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Developmental changes in cholesterol 7alpha- and 27-hydroxylases in the piglet
1Department of Food Science and Human Nutrition, Iowa State University, Ames 50011, USA. dslewis@iastate.edu
Insights
Hepatic cholesterol 7alpha-hydroxylase (CYP7A) activity increases after birth in piglets, regulated by pretranslational mechanisms. Fasting significantly reduces CYP7A activity and mRNA levels, with recovery after refeeding.
Area of Science:
- Biochemistry
- Developmental Biology
- Metabolic Regulation
Background:
- Cholesterol metabolism is crucial for development and is regulated by specific enzymes.
- Hepatic cholesterol 7alpha-hydroxylase (CYP7A) and sterol 27-hydroxylase are key enzymes in bile acid synthesis.
- Understanding the developmental regulation of these enzymes is essential for pediatric and metabolic research.
Purpose of the Study:
- To investigate the developmental expression and regulation of hepatic CYP7A and sterol 27-hydroxylase activities and mRNA levels in piglets.
- To determine the impact of nutritional status (suckling, weaning, fasting, refeeding) on these enzymes.
- To elucidate the regulatory mechanisms controlling CYP7A activity during development.
Main Methods:
- Measurement of hepatic CYP7A and sterol 27-hydroxylase enzyme activities using microsomes from piglets at various developmental stages.
- Quantification of hepatic CYP7A mRNA levels using Northern blot analysis.
- Analysis of enzyme activity and mRNA levels following periods of fasting and refeeding.
Main Results:
- Hepatic CYP7A activity and mRNA were undetectable in fetal and newborn piglets, increasing significantly by weaning age.
- Fasting for 14 hours reduced CYP7A activity and mRNA by over 80%, with delayed recovery after refeeding.
- Sterol 27-hydroxylase activity was also low at birth but increased by 21 days and showed rapid recovery after refeeding, unlike CYP7A.
Conclusions:
- Developmental regulation of hepatic CYP7A activity in piglets is primarily controlled at the pretranslational level.
- Nutritional status, particularly fasting and refeeding, significantly impacts CYP7A expression and activity.
- The distinct regulation patterns of CYP7A and sterol 27-hydroxylase highlight their specific roles in cholesterol metabolism during development.
Abstract:
Hepatic cholesterol 7alpha-hydroxylase (CYP7A) and sterol 27 hydroxylase activities were measured in fetal, newborn, suckling, and weaned piglets from 76 d into gestation to 49 d of age. Hepatic CYP7A activity was not detected in fetal microsomes, but it increased to 6.8 +/- 2.6 pmol/min x mg(-1) protein in suckling piglets at 21 d of age and to 18.2 +/- 2.5 in weaned piglets at 49 d of age. Hepatic CYP7A activity was not different between 49-d-old piglets weaned at 21 d and piglets suckled for 49 d (18.9 +/- 2.6 and 18.2 +/- 2.5 pmol/min x mg protein, respectively). Fasting for 14 h decreased CYP7A activity by 86% in both suckled and weaned piglets. Cholesterol 7alpha-hydroxylase activity remained decreased for at least 5 h after refeeding. Sterol 27-hydroxylase activity was also undetectable near birth, but was detectable by 21 d of age. Postnatally, sterol 27-hydroxylase activity was not influenced by age or suckling and weaning, as was CYP7A. Sterol 27-hydroxylase was decreased by 80% in piglets deprived of feed compared with piglets given free access. In contrast to CYP7A activity, 27-hydroxylase activity returned within 5 h after refeeding to levels observed in piglets given ad libitum access to feed. Similar to CYP7A enzyme activity, hepatic CYP7A mRNA was not detected in newborn piglets, but increased from 2.7 +/- 1.7 pg mRNA/microg RNA in suckling piglets at 21 d to 13.7 +/- 1.2 in 49-d-old piglets weaned at 21 d. As with enzyme activity, feed deprivation decreased CYP7A mRNA to barely detectable levels (< .5 pg/microg RNA), and which remained decreased for at least 5 h following refeeding (.6 +/- .3 and 2.67 +/- .4 pg mRNA/microg RNA for suckled and weaned piglets, respectively). In piglets allowed free access to feed, CYP7A mRNA concentrations were associated positively (P = .001) with enzyme activity. These results suggest that developmental regulation of CYP7A activity is the result of a pretranslational mechanism.