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The Cellular and Molecular Dynamics of Burn Injury Progression Following Partial Thickness Burns: The Effect of Early and Late Debridement
Ian Chow, BA, Wei Xu, PhD; Solmaz N. Niknam-Bienia, MD, MHA; Shengxian Jia, MD; Ping Xie, MD, PhD; Sumanas W. Jordan, MD, PhD; Seok J. Hong, PhD; Thomas A. Mustoe, MD; Robert D. Galiano, MD
Northwestern University, Chicago, IL, USA.
Burns are highly dynamic injuries characterized by an initial zone of necrosis that progresses to compromise tissue in the surrounding region. Burn wound extension has profound clinical implications resulting in significant diagnostic and therapeutic conundrums. Early debridement has long been the standard of care for deep partial thickness and full thickness burns, as it has been postulated that the removal of necrotic tissue reduces the release of inflammatory mediators, minimizes burn progression, and hastens repair.
Burn injury progression has not been thoroughly characterized at the cellular and molecular level. Connexins are gap junctional channels found in nearly all vertebrate cells. Connexin43(Cx43) represents the predominant connexin in the human epidermis. Recent investigations into CNS injury have demonstrated that communication of death signals via Cx43 exacerbates cell death in surrounding tissues following ischemic injury. Moreover, blockade of Cx43 has been shown to limit injury progression and inflammation following burn injury through an undetermined mechanism. Conversely, the constitutive expression of heat shock proteins(HSP), specifically HSP70 and 90, dramatically increases following thermal injury and may exert a cytoprotective effect on cells. As such, we hypothesized that there may be a temporal and spatial relationship between these two mediators/attenuators of burn injury, and have sought to characterize the complex dynamics of these mediators following thermal injury and debridement in a novel cutaneous burn model.
Deep partial thickness wounds were created on the ventral surface of rabbit ears by applying a 7mm brass rod heated to 80℃ for 30 seconds. Full-thickness debridements were performed either 24 or 72 hours following injury. Wounds were harvested at various time points with normal uninjured skin serving as a control. Cx43, HSP70, and HSP90 expression was quantified using PCR. Immunofluorescence and TUNEL staining were employed to correlate protein expression and apoptosis. The degree of apoptosis at the burn margins was quantified by counting apoptotic cells and dividing by DAPI stained cells.
Burns result in an immediate increase in Cx43 expression via phosphorylation and translocation to the cell membrane. Drastic increases in Cx43 and HSP70 mRNA expression are seen in the four hours following injury (p<0.05). High levels of Cx43 were expressed in the area of apoptosis surrounding the initial injury. Epidermal expression of Cx43, HSP70, and HSP90 rapidly returns to normal following early debridement, but remains persistently elevated in wounds debrided 72 hours following injury (p<0.05). Regardless of timing, apoptosis decreases rapidly following debridement.
Cx43 expression increases briskly following thermal injury, initially via protein phosphorylation and subsequently through increased gene expression. Expression levels correlate with the zone of apoptosis following burns, providing further evidence of a mechanistic link between Cx43 and burn injury progression. Despite persistent elevations in Cx43 in wounds debrided 72 hours after injury, apoptosis drastically increases following debridement suggesting the removal of the initial focus of injury reduces junctional death signals and allows the HSP response to predominate.
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