Chronic wounds associated with vascular disease, diabetes mellitus, or aging are leading causes of morbidity in western countries and represent an unresolved clinical problem. The development of innovative strategies to promote tissue repair is therefore an important task that requires a more thorough analysis of the underlying molecular pathophysiology. We propose that the understanding of the complex biological events that control tissue repair or its failure largely benefits from a broad analytical approach as provided by novel proteomic methodologies. Here we present the first comparative proteome analysis of wound exudates obtained from normal healing or nonhealing (venous leg ulcer) human skin wounds. A total of 149 proteins were identified with high confidence. A minority of proteins was exclusively present in exudate of the healing wound (23 proteins) or the nonhealing wound (26 proteins). Of particular interest was the differential distribution of specific proteins among the two different healing phenotypes. Whereas in the exudate obtained from the healing wound mediators characteristic for tissue formation were abundantly present, in the exudate obtained from the nonhealing wound numerous mediators characteristic for a persistent inflammatory and tissue destructive response were identified. Furthermore, the study also revealed interesting results regarding the identification of new proteins with yet unknown functions in skin repair. This analysis therefore represents an important basis for the search for potential biomarkers, which give rise to a better understanding and monitoring of disease progression in chronic wounds.

Identification and clearance of apoptotic cells prevents the release of harmful cell contents thereby suppressing inflammation and autoimmune reactions. Highly conserved annexins may modulate the phagocytic cell removal by acting as bridging molecules to phosphatidylserine, a characteristic phagocytosis signal of dying cells. In this study five members of the structurally and functionally related annexin family were characterized for their capacity to interact with phosphatidylserine and dying cells. The results showed that AnxA3, AnxA4, AnxA13, and the already described interaction partner AnxA5 can bind to phosphatidylserine and apoptotic cells, whereas AnxA8 lacks this ability. Sequence alignment experiments located the essential amino residues for the recognition of surface exposed phosphatidylserine within the calcium binding motifs common to all annexins. These amino acid residues were missing in the evolutionary young AnxA8 and when they were reintroduced by site directed mutagenesis AnxA8 gains the capability to interact with phosphatidylserine containing liposomes and apoptotic cells. By defining the evolutionary conserved amino acid residues mediating phosphatidylserine binding of annexins we show that the recognition of dying cells represent a common feature of most annexins. Hence, the individual annexin repertoire bound to the cell surface of dying cells may fulfil opsonin-like function in cell death recognition.Discrimination of viable from dying cells is a prerequisite for the efficient clearance of dying and dead cells and to suppress uncontrolled cell lysis and the release of potentially harmful cellular compounds to the local environment. During development and under normal physiological conditions, cells are removed through the process of apoptosis and undergo a strictly defined series of morphological and biochemical changes, before being engulfed by professional phagocytes such as macrophages or even by neighboring cells. A signature of specific "eat me" signals are exposed at the cell surface of apoptotic cells, which enable direct or indirect interactions with phagocytes and dying cells to promote the efficient clearance of apoptotic cells. This reduces the risk of accumulation of secondarily necrotic cells and the release of cellular content to the microenvironment. Exposure of apoptotic-cell associated molecular patterns together with recognition and interpretation of these by phagocytes are crucial steps in the appropriate response of phagocytes toward the engulfed cells (1).A hallmark of early apoptotic cells is the loss of membrane asymmetry and the exposure of anionic phosphatidylserine (PS) 3 on the outer lipid layer of the cells. In most cells PS predominantly resides in the inner leaflet of the plasma membrane, regulating membrane charge and protein localization (2). This membrane asymmetry is actively maintained by an inward transporting aminophospholipid translocase (3). Upon induction of apotosis, rising cytoplasmic Ca 2ϩ levels cause a loss of translocase activity and an activ...

Skin injury induces the formation of new blood vessels by activating the vasculature in order to restore tissue homeostasis. Vascular cells may also differentiate into matrix-secreting contractile myofibroblasts to promote wound closure. Here, we characterize a PECAM1+/Sca1+ vascular cell population in mouse skin, which is highly enriched in wounds at the peak of neoangiogenesis and myofibroblast formation. These cells express endothelial and perivascular markers and present the receptor CD38 on their surface. PECAM1+/Sca1+/CD38+ cells proliferate upon wounding and could give rise to α-SMA+ myofibroblast-like cells. CD38 stimulation in immunodeficient mice reduced the wound size at the peak of neoangiogenesis and myofibroblast formation. In humans a corresponding cell population was identified, which was enriched in sprouting vessels of basal cell carcinoma biopsies. The results indicate that PECAM1+/Sca1+/CD38+ vascular cells could proliferate and differentiate into myofibroblast-like cells in wound repair. Moreover, CD38 signaling modulates PECAM1+/Sca1+/CD38+ cell activation in the healing process implying CD38 as a target for anti-angiogenic therapies in human basal cell carcinoma.