Résumés disponibles (92) :

BOULINGUIEZ Alexis (INSERM U1011 éq. 01 - Steve LANCEL)
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@mail :  alexis.boulinguiez-2@etu.univ-lille2.fr      tél. :  0640132044

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Titre de la communication :
Rev-erb-α regulates skeletal muscle unfolded protein response by controlling calcium homeostasis
Auteurs (et leurs adresses) de la communication :
Boulinguiez Alexis, Duhem Christian, Mayeuf-Louchart Alicia, Pourcet Benoit, Sebti Yasmine, Delhaye Stéphane, Zecchin Mathilde, Thorel Quentin, Staels Bart, Duez Hélène, Lancel Steve Univ. Lille-Inserm-CHU Lille-Institut Pasteur de Lille-U1011-EGID
Résumé de la communication :
Background: Calcium is crucial for skeletal muscle contraction but also for proper protein folding, which occurs in the intracellular calcium storage compartment called the Sarcoplasmic Reticulum (SR). The Sarcoplasmic-Endoplasmic Calcium ATPase (SERCA) reuptakes calcium from cytosol to SR. Its activity is controlled by several inhibitory peptides, among which myoregulin that is highly expressed in skeletal muscle. Alterations in both calcium handling and protein folding have been described in the context of aging, metabolic diseases and myopathies.
Our team previously reported that the nuclear receptor Rev-erb-α promotes exercise capacity by enhancing mitochondrial biogenesis and reducing mitophagy. Nevertheless, its role on skeletal muscle calcium homeostasis and the Unfolded Protein Response (UPR) has never been explored.
Hypothesis: Rev-erb-α, by modulating calcium homeostasis, affects SR stress-response in skeletal muscle.

Methods: To test the effects of Rev-erb-α on calcium homeostasis, SERCA activity in microsomes isolated from gastrocnemius of wild-type and Rev-erb-α knockout mice and SR calcium content in C2C12 myotubes over-expressing Rev-erb-α were measured by the use of calcium green and fluo4-AM, respectively. To test the effects of chronic calcium depletion on SR stress-induced UPR, we treated 1h/day for two weeks C2C12 myotubes with a low dose (100nM) of the SERCA inhibitor thapsigargin, and then evaluated by RTqPCR and western-blot the effects of tunicamycin, a N-glycosylation inhibitor triggering SR stress. Then, tunicamycin was either injected in gastrocnemius muscle or added in the culture media to evaluate the effects of Rev-erb-α on SR stress-induced UPR. Finally, by ChIP-qPCR, we searched for new target genes of Rev-erb-α that could explain its effects on calcium homeostasis and UPR.

Results: SERCA activity is decreased in gastrocnemius muscle of Rev-erb-α knockout mice. In response to tunicamycin, chronic thapsigargin pretreatment in C2C12 myotubes causes lower induction of UPR gene expression (Grp78, Gadd34, Atf4, Atf6, Xbp1s, Chop) as well as CHOP and BIP protein, ATF6 cleavage and IRE-1 phosphorylation. This phenotype is recapitulated in tunicamycin injected-gastrocnemius muscle of Rev-erb-α knockout mice. By contrast, Rev-erb-α overexpressing cells present higher SR calcium content and exacerbation of tunicamycin-induced UPR. We find that Rev-erb-α binds to the myoregulin promotor and inhibits its transcription. Finally, myoregulin overexpression in C2C12 myotubes is able to partially counteract the Rev-erb-α overexpression consequences on calcium homeostasis and UPR.

Conclusion: Rev-erb-α controls calcium homeostasis and UPR in skeletal muscle by repressing the SERCA inhibitor myoregulin. Further studies will determine whether calcium and UPR modulation by pharmacological Rev-erb-α ligands improves skeletal muscle function in models of aging, metabolic diseases and myopathies.

BOULINGUIEZ Alexis (INSERM U1011 éq. 01 - Steve LANCEL)