Effect of a 24h corticosterone treatment on differentiated C2C12 myotubes
Long term glucocorticoïds treatment, e.g. corticosterone, induces insulin resistance in vivo and in vitro.  In vivo insulin resistance can trigger pancreatic beta cells adaptation in order to maintain glycemia. In particular, we observed that beta-cell mass adaptation can occur via beta-cell proliferation or via beta-cell neogenesis (de novo beta-cell production). Further, we demonstrated that beta-cell neogenesis was not a direct effect of GC, but rather due to the presence of pro-neogenic factors in the serum of GC-treated mice, suggesting a communication in-between insulin resistant tissues and the pancreas (Courty et al., Diabetes, 2019). Hence, the present work aims to decipher the role of the skeletal muscle in pancreatic adaptation in response to insulin resistance. We used an in vitro modeling in-between C2C12 differentiated myotubes treated for 24h with corticosterone (10-7M) or the same volume of solvant ethanol (VEH). Conditioned medium from corticosterone treated cells was tested on pancreatic buds E11.5 and proven to enhance beta-cell and other pro-endocrine lineage cellular differentiation in comparison to VEH conditioned medium. Subsequently, we analyzed the transcriptome of the C2C12 myotubes (n=3 per condition) using RNAsequencing (Illumina, NOVAseq 6000, 150bp paired-end sequencing). We found an enrichement for genes coding for secreted proteins in the CORT-treated myotubes. We narrowed down to 4 myokines candidates and validated the pro-neogenic potential of the candidate myokines using pancreatic buds E11.5 treated with recombinant proteins. Overall design: 3 replicates of C2C12 differentiated myotubes (below passage 7) were treated for 24h with either Corticosterone 10-7M or corresponding volumes (1uL/mL) of ethanol 100%. We then performed RNAseq analysis on 3 independant biological replicates per condition, using Illumina NOVAseq 6000 sequencer, 150bp paired end sequencing. We compared differentially expressed genes in-between CORT- or VEH- treated cells.