Cyclic strain upregulates VEGF and attenuates proliferation of vascular smooth muscle cells.

OBJECTIVE: Vascular smooth muscle cell (VSMC) hypertrophy and proliferation occur in response to strain-induced local and systemic inflammatory cytokines and growth factors which may contribute to hypertension, atherosclerosis, and restenosis. We hypothesize VSMC strain, modeling normotensive arterial pressure waveforms in vitro, results in attenuated proliferative and increased hypertrophic responses 48 hrs post-strain. METHODS: Using Flexcell Bioflex Systems we determined the morphological, hyperplastic and hypertrophic responses of non-strained and biomechanically strained cultured rat A7R5 VSMC. We measured secretion of nitric oxide, key cytokine/growth factors and intracellular mediators involved in VSMC proliferation via fluorescence spectroscopy and protein microarrays. We also investigated the potential roles of VEGF on VSMC strain-induced proliferation. RESULTS: Protein microarrays revealed significant increases in VEGF secretion in response to 18 hours mechanical strain, a result that ELISA data corroborated. Apoptosis-inducing nitric oxide (NO) levels also increased 43% 48 hrs post-strain. Non-strained cells incubated with exogenous VEGF did not reproduce the antimitogenic effect. However, anti-VEGF reversed the antimitogenic effect of mechanical strain. Antibody microarrays of strained VSMC lysates revealed MEK1, MEK2, phospo-MEK1T385, T291, T298, phospho-Erk1/2T202+Y204/T185+T187, and PKC isoforms expression were universally increased, suggesting a proliferative/inflammatory signaling state. Conversely, VSMC strain decreased expression levels of Cdk1, Cdk2, Cdk4, and Cdk6 by 25-50% suggesting a partially inhibited proliferative signaling cascade. CONCLUSIONS: Subjecting VSMC to cyclic biomechanical strain in vitro promotes cell hypertrophy while attenuating cellular proliferation. We also report an upregulation of MEK and ERK activation suggestive of a proliferative phenotype. Hhowever, the proliferative response appears to be aborogated by enhanced antimitogenic cytokine VEGF, NO secretion and downregulation of Cdk expression. Although exogenous VEGF alone is not sufficient to promote the quiescent VSMC phenotype, we provide evidence suggesting that strain is a necessary component to induce VSMC response to the antimitogenic effects of VEGF. Taken together these data indicate that VEGF plays a critical role in mechanical strain-induced VSMC proliferation and vessel wall remodeling. Whether VEGF and/or NO inhibit signaling distal to Erk 1/2 is currently under investigation.

In vitro modeling of repetitive motion injury and myofascial release.

OBJECTIVE: In this study we modeled repetitive motion strain (RMS) and myofascial release (MFR) in vitro to investigate possible cellular and molecular mechanisms to potentially explain the immediate clinical outcomes associated with RMS and MFR. METHOD: Cultured human fibroblasts were strained with 8h RMS, 60s MFR and combined treatment; RMS+MFR. Fibroblasts were immediately sampled upon cessation of strain and evaluated for cell morphology, cytokine secretions, proliferation, apoptosis, and potential changes to intracellular signaling molecules. RESULTS: RMS-induced fibroblast elongation of lameopodia, cellular decentralization, reduction of cell to cell contact and significant decreases in cell area to perimeter ratios compared to all other experimental groups (p<0.0001). Cellular proliferation indicated no change among any treatment group; however RMS resulted in a significant increase in apoptosis rate (p<0.05) along with increases in death-associated protein kinase (DAPK) and focal adhesion kinase (FAK) phosphorylation by 74% and 58% respectively, when compared to control. These responses were not observed in the MFR and RMS+MFR group. Of the 20 cytokines measured there was a significant increase in GRO secretion in the RMS+MFR group when compared to control and MFR alone. CONCLUSION: Our modeled injury (RMS) appropriately displayed enhanced apoptosis activity and loss of intercellular integrity that is consistent with pro-apoptotic dapk-2 and FAK signaling. Treatment with MFR following RMS resulted in normalization in apoptotic rate and cell morphology both consistent with changes observed in dapk-2. These in vitro studies build upon the cellular evidence base needed to fully explain clinical efficacy of manual manipulative therapies.

Importance of strain direction in regulating human fibroblast proliferation and cytokine secretion: a useful in vitro model for soft tissue injury and manual medicine treatments.

OBJECTIVE: Manual medicine treatments (MMTs) rely on biophysical techniques that use manually guided forces in numerous strain directions to treat injuries and somatic dysfunctions. Although clinical outcomes post-MMT are positive, the underlying cellular mechanisms responsible remain elusive. We previously described an in vitro model of strain-induced tissue injury and MMTs. Using this model, the current study sought to determine if strain direction (equibiaxial [EQUI] vs heterobiaxial [HETERO]) differentially regulates human fibroblast function. METHODS: Fibroblasts were strained EQUI at 10% beyond their resting length for 48 hours followed by assessment of cell morphology, proliferation, and cytokine secretion via protein cytokine array and enzyme-linked immunosorbent assay (ELISA). These observations were then compared with those obtained previously for HETERO fibroblasts. RESULTS: No alterations in cell morphology were seen in EQUI fibroblasts despite our report of such changes in HETERO cells. Fibroblasts secretion profiles for 60 cytokines (via cytokine protein array) showed that in EQUI strained cells, fractalkine significantly increased (121%), whereas macrophage-derived chemoattractant/chemokine and pulmonary and activation-regulated chemokine significantly decreased (32% and 10%, respectively) compared with nonstrained cells (P < .05). The EQUI fibroblasts when compared with HETERO fibroblasts exhibited a significant decrease in proliferation (22%), inflammatory interleukin 6 secretion (75%, measured by ELISA), and macrophage-derived chemoattractant/chemokine secretion (177%, measured by ELISA, P < .05). CONCLUSIONS: These divergent observations in HETERO vs EQUI strained fibroblasts may underlie the relative efficacies of MMTs carried out in different tissue strain directions. We are currently modeling MMTs such as myofascial release to further investigate this.

Modeled repetitive motion strain and indirect osteopathic manipulative techniques in regulation of human fibroblast proliferation and interleukin secretion.

CONTEXT: Clinical studies have supported the efficacy of a variety of osteopathic manipulative techniques. However, an evidence base for the cellular mechanisms underlying these clinical findings is lacking. OBJECTIVE: To investigate human fibroblast proliferation and interleukin secretory profiles in response to modeled repetitive motion strain (RMS) and modeled indirect osteopathic manipulative techniques (IOMT). The authors hypothesized that the RMS model would increase fibroblast proliferation and proinflammatory interleukin secretion, while the IOMT model would reverse these effects. METHODS: Human fibroblasts were exposed in vitro to one of three conditions: (1) an 8-hour RMS; (2) a 60-second IOMT; or (3) an 8-hour RMS followed by a 60-second IOMT. Data on fibroblast proliferation and interleukins present in conditioned media were obtained immediately after RMS, at 24 hours after RMS (24RMS), at 24 hours after IOMT (24IOMT), and at 24 hours after RMS and IOMT (24RMS+IOMT). Cytokine protein array and enzyme-linked immunosorbent assay were used in data analysis. Fibroblast proliferation was also measured colorimetrically with a cell proliferation assay. RESULTS: Fibroblasts that underwent RMS secreted several proinflammatory interleukins 24 hours after strain cessation, with substantially increased secretion of IL-1alpha, IL-1beta, IL-2, IL-3, IL-6, and IL-16. At 24 hours after strain cessation, fibroblasts subjected to RMS also secreted increased amounts of the anti-inflammatory IL-1ra, and they displayed 15% less proliferation, compared with baseline cells (P<.05). Fibroblasts that underwent IOMT, when analyzed at 24 hours after IOMT, did not display increased interleukin secretion or proliferation. However, they did display a 44% reduction in proinflammatory IL-3 secretion when compared with baseline cells (P<.05). The use of 24RMS+IOMT did not induce interleukin secretion in fibroblasts that were analyzed 24 hours after the combined exposure. However, cells in the 24RMS+IOMT group did display a 46% reduction in proinflammatory IL-6 secretion compared with RMS alone (24RMS; P<.05), as well as a 51% increase in proliferation compared with the 24RMS group (P<.05). CONCLUSION: An in vitro strain model that simulates RMS has different effects on fibroblast proliferation and interleukin secretion than does an in vitro model that simulates IOMT. Modeled RMS appears to cause a reduction in fibroblast proliferation and a delayed inflammatory response. Modeled IOMT not only fails to induce this response, it also reverses inflammatory effects in cells that have been strained repetitively. Data from the present study suggest that fibroblast proliferation and expression/secretion of proinflammatory and anti-inflammatory interleukins may contribute to the clinical efficacy of indirect osteopathic manipulative techniques.