Background. We previously reported that the expression of mitogen-activated protein kinases (MAPKs) is developmentally regulated. Dysregulation of MAPKs may lead to kidney malformation. Thus, we investigated the expression of MAPKs in human renal dysplasia, one of the most common kidney malformations. Methods. Prenatal (gestational ages 20 to 36 weeks, N = 6) and postnatal (2 years old, N = 1) dysplastic kidneys, and normal kidneys (gestational ages 19 to 34 weeks, N = 4) were examined. Immunohistochemical studies were performed using antibodies against extracellular signal-regulated kinase (ERK), p38 MAPK (p38), c-Jun N-terminal kinase (JNK), phospho-MAPKs (P-MAPKs), and proliferating cell nuclear antigen (PCNA). Apoptosis was detected by the TUNEL method. Results. In dysplastic kidneys, proliferation was prominent in dysplastic tubules and also found in cyst epithelia. TUNEL staining was detected in dysplastic tubules and cysts, and occasionally in undifferentiated cells. p38 and anti-phospho-p38 (P-p38) were strongly expressed in dysplastic epithelia, but not detected in normal kidneys at any stage examined. On the other hand, JNK and P-JNK were positive in tubular epithelia of normal kidneys, whereas their expression was barely detectable in dysplastic tubules and cysts. ERK was expressed in all tubular segments, and P-ERK was detected in distal tubules and collecting ducts of normal kidneys. Dysplastic kidney epithelia stained exclusively positive for ERK and P-ERK. Conclusions. p38 is ectopically expressed, and JNK is down-regulated in dysplastic kidney epithelia. Furthermore, dysplastic epithelia are exclusively positive for ERK and P-ERK. Activated p38 and ERK may mediate hyperproliferation of dysplastic tubules resulting in cyst formation, whereas down-regulated JNK expression may be the cause or the result of an undifferentiated state of dysplastic epithelia.
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