Effect of Vitamin D on Adipogenesis under Hypoxia

Background Obesity and pandemic vitamin D (vitD) deficiency both share similar pathological associations with adipose tissue chronic inflammation leading to well‐known conditions such as insulin resistance and hypertension. Understanding adipogenesis is of major relevance for human health, as increased adiposity leads to cellular hypoxia followed by inflammation, oxidative damage and adipocyte dysfunction resulting in metabolic diseases. We have shown earlier that vitD supplementation has significant beneficial effects on adipocyte inflammation and improved insulin sensitivity in vitD deficient mice. The modulation of adipogenesis under these circumstances might be beneficial in improving its metabolic functioning. Therefore, we hypothesize that vitD modulates adipogenesis in pathological conditions (hypoxia). Methods Human mesenchymal stem cells (hMSCs) were differentiated into adipocytes ± vitD [10 −7 M] containing adipogenic induction and maintenance medium under either hypoxic (1% O2) or normoxic (21% O2) conditions. At the end of differentiation cycles the process was assessed by the oil red O staining of the adipocytes. Fully differentiated adipocytes were stimulated with lipopolysaccharide (LPS 10 ng/ml) ± vitD [10 −7 M] for 24 hrs and cells and cell culture supernatants were collected from both hypoxic and normoxic basal ± vitD [10 −7 M] as well LPS stimulated ± vitD [10 −7 M]. The inflammatory marker interleukin‐6 (IL‐6) levels were measured by ELISA. RNA and cell lysate were prepared and analyzed for adipogenic, hypoxic and inflammation regulating proteins. Results The adipogenic differentiation of hMSCs under hypoxia was significantly inhibited in comparison to the normoxia. VitD [10 −9 M to 10 −7 M] significantly enhanced adipogenic differentiations dose dependently under both hypoxic and normoxic culture conditions. VitD [10 −7 M] inhibited basal IL‐6 secretion by 83% in hypoxic and 66% in normoxic hMSCs differentiated adipocytes in comparison to their respective controls (p<0.05). In addition, vitD dose dependently reduced LPS induced IL‐6 secretion from hMSCs differentiated adipocytes under both hypoxic (10 −7 M:10 −8 M:10 −7 M; 66%:40%:19%) and normoxic (10 −7 M:10 −8 M:10 −7 M; 56%:44%:2%) condition in comparison with the LPS 10 ng/ml alone. Conclusion Our data demonstrates that vitD enhances the adipogensis of hMSCs under hypoxic culture condition; it inhibits basal IL‐6 release as well LPS induced IL‐6 release under both hypoxia and normoxia. This suggests that sufficient vitD levels would be able to modulate the hypoxia induced inflammation and adipogenic differentiation potential in obese subjects. These vitD actions might therefore partially mediate the beneficial effect on insulin sensitivity of adipose tissue and reduce the risk of known co‐morbidities of obesity. Support or Funding Information Supported in part by the Academy of Finland and DynaHEALTH EU No.633595