Nerve growth factor (NGF) and NGF-receptor expression in diseased human kidneys

BACKGROUND: Nerve growth factor (NGF) has been indicated to be critical to normal renal development in rodents. However, little is known about the expression of NGF and the high-affinity NGF receptors in human kidneys which is essential for promoting the biological and functional activities of NGF. The present study examined the presence of NGF, low-affinity (p75) and high-affinity tyrosine kinase A (TrkA) NGF receptor (NGFR) immunoreactivity in diseased human kidneys. METHODS: Renal biopsies were performed in 24 patients (11 females and 13 males, ranging from 12 to 78 years of age), with various renal diseases. Kidney biopsy samples were fixed in Bouin fluid for 24 hours, washed, dehydrated, embedded in paraplast sections (3-micron thick) and immunostained for NGF, TrkA and p75 localization. Immunostained sections were evaluated under a Nikon Eclipse E600 microscope equipped with a x20 objective and a Nikon DMX 1200 digital camera connected to a PC computer, with the aid of a computerized image analysis system. RESULTS: The results demonstrate the existence of NGF and TrkA in tubular and glomerular cells and of p75-positivity in the interstitial and mesangial cells. It also shows colocalization of TrkA and NGF, but not TrkA and p75 in tubular and glomerular cells, implying that the synthesis and utilization of NGF might be autocrinally regulated. CONCLUSIONS: These findings suggest that NGF signaling may be important in human kidney and glomerular response to injury, though to understand the precise functional significance of these NGF elements in the human kidney, further studies need to be done.