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. 2013 Feb:28:44-8.
doi: 10.1016/j.bbi.2012.10.016. Epub 2012 Oct 24.

MMP-8 overexpression and persistence of neutrophils relate to stress-impaired healing and poor collagen architecture in mice

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MMP-8 overexpression and persistence of neutrophils relate to stress-impaired healing and poor collagen architecture in mice

Praveen K Gajendrareddy et al. Brain Behav Immun. 2013 Feb.

Abstract

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) are critical for tissue remodeling during wound repair. Psychological stress has been found to impair wound healing in humans and animals. The objective of this study was to assess MMP and TIMP gene expression during stress-impaired healing. Female SKH-1 mice (n=299) were divided into control and stress groups (13h restraint/day for 3days prior to and 5days post-wounding). Two 3.5mm cutaneous full-thickness wounds were placed on the dorsum of each mouse and wound measurements were performed daily. RT-PCR for gene expression of MMP-2, MMP-8, MMP-9, TIMP-1 and TIMP-2 was performed at days 1, 3 and 5. Immunohistochemical analyses of the healed wounds were performed at days 15 and 28. As expected, wounds healed more slowly in restraint-stressed mice compared to controls. Stressed mice exhibited MMP-8 overexpression and lower TIMP-1 levels during healing, and poorer collagen organization once healed. MMP-8 overexpression may have stemmed from a higher level of neutrophils, observed in wound tissue on days 3 and 5. These findings implicate higher neutrophil numbers, MMP-8 overexpression, and TIMP-1 under-expression, as mechanisms that may compromise wound outcomes such as scarring under conditions of stress.

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Figures

Fig. 1
Fig. 1
(A) Wound size ratios over 5 days post-wounding. (B) Relative gene expression for MMP-8 in wounded tissue. (C) Neutrophil levels during dermal healing. In (C) excised wound tissue was subjected to myeloperoxidase (MPO) extraction, MPO was quantified by a colorimetric assay and expressed as units of MPO/gram of wound tissue. Data represent mean ± SEM. *p < .05 compared to FWD. **p < 0.05 compared to FWD and RST/VEH, ***p < .001, #p = .092.
Fig. 2
Fig. 2
Picrosirius red staining for collagen deposition (shown at 40 × magnification): (A) FWD at 2 weeks. (B) RST at 2 weeks. (C) FWD at 4 weeks. (D) RST at 4 weeks. In the non-stress group, fibers were more clearly arranged and symmetrical both at 2 and 4 week assessments, demonstrating superior collagen organization in healed tissue.

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