Dynamic upregulation of CD24 in pre-adipocytes promotes adipogenesis

Abstract

The development of mature adipocytes from pre-adipocytes is a highly regulated process. CD24 is a glycophosphatidylinositol-linked cell surface receptor that has been identified as a critical cell surface marker for identifying pre-adipocytes that are able to reconstitute white adipose tissue (WAT) in vivo. Here, we examined the role and regulation of CD24 during adipogenesis in vitro. We found that CD24 mRNA and protein expression is upregulated early during adipogenesis in the 3T3-L1 pre-adipocytes and in murine primary pre-adipocytes isolated from subcutaneous and visceral WAT, followed by downregulation in mature adipocytes. CD24 mRNA expression was found to be dependent on increased transcription due to increased promoter activity in response to activation of a pre-existing transcriptional regulator. Furthermore, either intracellular cAMP or dexamethasone were sufficient to increase expression in pre-adipocytes, while both additively increased CD24 expression. Preventing the increase in CD24 expression, by siRNA-mediated knock-down, resulted in fewer mature lipid-laden adipocytes and decreased expression of mature adipogenic genes. Therefore, conditions experienced during adipogenesis in vitro are sufficient to increase CD24 expression, which is necessary for differentiation. Overall, we conclude that the dynamic upregulation of CD24 actively promotes adipogenesis in vitro.

Keywords:

• 3T3-L1
• adipogenesis
• CD24
• dexamethasone
• IBMX
• primary pre-adipocytes

Abbreviations:

• WAT, white adipose tissue
• SVF, stromal vascular fraction
• ADSC, adipose-derived stem cell
• GR, glucocorticoid receptor
• IBMX, 3-isobutyl-1-methylxanthine
• Dex, dexamethasone
• NCS, newborn calf serum
• KRH, krebs-ringer-HEPES bicarbonate buffer
• CHX, cycloheximide
• ActD, actinomycin-D
• BCA, bicinchoninic acid
• adipoq, adiponectin
• PKG, cGMP-dependent protein kinase

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank Sukhinder Cheema for helpful discussions and sharing of reagents. We gratefully acknowledge the technical contributions of Shamara Alexander and Lisa Pinto.

Funding

This work was funded by the Research and Development Corporation (RDC) of Newfoundland and the Canadian Institutes of Health Research (CIHR) Institute of Nutrition, Metabolism and Diabetes.