Ubiquitous localization of leukotriene A4 hydrolase in the rat nephron

Background. Leukotriene (LT) B-4 is a well-known inflammatory mediator and is implied to play some roles in gromerulonephritis. Although LTA(4) hydrolase, a final-step key enzyme to produce LTB4, is located in glomerular mesangial cells, as well as in leukocytes, platelets, and endothelial cells, its precise distribution in the kidney other than in mesangial cells remains unknown. Therefore, we have investigated the localization of mRNA, protein, and enzyme activity of LTA(4) hydrolase in the rat kidney. Methods. Microdissection reverse transcriptase-polymerase chain reaction was used for the determination of LTA(4) hydrolase mRNA. The enzyme protein was detected by Western blot, and immunohistochemistry was performed. Finally, LTA(4) hydrolase activity and LTB4 were assayed in kidney tissues. Results. LTA(4) hydrolase mRNA was detectable in all microdissected nephron segments of the cortex and outer medulla. The corresponding size of similar to 70 kDa protein was shown in descending order in the inner medullary > outer medullary greater than or equal to cortical homogenates. The immunohis tochemical study demonstrated the ubiquitous presence of the enzyme in all nephron segments of cortex, outer medulla, and inner collecting tubules. LTA(4) hydrolase activity was detected in the inner medullary greater than or equal to outer medullary > cortical tissue homogenates. LTB4 was demonstrated in the inner medullary > outer medullary cortical tissues during the basal condition, and was time-dependently increased by stimulation with arachidonic acid and ionomycin in the cytosolic fraction from outer medulla and in the glomerular suspension. Conclusions. These results strongly suggest that renal tubular cells as well as glomerular cells have an LTB4-forming potency, which may participate in physiological and pathophysiological roles in the kidney.