Mechanical stress is known to modulate fundamental events such as cell life and death. Mechanical stretch in particular has been identified as a positive regulator of proliferation in skin keratinocytes and other cell systems. In the present study it was investigated whether antiapoptotic signaling is also stimulated by mechanical stretch. It was demonstrated that mechanical stretch rapidly induced the phosphorylation of the proto-oncogene protein kinase B (PKB)/Akt at both phosphorylation sites (serine 473/threonine 308) in different epithelial cells (HaCaT, A-431, and human embryonic kidney-293). Blocking of phosphoinositide 3-OH kinase by selective inhibitors (LY-294002 and wortmannin) abrogated the stretch-induced PKB/Akt phosphorylation. Furthermore mechanical stretch stimulated phosphorylation of epidermal growth factor receptor (EGFR) and the formation of EGFR membrane clusters. Functional blocking of EGFR phosphorylation by either selective inhibitors (AG1478 and PD168393) or dominant-negative expression suppressed stretch-induced PKB/Akt phosphorylation. Finally, the angiotensin II type 1 receptor (AT1-R) was shown to induce positive transactivation of EGFR in response to cell stretch. These findings define a novel signaling pathway of mechanical stretch, namely the activation of PKB/Akt by transactivation of EGFR via angiotensin II type 1 receptor. Evidence is provided that stretch-induced activation of PKB/Akt protects cells against induced apoptosis.
"MS activates epidermal growth factor (EGF) receptor in keratinocytes , and stimulates proliferation of VSMC via the insulin-like growth factor (IGF) receptor  and platelet-derived growth (PDGF) receptor , with the latter implicated in MS-induced embryonic stem cell differentiation into VSMC . Among various growth factors, PDGF is the most potent VSMC mitogen released by platelets, endothelial cells, VSMC and many other cells at the site of injury . "
[Show abstract][Hide abstract] ABSTRACT: Increased blood pressure, leading to mechanical stress on vascular smooth muscle cells (VSMC), is a known risk factor for vascular remodeling via increased activity of matrix metalloproteinase (MMP) within the vascular wall. This study aimed to identify cell surface mechanoreceptors and intracellular signaling pathways that influence VSMC to produce MMP in response to mechanical stretch (MS). When VSMC was stimulated with MS (0-10% strain, 60 cycles/min), both production and gelatinolytic activity of MMP-2, but not MMP-9, were increased in a force-dependent manner. MS-enhanced MMP-2 expression and activity were inhibited by molecular inhibition of Akt using Akt siRNA as well as by PI3K/Akt inhibitors, LY293002 and AI, but not by MAPK inhibitors such as PD98059, SP600125 and SB203580. MS also increased Akt phosphorylation in VSMC, which was attenuated by AG1295, a PDGF receptor (PDGFR) inhibitor, but not by inhibitors for other receptor tyrosine kinase including EGF, IGF, and FGF receptors. Although MS activated PDGFR-α as well as PDGFR-β in VSMC, MS-induced Akt phosphorylation was inhibited by molecular deletion of PDGFR-β using siRNA, but not by inhibition of PDGFR-α. Collectively, our data indicate that MS induces MMP-2 production in VSMC via activation of Akt pathway, that is mediated by activation of PDGFR-β signaling pathways.
PLoS ONE 08/2013; 8(8):e70437. DOI:10.1371/journal.pone.0070437 · 3.23 Impact Factor
"One event is spreading on a solid substratum reducing cell thickness, a phenomenon directly related to proliferative activity (Greenspan and Folkman, 1977; Folkman and Moscona, 1978), most probably via the development of internal mechanical stress which is known to evoke reorganization of integrins acting as membrane bound receptors (Knies et al., 2006) and by this activates MAPK (mitogen-activated protein kinase) pathways (Kippenberger et al., 2005). These isolation and seedinginduced functional shifts are enhanced by components of the culture medium (serum or growth factors added) and by other culture parameters. "
[Show abstract][Hide abstract] ABSTRACT: Isolation of epithelial cells for cell culture is based on destruction of epithelial integrity. The consequences are manifold: cell polarity and specific cell functions are lost, cells acquire non-epithelial characteristics and start to proliferate. This situation may also occur in situ when parts of the epithelium are lost, either by apoptosis or necrosis by organ or tissue injury. During recovery from this injury, surviving epithelial cells proliferate and may restore epithelial integrity and finally re-differentiate into functional epithelial cells. In vitro, this re-differentiation is mostly not complete due to suboptimal culture conditions. Therefore, cultured epithelial cells resemble wounded or injured epithelia rather than healthy and well differentiated epithelia. The value of an in vitro cell model is the extent to which it helps to understand the function of the cells in situ. A variety of parameters influence the state of differentiation of cultured cells in vitro. Although each of these parameters had been studied, the picture how they coordinately influence the state of differentiation of epithelial cells in vitro is incomplete. Therefore, we discuss the influence of the isolation method and cell culture on epithelial cells, and outline strategies to achieve highly differentiated epithelial cells for the use as an in vitro model.
Cell Biology International 05/2012; 36(9). DOI:10.1042/CBI20120060 · 1.93 Impact Factor
"It was similar to the medium Okazaki et al. previously employed to assess melanogenetic paracrine cytokines   . In our investigation , FCS addition had an overwhelmingly effect on the influence of mechanical strain, described in previous reports     . Upregulation of ET-1 in our study is thought to be a functional alteration, rather than a secondary one resulting from constitutional alterations . "
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to investigate the possible pathological relation between mechanical stress and hyperpigmentation. We did this by investigating the influence of cyclic stretch on the expression of keratinocyte- and fibroblast-derived melanogenetic paracrine cytokines in vitro. Using primary human keratinocytes and fibroblasts, alterations of mRNA expression of melanogenetic paracrine cytokines due to cyclic stretch were investigated using a real-time polymerase chain reaction (PCR). The cytokines included basic fibroblast growth factor (bFGF), stem cell factor (SCF), granulocyte/macrophage colony-stimulating factor, interleukin-1α, and endothelin-1 (ET-1) for keratinocytes and bFGF, SCF, and hepatocyte growth factor for fibroblasts. The dose dependence of keratinocyte-derived ET-1 upregulation was further investigated using real-time PCR and an enzyme-linked immunosorbent assay. We also investigated the effects of cyclic stretch on the proliferation and differentiation of keratinocytes. Among the melanogenetic paracrine cytokines investigated, keratinocyte-derived ET-1 was consistently upregulated in all four cell lines. The degree of upregulation increased with the degree of the length and frequency of the stretch; in contrast, cell number and differentiation markers showed no obvious alterations with cyclic stretch. Keratinocyte-derived ET-1 upregulation possibly plays a significant role in the pathogenesis of pigmented disorders, such as friction melanosis, caused by mechanical stress.
Biochemical and Biophysical Research Communications 05/2011; 409(1):103-7. DOI:10.1016/j.bbrc.2011.04.118 · 2.30 Impact Factor
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