Osteocytes subjected to pulsating fluid flow regulate osteoblast proliferation and differentiation

Area of Science:

• Bone Biology
• Cell Signaling
• Mechanobiology

Background:

• Osteocytes are crucial for bone remodeling, but their signaling mechanisms remain incompletely understood.
• Investigating how mechanical stimuli, like pulsating fluid flow (PFF), influence osteocyte function is key to understanding bone adaptation.

Purpose of the Study:

• To determine if osteocytes, osteoblasts, and periosteal fibroblasts produce soluble factors in response to PFF that modulate bone cell proliferation and differentiation.
• To elucidate the role of nitric oxide (NO) in mediating these PFF-induced cellular responses.

Main Methods:

• Cells (osteocytes, osteoblasts, periosteal fibroblasts) were subjected to pulsating fluid flow (PFF).
• Conditioned media (CM) from PFF-treated cells were collected.
• The effects of CM on cultured osteoblast and periosteal fibroblast proliferation and differentiation were assessed.
• Nitric oxide synthase inhibitor (L-NAME) was used to investigate the role of NO.

Main Results:

• Osteocyte PFF CM significantly inhibited bone cell proliferation more than osteoblast or periosteal fibroblast CM.
• Osteocyte PFF CM stimulated osteoblast differentiation, indicated by increased alkaline phosphatase activity.
• Inhibition of nitric oxide synthase (NOS) with L-NAME attenuated both the inhibitory effect on proliferation and the stimulatory effect on differentiation by osteocyte PFF CM.

Conclusions:

• Osteocytes exposed to PFF release soluble factors that inhibit proliferation and stimulate differentiation of osteoblasts in vitro.
• These osteocyte-derived soluble factors are, at least partially, dependent on the activation of a nitric oxide (NO) pathway.
• Osteocytes exhibit greater responsiveness to PFF compared to osteoblasts and periosteal fibroblasts regarding the production of signaling molecules that impact osteoblast behavior.