The Matricellular Protein CCN1 in Wound Healing

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PROJECT SUMMARY In an environment replete with microbial invaders, mammals must mount a successful defense against microbes in cutaneous wounds, trauma, and tissue injury. Staphylococcus aureus and Pseudomonas aeruginosa are the most common bacteria isolated from chronic skin wounds and among the most prominent pathogens in community-acquired and nosocomial infections, and these organisms readily develop antibiotic resistance. The matricellular protein CCN1 has recently emerged as an important multifunctional regulator of the wound healing process. CCN1 directly induces myofibroblast senescence through integrin α6β1 in the maturation phase of wound repair, thereby initiating matrix remodeling and dampening fibrosis. Recent studies have uncovered additional unexpected but critical activities of CCN1 in wound repair: (1) CCN1 acts as a bridging molecule and triggers the phagocytic removal of apoptotic neutrophils in wounds, resulting in resolution of inflammation and allowing healing to proceed. (2) CCN1 promotes clearance of S. aureus and P. aeruginosa by inducing their phagocytosis by macrophages and neutrophils. Bacterial clearance is impaired in knockin mice expressing a CCN1 mutant unable to bind integrin αvβ3/αvβ5, and accelerated in mice injected with purified CCN1 protein. Moreover, treatment of excisional wounds with purified CCN1 protein accelerates closure in diabetic mice. Based on these findings, we hypothesize that CCN1 is a multifunctional protein that regulates disparate aspects of wound healing, including clearance of infecting microbes, resolution of inflammation, and indirectly lead to enhanced granulation tissue formation. We will scrutinize this hypothesis in three specific aims: Aim 1 evaluates the role of CCN1 in bacterial clearance in animal models of infection; Aim 2 dissects the molecular mechanism of CCN1 action in bacterial clearance; and Aim 3 investigates how CCN1 accelerates diabetic wound healing. Together, these studies will illuminate the mechanism of a novel arsenal in innate immunity against microbial invaders and may prompt new approaches toward the management of antibiotic-resistant infections and chronic non-healing wounds.