Defective lipid metabolism associated with mutation in klf-2 and klf-3: important roles of essential dietary salts in fat storage

BACKGROUND: Dietary salts are important factors in metabolic disorders. They are vital components of enzymes, vitamins, hormones, and signal transduction that act synergistically to regulate lipid metabolism. Our previous studies have identified that Krüppel-like factor −3 (KLF-3) is an essential regulator of lipid metabolism. However, it is not known if KLF-2 also regulates lipid metabolism and whether KLF-2 and −3 mediate the effects of dietary salts on lipid metabolism. METHODS: In this study, we used klf mutants [homozygous klf-2 (ok1043) V and klf-3 (ok1975) II mutants] to investigate the role of dietary salts in lipid metabolism. All gene expression was quantified by qRT-PCR. Localization of KLF-2 was analyzed by the expression of klf-2::gfp (in pPD95.75 vector) using a fluorescent microscope. Fat storage was measured by Oil Red O staining. RESULTS: Klf-2 was identified to express in the intestine during all stages of Caenorhabditis elegans development with peak expression at L3 stage. Mutation of klf-2 increased fat accumulation. Under regular growth media free of Ca(2+,) the expression of both klf-2 and −3 was inhibited slightly; further their expression reduced significantly in WT worms fed on 10X Ca(2+) diet. When klf-3 was mutated, the expression of klf-2 increased under 10X Ca(2+) diet; but when klf-2 was mutated, the expression of klf-3 was not altered under 10X Ca(2+) diet. Overall, Mg(2+) and K(+) were less effective on the gene expression of klfs. KLF target gene Ce-C/EBP-2 showed elevated expression in WT and klf-3 (ok1975) worms with changed Ca(2+) concentrations but not in klf-2 (ok1043) worms. However, high Ca(+2) diet exhibited inhibitory effect on Ce-SREBP expression in WT worms. CONCLUSION: Dietary Ca(2+) is most effective on fat storage and klf-2 expression, wherein high Ca(2+) diet decreased klf-2 expression and reduced fat buildup. Mechanistic study identified Ce-C/EBP (C48E7.3; lpd-2) and Ce-SREBP (Y47D3B.7; lpd-1) as the target genes of klf-2 and/or klf-3 to mediate lipid metabolism. This study identifies a new function of klf-2 in inhibiting fat buildup and reveals the interplay between dietary salts and klf-2 and klf-3 in lipid metabolism.