title: Defective autophagy in vascular smooth muscle cells alters contractility and Ca²⁺ homeostasis in mice.
abstract: Autophagy is an evolutionary preserved process that prevents the accumulation of unwanted cytosolic material through the formation of autophagosomes. Although autophagy has been extensively studied to understand its function in normal physiology, the role of vascular smooth muscle (SM) cell (VSMC) autophagy in Ca(2+) mobilization and contraction remains poorly understood. Recent evidence shows that autophagy is involved in controlling contractile function and Ca(2+) homeostasis in certain cell types. Therefore, autophagy might also regulate contractile capacity and Ca(2+)-mobilizing pathways in VSMCs. Contractility (organ chambers) and Ca(2+) homeostasis (myograph) were investigated in aortic segments of 3.5-mo-old mice containing a SM cell-specific deletion of autophagy-related 7 (Atg7; Atg7(fl/fl) SM22α-Cre(+) mice) and in segments of corresponding control mice (Atg7(+/+) SM22α-Cre(+)). Our results indicate that voltage-gated Ca(2+) channels (VGCCs) of Atg7(fl/fl) SM22α-Cre(+) VSMCs were more sensitive to depolarization, independent of changes in resting membrane potential. Contractions elicited with K(+) (50 mM) or the VGCC agonist BAY K8644 (100 nM) were significantly higher due to increased VGCC expression and activity. Interestingly, the sarcoplasmic reticulum of Atg7(fl/fl) SM22α-Cre(+) VSMCs was enlarged, which, combined with increased sarco(endo)plasmic reticulum Ca(2+)-ATPase 2 expression and higher store-operated Ca(2+) entry, promoted inositol 1,4,5-trisphosphate-mediated contractions of Atg7(fl/fl) SM22α-Cre(+) segments and maximized the Ca(2+) storing capacity of the sarcoplasmic reticulum. Moreover, decreased plasma membrane Ca(2+)-ATPase expression in Atg7(fl/fl) SM22α-Cre(+) VSMCs hampered Ca(2+) extrusion to the extracellular environment. Overall, our study indicates that defective autophagy in VSMCs leads to an imbalance between Ca(2+) release/influx and Ca(2+) reuptake/extrusion, resulting in higher basal Ca(2+) concentrations and significant effects on vascular reactivity.
authors.affiliation: Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium.
authors.forename: Cédéric F
authors.initials: CF
authors.lastname: Michiels
authors.affiliation: Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium.
authors.forename: Paul
authors.initials: P
authors.lastname: Fransen
authors.affiliation: Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium.
authors.forename: Dorien G
authors.initials: DG
authors.lastname: De Munck
authors.affiliation: Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium.
authors.forename: Guido R Y
authors.initials: GR
authors.lastname: De Meyer
authors.affiliation: Laboratory of Physiopharmacology, University of Antwerp, Antwerp, Belgium wim.martinet@uantwerpen.be.
authors.forename: Wim
authors.initials: W
authors.lastname: Martinet
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D000071193:Autophagy-Related Protein 7; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005260:Female; D006706:Homeostasis; D015640:Ion Channel Gating; D008297:Male; D008564:Membrane Potentials; D018345:Mice, Knockout; D008869:Microtubule-Associated Proteins / Q000172:deficiency / Q000235:genetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000473:pathology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: C502661:Atg7 protein, mouse; D002120:Calcium Channel Agonists; D015220:Calcium Channels; D008869:Microtubule-Associated Proteins; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000071193:Autophagy-Related Protein 7; D002118:Calcium
keywords: autophagy; calcium homeostasis; contractility; sarcoplasmic reticulum; vascular smooth muscle cells