A novel FADS2 isoform isolated from milk fat globules suppresses FADS2 mediated Δ6‐desaturation of omega‐3 fatty acids

Alternative mRNA splicing is increasingly recognized as a modulator of protein structure and function. Here we report identification of a novel alternative transcript of fatty acid desaturase 2 (FADS2) and characterization of its function, discovered during the study of alternative transcripts in human milkfat globules (MFG). Methods Human breastmilk collected from a single donor was used to isolate MFG. The isolated MFG was used to extract total RNA and construction of mRNA‐sequencing library. The constructed library was sequenced using an Illumina HiSeq instrument operating in high output mode. Expression levels of evolutionary conserved FADSAT were measured using cDNA from MFG by semi‐quantitative RT‐PCR assay. Results A total of 52 million reads were sequenced, showing expression of 15605 transcripts. Classical fatty acid desaturase 2 (FADS2), which catalyzes the rate limiting step in PUFA synthesis, is moderately expressed. A novel FADS2 alternative transcript ( FADS2AT2 ) with 386 amino acids was identified. When FADS2AT2 was transiently transfected to stable FADS2 MCF7 cells and incubated with omega‐3 fatty acid precursor 18:3n‐3, suppression of delta 6 desaturation (D6D) product 18:4n‐3 and its downstream 20:4n‐3 and 20:5n‐3 fatty acids were observed compared to control cells. No significant changes were observed when incubated with omega‐6 fatty acid precursor 18:2n‐6. FADS2 , FADS2AT1 and 5 out of 8 known FADS3AT were expressed in MFG. FADS1 , FADS3AT3 , and FADS3AT5 are undetectable. Conclusion FADS2AT2 regulates noncatalytically classical FADS2 mediated Δ6‐desaturation of n‐3 but not n‐6 PUFA biosynthesis. This novel spliced isoform mediated interaction is the first molecular mechanism by which desaturation of one PUFA family but not the other is modulated. Support or Funding Information AT007003