Podocytes are highly specialized epithelial cells with complex actin cytoskeletal architecture crucial for maintenance of the glomerular filtration barrier. The mammalian Rho GTPases Rac1 and Cdc42 are molecular switches that control many cellular processes, but are best known for their roles in the regulation of actin cytoskeleton dynamics. Here we employed podocyte-specific Cre-lox technology and found that mice with deletion of Rac1 display normal podocyte morphology without glomerular dysfunction well into adulthood. Using the protamine sulfate model of acute podocyte injury, podocyte-specific deletion of Rac1 prevented foot process effacement. In a long-term model of chronic hypertensive glomerular damage, however, loss of Rac1 led to an exacerbation of albuminuria and glomerulosclerosis. In contrast, mice with podocyte-specific deletion of Cdc42 had severe proteinuria, podocyte foot process effacement, and glomerulosclerosis beginning as early as 10 days of age. In addition, slit diaphragm proteins nephrin and podocin were redistributed and cofilin was de-phosphorylated. Cdc42 is necessary for the maintenance of podocyte structure and function, but Rac1 is entirely dispensable in physiologic steady state. However, Rac1 has either beneficial or deleterious effects depending on the context of podocyte impairment. Thus, our study highlights the divergent roles of Rac1 and Cdc42 function in podocyte maintenance and injury.

Ganglioside GM1 has been considered to have a neurotrophic factor-like activity. To analyze the effects of endogenously generated GM1, the rat pheochromocytoma cell line PC12 was transfected with the GM1/GD1b/ GA1 synthase gene and showed increased expression levels of GM1. To our surprise, GM1؉ -transfectant cells (GM1 ؉ cells) showed no neurite formation after stimulation with nerve growth factor (NGF). Autophosphorylation of NGF receptor TrkA and activation of ERK1/2 after NGF treatment were scarcely detected in GM1 ؉ cells. Binding of 125 I-NGF to PC12 cells was almost equivalent between GM1؉ cells and controls. However, dimer formation of TrkA upon NGF treatment was markedly suppressed in GM1؉ cells in both cross-linking analysis with Bis(sulfosuccinimidyl)suberate 3 and 125 I-NGF binding assay. The sucrose density gradient fractionation of the cell lysate revealed that TrkA primarily located in the lipid raft fraction moved to the non-raft fraction in GM1 ؉ cells. p75 NTR and Ras also moved from the raft to non-raft fraction in GM1 ؉ cells, whereas flotillin and GM1 persistently resided in the lipid raft. TrkA kinase activity was differentially regulated when GM1 was added to the kinase assay system in vitro, suggesting suppressive/enhancing effects of GM1 on NGF signals based on the concentration. Measurement of fluorescence recovery after photobleaching revealed that the membrane fluidity was reduced in GM1 ؉ cells. These results suggested that overexpressed GM1 suppresses the differentiation signals mediated by NGF/ TrkA by modulating the properties of the lipid raft and the intracellular localization of NGF receptors and relevant signaling molecules.

No abstract

Background and Aim Endoscopic resection is feasible for superficial tumors in patients with ulcerative colitis; however, endoscopic resection options have not been evaluated comprehensively. We evaluated the efficacy and safety of endoscopic submucosal dissection and endoscopic mucosal resection, and decision making regarding endoscopic resection options for patients with ulcerative colitis. Methods Endoscopically treated tumors from patients with ulcerative colitis were analyzed retrospectively. We evaluated en bloc and R0 resection, adverse events, local tumor recurrence, and metachronous lesion occurrence rates. Results We examined 102 tumors (mean size, 12 mm; non‐polypoid, 55 tumors) from 74 patients with ulcerative colitis, of whom, 39 and 63 underwent endoscopic submucosal dissection and endoscopic mucosal resection, respectively. The R0 resection rate was significantly higher for endoscopic submucosal dissection (97%) than for endoscopic mucosal resection (80%) (P = 0.0015). For 11–20‐mm tumors, the R0 resection rate was significantly higher for endoscopic submucosal dissection (94%) than for endoscopic mucosal resection (55%) (P = 0.0027); the endoscopic submucosal dissection and endoscopic mucosal resection R0 rates did not differ for ≤ 10‐mm tumors. The non‐polypoid tumor R0 resection rates were significantly higher for endoscopic submucosal dissection (100%) than for endoscopic mucosal resection (65%) (P < 0.001) and did not differ regarding the polypoid tumor R0 resection rates (75% vs 86%, P = 0.49). Four patients experienced intraoperative perforation during endoscopic submucosal dissection. No local recurrences occurred. Metachronous high‐grade dysplasia occurred in three patients during surveillance. Conclusions In patients with ulcerative colitis, endoscopic submucosal dissection is suitable for ≥ 11‐mm and non‐polypoid tumors, whereas endoscopic mucosal resection is acceptable for ≤ 10‐mm tumors.

Diabetic nephropathy is a major complication in diabetes and a leading cause of end-stage renal failure. Glomerular podocytes are functionally and structurally injured early in diabetic nephropathy. A non-obese type 2 diabetes model, the spontaneously diabetic Torii (SDT) rat, is of increasing preclinical interest because of its pathophysiological similarities to human type 2 diabetic complications including diabetic nephropathy. However, podocyte injury in SDT rat glomeruli and the effect of angiotensin II receptor blocker treatment in the early stage have not been reported in detail. Therefore, we have evaluated early stages of glomerular podocyte damage and the beneficial effect of early treatment with losartan in SDT rats using desmin as a sensitive podocyte injury marker. Moreover, we have developed an automated, computational glomerulus recognition method and illustrated its specific application for quantitatively studying glomerular desmin immunoreactivity. This state-ofthe-art method enabled automatic recognition and quantification of glomerular desminpositive areas, eliminating the need to laboriously trace glomerulus borders by hand. The image analysis method not only enabled assessment of a large number of glomeruli, but also clearly demonstrated that glomerular injury was more severe in the juxtamedullary region than in the superficial cortex region. This applied not only in SDT rat diabetic nephropathy but also in puromycin aminonucleoside-induced nephropathy, which was also studied. The proposed glomerulus image analysis method combined with desmin immunohistochemistry should facilitate evaluations in preclinical drug efficacy studies as well as elucidation of the pathophysiology of diabetic nephropathy.