LIPOPROTEIN LIPASE DEFICIENCY, HYPERTRIGLYCERIDEMIA, AND INSULIN
RESISTANCE
PhD student Sofia Beck Mikkelsen, Department of Endocrinology M, Odense University Hospital
The metabolic syndrome is comprised of a cluster of metabolic disorders, of which many
promote the development of atherosclerosis, increase the risk of cardiovascular disease and
diabetes. Insulin resistance is at the heart of the metabolic syndrome. Elevated serum
triglycerides commonly associate with insulin resistance and represent a valuable clinical
marker of the metabolic syndrome. Familial lipoprotein lipase (LPL) deficiency is an inherited
condition that disrupts the normal breakdown of triglycerides in the body. It is increasingly
being recognized that heterozygous mutations that cause decreased LPL activity are associated
with insulin resistance and the metabolic syndrome in humans, however, the molecular
mechanisms underlying this association is not known. We hypothesize that mutations within
the lipoprotein lipase gene lead to accumulation of lipid metabolites in skeletal muscle that
impairs insulin signalling and glucose metabolism which subsequently induce insulin resistance.
By means of molecular biology and biochemistry we aim to identify the molecular mechanisms
by which hypertriglyceridemia induces insulin resistance in skeletal muscle in human subjects.
Blood samples from hypertriglyceridemic subjects with and without Type 2 Diabetes are used
to identify novel mutations within the LPL gene or within regulators of LPL activity. Whereas
blood samples and muscle biopsies taken from patients with hypertriglyceridemia carrying a
well-defined LPL mutation and healthy subjects is used to identify and quantify alterations in
the
lipid
composition
of
plasma
and
muscle
cells,
and
to
examine
how
severe
hypertriglyceridemia (induced by LPL mutations) affects insulin sensitivity, glucose and fat
metabolism, and insulin signalling in skeletal muscle in vivo.
Novel LPL mutations are identified by DHPLC, and candidates will be selected and identified by
DNA sequencing. Lipidomic profiling in response to loss of lipoprotein lipase activity is
determined by lipid mass spectrometry, and the overall fatty acid- and acyl-coA composition is
examined by gas chromatography and HPLC, respectively. Genes previously described to be
regulated by insulin and possible regulatory genes will be examined by qRT-PCR. The level and
phosphorylation of protein components involved in insulin signalling including the insulin
receptor, IRS proteins, Akt1/PKB, GSK3, and FOXOs will be examined by Western Blotting.
Based on the results obtained from the qRT-PCR and Western blotting analyses, mechanistic
studies in cultured muscle cells are performed.