Fluid flow-induced soluble vascular endothelial growth factor isoforms regulate actin adaptation in osteoblasts.
Although load-induced mechanical signals play a key role in bone formation and maintenance of bone mass and structure, the cellular mechanisms involved in the translation of these signals are still not well understood. Recent identification of a novel flow-induced mechanosignaling pathway involving VEGF in osteoblasts and the known VEGF regulation of actin reorganization in various cell types has led us to hypothesize that fluid shear stress-induced Vegf up-regulation underlies the actin cytoskeleton adaptation observed in osteoblasts during mechanotransduction. Our results show that MC3T3-E1 cells secrete significant VEGF in response to 5 h of pulsatile fluid shear stress (PFSS; 5 dynes/cm(2) at 1 Hz), whereas expression of VEGF receptors (VEGFR-1, VEGFR-2, or NRP1) is unaffected. These receptors, in particular VEGFR-2, participate in PFSS-induced VEGF release. Exposure to flow-conditioned medium or exogenous VEGF significantly induces stress fiber formation in osteoblasts that is comparable with PFSS-induced stress fiber formation, whereas VEGF knockdown abrogates this response to PFSS, thereby providing evidence that flow-induced VEGF release plays a role in actin polymerization. Using neutralizing antibodies against the receptors and VEGF isoforms, we found that soluble VEGFs, in particular VEGF(164), play a crucial role in transient stress fiber formation during osteoblast mechanotransduction, most likely through VEGFR-2 and NRP1. Based on these data we conclude that flow-induced VEGF release from osteoblasts regulates osteoblast actin adaptation during mechanotransduction and that VEGF paracrine signaling may provide potent cross-talk among bone cells and endothelial cells that is essential for fracture healing, bone remodeling, and osteogenesis.
Thi
Mia M
MM
Department of Orthopaedic Surgery, Albert Einstein College of Medicine of Yeshiva University, Bronx, New York 10461, USA.
Suadicani
Sylvia O
SO
Spray
David C
DC
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D022502:Stress Fibers / Q000378:metabolism; D013312:Stress, Physiological / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
D000199:Actins; D020033:Protein Isoforms; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2