Li Kang, Wesley H. Mayes, Freyja D. James, Deanna P. Bracy, David H. Wasserman
Increased extracellular matrix (ECM) collagen is a characteristic of muscle insulin resistance. Matrix metalloproteinase (MMP) 9 is a primary enzyme that degrades collagen IV (ColIV). As a component of the basement membrane, ColIV plays a key role in ECM remodelling. We tested the hypotheses that genetic deletion of MMP9 in mice increases muscle ColIV, induces insulin resistance in lean mice and worsens diet-induced muscle insulin resistance.
Wild-type (Mmp9 +/+) and Mmp9-null (Mmp9 −/−) mice were chow or high-fat (HF) fed for 16 weeks. Insulin action was measured by the hyperinsulinaemic–euglycaemic clamp in conscious weight-matched surgically catheterised mice.
Mmp9 −/− and HF feeding independently increased muscle ColIV. ColIV in HF-fed Mmp9 −/− mice was further increased. Mmp9 −/− did not affect fasting insulin or glucose in chow- or HF-fed mice. The glucose infusion rate (GIR), endogenous glucose appearance (EndoRa) and glucose disappearance (Rd) rates, and a muscle glucose metabolic index (Rg), were the same in chow-fed Mmp9 +/+ and Mmp9 −/− mice. In contrast, HF-fed Mmp9 −/− mice had decreased GIR, insulin-stimulated increase in Rd and muscle Rg. Insulin-stimulated suppression of EndoRa, however, remained the same in HF-fed Mmp9 −/− and Mmp9 +/+ mice. Decreased muscle Rg in HF-fed Mmp9 −/− was associated with decreased muscle capillaries.
Despite increased muscle ColIV, genetic deletion of MMP9 does not induce insulin resistance in lean mice. In contrast, this deletion results in a more profound state of insulin resistance, specifically in the skeletal muscle of HF-fed mice. These results highlight the importance of ECM remodelling in determining muscle insulin resistance in the presence of HF diet.