Burn Injury Alters Epidermal Cholinergic Mediators and Increases HMGB1 and Caspase 3 in Autologous Donor Skin and Burn Margin

Abstract

Burn wound healing complications, such as graft failure or infection, are a major source of morbidity and mortality in burn patients. The mechanisms by which local burn injury alters epidermal barrier function in autologous donor skin and surrounding burn margin are largely undefined. We hypothesized that defects in the epidermal cholinergic system may impair epidermal barrier function and innate immune responses. The objective was to identify alterations in the epidermal cholinergic pathway, and their downstream targets, associated with inflammation and cell death. We established that protein levels, but not gene expression, of the α7 nicotinic acetylcholine receptor (CHRNA7) were significantly reduced in both donor and burn margin skin. Furthermore, the gene and protein levels of an endogenous allosteric modulator of CHRNA7, secreted mammalian Ly-6/urokinase-type plasminogen activator receptor-related protein-1 (SLURP1) and acetylcholine were significantly elevated in donor and burn margin skin. As downstream proteins of inflammatory and cell death targets of nAChR activation, we found significant elevations in epidermal High Mobility Group Box Protein 1 (HMGB1) and caspase 3 in donor and burn margin skin. Lastly, we employed a novel in vitro keratinocyte burn model to establish that burn injury influences the gene expression of these cholinergic mediators and their downstream targets. These results indicate that defects in cholinergic mediators and inflammatory/apoptotic molecules in donor and burn margin skin may directly contribute to graft failure or infection in burn patients.

Burn Injury: Mechanisms of Keratinocyte Cell Death

“…Cell stress, such as UV irradiation, can result in mitochondrial release of cytochrome c and APAF 1, which recruit procaspase 9, forming the apoptosome and subsequently activating caspase 9 [ 26 ]. While the involvement of the initiator caspase 9 has not been studied in thermal injury, Holmes et al were able to detect the executioner caspase 3 after thermal stress in vitro, indicating a caspase-dependent pathway in thermally injured keratinocytes [ 27 ].…”

New Insights on Neuronal Nicotinic Acetylcholine Receptors as Targets for Pain and Inflammation: A Focus on α7 nAChRs

“…Many other downstream pathways may involve α7 nAChRs and TLR4 interaction, such as overexpression of IL-1 receptor-associated kinase M (IRAK-M), a negative regulator of TLR4, in macrophages resulted in decreased TNF-α production through a Jak2-STAT3 signaling pathway by α7 nAChR activation [ 82 ]. HMGB1, a cytokine mediator of inflammation, has been reported to upregulate α7 nAChR expression [ 83 ]. In addition, vagus nerve stimulation or cholinergic receptor agonists have been suggested to inhibit the activation of NACHT, LRR, PYD domains-containing protein 3 (NLRP3) inflammasome, a key modulator of innate immunity, whereas genetic deletion of α7 nAChR enhances inflammasome activation.…”

Alerting the Body to Tissue Injury: The Role of Alarmins and DAMPs in Cutaneous Wound Healing

“…In addition, HMGB-1 staining may be useful for visualizing burn progression, as the initially healthy area of tissue surrounding the burn eventually becomes non-viable due to expansion of the necrotic zone [14, 16]. A recent study has also suggested a link between HMGB-1 and cholinergic activation, as alterations in cholinergic mediators are associated with the induction of HMGB-1 after burn injury [17].…”