Delta-6-desaturase links polyunsaturated fatty acid metabolism with phospholipid remodeling and disease progression in heart failure.

BACKGROUND: Remodeling of myocardial phospholipids has been reported in various forms of heart failure for decades, but the mechanism and pathophysiological relevance of this phenomenon have remained unclear. We examined the hypothesis that δ-6 desaturase (D6D), the rate-limiting enzyme in long-chain polyunsaturated fatty acid biosynthesis, mediates the signature pattern of fatty acid redistribution observed in myocardial phospholipids after chronic pressure overload and explored plausible links between this process and disease pathogenesis. METHODS AND RESULTS: Compositional analysis of phospholipids from hearts explanted from patients with dilated cardiomyopathy revealed elevated polyunsaturated fatty acid product/precursor ratios reflective of D6D hyperactivity, manifesting primarily as lower levels of linoleic acid with reciprocally higher levels of arachidonic and docosahexaenoic acids. This pattern of remodeling was attenuated in failing hearts chronically unloaded with a left ventricular assist device. Chronic inhibition of D6D in vivo reversed similar patterns of myocardial polyunsaturated fatty acid redistribution in rat models of pressure overload and hypertensive heart disease and significantly attenuated cardiac hypertrophy, fibrosis, and contractile dysfunction in both models. D6D inhibition also attenuated myocardial elevations in pathogenic eicosanoid species, lipid peroxidation, and extracellular receptor kinase 1/2 activation; normalized cardiolipin composition in mitochondria; reduced circulating levels of inflammatory cytokines; and elicited model-specific effects on cardiac mitochondrial respiratory efficiency, nuclear factor κ B activation, and caspase activities. CONCLUSIONS: These studies demonstrate a pivotal role of essential fatty acid metabolism in myocardial phospholipid remodeling induced by hemodynamic stress and reveal novel links between this phenomenon and the propagation of multiple pathogenic systems involved in maladaptive cardiac remodeling and contractile dysfunction [corrected].

Regulation of stearoyl-coenzyme A desaturase and fatty acid delta-6 desaturase-2 expression by linoleic acid and arachidonic acid in human sebocytes leads to enhancement of proinflammatory activity but does not affect lipogenesis.

BACKGROUND: Treatment of SZ95 sebocytes with the essential fatty acid linoleic acid (LA) and the polyunsaturated fatty acid arachidonic acid (AA) leads to sebaceous lipogenesis. Animal data indicate that stearoyl-coenzyme A desaturase (SCD), a key enzyme in fatty acid biosynthesis, is involved in sebaceous lipogenesis and proinflammatory signalling in the sebaceous gland. On the other hand, fatty acid delta-6 desaturase-2 (FADS2) catalyses the conversion of LA to AA. OBJECTIVES: To identify the effects of LA and AA on the expression of SCD and FADS2 and to detect its biological relevance. METHODS: SZ95 sebocytes were treated with LA (10(-5) and 10(-4) mol L(-1) ), AA (10(-6) and 10(-5) mol L(-1) ) and the combination of LA (10(-4) mol L(-1) ) and testosterone (2 × 10(-8) mol L(-1) ), with or without addition of the SCD inhibitor FPCA (10(-8) and 10(-6) mol L(-1) ). Cytotoxicity was determined by the lactate dehydrogenase assay. SCD and FACS2 mRNA levels were assessed by semiquantitative reverse transcription-polymerase chain reaction and protein expression by Western blot analysis. SZ95 sebocyte lipid content and cell number were measured by the Nile red and the fluorescein diacetate microassays, respectively. Determination of interleukin (IL)-6 and IL-8 release was evaluated by enzyme-linked immunosorbent assay. RESULTS: LA treatment induced an increase of SCD and FADS2 at mRNA and protein levels in SZ95 sebocytes after 1·5 h. Treatment with AA led to an increase of SCD but to a decrease of FADS2 mRNA levels. LA/testosterone cotreatment stimulated lipogenesis in SZ95 sebocytes. A distinct proinflammatory pattern was registered: whereas LA strongly upregulated IL-6 secretion only, AA induced a mild level of IL-6 and IL-8 release from SZ95 sebocytes. Treatment with the SCD inhibitor FPCA reduced the LA/testosterone-upregulated SCD and FADS2 mRNA levels and resulted in an anti-inflammatory effect, but did not affect sebaceous lipogenesis. CONCLUSIONS: LA-induced sebaceous lipogenesis is likely to be an SCD-independent effect. Regulation of SCD and FADS2 expression by LA and AA leads to enhancement of proinflammatory activity but does not affect lipogenesis in human sebocytes.

Regulation of desaturase expression in HL60 cells.

The expression of delta 5 desaturase (D5D), delta 6 desaturase (D6D) and delta 9 desaturase (D9D) was determined by RT-PCR in the human promyelocytic cell line HL60. During 72 h of culture with 10% FBS, D5D and D6D were upregulated 5 to 6-fold, whereas D9D approximately doubled. The addition of fatty acids (FAs) to the culture medium suppressed upregulation of all desaturases. N-3 and n-6 FA appeared to be more effective than n-9 or saturated FA. When FAs were added after 72 h, further upregulation during the next 24 h was suppressed for nearly all desaturases and FAs tested, except for D5D when oleic acid (OA) or stearic acid (SA) was added. In cells cultured with restricted amounts of FBS, desaturase expression increased with decreasing concentrations of FBS. Cellular FA content decreased by 60% in the neutral lipid fraction, whereas that of the phospholipid fraction decreased by 10% during 72 h of culture. The largest decrease occurred in the sum of n-3 and n-6 FA of the neutral lipid fraction, which was reduced by 83%, whereas the content of these FAs in the phospholipid fraction decreased by 32%. The results indicate that when the supply of FA to HL60 cells is limited, the intracellular content of n-3 and n-6 FA decreases and this leads to upregulation of the desaturases, particularly D5D and D6D. Since HL60 cells resemble human leukocytes, the results suggest that desaturase expression in leukocytes may be exploited as a biomarker for FA status.