Macrophage elastase (MMP-12) in expanding murine adipose tissue.

BACKGROUND: Matrix metalloproteinases (MMPs) are known to play a role in adipose tissue development, but little information is available on the role of individual proteinases. Expansion of adipose tissue is associated with an increased macrophage content. Macrophage elastase (MMP-12) has an important role in macrophage infiltration, which induces pro-inflammatory effects in adipose tissue.
METHODS: The role of MMP-12 was investigated in adipose tissues of MMP-12 deficient and wild-type control mice kept on normal chow or on high fat diet for 15 weeks.
RESULTS: MMP-12 deficiency had no significant effect on total body weight or on subcutaneous (SC) or gonadal (GON) adipose tissue mass. Adipocyte and blood vessel size and density in SC and GON adipose tissues of obese mice were also comparable in MMP-12 deficient and control mice. Macrophage infiltration in SC and GON adipose tissues was not affected by MMP-12 deficiency, but the amount of crown-like structures (CLS) was significantly lower. MMP-12 deficiency did not affect elastin content in the extracellular matrix of SC or GON adipose tissue.
CONCLUSIONS: Adipose tissue mass and composition in mice with nutritionally induced obesity was not markedly affected by MMP-12 deficiency, except for an apparently lower degree of CLS. GENERAL SIGNIFICANCE: MMP-12 does not seem to be essential for macrophage infiltration in adipose tissue, but contributes to the formation of CLS surrounding moribund adipocytes.