GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes

BACKGROUND

Glycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance.

OBJECTIVE

We asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur.

METHODS

Mouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined.

RESULTS

Overexpressing GPAT1 in mouse hepatocytes impaired insulin's suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects.

CONCLUSION

These data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin's ability to suppress hepatic glucose production in primary mouse hepatocytes.

Charge form factor of the neutron at low momentum transfer from the 2H-->(e-->,e'n)1H reaction

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.

Serologic study of specimens with borderline FTA-ABS test reactivity

The treponemal group-specific absorbed fluorescent antibody test (FTA-ABS) does not yield clearly positive or negative results in all instances. This study was designed to analyze those sera showing borderline reactivity, in order to determine whether additional tests may help to resolve serodiagnostic problem cases. FTA-ABS tests on 23,807 sera submitted to the Wisconsin State Laboratory of Hygiene yielded borderline results with 479 specimens (2%). Patients showing inconclusive FTA-ABS test reactivity were equally distributed among older and younger age groups, and 6% of borderline cases were women. Of all the 479 specimens, only five sera (1%) gave a non-specific hemagglutination with the Treponema pallidum microhemagglutination (MHA-TP) test, with 82.5% of the FTA-ABS test borderline sera yielding negative results with the MHA-TP test. Because recent findings had shown atypical false fluorescence with the FTA-ABS test on sera from patients with antinuclear antibody, the fluorescent antinuclear antibody test (FANA) was also performed on specimens inconclusive with the FTA-ABS test. Only seven sera (1.5%) were reactive by the FANA test, suggesting that antinuclear antibody was not a significant cause of borderline FTA-ABS reactions. The implications of these findings to venereal disease serology laboratory practice are discussed.