Interleukin 1-beta decreases myoblast fusion in vitro

During times of stress, systemic pro-inflammatory cytokine levels are increased, which may prevent optimal growth and development of muscle and/or induce muscle atrophy. Pro-inflammatory cytokines can induce negative responses in muscle by altering the balance of protein synthesis and degradation in established myofibers, or by influencing the proliferation and differentiation of myoblasts. Interleukin-1 beta (IL-1β) is a pro-inflammatory cytokine involved in stress and disease responses, but little is known about how IL-1β affects myoblast function. We hypothesized that IL-1β would decrease myoblast proliferation and/or differentiation. To test this hypothesis, C2C12 mouse myoblasts were treated with 0.1 ng/mL or 1.0 ng/mL of IL-1β, or carrier only (control). To determine proliferation rate, myoblasts were plated at 2.6x103 cells/cm2 and cultured for 48 h in the presence or absence of IL-1β. Cells were pulsed with bromodeoxyuridine (BrdU), fixed, and immunostained. The number of BrdU positive cells was quantified as a percent of total nuclei (identified by Hoescht 33342). To determine if IL-1β affected fusion, myoblasts were plated at 2.0x104 cells/cm2 in growth media for 48 h at which time media was changed into differentiation media supplemented with 0.