| Podocyte is an important component of the glomerular filtration barrier. The maintenance of normal podocytical cytoskeleton is the foundation of its biological function. The destroy of podocyte cytoskeleton morphology, such as foot process effacement or detachment always causes permeability increase of glomerular filtration, leading to the proteinuria. However, the formation mechanism of the podocyte foot process morphology is still not completely clear. Growing evidence suggests that there are many common cell biological features shared by neuron and podocyte, for example they are both terminally differentiated cells with special cell protrusion structure. Among process-bearing cells, the neuron is the most intensively investigated so far. Careful comparison between neurons and podocytes may provide certain clues for understanding the pathophysiological mechanism of podocytopathy and nephropathy, as well as for opening a new way to novel therapeutic approaches. Studies have shown that some podocyte’s mature proteins like Podocin, Nephrin and Synaptopodin were expressed in neuron and played an important role in neuronal differentiation regulatory. Based on the studies above, we speculated that some of the neuronal iconic molecules may also expresse in podocytes, and the molecules could play an important role in podocytes differentiation. Up to now, there are no relevant reports about it. In this study, using cell biological experiments and immunohistochemical technique, we showed that some neuronal iconic molecules, such as NSE, Nestin, NeuN, synaptopodin, S100 etc, did expresse in podocyte. We further inhibited the expression of NSE, Nestin, Synaptopodin and UCH-L1 by siRNA in cultured mouse podocyte, and the significant morphologic changes of podocyte was observed in treated cells. When podocyte was treated with Adriamycin, the protein expression of NSE, Nestin, Synaptopodin and UCH-L1 decreased with time dependence. Meanwhile, the podocytical morphologic changes consisted with result of their siRNA treatment. The data proved that neuronal iconic proteins mentioned above play important roles in maintaining and regulating the podocyte’ process formation and function. When the expression of NeuN and S100 were inhibited by siRNA, the morphology of podocyte had no change compared with the normal ones, and the cytoskeleton fibers arrange orderly, which suggested that these two neuronal iconic proteins didn’t involve in the formation of podocytical cytoskeleton and may had other biological functions.As an important molecule in mature podocyte, synaptopodin plays an important role in forming of the podocyte cytoskeleton. In order to clarify the regulation mechanism of synaptopodin for cytoskeleton formation in podocyte, we investigated synaptopodin expression in pathologic (43 cases) and normal (5 cases) renal samples by using immunohistochemical technique, ascertained the relationship between synaptopodin expression and the damages of podocytes in different kinds of glomerulonephritis. The result found that the synaptopodin expression in all kinds of glomerulonephritis reduced significantly contrasted with normal renal samples, especially in focal segmental glomerulosclerosis (FSGS), and in IgA nephropathy (IgAN), acute diffuse proliferative glomerulonephritis (APGN), lupus erythematesis nephrites (LN), membranous glomerulonephritis (MN) as well as minimal change disease (MCD), the expression steps down, which implied that the changes of synaptopodin expression in podocytes had a relationship with the damage of podocytes in glomerulonephritis, and also had a high correlation with the pathological types and changing degree of nephritis. Besides, we stimulated cultured podocytes by using inflammatory cytokines as TNF-α, ATS+serum, TGF-β1 and IL-1. The expression of synaptopodin we observed with the changes from decreased in early stages to little increased in late stage along with the stimulation time, which implied that the decreased synaptopodin expression was closely related with injury stimulation at first, then the little rise again mey be caused by regeneration and repairment of podocytes in inflammation. However, in the adriamycin stimulated cultured podocytes as well as in adriamycin nephropathy rats, the expression of synaptopodin was decreased, which indicated the damage induced by adriamycin on podocyte persisted.Some scholars pointed out that the RhoA pathway play an important role in regulating the cytoskeleton arrangement of neurons. To clarify if the RhoA pathway is involved in the regulation of podocyte cytoskeleton arrangement, we used Y-27632 the inhibitor of RhoA to block the RhoA pathway in podocyte and then stained the cytoskeleton F-actin. It was founf that the normal podocytical skeleton was destroyed in RhoA blocking cells, which proved that RhoA pathway was involved in the regulation of podocytical cytoskeleton arrangement. Then we inhibited the expression of synaptopodin by RNA interference, the expression of RhoA proteins decreased, meanwhile, the podocyte cytoskeleton structure changed, which confirmed synaptopodin regulated the podocyte cytoskeleton structure through RhoA pathway.In conclusion, there is a common mechanism in cytoplasm protrusion formation and cytoskeleton regulation between neurons and podocyte. Some neuronal iconic proteins also can be expressed in podocyte and play important roles in maintaining and regulating the podocyte’ process formation. The synaptopodin expression in all kinds of glomerulonephritis was found to be reduced significantly contrasted with normal renal samples. Synaptopodin regulated the podocyte cytoskeleton structure through RhoA pathway. Comparing the mechanism of process formation between two cells is instructive for us to get some useful guidance from the progresses of neuron research, further elucidate the mechanism of podocyte injury and explore the new therapeutic targets in nephrosis. |
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