Assessing the contribution of thrombospondin-4 induction and ATF6α activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

Katarzyna K Krawczyk; Mari Ekman; Catarina Rippe; Mario Grossi; Bengt-Olof Nilsson; Sebastian Albinsson; Bengt Uvelius; Karl Swärd

doi:10.1038/srep32449

Assessing the contribution of thrombospondin-4 induction and ATF6α activation to endoplasmic reticulum expansion and phenotypic modulation in bladder outlet obstruction

Sci Rep. 2016 Sep 1:6:32449. doi: 10.1038/srep32449.

Authors

Katarzyna K Krawczyk¹, Mari Ekman¹, Catarina Rippe¹, Mario Grossi¹, Bengt-Olof Nilsson¹, Sebastian Albinsson¹, Bengt Uvelius², Karl Swärd¹

Affiliations

¹ Department of Experimental Medical Science, Lund University, Lund, Sweden.
² Department of Urology, Clinical Sciences, Lund University, Lund, Sweden.

Abstract

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 ATF6α 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 ATF6α activation and ER expansion. Thrombospondin-4 was induced and ATF6α 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 ATF6α, Calr, Manf, Sdf2l1 and Pdi increased as did ER size, whereas contractile markers were reduced. Overexpression of ATF6α, 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 ATF6α target genes, and repression of contractile markers was the same, even if ATF6α activation was curtailed. Increases of Xbp1s, Atf4 and Creb3l2 were similar. Our findings demonstrate reciprocal regulation of the unfolded protein response, including ATF6α 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.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Activating Transcription Factor 4 / genetics
Activating Transcription Factor 4 / metabolism
Activating Transcription Factor 6 / genetics*
Activating Transcription Factor 6 / metabolism
Animals
Basic-Leucine Zipper Transcription Factors / genetics
Basic-Leucine Zipper Transcription Factors / metabolism
Calbindin 2 / genetics
Calbindin 2 / metabolism
Disease Models, Animal
Endoplasmic Reticulum / metabolism*
Endoplasmic Reticulum / ultrastructure
Endoplasmic Reticulum Stress / genetics
Female
Gene Expression Regulation
Membrane Proteins / genetics
Membrane Proteins / metabolism
Mice
Mice, Knockout
Myocytes, Smooth Muscle / metabolism*
Myocytes, Smooth Muscle / pathology
Nerve Growth Factors / genetics
Nerve Growth Factors / metabolism
Primary Cell Culture
Rats
Rats, Sprague-Dawley
Signal Transduction
Thrombospondins / deficiency
Thrombospondins / genetics*
Unfolded Protein Response*
Urethra / surgery
Urinary Bladder Neck Obstruction / genetics*
Urinary Bladder Neck Obstruction / metabolism
Urinary Bladder Neck Obstruction / pathology
X-Box Binding Protein 1 / genetics
X-Box Binding Protein 1 / metabolism

Substances

Activating Transcription Factor 6
Atf4 protein, rat
Atf6 protein, mouse
Basic-Leucine Zipper Transcription Factors
Calb2 protein, rat
Calbindin 2
Creb3l2 protein, mouse
MANF protein, rat
Membrane Proteins
Nerve Growth Factors
Thrombospondins
X-Box Binding Protein 1
Xbp1 protein, rat
sdf2l1 protein, mouse
thrombospondin 4
Activating Transcription Factor 4