The Role of Angiotensin II Receptor Subtype in Conjunctival Injury

Abstract

Abstract: : Purpose: Angiotensin II (Ang II) plays an important role in the regulation of cardiovascular structure and hemodynamics. Two major Ang II receptor subtypes, named type 1 (AT₁) and type 2 (AT₂) receptors, have been previously reported. Recent studies suggest that Ang II regulates wound healing process through these receptors. However, the detailed mechanism is not clarified. We investigated the role of AT₁ and AT₂ receptor subtypes in subconjunctival injury using wound healing model. Methods:Wound healing model was developed by subconjuncival blunt dissection in male wild type (WT; C57BL/6J), AT_1a null (AT_1aKO) and AT₂ null (AT₂KO) mice (10 to 12 weeks of age). The eyes were enucleated at 12 hours, 1, 2, 4, 7 and 14 days after surgery. Histological studies were performed to evaluate subconjunctival wound healing and extracellular matrix deposition. Expression of mRNA for collagen, and tissue inhibitor of metalloproteinase–1 (TIMP–1) were determined by real time RT–PCR. Results:Subconjunctival injury induced collagen deposition. Subconjunctival collagen deposition detected by histological analysis at 14 days after injury was higher in AT₂KO mice than in WT mice, but it was lower than in AT_1aKO mice than in WT mice. The level of mRNA for type 1 collagen at 7 days was increased in subconjunctival tissue including conjunctiva after injury. This increase was significantly higher in AT₂KO mice, but it was lower than in AT_1aKO mice than in WT mice. To examine the mechanism of action of AT1 and AT2 receptors on collagen synthesis regulation, we assayed the expression of TIMP–1. The level of mRNA was also increased at 12 hours after injury after subconjuntival damage. However, the increase in TIMP–1 expression was significantly higher in AT_1aKO mice, but lower than in AT₂KO mice than in WT mice. Conclusions:These results suggest an antagonistic action between AT_1a receptor– and AT₂ receptor–mediated signals in the regulation of wound healing process after subconjunctival injury through TIMP–1.

Keywords: conjunctiva • wound healing • receptors: pharmacology/physiology