Assessing the contribution of thrombospondin-4 induction and ATF6 alpha activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

作者：Krawczyk Katarzyna K; Ekman Mari; Rippe Catarina; Grossi Mario; Nilsson Bengt Olof; Albinsson Sebastian; Uvelius Bengt; Sward Karl^*

来源：Scientific Reports, 2016, 6(1): 32449.

DOI：10.1038/srep32449

Phenotypic modulation of smooth muscle cells is a hallmark of disease. The associated expansion of endoplasmic reticulum (ER) volume remains unexplained. Thrombospondin-4 was recently found to promote ATF6 alpha activation leading to ER expansion. Using bladder outlet obstruction as a paradigm for phenotypic modulation, we tested if thrombospondin-4 is induced in association with ATF6 alpha activation and ER expansion. Thrombospondin-4 was induced and ATF6 alpha was activated after outlet obstruction in rodents. Increased abundance of spliced of Xbp1, another ER-stress sensor, and induction of Atf4 and Creb3l2 was also seen. Downstream of ATF6 alpha, Calr, Manf, Sdf2l1 and Pdi increased as did ER size, whereas contractile markers were reduced. Overexpression of ATF6 alpha, but not of thrombospondin-4, increased Calr, Manf, Sdf2l1 and Pdi and caused ER expansion, but the contractile markers were inert. Knockout of thrombospondin-4 neither affected bladder growth nor expression of ATF6 alpha target genes, and repression of contractile markers was the same, even if ATF6 alpha activation was curtailed. Increases of Xbp1s, Atf4 and Creb3l2 were similar. Our findings demonstrate reciprocal regulation of the unfolded protein response, including ATF6 alpha activation and ER expansion, and reduced contractile differentiation in bladder outlet obstruction occurring independently of thrombospondin-4, which however is a sensitive indicator of obstruction.

• 出版日期2016-9-1