomerular extracellular matrices with age was not accompanied by significant alteration in glomerular anionic sites.

Chronic serum sickness nephritis was induced in rats by sensitization with egg albumin. The glomeruli were then examined by the quick-freezing and deep-etching method with immunohistochemical identification of immune complex deposits on replica membranes. In control rats, the glomerular basement membrane showed a three-layered structure. The middle layer was composed of a compact meshwork of fine fibrils that was connected to adjacent endothelial and epithelial cells by perpendicular fibrils in the inner and outer layers. The mesangial matrix contained a similar but looser meshwork structure. In the nephritic rats, small granular deposits were observed within the meshwork, distorting its fine structure. Larger nodular aggregates extended continuously from the middle layer to the epithelial side. Disruption of the connecting fibrils overlying these larger aggregates was noted. The deposits were stained by antiegg albumin or antirat IgG antibodies. Gold particles immunostaining for the sensitizing antigen were also localized within the deposits. These findings suggest that the deposition of immune complexes occurs in the fibrillary meshworks of the mesangium and lamina densa in this experimental model, with the resultant distortion of their meshwork structures and the formation of nodular aggregates.

Histopathological analysis was performed in the first renal biopsy specimens of patients over and under 10 yrs of IgA nephritis. They were divided clinically into two groups, the one with remission and the other with prolonged disease state respectively. Increased mesangial sclerosis, frequent occurrence of segmental glomerular lesions and tubulointerstitial change were significantly evident in the group with prolonged disease state. It is suggested that similar glomerular events are progressing in IgA nephritis which is carried over to adult age.

Alterations in glomerular basement membrane (GBM) anionic sites associated with immune deposits (ID) were observed using polyethyleneimine (PEI) as a cationic probe in serum sickness nephritis induced by egg albumin (EA). The anionic sites were fewer in number than in other GBM segments and were irregular in distribution in most, but not all, of the segments of the GBM with ID on the epithelial side of the lamina densa (LD). The disappearance of anionic sites was obvious in areas where the internal aspects of the lamina rara externa (LRE) of the GBM were occupied by ID, even if the ID were very small. In contrast, the disappearance of anionic sites was not evident, even though no change in anionic sites was found in some areas, where the ID had departed from the internal aspects of the LRE and a pale band was seen between the ID and the LD. Further, PEI aggregates, showing localization of anionic sites, were seen within the low density ID, but no PEI aggregates were seen within the high density ID. The results suggest that: 1) whether or not ID induce the disappearance of anionic sites is independent of the size of the ID, but is dependent on the density of and the place occupied by the ID, and 2) the ID seem to induce the disappearance of anionic sites by masking rather than destroying them.

Serum sickness nephritis was induced in Fisher rats by immunization with egg albumin (EA) and correlations between immune complex deposition, alterations of podocytes and development of proteinuria were analysed. Immunoelectron microscopy showed that EA, rat IgG and C3 were confined to the electron-dense deposits (Ds). From 3 weeks, when significant proteinuria had developed, the subepithelial region was filled with large numbers of Ds on the peripheral capillary wall as well as in the paramesangium. The loss of slit diaphragms and detachment of foot processes overlying Ds were observed and the escape of Ds into urinary space was frequently detected. Morphometric evaluation showed that the volume of subepithelial Ds and the number of the sites of podocytic detachment correlate significantly with the amount of proteinuria. In addition, the native ferritin injected via the abdominal aorta was seen in large amounts in the urinary space near the areas devoid of epithelial covering. The development of podocytic detachment was clearly coincident with the appearance of proteins with a larger molecular weight in urine. From these results, it is suggested that the loss of slit diaphragms and the detachment of podocytes resulting from the progressive accumulation of Ds will allow the leakage of proteins of larger molecular weight across the capillary wall. These podocytic lesions may be one of the main aetiologies for the development of heavy proteinuria in this model.