One major difference between limb and extraocular muscles (EOM) is the presence of an enriched population of Pitx2-positive myogenic precursor cells in EOM compared to limb muscle. We hypothesize that retinoic acid regulates Pitx2 expression in EOM myogenic precursor cells and that its effects would differ in leg muscle. The two muscle groups expressed differential retinoic acid receptor (RAR) and retinoid X receptor (RXR) levels. RXR co-localized with the Pitx2-positive cells but not with those expressing Pax7. EOM-derived and LEG-derived EECD34 cells were treated with vehicle, retinoic acid, the RXR agonist bexarotene, the RAR inverse agonist BMS493, or the RXR antagonist UVI 3003. In vitro, fewer EOM-derived EECD34 cells expressed desmin and fused, while more LEG-derived cells expressed desmin and fused when treated with retinoic acid compared to vehicle. Both EOM and LEG-derived EECD34 cells exposed to retinoic acid showed a higher percentage of cells expressing Pitx2 compared to vehicle, supporting the hypothesis that retinoic acid plays a role in maintaining Pitx2 expression. We hypothesize that retinoic acid signaling aids in the maintenance of large numbers of undifferentiated myogenic precursor cells in the EOM, which would be required to maintain EOM normalcy throughout a lifetime of myonuclear turnover.
Bibliographical noteFunding Information:
This work was supported by NIH EY55137 (LKM), NIH P30AR0507220 , NIH P30 EY11375 , Marzolf Scholarship (SLH) , NIDCR T32DE007288 (SLH), the Minnesota Lions Foundation , an unrestricted grant to the Department of Ophthalmology and Visual Neurociences from Research to Prevent Blindness, Inc . In addition, this work was supported in part by NIH P30 CA77598 utilizing the Masonic Cancer Center University of Minnesota Flow Cytometry Resource.
- Extraocular muscle
- Muscle stem cells
- Retinoic acid
- Retinoic acid signaling