Hepatic lipin 1beta expression is diminished in insulin-resistant obese subjects and is reactivated by marked weight loss.
OBJECTIVE
Lipin 1 plays critical roles in controlling energy metabolism. We sought to determine the expression of lipin 1 isoforms (lipin 1alpha and -beta) in liver and adipose tissue of obese subjects and to evaluate cellular mechanisms involved in the regulation of lipin 1 expression by physiologic stimuli.


METHODS
The expression of lipin 1alpha and -beta was quantified in liver and adipose tissue of extremely obese (average BMI 60.8 kg/m(2)) human subjects undergoing gastric bypass surgery (GBS). Second, the expression of lipin 1 was evaluated in HepG2 cells in response to overexpression of peroxisome proliferator-activated receptor-gamma coactivator (PGC)-1alpha under normal or hyperinsulinemic conditions.


RESULTS
The expression of lipin 1beta in liver and adipose tissue was inversely related to BMI, fasting plasma insulin concentration, and the homeostasis model assessment of insulin resistance but was significantly increased by marked weight loss and insulin sensitization following GBS. Hepatic lipin 1beta mRNA levels were strongly correlated with the expression of PGC-1alpha, and overexpression of PGC-1alpha in HepG2 cells increased lipin 1 expression. Conversely, hyperinsulinemic culture conditions downregulated the expression of lipin 1beta, PGC-1alpha, and their known target genes involved in mitochondrial metabolism in HepG2 cells. Finally, overexpression of lipin 1beta or PGC-1alpha reversed the effect of hyperinsulinemia on the expression of their target genes.


CONCLUSIONS
These studies suggest that hepatic lipin 1beta and PGC-1alpha expression are downregulated by obesity and obesity-related metabolic perturbations in human subjects, likely due to alterations in insulin concentration or sensitivity.
Croce
Michelle A
MA
Center for Human Nutrition, Washington University School of Medicine, St. Louis, MO 63110, USA.
Eagon
J Christopher
JC
LaRiviere
Lori L
LL
Korenblat
Kevin M
KM
Klein
Samuel
S
Finck
Brian N
BN
D000273:Adipose Tissue / Q000503:physiopathology*; D050110:Bariatric Surgery; D003920:Diabetes Mellitus / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics*; D008099:Liver / Q000502:physiology / Q000503:physiopathology*; D009687:Nuclear Proteins / Q000235:genetics*; D009765:Obesity / Q000503:physiopathology*; D009767:Obesity, Morbid / Q000235:genetics / Q000503:physiopathology / Q000601:surgery; D010711:Phosphatidate Phosphatase; D015431:Weight Loss
D009687:Nuclear Proteins; C485999:LPIN1 protein, human; D010711:Phosphatidate Phosphatase