The commonly used antibiotic streptomycin reduces protein synthesis and differentiation in cultured C2C12 myotubes.

The antibiotic streptomycin is an integral part of cell culture medium. Because streptomycin inhibits bacterial protein synthesis, streptomycin might also have off-target effects on muscle cell function. Here, we studied the effect of streptomycin on C2C12 myoblasts, myofiber growth, and metabolism. C2C12 myoblasts were cultured with or without streptomycin. The control condition consisted of carbenicillin and ampicillin. Streptomycin did not impair myoblast proliferation rate. Streptomycin exposure led to a ~ 40% reduction in myotube diameter and reduced protein synthesis rate. Myotubes with streptomycin showed a 25% lower differentiation and 60% lower fusion index. Expression of cell stress markers was upregulated by streptomycin. Mitochondrial respiration rate was unaffected by streptomycin, but gene expression levels of Myh3 and Acta1 were lower, as well as the protein content of mitochondrial complex I subunits. Myotubes cultured in the presence of streptomycin showed fragmentation of the mitochondrial network, a smaller mitochondrial footprint (-64%), and shorter branch lengths (-34%). Streptomycin does not alter C2C12 myoblast proliferation but reduces global protein synthesis rates in differentiating myotubes. The routine use of streptomycin in muscle cell cultures should be carefully evaluated, particularly when investigating muscle growth, metabolism, or protein synthesis, where off-target effects may confound experimental outcomes.