Serendipitous Discovery of T Cell-Produced KLK1b22 as a Regulator of Systemic Metabolism.

In order to study mechanistic/mammalian target of rapamycin's role in T cell differentiation, we generated mice in which Rheb is selectively deleted in T cells (T-Rheb-/- C57BL/6J background). During these studies, we noted that T-Rheb-/- mice were consistently heavier but had improved glucose tolerance and insulin sensitivity as well as a marked increase in beige fat. Microarray analysis of Rheb-/- T cells revealed a marked increase in expression of kallikrein 1-related peptidase b22 (Klk1b22). Overexpression of KLK1b22 in vitro enhanced insulin receptor signaling, and systemic overexpression of KLK1b22 in C57BL/6J mice also enhances glucose tolerance. Although KLK1B22 expression was markedly elevated in the T-Rheb-/- T cells, we never observed any expression in wild-type T cells. Interestingly, in querying the mouse Immunologic Genome Project, we found that Klk1b22 expression was also increased in wild-type 129S1/SVLMJ and C3HEJ mice. Indeed, both strains of mice demonstrate exceptionally improved glucose tolerance. This prompted us to employ CRISPR-mediated knockout of KLK1b22 in 129S1/SVLMJ mice, which in fact led to reduced glucose tolerance. Overall, our studies reveal (to our knowledge) a novel role for KLK1b22 in regulating systemic metabolism and demonstrate the ability of T cell-derived KLK1b22 to regulate systemic metabolism. Notably, however, further studies have revealed that this is a serendipitous finding unrelated to Rheb.