GPR39 expressed by thymic ECs is the central mediator of Zn-centered regeneration. (A) exECs were stimulated for 24 hours with ZnSO4 (100 μM) with or without the Zn ionophor pyrythione. Bmp4 expression was measured by qPCR (n = 6 combined from 2 independent experiments). (B) GPR39 expression across subsets in the thymus by flow cytometry at baseline. Displayed are concatenated plots from 1 experiment. (C) Expression of GPR39 on cTECs, mTECs, ECs, and fibroblasts at days 0, 4, and 7 after TBI. Displayed are concatenated plots from 1 experiment. (D) exECs were stimulated for 24 hours with ZnSO4 (100 μM) with or without the ERK inhibitor FR180204. BMP4 was measured by ELISA. (E) ERK phosphorylation in situ assessed at steady state and at day 4 in thymus after TBI (550 cGy) in 6-week-old female C57BL/6 mice. pERK is shown in green, DAPI for nuclear staining in blue. (F) Average quantification of pERK intensity/region of interest (ROI) in thymuses at day 0 and day 4 after SL-TBI. (G) GPR39 expression was silenced in exECs by siRNA and stimulated for 24 hours with ZnSO4 (100 μM), after which Bmp4 expression was measured by qPCR (n = 3/group). (H) Bmp4 expression in exEC cultured for 24 hours in presence of ZnSO4 (100 μM) and/or the GPR39 agonist TC-G1008 (25 μM) (n = 5-15 combined from 5 independent experiments). Graphs represent mean ± SEM; each dot represents a biologically independent observation. *P < .05; **P < .01; ***P < .001.