Adipsin and an endogenous pathway of complement from adipose cells

Area of Science:

• Immunology
• Metabolic Research
• Adipose Tissue Biology

Background:

• The alternative complement pathway is crucial for immune responses against pathogens.
• Adipose cells synthesize adipsin (complement factor D homolog), with reduced levels in obesity.
• The role of adipose tissue in complement activation is not fully understood.

Purpose of the Study:

• To investigate the synthesis and activation of alternative complement pathway components by adipose cells and tissue.
• To determine if adipose tissue can activate the proximal alternative complement pathway independently of infection.
• To examine the impact of obesity on localized complement activation in adipose tissue.

Main Methods:

• In vitro synthesis of complement factors C3 and B by cultured adipocytes and adipose tissue explants.
• Detection of complement activation products, including anaphylatoxin C3a.
• Comparison of complement activation in adipose tissue from lean and obese mice.

Main Results:

• Adipose cells and tissue synthesize complement factors C3 and B.
• Adipose tissue activates the proximal alternative complement pathway, producing bioactive polypeptides like C3a.
• This activation occurs without triggering the terminal lytic pathway and is impaired in obese mice.
• Cultured adipocytes require cytokine stimulation, while adipose tissue explants do not.

Conclusions:

• Adipose tissue represents a localized site for alternative complement pathway activation.
• This pathway activation in adipose tissue is linked to metabolic state and potentially energy balance.
• Impaired complement activation in obesity suggests a novel role in metabolic dysfunction.