Increased CTGF expression in alveolar epithelial cells by cyclic mechanical stretch: Its mechanism and the therapeutic effect of pirfenidone

The mechanisms of fibrosis onset and development remain to be elucidated. However, it has been reported that mechanical stretch promotes fibrosis in various organs and cells, and may be involved in the pathogenesis of pulmonary fibrosis. We demonstrated that ventilator-induced lung hyperextension stimulation in mice increased the expression of connective tissue growth factor (CTGF), a profibrotic cytokine, in lung tissue. Increased CTGF expression induced by cyclic mechanical stretch (CMS) was also observed in vitro using A549 human alveolar epithelial cells. Pathway analysis revealed that the induction of CTGF expression by CMS involved MEK phosphorylation. Furthermore, early growth response 1 (Egr-1) was identified as a transcription factor associated with CTGF expression. Finally, the antifibrotic drug pirfenidone significantly reduced CTGF expression, MEK phosphorylation, and Egr-1 levels induced by CMS. Thus, our results demonstrated that profibrotic cytokine CTGF induced by CMS may be a therapeutic target of pirfenidone.

Nrf2 activation is involved in osteogenic differentiation of periodontal ligament stem cells under cyclic mechanical stretch

During orthodontic treatment, mechanical stretch serves a crucial function in osteogenic differentiation of periodontal ligament stem cells (PDLSCs). Up-regulated reactive oxygen species (ROS) level is a result of cyclic mechanical stretch in many cell types. Nuclear factor erythroid-2-related factor-2 (Nrf2) is a master regulator in various antioxidants expression. However, it is not known whether cyclic mechanical stretch could induce the ROS generation in PDLSCs and whether Nrf2 participated in this process. The present study was aimed to investigate the role of Nrf2 in PDLSCs under cyclic mechanical stretch. Our results showed that cyclic mechanical stretch increased ROS level and the nuclear accumulation of Nrf2 during osteoblast differentiation. Knocking down Nrf2 by siRNA transfection increased ROS formation and suppressed osteogenic differentiation in PDLSCs. T-BHQ, a Nrf2 activator, promoted the osteogenic differentiation in PDLSCs under cyclic mechanical stretch, and improved the microstructure of alveolar bone during orthodontic tooth movement in rats by employing micro-CT system. Taken together, Nrf2 activation was involved in osteogenic differentiation under cyclic mechanical stretch in PDLSCs. T-BHQ could promote the osteogenic differentiation in vitro and in vivo, suggesting a promising option for the remodeling of the alveolar bone during orthodontic tooth movement.

MiR-147 inhibits cyclic mechanical stretch-induced apoptosis in L6 myoblasts via ameliorating endoplasmic reticulum stress by targeting BRMS1

Functional orthopedic treatment is effective for the correction of malformation. Studies demonstrated myoblasts undergo proliferation and apoptosis on certain stretch conditions. MicroRNAs (miRNAs) function in RNA silencing and post-transcriptional regulation of gene expression, and participate in various biological processes, including proliferation and apoptosis. One hypothesis suggested that miRNA was involved into the procedure via suppressing its target genes then triggered endoplasmic reticulum stress-induced apoptosis. Therefore, miRNAs play important roles in the regulation of the proliferation and apoptosis of myoblasts. In our study, the miR-147 has been explored. A cyclic mechanical stretch model was established to observe the features of rat L6 myoblasts. The detection of mRNA and protein levels was performed by qRT-PCR and western blot. L6 cell proliferation/apoptosis was checked by CCK-8 assay, DNA fragmentation assay, and caspase-3 activity assay. MiRNA transfections were performed as per the manufacturer's suggestions: (1) cyclic mechanical stretch induced apoptosis of L6 myoblasts and inhibition of miR-147; (2) miR-147 attenuated cyclic mechanical stretch-induced apoptosis of L6 myoblasts; (3) miR-147 attenuated cyclic mechanical stretch-induced L6 myoblast endoplasmic reticulum stress; (4) BRMS1 was a direct target of miR-147 in L6 myoblasts; (5) miR-147/BRMS1 axis participated in the regulation of cyclic mechanical stress on L6 myoblasts. MiR-147 attenuates endoplasmic reticulum stress by targeting BRMS1 to inhibit cyclic mechanical stretch-induced apoptosis of L6 myoblasts.

Cyclic Mechanical Stretch Induced Smooth Muscle Cell Changes in Cerebral Aneurysm Progress by Reducing Collagen Type IV and Collagen Type VI Levels

BACKGROUND/AIMS

Cerebral aneurysm growth is characterized by continuous structural weakness of local smooth muscle cells, though the mechanism is unclear. In this study, we examine protein changes in cerebral aneurysm and human brain vascular smooth muscle cells after cyclic mechanical stretch. We further explore the relationship between the smooth muscle cell changes and reductions in the levels of collagen types IV and VI.

METHODS

Saccular cerebral aneurysms (n=10) were collected, and temporal artery samples were used as controls. Quantitative proteomics were analyzed and histopathological changes were examined. Smooth muscle cells were cultured in a flexible silicone chamber and subjected to 15% cyclic mechanical stretch. The effect of stretch on the cell viability, function, gene and protein expression were further studied for the understanding the molecular mechanism of aneurysm development.

RESULTS

Proteomics analysis revealed 92 proteins with increased expression and 88 proteins with decreased expression compared to the controls (p<0.05). KEGG pathway analysis showed that the change in focal adhesion and extracellular matrix-receptor interaction, suggesting the involvement of collagen type IV and VI. The aneurysm tissue exhibited fewer smooth muscle cells and lower levels of collagen type IV and VI. Human brain vascular smooth muscle cell culture showed spindle-like cells and obvious smooth muscle cell layer. Cell proteomics analysis showed that decreased expression of 118 proteins and increased expression of 32 proteins in smooth muscle cells after cyclic mechanical stretch. KEGG pathway analysis indicated that focal adhesion and ECM-receptor interaction were involved. After cyclic mechanical stretch, collagen type IV and IV expression were decreased. Moreover, the stretch induced MMP-1 and MMP-3 expression elevation.

CONCLUSION

We demonstrated that collagen type IV and VI were decreased in cerebral aneurysms and continuous cyclic mechanical stretch induced smooth muscle cell changes. Smooth muscle cell protection provides an additional therapeutic option to prevent the growth of cerebral aneurysms.

Role of androgen receptor on cyclic mechanical stretch-regulated proliferation of C2C12 myoblasts and its upstream signals: IGF-1-mediated PI3K/Akt and MAPKs pathways

OBJECTS

To detect the effects of androgen receptor (AR) on cyclic mechanical stretch-modulated proliferation of C2C12 myoblasts and its pathways: roles of IGF-1, PI3K and MAPK.

METHODS

C2C12 were randomly divided into five groups: un-stretched control, six or 8 h of fifteen percent stretch, and six or 8 h of twenty percent stretch. Cyclic mechanical stretch of C2C12 were completed using a computer-controlled FlexCell Strain Unit. Cell proliferation and IGF-1 concentration in medium were detected by CCK8 and ELISA, respectively. Expressions of AR and IGF-1R, and expressions and activities of PI3K, p38 and ERK1/2 in stretched C2C12 cells were determined by Western blot.

RESULTS

①The proliferation of C2C12 cells, IGF-1 concentration in medium, expressions of AR and IGF-1R, and activities of PI3K, p38 and ERK1/2 were increased by 6 h of fifteen percent stretch, while decreased by twenty percent stretch for six or 8 h ②The fifteen percent stretch-increased proliferation of C2C12 cells was reversed by AR inhibitor, Flutamide. ③The increases of AR expression, activities of PI3K, p38 and ERK1/2 resulted from fifteen percent stretch were attenuated by IGF-1 neutralizing antibody, while twenty percent stretch-induced decreases of the above indicators were enhanced by recombinant IGF-1. ④Specific inhibitors of p38, ERK1/2 and PI3K all decreased the expression of AR in fifteen percent and twenty percent of stretched C2C12 cells.

CONCLUSIONS

Cyclic mechanical stretch modulated the proliferation of C2C12 cells, which may be attributed to the alterations of AR via IGF-1-PI3K/Akt and IGF-1-MAPK (p38, ERK1/2) pathways in C2C12 cells.

Cyclic mechanical stretch-induced oxidative stress occurs via a NOX-dependent mechanism in type II alveolar epithelial cells

Cyclic mechanical stretching (CMS) of the alveolar epithelium is thought to contribute to alveolar epithelial injury through an increase in oxidative stress. The aim of this study was to investigate the mechanisms of CMS-induced oxidative stress in alveolar epithelial cells (AECs). A549 cells were subjected to CMS, and the levels of 8-isoprostane and 3-nytrotyrosine were measured. Twenty-four hours of CMS induced a significant increase in the levels of 8-isoprostane and 3-nytrotyrosine. Although CMS did not increase the xanthine oxidase activity or the mitochondrial production of reactive oxygen species, it upregulated the expression of nicotine adenine dinucleotide phosphate oxidase (NOX) 2, 4, 5 and DUOX2. The NOX inhibitors DPI and GKT137831 significantly attenuated CMS-induced oxidative stress. Furthermore, the measurement of annexin V/propidium iodide by flow cytometry showed that CMS induced late-phase apoptosis/necrosis, which was also attenuated by both DPI and GKT137831. These data suggest that CMS mainly induces oxidative stress, which may lead to cell injury by activating NOX in AECs.

Gene expression in response to cyclic mechanical stretch in primary human dermal fibroblasts

The human dermal skin is permanently exposed to mechanical stress, for instance during facial expression, which might cause wrinkles with age. Cyclic mechanical stretching of cells results in cellular and cytoskeleton alignment perpendicular to the stretch direction regulating cellular response. With gene expression profiling it was aimed to identify the differentially expressed genes associated with the regulation of the cytoskeleton to investigate the stretch-induced cell alignment mechanism. Here, the transcription activity of the genome in response to cyclic mechanical stress was measured using DNA microarray technology with Agilent SurePrint G3 Human GE 8x60k Microarrays, based on the overall measurement of the mRNA. Gene expression was measured at the beginning of the alignment process showing first reoriented cells after 5 h stretching and at the end after 24 h, where nearly all cells are aligned. Gene expression data of control vs. stretched primary human dermal fibroblasts after 5 h and 24 h demonstrated the regulation of differentially expressed genes associated with metabolism, differentiation and morphology and were deposited at http://www.ncbi.nlm.nih.gov/geo with the accession number GSE58389.