Reduced lipoprotein lipase activity in postural skeletal muscle during aging.

Lipoprotein lipase (LPL) is a key enzyme for fatty acid and lipoprotein metabolism in muscle. However, the effect of aging on LPL regulation in skeletal muscle is unknown. We report the effect of aging on LPL regulation in the soleus (red oxidative postural) muscle and the tibialis anterior (white glycolytic non-weight-bearing) muscle in 4- and 24-mo-old Fischer 344 rats and 18- and 31-mo-old Fischer 344 x Brown-Norway F1 (F-344 x BN F1) rats. Total and heparin-releasable LPL (HR-LPL) activities were decreased 38% (P < 0.01) and 52% (P < 0.05), respectively, in the soleus muscle of the older Fischer 344 rats. There was a 32% reduction (P < 0.05) of total LPL protein mass in the soleus muscle with aging. The results were confirmed in another strain. A decrease of total LPL activity (-50%, P < 0.05) was also found in the soleus muscle between 18- and 31-mo-old F-344 x BN F1 rats. LPL mRNA concentration in the soleus muscle was not different between ages. Total LPL protein mass was reduced by 46% (P < 0.05) in the soleus muscle of the 31-mo-old F-344 x BN F1 rats. In the tibialis anterior muscle, neither LPL activity nor mRNA concentration was affected by age in either strain. In conclusion, LPL regulation in a non-weight-bearing muscle was not affected by aging. However, there was a pronounced reduction in LPL activity and LPL protein mass in postural muscle with aging.