Adrenergic Regulation of cAMP/Protein Kinase A Pathway in Corneal Epithelium and Endothelium

Abstract

Purpose: The G-protein-coupled receptor/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway is one of the most common and versatile signal pathways in eukaryotic cells. The aim of this study was to characterize subtypes of adrenergic G-protein-coupled receptors and their influence on cAMP concentration and PKA activity in bovine corneal epithelial and endothelial cells. Procedures: Adrenergic receptors and PKA were studied using polyclonal antibodies. cAMP concentration was determined with an enzyme immunoassay, and PKA activity was estimated by the kinases consumption of adenosine triphosphate. Results: In bovine corneal epithelial and endothelial cells, immunocytochemistry and Western blot were positive for α₁-, α_2A-, β₁- and β₂-adrenergic receptors. Stimulation of corneal epithelial and endothelial β-adrenoceptors with isoprenaline led to a dose-dependent increase in cAMP concentration and activation of PKA. Stimulation of corneal α_2A-adrenoceptors with brimonidine resulted in a dose-dependent decrease in cAMP concentration and the inhibition of PKA activity. Conclusions: In corneal epithelial and endothelial cells, β-adrenergic stimulation leads to activation of PKA via stimulation of adenylyl cyclase, and α_2A-adrenoceptor stimulation inhibits PKA activity via inhibition of adenylyl cyclase. Stimulation and inhibition of the corneal cAMP-PKA pathway may play a role in important corneal functions such as wound healing or homeostasis. Long-term therapy with α_2A-agonists or β-antagonists may influence these functions in a currently unknown way.

GADD34 Function in Protein Trafficking Promotes Adaptation to Hyperosmotic Stress in Human Corneal Cells

“…These inhibitors have similar structures; however, Guanabenz is also a potent agonist of the α2-adrenergic receptor (Das et al, 2015; Tsaytler et al, 2011). Because this receptor has been reported in corneal epithelial cells (Grueb et al, 2008), we studied both compounds to exclude any contribution of adrenergic signaling. GADD34/PP1 inhibitors showed dose-dependent inhibition of the hyperosmolarity-induced SNAT2 transport activity (Fig.…”

Early publication on intraoperative retinoscopy

“…Stimulation and inhibition of the corneal cAMP/PKA pathway may play a role in important corneal functions such as wound healing and homeostasis. 3 Accordingly, cAMP potentiates the stimulation of corneal epithelial migration by epidermal growth factor in vitro, suggesting that endogenous cAMP might function as a modulator of epithelial wound healing promoted by this growth factor in vivo. 4 It has also been demonstrated that topical application of agents known to increase cAMP increase tear secretion.…”

“…They also reported the deficiencies of the latter method compared with intraoperative retinoscopy. The authors apparently overlooked my original publication 3 Early flap dislocation with perioperative brimonidine use in laser in situ keratomileusis…”

“…4 It has also been demonstrated that topical application of agents known to increase cAMP increase tear secretion. 5 Given that stimulation of corneal a(2A)-adrenoceptors with brimonidine results in a dose-dependent decrease in cAMP concentration, 3 topical application of this agent may interfere with corneal epithelial wound healing or tear secretion. Finally, it has been shown that among all antiglaucoma drugs, only brimonidine decreases aqueous [Ca2C]i concentration significantly, which can lead to decreased endothelial pump function and disturbed corneal homeostasis.…”

Brimonidine Protects Auditory Hair Cells from in vitro-Induced Toxicity of Gentamicin

“…Furthermore, brimonidine inhibits protein kinase A [Grueb et al, 2008]. Interestingly, Navaratnam et al [1996] demonstrated that the proliferation and regeneration of the avian auditory epithelium depends on the activation of protein kinase A, which is cAMP-dependent, and that inhibition of protein kinase A correlates with decreased regeneration.…”