Endocrine Abstracts

Obesity (excess adipose tissue generated by hypertrophy and hyperplasia) predisposes to poor health. Adipogenesis (hyperplasia) involves the differentiation of adherent preadipocytes into non-adherent adipocytes and is accompanied by alterations to the extracellular matrix of which hyaluronan (HA) is a component. Used in vitro to promote lineage specific differentiation, little is known of HA’s role in adipogenesis. We hypothesise that HA modifications must occur during adipogenesis and have undertaken studies to investigate.

Experiments were performed in complete (CM) and differentiation medium (DM), containing a PPARγ agonist. Human preadipocytes were obtained (with ethical approval and informed consent) from sub-cutaneous adipose tissue and treated with or without 0.1 mM 4-methylumbelliferone (4 MU, inhibitor of HA synthesis) for 20 days. HA in medium (ELISA) and HA synthase (HAS) transcripts (QPCR) were measured. Adipogenesis was assessed by oil red O (ORO) staining, counting adipogenic foci and QPCR measurement of differentiation markers (LPL). Protein expression of phospho-Akt and PPARγ were analyzed by western-blot.

Human primary preadipocytes (n=6) cultured for 20 days in DM displayed morphological and other signs of adipogenesis; this was accompanied by significant decrease in transcripts for HAS1, HAS2, and HAS3 and HA secreted into the culture medium compared with CM. Addition of 4 MU to DM, enhanced adipogenesis and produced fold increases of 4.1±0.63 (foci), 2.6±0.21 (LPL transcripts) and 1.52±0.18 (ORO). Surprisingly, although 4 MU treatments decreased HA production in preadipocytes in CM, this did not occur in DM. However, levels of pAkt and PPARγ protein were increased 20% (P=0.04) and 40% PPARγ (P=0.01) respectively when comparing DM with/without 4 MU.

Our study demonstrates that HAS transcripts and HA are decreased during adipogenesis and that the process is enhanced by an HA inhibitor. However the mechanism underlying the observations may involve signaling within the cell (e.g. pAkt) rather than through a surface receptor, further investigations are required.