Abstract
The anti-aging gene klotho plays an important role in Ca(2+) and phosphate homeostasis. Membrane-bound klotho is an essential coreceptor for fibroblast growth factor-23 and can be cleaved by proteases, including a disintegrin and metalloproteinase (ADAM)10 and ADAM17. Cleavage of klotho occurs at a site directly above the plasma membrane (alpha-cut) or between the KL1 and KL2 domain (beta-cut), resulting in soluble full-length klotho or KL1 and KL2 fragments, respectively. The aim of the present study was to gain insights into the mechanisms behind klotho cleavage processes in the kidney. Klotho shedding was demonstrated using a Madin-Darby canine kidney cell line stably expressing klotho and human embryonic kidney-293 cells transiently transfected with klotho. Here, we report klotho expression on both the basolateral and apical membrane, with a higher abundance of klotho at the apical membrane and in the apical media. mRNA expression of ADAM17 and klotho were enriched in mouse distal convoluted and connecting tubules. In vitro ADAM/matrix metalloproteinase inhibition by TNF484 resulted in a concentration-dependent inhibition of the alpha-cut, with a less specific effect on beta-cut shedding. In vivo TNF484 treatment in wild-type mice did not change urinary klotho levels. However, ADAM/matrix metalloproteinase inhibition did increase renal and duodenal mRNA expression of phosphate transporters, whereas serum phosphate levels were significantly decreased. In conclusion, our data show that renal cells preferentially secrete klotho to the apical side and suggest that ADAMs are responsible for alpha-cut cleavage.
