Responses of Adipose and Muscle Lipoprotein Lipase to Chronic Infection and Subsequent Acute Lipopolysaccharide Challenge

Abstract

ABSTRACT Infection of male Swiss Webster mice with Toxoplasma gondii or Neospora caninum leads to long-term alterations in energy balance. Following an initial 20 to 30% weight loss in all T. gondii -infected mice, half of the animals regain most of the lost weight (gainers), whereas the others maintain their low body weight (nongainers). Infection with N. caninum does not elicit weight loss. Lipoprotein lipase (LPL), the enzyme responsible for plasma triglyceride (TG) clearance and partitioning among tissues, is under tissue-specific modulation associated with energy balance. It is also a major determinant of infection-induced hypertriglyceridemia. This study aimed to assess the long-term modulation of adipose and muscle LPL activity in mice infected with T. gondii or N. caninum , to evaluate the effects of subsequent acute lipopolysaccharide (LPS) administration, and to relate LPL modulation in these conditions with infection-related changes in body weight gain. Twenty-eight days after infection, LPL activity in muscle of both gainer and nongainer T. gondii -infected mice was reduced by 40 to 50% compared with the levels in controls and N. caninum -infected mice, whereas LPL activity in adipose depots remained unchanged in all infected groups compared to the level in controls. LPS (from Escherichia coli , 100 ng/kg) injection induced a global reduction in adipose LPL in all groups, as assessed 90 min later. In both T. gondii -infected subgroups, muscle LPL was not further reduced by LPS treatment, whereas it was decreased by 40 to 50% in muscles of control and N. caninum -infected mice. Pre-LPS TG levels in plasma were similar in all groups. LPS greatly increased TG levels in plasma in both control and N. caninum -infected animals, whereas it did not alter those of T. gondii -infected gainer or nongainer animals. These results show that (i) independently of the extent of postinfection weight gain, long-term infection with T. gondii chronically reduces muscle LPL, which becomes unresponsive to acute endotoxemia; (ii) modulation of tissue LPL activity during chronic T. gondii infection favors TG partitioning towards adipose tissue; and (iii) skeletal muscle LPL is a key determinant of the acute response of triglyceridemia to LPS.