Angiotensin II stimulates canonical TGF-β signaling pathway through angiotensin type 1 receptor to induce granulation tissue contraction
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Hypertrophic scar contraction (HSc) is caused by granulation tissue contraction propagated by myofibroblast and fibroblast migration and contractility. Identifying the stimulants that promote migration and contractility is key to mitigating HSc. Angiotensin II (AngII) promotes migration and contractility of heart, liver, and lung fibroblasts; thus, we investigated the mechanisms of AngII in HSc. Human scar and unwounded dermis were immunostained for AngII receptors angiotensin type 1 receptor (AT1 receptor) and angiotensin type 2 receptor (AT2 receptor) and analyzed for AT1 receptor expression using Western blot. In vitro assays of fibroblast contraction and migration under AngII stimulation were conducted with AT1 receptor, AT2 receptor, p38, Jun N-terminal kinase (JNK), MEK, and activin receptor-like kinase 5 (ALK5) antagonism. Excisional wounds were created on AT1 receptor KO and wild-type (WT) mice treated with AngII ± losartan and ALK5 and JNK inhibitors SB-431542 and SP-600125, respectively. Granulation tissue contraction was quantified, and wounds were analyzed by immunohistochemistry. AT1 receptor expression was increased in scar, but not unwounded tissue. AngII induced fibroblast contraction and migration through AT1 receptor. Cell migration was inhibited by ALK5 and JNK, but not p38 or MEK blockade. In vivo experiments determined that absence of AT1 receptor and chemical AT1 receptor antagonism diminished granulation tissue contraction while AngII stimulated wound contraction. AngII granulation tissue contraction was diminished by ALK5 inhibition, but not JNK. AngII promotes granulation tissue contraction through AT1 receptor and downstream canonical transforming growth factor (TGF)-β signaling pathway, ALK5. Further understanding the pathogenesis of HSc as an integrated signaling mechanism could improve our approach to establishing effective therapeutic interventions.
AT1 receptor expression is increased in scar tissue compared to unwounded tissue.
AngII stimulates expression of proteins that confer cell migration and contraction.
AngII stimulates fibroblast migration and contraction through AT1 receptor, ALK5, and JNK.
AngII-stimulated in vivo granulation tissue contraction is AT1 receptor and ALK5 dependent.
KeywordsAngiotensin II AT1 receptor Hypertrophic scar contraction ALK 5
This study was supported by a grant from the National Institutes of Health, 5 K08GM085562-05, PI Levinson, Howard. The authors wish to thank Bruce Klitzman, PhD, for his supervision of animal experiments and Dr. Zuowei Su for his technical assistance with immunohistochemical staining. The authors are also grateful to Thomas M. Coffman, MD, for providing the AT1 KO mice. We would like to acknowledge Maragatha Kuchibhatla, PhD, for providing her expertise in statistical analysis.
The authors have no financial or personal conflict of interest to disclose in connection with this submitted material.
Tosan Ehanire, MHS: Experimental design and planning, Western blot analysis, fibroblast-populated collagen lattice assays, and manuscript and figure preparation.
Licheng Ren, MD: In vivo and immunohistology studies with losartan-treated mice and manuscript preparation.
Jennifer Bond, PhD: Experimental design and planning and manuscript preparation.
Manuel Medina, MD: In vivo studies with ALK5/JNK signaling blockade, immunohistochemistry, and manuscript preparation.
George Li, BSc: Cell scratch migration and assays and manuscript preparation.
Latif Bashirov, MD: In vivo studies with ALK5/JNK signaling blockade, immunohistochemistry, and manuscript preparation.
Lei Chen, MD: Immunohistology of human scar and normal fibroblast and manuscript preparation.
George Kokosis, MD: In vivo studies with AT1 KO mice and manuscript preparation.
Angelica Selim, MD: Immunohistology and manuscript preparation.
Gerard C. Blobe, MD, PhD: Experimental design and manuscript preparation.
Howard Levinson, MD: Experimental design and manuscript preparation.
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