PhD Scientific Days 2022

Molecular Sciences V.

Combined effect of the rs2234970 polymorphism results in elevated intracellular levels of human Stearoyl-CoA desaturase-1 – a potential risk factor for type 2 diabetes mellitus

Text of the abstract

Introduction. Many syndromes associated with excessive food intake and sedentary lifestyle may be due to systemic disturbances in lipid metabolism. A crucial enzyme in the defense against lipotoxicity is the Stearoyl-CoA desaturase-1 (SCD1), catalyzing the unsaturated fatty acid synthesis. The increased activity or overexpression of the enzyme is potential risk factor for type II diabetes mellitus (T2DM).
Aims. In this study, we sought to answer whether the missense polymorphism rs2234970 (M224L) might affect SCD1 enzyme function.
Methods. The untagged and Glu-Glu-tagged version of SCD1 and their polymorphic variant were studied in HEK293T and HepG2 cellular systems. Cycloheximide and BSA-conjugated fatty acid treatments were performed. Protein levels were monitored by immunoblotting, changes in mRNA expression by qPCR, and enzyme activities by GC-FID. Genotyping of control and T2DM samples was performed with self-designed TaqMan probes.
Results. We demonstrated that the Leu224 polymorphic enzyme is present in higher amounts in cells due to slower protein degradation and more stable mRNA structure. The elevated amount of enzyme increases the ratio of unsaturated and saturated fatty acids, significantly increasing the intracellular amounts of C18:1 and C16:1. We have shown that in the presence of fatty acids (oleate, palmitate, palmitoleate, linoleate, stearate) the stability of Leu224 is further enhanced, whereas the level of Met224 SCD1 is not affected. By examining the artificial variant Ala224, we demonstrated that the loss of methionine stabilizes the polymorphic protein and the appearance of leucine results in higher mRNA levels and fatty acid-dependent protein stability. The Leu224 variation is found in both control and type 2 diabetic patients. The minor allele, although not reaching the level of statistical significance, appears to be enriched in the affected population.
Conclusions. From our results, we concluded that the M224L polymorphism may be a potential risk factor for T2DM by increasing the intracellular level of the SCD1 protein.
Fundings. Our work was supported by NKFIH grants K_125201 and FK_138115.