OSTEOCYTE ENHANCEMENT OF ANGIOGENESIS IN VITRO

Erica Takai, Juan M. Taboas, Steven D. Hudson, Rocky S. Tuan

Polymers Division, National Institute of Standards and Technology, Gaithersburg, MD

Although it is well known that an intimate relationship exists between vascularization and bone formation during development and fracture healing, where new bone formation is preceded by local vascularization, the cellular cues that lead to increased or maintained vascularization of bone remain unclear.  Specifically, it is not clear whether osteoblasts, osteocytes (OCY), and/or osteoclasts are involved in the recruitment of new vasculature.  Since OCYs form extensive interconnected cellular networks throughout the bone tissue and respond to a variety of mechanical and chemical stimuli, they have been proposed to be the mechano/chemostat cells of bone tissue.  Thus OCYs may play an important role in vascular recruitment both with and without mechanical loading.  The objective of this study was to examine the ability of OCYs subjected to various physiologic stimuli to enhance angiogenesis in vitro.

            Osteocytic MLO-Y4 cells grown to 90% confluence were subjected to the following treatments and cultured under static conditions for 24 hours to generate conditioned medium (CM): 1) static culture; 2) hypoxia (5% oxygen, 24 hours); 3) dynamic hydrostatic pressure loading (DHP, 1Hz peak 40kPa); or steady fluid shear (steady, 8 dynes/cm²).  Human microvascular endothelial cells (HMVECs) were seeded into 96-well plates or growth factor reduced matrigel-coated 24 well plates and treated with control medium or one of the CM described above, and cell proliferation and capillary-like network formation were assessed.

All CM treated groups except hypoxia CM showed increased cell proliferation compared to the control group.  There was a trend of increased proliferation in the mechanically loaded CM groups compared to the static CM group.  Capillary-like network formation was similar in HMVECs cultured in control medium, static CM, and hypoxia CM. However, HMVECs cultured in DHP or flow CM showed more extensive capillary-like network formation compared to control media.

In this study we have demonstrated the ability of OCYs to enhance proliferation and capillary-like network formation of HMVECs in vitro.  A better understanding of the interactions between OCYs and endothelial cells may lead to treatments that can enhance bone formation.

Your name: Erica Takai

Mentor’s name: Steven D. Hudson

Division: Polymers (854)

Laboratory: Materials Science and Engineering

Room and Building address: B118 Bldg. 224

Mail Stop: 8543

Telephone #: (301) 975-4631

FAX #: (301) 975-4977

Email: erica.takai@nist.gov

Sigma Xi member: No

Category: Biology