Fig. 1.

Activation and differentiation of muscle-resident satellite cells. Factors from local injury site activate quiescent satellite cells (1). Activated satellite cells and factors secreted by injured muscle attract monocyte into site of damage (2). Under environmental signal monocyte differentiates into M1 (pro-inflammatory) or M2 (supportive for muscle regeneration) macrophages (2). Activated satellite cells shift into differentiation cascade via committed MyoD⁺ cells (3) into myoblasts expressing myogenin. Non-satellite cells FAP/MSC and PICs secrete trophic factors into environment (4) supporting committed MyoD⁺ satellite cells activity. After proliferation and terminal differentiation myoblasts fuse to pre-existing injured myofibre or fuse one to another to form new myotubes, thus completing regenerative process (5). Quiescent satellite cell pool is renewed. FKN: fractalkine; MCP-1: monocyte chemotactic protein 1