Mice that lack matrix metalloproteinase-9 display delayed wound healing associated with delayed reepithelization and disordered collagen fibrillogenesis.

Matrix metalloproteinase- (MMP-9) is involved in processes that occur during cutaneous wound healing such as inflammation, matrix remodeling, and epithelialization, To investigate its role in healing, full thickness skin wounds were made in the dorsal region of MMP-9-null and control mice and harvested up to 14 days post wounding. Gross examination and histological and immunohistochemical analysis indicated delayed healing in MMP-9-null mice. Specifically, MMP-9-null wounds displayed compromised reepithelialization and reduced clearance of fibrin clots. In addition, they exhibited abnormal matrix deposition, as evidenced by the irregular alignment of immature collagen fibers. Despite the presence of matrix abnormalities, MMP-9-null wounds displayed normal tensile strength. Ultrastructural analysis of wounds revealed the presence of large collagen fibrils, some with irregular shape. Keratinocyte proliferation, inflammation, and angiogenesis were found to be normal in MMP-9-null wounds. In addition, VEGF levels were similar in control and MMP-9-null wound extracts. To investigate the importance of MMP-9 in wound reepithelialization we tested human and murine keratinocytes in a wound migration assay and found that antibody-based blockade of MMP-9 function or MMP-9 deficiency retarded migration. Collectively, our observations reveal defective healing in MMP-9-null mice and suggest that MMP-9 is required for normal progression of wound closure.

A model for studying epithelial attachment and morphology at the interface between skin and percutaneous devices.

Percutaneous devices are indispensable in modern medicine, yet complications from their use result in significant morbidity, mortality, and cost. Bacterial biofilm at the device exit site accounts for most infections in short-term devices. We hypothesize that advanced biomaterials can be developed that facilitate attachment of skin cells to percutaneous devices, forming a seal to preclude bacterial invasion. To study the skin/biomaterial interface systematically, we first identified biomaterials with physical properties compatible with histological processing of skin. Second, we developed an organ culture system to study skin response to implants. Organ cultures implanted with porous poly(2-hydroxyethyl methacrylate) [poly(HEMA)] or polytetrafluoroethylene (PTFE) could easily be evaluated histologically with preservation of the skin/biomaterial interface. Epithelial cells migrated down the cut edges of the biomaterial in a pattern seen in marsupialization of percutaneous devices in vivo. This in vitro model maintains skin viability and allows histologic evaluation of the skin/biomaterial interface, making this a useful, inexpensive test-bed for studies of epidermal attachment to modified biomaterials.

Primary mouse keratinocyte culture.

Mouse epidermal keratinocytes have traditionally been difficult to grow in vitro. In this chapter, we present a method for isolating epidermal keratinocytes from a single, newborn mouse pup for long-term culture. The protocols we describe will be especially useful for the isolation and analysis of cells harvested from transgenic or knockout mice. We explain how to use a supplemented fibroblast-conditioned medium, along with mouse collagen IV-coated culture dishes, to establish and subculture these fastidious cells for multiple passages. We describe how to induce expression of markers of the late stages of epidermal differentiation in cultured cells and how to ship whole mouse skins for culture at a site removed from the mice, should it be required. This chapter also contains a method of cryopreservation that ensures high cell viability after periods of storage over liquid nitrogen. The techniques described here in detail should be of interest to investigators currently producing transgenic or null mice with epidermal defects.