Increased thermoregulation in cold-exposed transgenic mice overexpressing lipoprotein lipase in skeletal muscle: An avian phenotype?

LPL is an enzyme involved in the breakdown and uptake of lipoprotein triglycerides. In the present study, we examined how the transgenic (Tg) overexpression of human LPL in mouse skeletal muscle affected tolerance to cold temperatures, cold-induced thermogenesis, and fuel utilization during this response. Tg mice and their non-transgenic controls were placed in an environmental chamber and housed in metabolic chambers that monitored oxygen consumption and carbon dioxide production with calorimetry. When exposed to 4°C, an attenuation in the decline in body temperature in Tg mice was accompanied by an increased metabolic rate (15%; P < 0.001) and a reduction in respiratory quotient (P < 0.05). Activity levels, the expression of uncoupling proteins in brown fat and muscle, and lean mass failed to explain the enhanced cold tolerance and thermogenesis in Tg mice. The more oxida- tive type IIa fibers were favored over the more glycolytic type IIb fibers ( P < 0.001) in the gastrocnemius and quadriceps muscles of Tg mice.