Genetic Disruption of Serine Biosynthesis is a Key Driver of Macular Telangiectasia Type 2 Etiology and Progression

PurposeMacular telangiectasia type 2 (MacTel) is a rare, heritable and largely untreatable retinal disorder, often comorbid with diabetes. Genetic risk loci subtend retinal vascular calibre, and glycine/serine/threonine metabolism genes. Serine deficiency may contribute to MacTel via neurotoxic deoxysphingolipid production, however, an independent vascular contribution is also suspected. Here we use statistical genetics to dissect the causal mechanisms underpinning this complex disease.MethodsWe integrated genetic markers for MacTel, vascular, and metabolic traits, and applied Mendelian randomization, MTAG, and conditional/interaction genome-wide association analysis to discover causal contributors to both disease, and spatial retinal imaging sub-phenotypes.ResultsSerine was a key causal driver of disease occurrence and progression, with a lesser contribution to type 2 diabetes risk. Conversely, glycine, threonine and retinal vascular traits are unlikely to be causal for MacTel. Conditional regression analysis resolved three novel disease loci independent of endogenous serine biosynthetic capacity. By aggregating retinal phenotypes into endophenotypes, we demonstrate that SNPs constituting independent risk loci act via related endophenotypes.DiscussionOur findings will aid in early diagnosis and accurate prognosis of MacTel, and improve prospects for effective therapeutic intervention. Our integrative genetics approach also serves as a useful template for post-GWAS analyses in other disorders.

In Vivo Interactions between Toxin-Antitoxin Proteins Epsilon and Zeta of Streptococcal Plasmid pSM19035 in Saccharomyces cerevisiae

ABSTRACT The widespread prokaryotic toxin-antitoxin (TA) systems involve conditional interaction between two TA proteins. The interaction between the Epsilon and Zeta proteins, constituting the TA system of plasmid pSM19035 from Streptococcus pyogenes, was detected in vivo using a yeast two-hybrid system. As we showed using Saccharomyces cerevisiae, the Zeta toxin hybrid gene also exerts its toxic effects in a dose-dependent manner in eukaryotic cells. Analysis of mutant proteins in the two-hybrid system demonstrated that the N-terminal part of Zeta and the N-terminal region of Epsilon are involved in the interaction. The N-terminal region of the Zeta protein and its ATP/GTP binding motif were found to be responsible for the toxicity.

Estradiol and leptin as conditional prognostic IVF markers

We studied the concentration of serum estradiol and serum and follicular fluid leptin in 200 women undergoing their first in vitro fertilization with embryo transfer (IVF-ET) program at the time of human chorionic gonadotrophin administration and oocyte retrieval, in an attempt to assess their concerted role on embryo quality and the prognosis of IVF outcome. Low serum (46.49 ± 8.4 ng/ml) and follicular fluid (52 ± 9.8 ng/ml) leptin levels were associated with a high number of ‘good-quality’ embryos (73.6%) and high implantation (11.2%) and pregnancy (35.8%) rates and were observed in women with normal peak estradiol levels of between 1000 and 2000 pg/ml. It appears that leptin and estradiol interact coordinately in a concentration-dependent manner to control IVF outcome. Further studies will be required to substantiate and clarify the mechanism of proposed conditional interaction between the two hormonal systems.