ACTA1 and polyarteritis nodosa: Calcitriol treatment was able to minimize the overexpression of FSP1 and α-SMA induced by PAN, suggesting that the beneficial effects of calcitriol supplementation on fibrogenesis were mediated, at least in part, by reduced fibroblast activation, although the origin of fibroblasts, either resident and/or infiltrating, was not determined in the present study.