Microgravity modulation of syncytin-A expression enhance osteoclast formation

Area of Science:

• Space biology
• Cell biology
• Bone physiology

Background:

• Spaceflight-induced microgravity causes accelerated bone loss.
• The molecular mechanisms underlying microgravity-induced bone loss are not fully understood.
• Osteoclasts (OCLs) are key cells responsible for bone resorption.

Purpose of the Study:

• To investigate the role of syncytin-A in microgravity-induced osteoclast formation.
• To determine the effect of osteotropic factors on syncytin-A expression under microgravity.
• To explore the relationship between syncytin-A, autophagy, and osteoclastogenesis.

Main Methods:

• Utilized RAW264.7 preosteoclast cells and mouse bone marrow cultures.
• Simulated microgravity (μXg) and ground-based conditions (Xg) were employed.
• Assessed syncytin-A expression, autophagy activity (acridine orange staining), and osteoclast formation.
• Employing siRNA for syncytin-A knockdown and confocal microscopy for co-localization studies.

Main Results:

• Microgravity upregulated syncytin-A expression in preosteoclast cells independently of RANKL.
• Syncytin-A expression was found to co-localize with lysosomes.
• RANKL stimulation elevated autophagy, and syncytin-A suppression inhibited autophagy.
• Knockdown of syncytin-A significantly reduced microgravity-induced osteoclast formation.

Conclusions:

• Microgravity induces syncytin-A expression, which promotes autophagy and osteoclast formation.
• Syncytin-A plays a critical role in microgravity-induced bone loss.
• Targeting syncytin-A presents a potential therapeutic strategy to counteract bone loss in spaceflight.