Vitamin D and adipose tissue-more than storage

Area of Science:

• Endocrinology
• Metabolic Research
• Nutritional Science

Background:

• Obesity rates increased during the pandemic, correlating inversely with vitamin D levels.
• Higher Body Mass Index (BMI) is causally linked to lower 25-hydroxyvitamin D (25(OH)D) levels.
• Adipose tissue inflammation is a key factor in metabolic disorders like metabolic syndrome.

Purpose of the Study:

• To investigate the physiological functions of 1,25(OH)2D3 (calcitriol) in adipose tissue.
• To clarify the molecular interactions of 1,25(OH)2D3, vitamin D binding proteins (VDBPs), and the vitamin D receptor (VDR) within adipose tissue.
• To understand the role of vitamin D in regulating adipogenesis, inflammation, and adipocyte secretion.

Main Methods:

• Analysis of existing microarray datasets from human adipocytes.
• Examination of VDR knock out (VDR(-/-)) and CYP27B1 knock out (CYP27B1 (-/-)) mouse models.
• Review of experimental studies on 1,25(OH)2D3 effects in cell lines and animal models.

Main Results:

• Higher BMI causally relates to lower 25(OH)D, but not vice versa.
• 1,25(OH)2D3 and its metabolites inhibit adipocyte formation in mouse cell lines but promote preadipocyte differentiation in human cell cultures.
• VDR(-/-) and CYP27B1(-/-) mice show resistance to diet-induced weight gain; VDR overexpression in adipose tissue increases fat mass.
• Human adipocytes can produce active 1,25(OH)2D3, indicated by VDR and CYP27B1 gene upregulation.
• Experimental studies confirm 1,25(OH)2D3 modulates adipose tissue inflammation, adipogenesis, and secretion.

Conclusions:

• 1,25(OH)2D3 actively influences adipose tissue by modulating inflammation, adipogenesis, and secretion.
• While vitamin D's role in adipose tissue is evident, further in vivo studies are required.
• Determining effective dosages and in vivo effects of vitamin D in human adipose tissue is crucial for understanding its relevance in associated diseases.