(WHS-K3.06) CHANGES IN THE CATECHOLAMINE ADRENERGIC NETWORK SUPPORT WOUND HEALING IN HEALTHY PIGS
Thursday, May 16, 2024
9:15 AM – 10:15 AM East Coast USA Time
Predictable series of chemical and biological changes in each wound stage propel the healing process forwards. The catecholamines norepinephrine (NOR), epinephrine (EPI), and dopamine (DOP) are small molecule neurotransmitters present in the wound that can affect healing. Previously, we showed that physiological levels of EPI activate the alpha 2b adrenergic receptors (A2AR) on keratinocytes and accelerate their migration in-vitro, while activation of beta 2 adrenergic receptors (B2AR) by supra-physiological levels decreased their migration (Yang et al., 2021). Thus, either changes in the wound concentration of epinephrine or in alpha/beta receptor expression may affect re-epithelialization. Here we examined catecholamines and related gene expression in the wound environment during normal wound healing in porcine skin wounds. Twelve full-thickness 20 mm diameter circular wounds were placed on 6 pigs and blood and wound tissue were sampled at intervals over 21 days. Wound outcomes were imaging, tissue RNASeq and histology, and reverse phase HPLC analysis of serum catecholamines. Wound image area and histologic re-epithelialization demonstrated that most wounds healed by days 16-21. Expression of the alpha 2a AR (ADRA2A) was immediately decreased following wounding and remained so through day 7 of healing; expression was increased on days 9 through day 21, peaking at day 16. Expression of the alpha 2b AR (ADRA2B) was bi-modal with peaks on days 2 and 13, and a gradual return to baseline on intervening days. Beta 2 AR (ADRB2) expression increased after wounding, peaking at day 2 and gradually returning to baseline by day 6 through day 21. Expression of dopa decarboxylase (DDC) only began to increase on day 7 of healing, peaking on day 11 and returning to baseline by day 21. DDC is essential to convert L-dopa to DOP, a known mediator of healing. Serum DOP remained at baseline through day 11 and then increased significantly through day 21, concurrent with elevated DDC expression in the wound. The concurrent peaking of DDC, ADRA2A, and ADRA2B suggest their role in enhancing keratinocyte migration in the latter half of the healing process. Serum EPI levels increased immediately after wounding and remained elevated through day 7, gradually returning to baseline by day 12, but effects could be mitigated by the concurrent increase of degrading enzyme monoamine oxidase B (MAOB) in the wound tissue. Likewise, the elevated expression of solute carrier family 6 a2 (SLC6A2, responsible for NOR reuptake) in the first half of the healing process could abrogate the anti-migratory effects of elevated ADRB2 expression in early healing. Taken together, these results show how the complex dynamics of the adrenergic network in the skin change during normal wound healing to support wound closure.