Effect of Fluid Flow on Smooth Muscle Cells in a 3-Dimensional Collagen Gel Model

Abstract

Abstract-A 3D collagen gel model was developed to simulate interstitial fluid flow and to assess the importance of this flow on the biochemical production rates of vascular smooth muscle cells (SMCs). Rat aortic SMCs were suspended in type I collagen, and the gel was supported by nylon fibers that allowed a 9-cm length of the SMC-gel model to withstand 90 cm H 2 O differential pressure over a 6-hour period without significant compaction. Up to 1 dyne/cm 2 shear stress on the suspended SMCs could be induced by the pressure-driven interstitial flow. The suspended SMCs were globular, had a diameter of Ϸ10 m, and were distributed uniformly throughout the gel. The collagen fibers formed a network that was connected randomly with the surface of SMCs and nylon fibers. The diameter of the collagen fibers was Ϸ100 nm, and the concentration of collagen was 2.5 mg/mL. Using these parameters, fiber matrix theory predicted a Darcy permeability coefficient (K p ) of 1.22ϫ10 Ϫ8 cm 2 , which was close to the measured value of K p . The production rates of prostaglandin (PG) I 2 and PGE 2 were used as markers of biochemical responsiveness of SMCs to fluid shear stress. Both PGI 2 and PGE 2 production rates under 1 dyne/cm 2 shear stress were significantly elevated relative to static (no-flow) controls. The production rates, however, were Ϸ10 times lower than observed when the same cells were plated on collagen-treated glass slides (2D model) and exposed to the same level of shear stress by use of a rotating disk apparatus. which affects their physiological function and is believed by many to play a role in the localization of atherosclerotic plaques in arteries. 1 Smooth muscle cells (SMCs) are not normally exposed directly to the fluid shear stresses of blood flow, because they lie beneath the intact intima. In the case of injury to the intima, as occurs, for example, in angioplasty, near the anastomoses of vascular grafts, and in atherosclerotic disease, the superficial layers of SMCs are exposed directly to blood flow shear stresses (order of magnitude, 10 dyne/cm 2 ). 2 Several groups have studied the effects of fluid shear stress on SMCs using cultured cells grown in monolayers on impermeable substrates. Using these 2D models, they have shown that vascular SMCs are responsive to shear stress in the range 1 to 25 dyne/cm 2 and increase their synthesis of transforming growth factor-␤ and tissue plasminogen activator, 3 heme oxygenase-1, 4 and nitric oxide. 5 Protease-activated receptor-1 and tissue plasminogen activator gene expression are also regulated by shear stress on SMCs. 6 A more subtle mechanism by which SMCs are exposed to fluid shear stress derives from the transmural pressure gradient (typically 100 mm Hg in an artery), which drives transmural interstitial flow across the vessel wall. Using the Brinkman model of porous medium flow, Wang and Tarbell 7 estimated that for an artery with an intact intima at normal physiological pressure, the transmural flow would induce a shear stress on the SMCs in the tunica media o...

A driving force for change: interstitial flow as a morphoregulator

“…Transvascular flow across the arterial wall provides nutrient transport to the metabolically active cells there, and seemingly has a crucial role in maintaining arterial smooth muscle tone [21][22][23]. In cartilage, where lymphatics are absent and intercellular distances are large, interstitial fluid flow is driven by mechanical loading and is necessary for nutrient transport and cell-cell communication when diffusion is inadequate [24][25][26].…”

Darcian permeability constant as indicator for shear stresses in regular scaffold systems for tissue engineering

“…Shear stress is also considered as an important parameter for in vivo systems. Wang and Tarbell (2000) found by experiments for smooth muscle cells that with increasing shear stress the production of prostaglandins increased. The results of Wang and Tarbell (2000) indicate that the blood flow rate plays a role in the signal communication system from the blood vessels to the smooth muscle cells.…”

“…However, if we realize that the pressure drop caused by fluid-wall interaction in a structure is proportional to permeability of the structure, then it is also an option to link the shear stress to permeability constants. Wang and Tarbell (2000) use the permeability constant from Darcy's law to derive the average shear stress from experiments on a collagen gel. The permeability constant was determined using the viscosity of the perfusing medium, the measured volumetric flow rate, the cross-sectional area and the imposed pressure drop over the length of the reactor.…”

Interstitial flow influences direction of tumor cell migration through competing mechanisms

“…This autocrine signaling mechanism, termed autologous chemotaxis, arises in a flow field where convection distributes autocrine chemokine factors creating a transcellular chemokine gradient, which in turn provides a chemotactic signal. For CCL21 at physiologically relevant flow velocities, flow increases the concentration of ligand at the downstream side of the cell, providing a positive downstream chemotactic signal (14).The transwell assay used by Shields et al to develop the autologous chemotaxis model and other similar in vitro assays have provided valuable insight into the metastatic process and tumor cell migration by allowing the systematic study of isolated stimuli on tumor cells (9,10,(15)(16)(17)(18)(19). However, recent work has demonstrated that focal adhesion (FA) formation and regulation are a function of dimensionality of cell culture (20), and previous work has demonstrated FA formation is important in regulating endothelial cell (EC) response to laminar shear stress (21).…”