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Updated: Apr 26, 2026
Pseudomonas aeruginosa Induced Lung Injury Model
Published on: October 29, 2014
Protective effect of Growth Hormone-Releasing Hormone agonist in bacterial toxin-induced pulmonary barrier
Istvan Czikora1, Supriya Sridhar1, Boris Gorshkov1
1Department of Pharmacology and Toxicology, Vascular Biology Center, Georgia Regents University Augusta, GA, USA.
Rationale:
Antibiotic treatment of patients infected with G(-) or G(+) bacteria promotes release of the toxins lipopolysaccharide (LPS) and pneumolysin (PLY) in their lungs. Growth Hormone-releasing Hormone (GHRH) agonist JI-34 protects human lung microvascular endothelial cells (HL-MVEC), expressing splice variant 1 (SV-1) of the receptor, from PLY-induced barrier dysfunction. We investigated whether JI-34 also blunts LPS-induced hyperpermeability. Since GHRH receptor (GHRH-R) signaling can potentially stimulate both cAMP-dependent barrier-protective pathways as well as barrier-disruptive protein kinase C pathways, we studied their interaction in GHRH agonist-treated HL-MVEC, in the presence of PLY, by means of siRNA-mediated protein kinase A (PKA) depletion.
Methods:
Barrier function measurements were done in HL-MVEC monolayers using Electrical Cell substrate Impedance Sensing (ECIS) and VE-cadherin expression by Western blotting. Capillary leak was assessed by Evans Blue dye (EBD) incorporation. Cytokine generation in broncho-alveolar lavage fluid (BALF) was measured by multiplex analysis. PKA and PKC-α activity were assessed by Western blotting.
Results:
GHRH agonist JI-34 significantly blunts LPS-induced barrier dysfunction, at least in part by preserving VE-cadherin expression, while not affecting inflammation. In addition to activating PKA, GHRH agonist also increases PKC-α activity in PLY-treated HL-MVEC. Treatment with PLY significantly decreases resistance in control siRNA-treated HL-MVEC, but does so even more in PKA-depleted monolayers. Pretreatment with GHRH agonist blunts PLY-induced permeability in control siRNA-treated HL-MVEC, but fails to improve barrier function in PKA-depleted PLY-treated monolayers.
Conclusions:
GHRH signaling in HL-MVEC protects from both LPS and PLY-mediated endothelial barrier dysfunction and concurrently induces a barrier-protective PKA-mediated and a barrier-disruptive PKC-α-induced pathway in the presence of PLY, the former of which dominates the latter.
Insights
Growth Hormone-releasing Hormone (GHRH) agonist JI-34 protects lung endothelial cells from bacterial toxins lipopolysaccharide (LPS) and pneumolysin (PLY). GHRH signaling activates protective pathways that dominate over disruptive ones, preserving barrier function.
Area of Science:
- Endothelial biology
- Cellular signaling pathways
- Bacterial toxin research
Background:
- Antibiotic treatment can release lipopolysaccharide (LPS) and pneumolysin (PLY) from bacteria, potentially damaging lung endothelial cells.
- Growth Hormone-releasing Hormone (GHRH) agonist JI-34 has shown protective effects against PLY-induced barrier dysfunction in human lung microvascular endothelial cells (HL-MVEC).
Purpose of the Study:
- To investigate if GHRH agonist JI-34 can also mitigate LPS-induced hyperpermeability in HL-MVEC.
- To explore the interplay between cAMP-dependent protective pathways and protein kinase C (PKC)-dependent disruptive pathways in GHRH-R signaling during toxin exposure.
Main Methods:
- Barrier function was assessed using Electrical Cell Substrate Impedance Sensing (ECIS) and VE-cadherin expression.
- Capillary leak was measured via Evans Blue Dye (EBD) incorporation.
- Cytokine generation, Protein Kinase A (PKA), and PKC-α activity were quantified.
Main Results:
- GHRH agonist JI-34 significantly reduced LPS-induced barrier dysfunction by preserving VE-cadherin expression without altering inflammation.
- JI-34 activated both PKA and PKC-α in PLY-treated HL-MVEC.
- While PLY decreased cell resistance, this effect was exacerbated in PKA-depleted cells; JI-34's protective effect against PLY was lost in PKA-depleted cells.
Conclusions:
- GHRH signaling in HL-MVEC provides protection against both LPS and PLY-induced endothelial barrier dysfunction.
- GHRH signaling activates a dual pathway: a protective PKA-mediated pathway and a disruptive PKC-α-mediated pathway, with the PKA pathway dominating in the presence of PLY.
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