Gene expression, synthesis and degradation of hyaluronan during differentiation of 3T3-L1 adipocytes

The high molecular weight glycosaminoglycan hyaluronan (HA) is an essential component of the extracellular matrix (ECM), however, the link between HA regulation and development of the adipocyte ECM, which is essential for differentiation, remains undefined. Hyaluronan synthase gene expression, HA synthetic rate and molecular weight during differentiation of 3T3-L1 pre-adipocytes were compared to undifferentiated 3T3-L1 pre-adipocytes and non-adipogenic NIH/3T3 fibroblasts. In the 3T3-L1 pre-adipocytes, the predominant genes associated with HA metabolism were found to be HA synthase-2 (Has-2) and hyaluronidase-2 (Hyal-2) demonstrating a co-regulation of expression which was stimulated by adipogenic induction consequently resulting in increased synthesis of high molecular weight HA (>10 MDa) and its simultaneous degradation. Accumulation of HA correlated positively with cell number, although synthetic rate was inversely related suggesting a regulatory feedback mechanism. Within 24 h post-induction, pre-adipocytes responded with a higher HA synthetic rate and later, accumulated cytoplasmic lipid. In contrast, undifferentiated pre-adipocytes had a reduced HA synthetic rate during clonal expansion and did not accumulate lipid. HA was continuously and rapidly metabolised throughout 3T3-L1 adipogenesis, where terminal differentiation coincided with the increased generation of low molecular weight, angiogenic HA fragments, a likely prerequisite for concurrent neovascularisation of adipose tissue. This study has highlighted a relationship between HA metabolism and adipocyte differentiation, suggesting that the balance between the formation and regulation of the adipocyte extracellular matrix is finely coordinated in a growth phase-specific dependent manner.