Supplementary immunocytochemistry of hepatocyte growth factor production in activated macrophages early in muscle regeneration

Abstract

Regenerative intramuscular motor-innervation is thought to reside in the spatiotemporal expression of axon-guidance molecules. Our previous studies showed that resident myogenic stem cells, satellite cells, up-regulate a secreted neural-chemorepellent semaphorin 3A (Sema3A) during the early-differentiation period, in response to hepatocyte growth factor (HGF) elevated in injured muscle. However, a paracrine source of the HGF release is still unknown. Very recently, we proposed a possible contribution of anti-inflammatory macrophages (CD206-positive M2) by showing that M2 cells infiltrate predominantly at the early-differentiation phase (3-5 days post-injury) and produce/secrete large amounts of HGF. However, in understanding this concept there still remains a critical need to examine if phagocytotic pro-inflammatory macrophages (CD86-positive M1), another activated-phenotype still present at the early-differentiation phase concerned, produce HGF upon muscle injury. The current immunocytochemical study demonstrated that the HGF expression is negative for M1 prepared from cardiotoxin-injured Tibialis anterior muscle at day 5, in contrast to the intense fluorescent-signal of M2 served as a positive control. This supplementary result advances our understanding of a spatiotemporal burst of HGF secretion from M2 populations (not M1) to impact Sema3A expression, which ensures a coordinated delay in attachment of motoneuron terminals onto damaged and generating fibers during the early phase of muscle regeneration.

Transmembrane proteoglycans syndecan-2, 4, receptor candidates for the impact of HGF and FGF2 on semaphorin 3A expression in early-differentiated myoblasts

“…Although further studies are required to elucidate the detailed molecular mechanisms including SDC2, 4 phosphorylation upon ligand binding and the downstream signaling pathways, heparan and chondroitin sulfate chains are now expected to be primary elements of the HGF and FGF2 binding sites in SDC2, 4 ectodomains. The present findings, therefore, extend our understanding of a new concept of regenerative motoneuritogenesis that is centered on the functional coupling of M2 macrophages (a paracrine source of the ligand, HGF at the early differentiation phase; see Shono et al 2013;Sakaguchi et al 2014;Sawano et al 2014) with myoblasts (via activation of the SDC2, 4 receptor and induction of Sema3A secretion) and a motoneuron terminal (Sema3A target). This coupling of HGF/FGF2-SDC2, 4 and Sema3A may coordinate a delay in the attachment of motor neuron terminals onto damaged and regenerating new fibers early in myogenic repair, and thus synchronize the recovery of nerve-muscle integrity.…”

“…2014; Sawano et al. 2014) with myoblasts (via activation of the SDC2, 4 receptor and induction of Sema3A secretion) and a motoneuron terminal (Sema3A target). This coupling of HGF/FGF2-SDC2, 4 and Sema3A may coordinate a delay in the attachment of motor neuron terminals onto damaged and regenerating new fibers early in myogenic repair, and thus synchronize the recovery of nerve–muscle integrity.…”

Slow-Myofiber Commitment by Semaphorin 3A Secreted from Myogenic Stem Cells

“…Notably, our previous studies demonstrated that Sema3A secretion may occur in response to a burst of HGF secretion from anti‐inflammatory macrophages (CD206‐positive M2) that infiltrate regenerating muscle and recruit myoblasts to the injury site at 3–7 days post‐CTX injury. The M2 infiltration follows the rapid invasion of phagocytic pro‐inflammatory macrophages (CD86‐positive M1) immediately post‐injury . Together with these reports, the current investigation extends our understanding of the physiological significance of M2 macrophage‐satellite cell (myoblast) coupling in myogenic regeneration to include fiber‐type commitment in early‐differentiation, illustrated in the dashed‐line box in Figure , far left.…”

Macrophage and nerve interaction in endometriosis

“…They are proteins for axonal guidance including semaphorins and their plexin and neuropilin receptors [62], slit ligands and their roundabout (ROBO) receptors [80], and ephrins and their Eph receptors [81], etc. The axon-repulsive guidance factor, Sema3A, has been detected in the endometriotic lesion [62], and the regulation of Sema3A by M2 macrophage is already confirmed [82]. However, the co-existence of a nerve-repellent factor (Sema3A) and a nerve-promoting factor (NGF) in the lesion seems to be inconsistent with the nerve-sprouting phenomenon.…”