Relationships between nerves and myofibroblasts during cutaneous wound healing in the developing rat

Abstract

Contraction of skin excision wounds is affected by age and the presence of peripheral nerves. The present study examined relationships between peripheral innervation, wound contractile cells, and rate of wound closure to determine whether these are altered during development. Full-thickness 4-mm-diameter circular flaps were excised from the interscapular skin of rats on postnatal day (PND) 5, PND 12, or PND 60. Wounds of PND 5 and PND 12 rats contracted 45% between post-wound days (WD) 3 and 5 and more slowly thereafter, with a scar 9-14% of the original wound size by WD 21. In contrast, PND 60 wounds contracted only 22% between WD 3 and 5, and the residual scar at WD 21 was 40% of the original wound size. In younger rats, alpha-smooth muscle actin-immunoreactive myofibroblasts first appeared on WD 2 and attained maximum density at WD 5. Innervation, as assessed by protein gene product 9.5 immunoreactivity, appeared by WD 3 and increased rapidly through WD 7 in younger rats. In PND 60 wounds, myofibroblasts did not appear until WD 5 and did not attain a maximum until day 10. Nerve ingrowth was not significant until WD 10 and was depressed relative to younger rats throughout the healing phase. Wound nerves were predominantly immunoreactive to calcitonin gene-related peptide, and synaptophysin-immunostaining revealed close associations between varicosities and myofibroblasts. These findings suggest that wound myofibroblasts may be a target of peripheral nerves, and delayed wound closure in mature rats is associated with deficiencies in both myofibroblasts and innervation.

Sympathetic hyperinnervation and inflammatory cell NGF synthesis following myocardial infarction in rats

“…As the wound heals, numbers of inflammatory cells diminish in concert with formation of a stable scar (Hasan, et al, 2000). In addition, both cutaneous wounds and myocardial infarction display peri-wound hyperinnervation (Reynolds and Fitzgerald, 1995;Liu, et al, 1999), suggesting that this is a common feature associated with inflammatory cell proliferation during wound healing. However, cutaneous wounds exhibit hyperinnervation by sensory nociceptor CGRPir axons whereas sympathetic nerves avoid the wound (Reynolds and Fitzgerald, 1995;Liu, et al, 1999).…”

“…In addition, both cutaneous wounds and myocardial infarction display peri-wound hyperinnervation (Reynolds and Fitzgerald, 1995;Liu, et al, 1999), suggesting that this is a common feature associated with inflammatory cell proliferation during wound healing. However, cutaneous wounds exhibit hyperinnervation by sensory nociceptor CGRPir axons whereas sympathetic nerves avoid the wound (Reynolds and Fitzgerald, 1995;Liu, et al, 1999). In contrast, cardiac peri-infarct tissue is hyperinnervated by sympathetic nerves but sensory and parasympathetic axons are scarce.…”

Impaired cutaneous wound healing after sensory denervation in developing rats: effects on cell proliferation and apoptosis

“…Wound tissue contains a rich nerve supply (the 'cicatricial plexus') (Aldskogius et al 1987;Kishimoto et al 1981;Liu et al 1999;Marfurt et al 1993;Ramón y Cajal 1991;Reynolds and Fitzgerald 1995), and rendering innervation deficient through pathological or experimental means reportedly impairs healing of some types of cutaneous wounds (Basson and Burney 1982;Carr et al 1993;Engin et al 1996;Peskar et al 1995;Westerman et al 1993). There is accumulating evidence that sensory neuropeptides may mediate the actions of sensory nerves in wound repair, as healing is improved by their exogenous application (Engin 1998; and impaired by their depletion (Khalil and Helme 1996;Peskar et al 1995).…”

“…Sensory nerves associate closely with some wound cell types including endothelial cells, macrophages, and myofibroblasts, whose appearance within the wound precedes ingrowth of sensory nerves (Liu et al 1999;Manek et al 1993;Toriya et al 1997). Cutaneous wound macrophages and myofibroblasts both synthesize nerve growth factor (NGF) (Hasan et al 2000), a neurotrophic factor required for nociceptor nerve ingrowth into wound tissue (Reynolds et al 1997).…”

Normal and Pathologic Soft Tissue Remodeling: Role of the Myofibroblast, with Special Emphasis on Liver and Kidney Fibrosis

“…Neuropeptides also stimulate proliferation of endothelial cells and fibroblasts in vitro (Nilsson et al, 1986;Ziche et al, 1990) and the production of cytokines by keratinocytes (Song et al, 2000). In rats, myofibroblastic differentiation precedes nerve regeneration probably because myofibroblasts produce neurotrophic factors (Liu et al, 1999), evincing mutual stimulation between fibroblasts-myofibroblasts and nerve cells. In the absence of noradrenergic signaling induced by chemical denervation with the toxic 6-hydroxydopamine (OHDA), which induces degeneration of dopaminergic terminal fibers, the healing of incisional cutaneous lesions is impaired (Kim et al, 1998).…”