Osteoblast response to fluid induced shear depends on substrate microarchitecture and varies with time

Abstract

Osteoblasts are exposed to fluid shear in vivo but the effects are not well understood, particularly how substrate properties or length of exposure modify the response. Short exposure (1 h) to shear reduces the stimulatory effect of micron-scale surface structure on osteoblast differentiation, but the effects of longer term exposures are not known. To test the hypothesis that substrate-dependent responses of osteoblasts to shear depend on the length of exposure to fluid flow, MG63 osteoblasts were grown on tissue culture glass, which has an average roughness (Ra) < 0.2 microm; machined Ti disks (PT, Ra < 0.6 microm); Ti disks with a complex microarchitecture [sand blasted acid etched (SLA), Ra = 4-5 microm); and Ti plasma-sprayed surfaces [Ti via plasma spray (TPS), Ra = 7 microm]. Confluent cultures were exposed to pulsatile flow at shear forces of 0, 1, and 14 dynes/cm(2) for 0, 6, 12, and 24 h. Shear reduced cell number on all surfaces, with greatest effects on TPS. Shear had no effect on alkaline phosphatase on smooth surfaces but increased enzyme activity on SLA and TPS in a time-dependent manner. Its effects on osteocalcin, TGF-beta1, and PGE(2) in the conditioned media were greatest on these surfaces as well. Responses to fluid-induced shear were blocked by the general Cox inhibitor indomethacin and the Cox-2 inhibitor meloxicam, indicating that response to shear is mediated by prostaglandin produced via a Cox-2 dependent mechanism. These results show that the effects of fluid induced shear change with time and are substrate dependent, suggesting that substrate microarchitecture regulates the osteoblast phenotype and effects of shear are determined by the maturation state of the responding population.

Osteoblast Response to Rest Periods During Bioreactor Culture of Collagen–Glycosaminoglycan Scaffolds

“…COX-2 is vital for the production of PGE 2 25 and the increase in COX-2 expression resulted in higher PGE 2 production in all flow groups over the static control at both 25 and 49 h. PGE 2 is involved in osteoblast differentiation 26 and may be linked to osteocalcin expression. 27,28 In 2D studies, it has been found that PGE 2 release is similar for continuous and short-term rest-inserted loading, a finding which is similar in 3D in this case. 19 COL-1 expression decreased for all bioreactor groups compared with the static control.…”

Inibição seletiva da ciclo-oxigenase-2: riscos e benefícios

“…48 Studies in healthy volunteers have shown that selective COX-2 inhibitors reduce prostacyclin (PGI 2 ) formation. 37,38 Taken into account with other studies, 49,50 these data indicate that 60%-70% of PGI 2 production in healthy humans is derived from COX-2. Thus, COX-2 would be the predominant COX isoform in the vascular endothelium, and would be directly associated with prostacyclin production in normal circulation.…”

“…Adapted from Grosser et al 50 (CI 50 COX-1/CI 50 COX-2; the higher the value, the higher the COX-2 selectivity). CI 50 : necessary concentration of the drug to inhibit 50% of COX-1 or 50% of COX-2.…”

“…CI 50 : necessary concentration of the drug to inhibit 50% of COX-1 or 50% of COX-2. Adapted from Hinz et al, 24 and Patrignani et al 25 …”

Adipose-Derived Stem Cells in Functional Bone Tissue Engineering: Lessons from Bone Mechanobiology

“…55 Additional work has suggested osteoblast and osteocyte behavioral response to fluid flow is further modulated by the surface micro-architecture of the cell substrate. 56 Generally, in both in vitro and in vivo studies, bone cells have shown sensitivity to dynamic fluid shear, which has led directly to its exploration as a mechanical stimulation modality in ASC, as discussed in section Fluid flow and shear stress. 34 Uniaxial tensile strain has been used as another mode of mechanical stimulation to successfully induce bone regeneration in vivo via distraction osteogenesis.…”