Commitment of Satellite Cells Expressing the Calcium Channel α2δ1 Subunit to the Muscle Lineage

Abstract

Satellite cells can maintain or repair muscle because they possess stem cell properties, making them a valuable option for cell therapy. However, cell transplants into skeletal muscle of patients with muscular dystrophy are limited by donor cell attachment, migration, and survival in the host tissue. Cells used for therapy are selected based on specific markers present in the plasma membrane. Although many markers have been identified, there is a need to find a marker that is expressed at different states in satellite cells, activated, quiescent, or differentiated cell. Furthermore, the marker has to be present in human tissue. Recently we reported that the plasma membrane α2δ1 protein is involved in cell attachment and migration in myoblasts. The α2δ1 subunit forms a part of the L-type voltage-dependent calcium channel in adult skeletal muscle. We found that the α2δ1 subunit is expressed in the majority of newly isolated satellite cells and that it appears earlier than the α1 subunits and at higher levels than the β or γ subunits. We also found that those cells that expressed α2δ1 would differentiate into muscle cells. This evidence indicates that the α2δ1 may be used as a marker of satellite cells that will differentiate into muscle.

Temporal Expression of Calcium Channel Subunits in Satellite Cells and Bone Marrow Mesenchymal Cells

“…The early appearance of α2δ1 in MSC is consistent with our previous studies with satellite cells, where this subunit was the first one to be expressed [7]. As with satellite cells, this suggests that α2δ1 may have other functions independent from calcium channels in MSC as well.…”

“…In summary, our data show that the α2δ1 subunit is the first subunit of calcium channels expressed in MSC and confirms our previous results with satellite cells [7], suggesting that the α2δ1 subunit may be involved in signaling mechanisms that do not involve ion channels. We also showed that the mRNA and protein of several α1 subunits is expressed simultaneously in the same cell type, but that the recorded calcium currents have predominantly characteristics of the slowly-activating skeletal type current.…”

“…Whereas the α2δ1 subunit showed only a 4-fold (control MSC) or 8-fold (BMP4-treated MSC) increase at D12 compared to D0, the β subunit increased by more than 20-fold under both conditions at D12 compared to D0 and the γ subunit increased by more than 80-fold (control MSC) or 120-fold (BMP4-treated MSC) after D12. The ratios of increase of the associated subunits in MSC resemble those previously reported for satellite cells [7] although the nature of the α1 subunit is different between satellite cells (Ca v 1.1) and MSC (Ca v 1.2).…”

“…Interestingly, the subunits of skeletal muscle L-type calcium channel are not expressed simultaneously during differentiation of myotubes in vitro. We have shown that the α2δ1 subunit is the first one to be expressed in freshly dissociated satellite cells and is followed by expression of the α1, β, and γ subunits [6,7]. Further, we have shown that more than 50 % of freshly isolated satellite cells express α2δ1 subunit and that these cells commit to the muscle lineage to form myotubes [7].…”

“…Table 2 shows a comparison between the RNA expression of calcium channel subunits in satellite cells with those of MSC at the beginning of differentiation in 2 % serum (D0). Results were normalized with respect to the α2δ1 expression in satellite cells since we have shown that this subunit is present in freshly dissociated cells [7]. The table shows that α2δ1 expression in satellite cells was nearly 1.4 times higher than in MSC.…”