Long-chain acyl-CoA synthetase 1 interacts with key proteins that activate and direct fatty acids into niche hepatic pathways

Abstract

Fatty acid channeling into oxidation or storage modes depends on physiological conditions and hormonal signaling. However, the directionality of this channeling may also depend on the association of each of the five acyl-CoA synthetase isoforms with specific protein partners. Long-chain acyl-CoA synthetases (ACSLs) catalyze the conversion of long-chain fatty acids to fatty acyl-CoAs, which are then either oxidized or used in esterification reactions. In highly oxidative tissues, ACSL1 is located on the outer mitochondrial membrane (OMM) and directs fatty acids into mitochondria for β-oxidation. In the liver, however, about 50% of ACSL1 is located on the endoplasmic reticulum (ER) where its metabolic function is unclear. Because hepatic fatty acid partitioning is likely to require the interaction of ACSL1 with other specific proteins, we used an unbiased protein interaction technique, BioID, to discover ACSL1-binding partners in hepatocytes. We targeted ACSL1 either to the ER or to the OMM of Hepa 1-6 cells as a fusion protein with the biotin ligase, BirA*. Proteomic analysis identified 98 proteins that specifically interacted with ACSL1 at the ER, 55 at the OMM, and 43 common to both subcellular locations. We found subsets of peroxisomal and lipid droplet proteins, tethering proteins, and vesicle proteins, uncovering a dynamic role for ACSL1 in organelle and lipid droplet interactions. Proteins involved in lipid metabolism were also identified, including acyl-CoA-binding proteins and ceramide synthase isoforms 2 and 5. Our results provide fundamental and detailed insights into protein interaction networks that control fatty acid metabolism.

Metabolic implications of organelle–mitochondria communication

“…Mitochondria-LD contacts are modulated by nutrient availability in various tissues. Thus, glucose deficiency promotes LD interaction with mitochondria in monkey kidney Vero cells and in mouse primary hepatocytes [209,216]. The interaction of ACSL1 with SNAP23 and VAMP4 is enhanced upon glucose deprivation in mouse primary hepatocytes [209].…”

“…PLIN5 is likely to promote the mitochondrial uptake of fatty acids since it interacts with adipose triglyceride lipase (ATGL) and its activator ABHD5 on the LD surface , leading to enhanced lipolysis. During glucose deprivation, ACSL1 interacts with SNAP23 and VAMP4 and thus increases mitochondria–LD contact sites . Under these conditions, ACSL1 promotes the synthesis of acyl‐CoA from fatty acids released by LDs, which are then channeled through mitochondrial beta‐oxidation.…”

Organelle interplay—peroxisome interactions in health and disease

“…Proximity of the organelles and membrane‐bound proteins involved in fatty acid metabolism within the peroxisome‐ER hub may allow coordinated channeling of fatty acids either towards elongation (and use in esterification reactions or PUFA synthesis; see Section 2.5) or degradation by peroxisomal β‐oxidation (eg, when VLCFA concentration is too high) (Figure ). In a recent BioID study, the long‐chain acyl‐CoA synthetase ACSL1 was identified as a direct interaction partner of ACBD5 and VAPB . In the liver, about 50% of ACSL1 is located on the ER indicating that ACSL1 is present at the ER‐peroxisome interface to activate fatty acids destined for peroxisomal metabolism (Figure ).…”

Triple-knockout, synuclein-free mice display compromised lipid pattern

“…Five isoforms of ACSL (ACSL1, ACSL3, ACSL4, ACSL5, and ACSL6) have been identi ed in humans and rodents. Although ACSL are ubiquitously expressed, they have individual functions in FA metabolism, depending on substrate preferences and tissue speci city as well as on physiological conditions and hormonal signaling [80]. ACSL1 shows a broad substrate speci city expressing the liver, heart, and adipose tissue where various FA are used for energy production and storage.…”

“…ACSL4 is a ubiquitous peripheral membrane protein, but highly expressed in brain and adrenal glands, being selective for LCPUFA. ACSL5, the major intestinal ACSL isoform, targets a wide range of FA, mainly dietary, for TAG esteri cation that are secreted into the circulation [80].…”