Acyl CoA synthetase 5 (ACSL5) ablation in mice increases energy expenditure and insulin sensitivity and delays fat absorption

Objective

The family of acyl-CoA synthetase enzymes (ACSL) activates fatty acids within cells to generate long chain fatty acyl CoA (FACoA). The differing metabolic fates of FACoAs such as incorporation into neutral lipids, phospholipids, and oxidation pathways are differentially regulated by the ACSL isoforms. In vitro studies have suggested a role for ACSL5 in triglyceride synthesis; however, we have limited understanding of the in vivo actions of this ACSL isoform.

Methods

To elucidate the in vivo actions of ACSL5 we generated a line of mice in which ACSL5 expression was ablated in all tissues (ACSL5^−/−).

Results

Ablation of ACSL5 reduced ACSL activity by ∼80% in jejunal mucosa, ∼50% in liver, and ∼37% in brown adipose tissue lysates. Body composition studies revealed that ACSL5^−/−, as compared to control ACSL5^loxP/loxP, mice had significantly reduced fat mass and adipose fat pad weights. Indirect calorimetry studies demonstrated that ACSL5^−/− had increased metabolic rates, and in the dark phase, increased respiratory quotient. In ACSL5^−/− mice, fasting glucose and serum triglyceride were reduced; and insulin sensitivity was improved during an insulin tolerance test. Both hepatic mRNA (∼16-fold) and serum levels of fibroblast growth factor 21 (FGF21) (∼13-fold) were increased in ACSL5^−/− as compared to ACSL5^loxP/loxP. Consistent with increased FGF21 serum levels, uncoupling protein-1 gene (Ucp1) and PPAR-gamma coactivator 1-alpha gene (Pgc1α) transcript levels were increased in gonadal adipose tissue. To further evaluate ACSL5 function in intestine, mice were gavaged with an olive oil bolus; and the rate of triglyceride appearance in serum was found to be delayed in ACSL5^−/− mice as compared to control mice.

Conclusions

In summary, ACSL5^−/− mice have increased hepatic and serum FGF21 levels, reduced adiposity, improved insulin sensitivity, increased energy expenditure and delayed triglyceride absorption. These studies suggest that ACSL5 is an important regulator of whole-body energy metabolism and ablation of ACSL5 may antagonize the development of obesity and insulin resistance.

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Role of acyl CoA synthetase 5 (ACSL5) in systemic metabolism was studied in an ACSL5 deficient mouse.

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ACSL5 deficiency reduced total ACSL activity in liver, intestine, and brown adipose tissue.

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ACSL5 deficient mice had increased hepatic and circulating FGF21 expression and energy expenditure.

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ACSL5 deficient mice demonstrated delayed triglyceride absorption.

Acquired mutations in the MXR/BCRP/ABCP gene alter substrate specificity in MXR/BCRP/ABCP-overexpressing cells

A disparity was noted in the transport of rhodamine 123 among nine MXR/BCRP/ABCP-overexpressing cells studied; all demonstrated mitoxantrone transport, whereas only two effluxed rhodamine 123. When the MXR/BCRP/ABCP gene was sequenced in the cell lines studied, differences were noted at amino acid 482, predicted to be at the start of the third transmembrane domain. Sequencing genomic DNA revealed wild-type MXR/BCRP/ABCP to have an arginine at position 482. Cells having a threonine or glycine at position 482 were able to efflux rhodamine 123, whereas cells having an arginine were not. A vaccinia virus expression system confirmed that rhodamine as well as doxorubicin efflux is observed with R482T or R482G but not with the wild-type R482; all three MXR/BCRP/ABCP forms transported mitoxantrone. Cross-resistance studies suggest that, compared with wild-type MXR/BCRP/ABCP, cells having an R482T mutation have higher anthracycline resistance, whereas an R482G mutation seems to confer relatively less resistance to SN-38 and topotecan. These results suggest that amino acid 482 has a crucial role in MXR/BCRP/ABCP function and that mutation of a single amino acid residue significantly changes substrate specificity, thus altering the drug resistance phenotype.

Indirect neurotrophic effect of neuropeptide ZNC(C)PR on PC12 cells via peptide-stimulation of C6 cells

AIM

To understand the mechanism of neurotrophic action of neuropeptide ZNC(C)PR and its effect on which could affect both growth and apoptosis of C6 cells.

METHODS

Effects of ZNC(C)PR-treated C6 conditioned medium was observed on on culture of PC12 cells. The development of PC12 cells was determined by ratio of neurite-bearing cells in the total cells. The specific binding of ZNC(C)PR on C6 cells was determined by radioligand binding assay (RBA).

RESULTS

ZNC(C)PR-treated C6 conditioned medium increased the ratio of neurite-bearing PC12 cells by 36% compared to the untreated C6 conditioned medium or to a mixture of ZNC(C)PR with the untreated C6 conditioned medium. RBA showed a specific binding site of ZNC(C)PR on C6 cells with Kd value of 2.74 nmol.L-1 and Bmax value of 19 pmol.g-1 protein.

CONCLUSION

ZNC(C)PR enhanced C6 cells induced secretion of some neurotrophic factors which acted as enhancers for PC12 cells differentiation, through its specific receptor sites on the neuroglioma cell.

Function and molecular basis of action of vasopressin 4-8 and its analogues in rat brain

VP 4-8 as a highly potent behavioral-active metabolite of arginine-vasopressin (VP) has been studied in detail at four levels, i.e. ligand level, membrane binding level, intracellular level and nuclear level. The purpose of this chapter is to review and discuss the main results obtained from our recent pharmacological and biochemical investigations which are described as follows: 1, structure-function relationship of VP 4-8 and its analogs; 2, some characters of VP 4-8-specific binding, the distribution of the binding sites in the rat brain and the consequent effect on long-term potentiation of synaptic transmission; 3, a putative receptor-mediated signaling pathway involving second messenger IP3, immediately-early gene c-fos transcription and protein kinase PKC, CaMKII and MAPK; 4, peptide-induced enhancement of some crucial functional proteins such as calmodulin, nerve growth factor (NGF) and brain-derived nerve growth factor (BDNF). The physiological significance of the events following VP 4-8 administration and particularly, its possible role in learning and memory processes are discussed.