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. Author manuscript; available in PMC: 2017 Oct 26.
Published in final edited form as: Vitam Horm. 2016 Mar 24;101:257–310. doi: 10.1016/bs.vh.2016.02.007

Fig. 1.

Fig. 1

Source of circulatory αKlotho. αKlotho protein is expressed in a few organs, but the kidney is a main resource of circulating αKlotho under physiological conditions. The contribution of parathyroid gland and brain is not clear. Both renal proximal (PT) and distal tubules (DT) express membrane αKlotho protein and may also produce a secreted αKlotho protein which only contains kl1 domain and is directly secreted into the blood circulation. Extracellular domain of membrane αKlotho-containing kl1 and kl2 repeats is shed and cleaved by α and β-secretases, and released into the blood circulation.