Decreased lipid absorption due to reduced pancreatic lipase activity in aging male mice

Malnutrition due to aging is partly caused by decreased absorption of nutrients by the gastrointestinal tract. However, the underlying mechanism is unclear and changes in lipid absorption with aging are poorly understood. In this study, changes in lipid absorption with aging were examined in mice aged 3 and 25 months. After overnight fasting, blood samples were collected from snipped tails and then soybean oil was administered orally. Three hours later, mice were sacrificed by decapitation and the liver, pancreas, small intestine and blood were collected. The increase in serum triacylglycerol after soybean oil administration was significantly lower in the older mice, indicating a decrease in lipid absorption with aging. Measurement of mRNA levels for triacylglycerol absorption-related genes showed that mRNA for pancreatic lipase tended to decrease in 25-month-old mice. There was no significant difference in the protein level of pancreatic lipase, but the enzyme activity showed a significant decrease in the older mice. To examine this mechanism, expression levels of mRNA for protein turnover-related genes in the pancreas were measured. The level of a proteasomal mRNA showed a significant decrease in 25-month-old mice. This suggests that the ability to degrade unfolded protein decreases in the aging pancreas, and that this leads to reduction of pancreatic lipase activity and a decrease in lipid absorption.