Erdr1 Drives Macrophage Programming via Dynamic Interplay with YAP1 and Mid1.

Erythroid differentiation regulator 1 (Erdr1) is a stress-induced, widely expressed, highly conserved secreted factor found in both humans and mice. Erdr1 is linked with the Hippo-YAP1 signaling. Initially identified as an inducer of hemoglobin synthesis, Erdr1 emerged as a multifunctional protein, especially in immune cells. Although Erdr1 has been implicated in regulating T cells and NK cell function, its role in macrophage remains unclear. This study explored the function and mechanism of Erdr1 in macrophage inflammatory response. The data demonstrated that Erdr1 could promote anti-inflammatory cytokine production, a function that also has been reported by previous research. However, I found Erdr1 also could play a proinflammatory role. The function of Erdr1 in macrophages depends on its dose and cell density. I observed that Erdr1 expression was inhibited in M1 macrophages but was upregulated in M2 macrophages compared with unpolarized macrophages. I hypothesized that Erdr1 balances the inflammatory response by binding with distinct adaptors dependent on varying concentrations. Mechanistically, I demonstrated YAP1 and Mid1 as the two adaptor proteins of Erdr1. The Erdr1-YAP1 interaction promotes anti-inflammatory cytokine production when Erdr1 levels are elevated, whereas the Erdr1-Mid1 interaction induces proinflammatory cytokine production when Erdr1 levels are decreased. This study highlights the effects of Erdr1 on regulating cytokine production from polarized macrophages potentially by regulating YAP1 in the nonclassical Hippo pathway.