α-Klotho Expression in Human Tissues

Context: alpha-Klotho has emerged as a powerful regulator of the aging process. To date, the expression profile of alpha-Klotho in human tissues is unknown, and its existence in some human tissue types is subject to much controversy. Objective: This is the first study to characterize system wide tissue expression of transmembrane alpha-Klotho in humans. We have employed next-generation targeted proteomic analysis using parallel reaction monitoring in parallel with conventional antibody-based methods to determine the expression and spatial distribution of human alpha-Klotho expression in health. Results: The distribution of alpha-Klotho in human tissues from various organ systems, including arterial, epithelial, endocrine, reproductive, and neuronal tissues, was first identified by immunohistochemistry. Kidney tissues showed strong alpha-Klotho expression, whereas liver did not reveal a detectable signal. These results were next confirmed by Western blotting of both whole tissues and primary cells. To validate our antibody-based results, alpha-Klotho-expressing tissues were subjected to parallel reaction monitoring mass spectrometry (data deposited at ProteomeXchange, PXD002775) identifying peptides specific for the full-length, transmembrane alpha-Klotho isoform. Conclusions: The data presented confirm alpha-Klotho expression in the kidney tubule and in the artery and provide evidence of alpha-Klotho expression across organ systems and cell types that has not previously been described in humans.