Intraperitoneal Administration of Short-Chain Fatty Acids Improves Lipid Metabolism of Long–Evans Rats in a Sex-Specific Manner

Short-chain fatty acids (SCFAs) are microbial metabolites, mainly generated by the action of gut microbiota on dietary fibers. Acetate, propionate, and butyrate are the three main SCFAs produced typically in a 60:20:20 molar ratio in the colon. Acetate, propionate, and butyrate, when given individually as supplements, have shown a protective role in obesity and hyperglycemia; however, the sex-specific effects of a mixture of SCFAs, when given in 60:20:20 ratio, on the regulation of lipid metabolism and lipid profile are not known. Male and female Long–Evans rats were given a mixture of SCFAs (acetate, propionate, and butyrate; molar ratio 60:20:20) each day for seven days intraperitoneally; plasma and hepatic lipids, gene expression, and lipidomics profile were analyzed. SCFAs significantly decreased plasma and hepatic triglycerides and cholesterol in males, whereas the fatty acyl composition of cholesteryl esters, triglycerides, and phospholipids was modulated in females. SCFAs decreased the mRNA expression of hepatic acetyl-CoA carboxylase-1 in both males and females. Our findings demonstrate for the first time that SCFAs (60:20:20) improved plasma and hepatic lipid levels and fatty acyl composition in a manner that may provide cardio-protective and anti-inflammatory effects in both sexes, via independent mechanisms.

A Novel Lysophosphatidic Acid Acyltransferase of Escherichia coli Produces Membrane Phospholipids with a cis-vaccenoyl Group and Is Related to Flagellar Formation

Lysophosphatidic acid acyltransferase (LPAAT) introduces fatty acyl groups into the sn-2 position of membrane phospholipids (PLs). Various bacteria produce multiple LPAATs, whereas it is believed that Escherichia coli produces only one essential LPAAT homolog, PlsC—the deletion of which is lethal. However, we found that E. coli possesses another LPAAT homolog named YihG. Here, we show that overexpression of YihG in E. coli carrying a temperature-sensitive mutation in plsC allowed its growth at non-permissive temperatures. Analysis of the fatty acyl composition of PLs from the yihG-deletion mutant (∆yihG) revealed that endogenous YihG introduces the cis-vaccenoyl group into the sn-2 position of PLs. Loss of YihG did not affect cell growth or morphology, but ∆yihG cells swam well in liquid medium in contrast to wild-type cells. Immunoblot analysis showed that FliC was highly expressed in ∆yihG cells, and this phenotype was suppressed by expression of recombinant YihG in ∆yihG cells. Transmission electron microscopy confirmed that the flagellar structure was observed only in ∆yihG cells. These results suggest that YihG has specific functions related to flagellar formation through modulation of the fatty acyl composition of membrane PLs.

Sec17 can trigger fusion of trans-SNARE paired membranes without Sec18

Sec17 [soluble N-ethylmaleimide–sensitive factor (NSF) attachment protein; α-SNAP] and Sec18 (NSF) perform ATP-dependent disassembly of cis-SNARE complexes, liberating SNAREs for subsequent assembly of trans-complexes for fusion. A mutant of Sec17, with limited ability to stimulate Sec18, still strongly enhanced fusion when ample Sec18 was supplied, suggesting that Sec17 has additional functions. We used fusion reactions where the four SNAREs were initially separate, thus requiring no disassembly by Sec18. With proteoliposomes bearing asymmetrically disposed SNAREs, tethering and trans-SNARE pairing allowed slow fusion. Addition of Sec17 did not affect the levels of trans-SNARE complex but triggered sudden fusion of trans-SNARE paired proteoliposomes. Sec18 did not substitute for Sec17 in triggering fusion, but ADP- or ATPγS-bound Sec18 enhanced this Sec17 function. The extent of the Sec17 effect varied with the lipid headgroup and fatty acyl composition of the proteoliposomes. Two mutants further distinguished the two Sec17 functions: Sec17L291A,L292A did not stimulate Sec18 to disassemble cis-SNARE complex but triggered the fusion of trans-SNARE paired membranes. Sec17F21S,M22S, with diminished apolar character to its hydrophobic loop, fully supported Sec18-mediated SNARE complex disassembly but had lost the capacity to stimulate the fusion of trans-SNARE paired membranes. To model the interactions of SNARE-bound Sec17 with membranes, we show that Sec17, but not Sec17F21S,M22S, interacted synergistically with the soluble SNARE domains to enable their stable association with liposomes. We propose a model in which Sec17 binds to trans-SNARE complexes, oligomerizes, and inserts apolar loops into the apposed membranes, locally disturbing the lipid bilayer and thereby lowering the energy barrier for fusion.