New anti-fibrotic mechanisms of n-acetyl-seryl-aspartyl-lysyl-proline in silicon dioxide-induced silicosis.
OBJECTIVE
We previously reported that tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) inhibited pulmonary inflammation and fibrosis in SiO(2)-induced silicosis. This study aimed to explore the precise mechanism involved.


METHODS
Rats were divided into 3 groups: 1) sham (saline), 2) silicosis+vehicle, and 3) silicosis+Ac-SDKP [800 microg/(kgd)]. SiO(2) particles or saline were administered by tracheal instillation and Ac-SDKP or vehicle (saline) via a mini-osmotic pump planted into the abdominal cavity 48 h before instillation. Animals were observed for 4 weeks. Silicotic nodule fraction (SNF) and macrophage infiltration (ED-1 positive cells) were measured by hematoxylin and eosin (H.E.) and immunohistochemical staining respectively. Collagen I and III, transforming growth factor-beta1 (TGF-beta1) proteins and monocyte chemotactic protein-1 (MCP-1) mRNA were detected by Western Blot (WB) and real-time RT-PCR respectively. In vitro, pulmonary fibroblasts were stimulated by TGF-beta1 (5 microg/ml) with or without Ac-SDKP. Phosphorylated c-Jun N-terminal Kinase (p-JNK) was detected by WB and p-JNK nuclear translocation by confocal analysis.


RESULTS
SiO(2) significantly increased the SNF, collagen I and III proteins, TGF-beta1, MCP-1 mRNA and macrophage infiltration. All these pathological changes were inhibited by Ac-SDKP. TGF-beta1 resulted in fibroblast proliferation, increased expression of collagen I and III proteins, p-JNK and its subsequent nuclear translocation. Addition of Ac-SDKP markedly suppressed these changes.


CONCLUSIONS
These data indicate that the anti-fibrotic effect of Ac-SDKP in silicosis is mediated by inhibiting chronic inflammation, TGF-beta1 production, and TGF-beta1-induced pulmonary fibroblast proliferation and collagen synthesis.
Sun
Ying
Y
Department of Pathology, North China Coal Medical College, No. 57 South Construction Road, Tangshan City, Hebei Province, China.
Yang
Fang
F
Yan
Jingbo
J
Li
Qian
Q
Wei
Zhongqiu
Z
Feng
Haili
H
Wang
Ruimin
R
Zhang
Lijuan
L
Zhang
Xuepeng
X
D000818:Animals; D002464:Cell Migration Inhibition; D049109:Cell Proliferation / Q000187:drug effects; D018932:Chemokine CCL2 / Q000235:genetics / Q000276:immunology; D003094:Collagen / Q000276:immunology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D005355:Fibrosis; D005786:Gene Expression Regulation / Q000187:drug effects; D048031:JNK Mitogen-Activated Protein Kinases / Q000276:immunology; D008168:Lung / Q000187:drug effects / Q000276:immunology / Q000473:pathology*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D008297:Male; D009842:Oligopeptides / Q000627:therapeutic use*; D021381:Protein Transport; D051381:Rats; D017208:Rats, Wistar; D012822:Silicon Dioxide; D012829:Silicosis / Q000188:drug therapy* / Q000276:immunology / Q000473:pathology*; D053773:Transforming Growth Factor beta1 / Q000276:immunology
D018932:Chemokine CCL2; D009842:Oligopeptides; D053773:Transforming Growth Factor beta1; D012822:Silicon Dioxide; D003094:Collagen; D048031:JNK Mitogen-Activated Protein Kinases; C058504:goralatide