SLC7A14 imports GABA to lysosomes and impairs hepatic insulin sensitivity via inhibiting mTORC2.

Lysosomal amino acid accumulation is implicated in several diseases, but its role in insulin resistance, the central mechanism to type 2 diabetes and many metabolic diseases, is unclear. In this study, we show the hepatic expression of lysosomal membrane protein solute carrier family 7 member 14 (SLC7A14) is increased in insulin-resistant mice. The promoting effect of SLC7A14 on insulin resistance is demonstrated by loss- and gain-of-function experiments. SLC7A14 is further demonstrated as a transporter resulting in the accumulation of lysosomal γ-aminobutyric acid (GABA), which induces insulin resistance via inhibiting mTOR complex 2 (mTORC2)'s activity. These results establish a causal link between lysosomal amino acids and insulin resistance and suggest that SLC7A14 inhibition may provide a therapeutic strategy in treating insulin resistance-related and GABA-related diseases and may provide insights into the upstream mechanisms for mTORC2, the master regulator in many important processes.

Slc7a14 Is Indispensable in Zebrafish Retinas.

Previous study has identified SLC7A14 as a new causative gene of retinitis pigmentosa (RP). However, the role of SLC7A14 has not been fully characterized. The goal of this study was to investigate the biological features of slc7a14 in zebrafish. To determine the expression of slc7a14 in developing zebrafish, we performed in situ hybridization (ISH) and quantitative real-time PCR. Morpholino knockdown and overexpression experiments were performed to study the role of slc7a14 in zebrafish retinas. Immunostaining was carried out to observe structural changes. Visual motor responses (VMR) and optokinetic responses (OKR) were analyzed to assess visual behaviors. Terminal deoxynucleotidyl transferase (dUTP) nick-end labeling (TUNEL) staining was performed to survey apoptotic retinal cells. We found that slc7a14 was highly expressed in neuronal tissues, including the brain, spinal cord and retina, and that the expression levels increased during early embryogenesis. Consistently, ISH showed a similar expression pattern. Knockdown of slc7a14 led to dose-dependent microphthalmia that was reversed by overexpression. The immunostaining results revealed that the rod-specific protein zpr-3 and the retinal pigment epithelium-specific protein zpr-2 (decreased to 44.48%) were significantly suppressed in the slc7a14-silenced morphants. Notably, visual behaviors (the VMR and the OKR) were severely impaired in the slc7a14-deficient morphant, especially the VMR OFF response. In addition, apoptotic cells were observed in the retina at 3 days post fertilization (dpf) and 5 dpf by TUNEL assay. Our results demonstrated that slc7a14 is essential for visually mediated behaviors in zebrafish. Temporary silencing of slc7a14 in larvae led to severe visual impairments, consistent with the manifestations observed in RP patients. Our findings provide further insights into the genetic mechanisms of RP predisposition caused by SLC7A14 mutations.

Human Genetic Susceptibility to Native Valve Staphylococcus aureus Endocarditis in Patients With S. aureus Bacteremia: Genome-Wide Association Study.

Staphylococcus aureus infective endocarditis (SaIE) is a severe complication of S. aureus bacteremia (SAB) occurring in up to 22% of patients. Bacterial genetic factors and host conditions for SaIE have been intensely studied before; however, to date no study has focused on predisposing host genetic factors to SaIE. The present study aimed to identify genetic polymorphisms associated with SaIE by a Genome-Wide Association Study (GWAS) of 67 patients with definite native valve SaIE (cases) and 72 matched native valve patients with SAB but without IE (controls). All patients were enrolled in the VIRSTA cohort (Le Moing et al., 2015) study. Four single nucleotide polymorphisms (SNPs) located on chromosome 3 were associated with SaIE (P < 1 × 10-5) without reaching conventional genome-wide significance. For all, the frequency of the minor allele was lower in cases than in controls, suggesting a protective effect of the minor allele against SaIE. The same association was observed using an independent Danish verification cohort of SAB with (n = 57) and without (n = 123) IE. Ex vivo analysis of aortic valve tissues revealed that SaIE associated SNPs mentioned above were associated with significantly higher mRNA expression levels of SLC7A14, a predicted cationic amino acid transporter protein. Taken together, our results suggest an IE-protective effect of SNPs on chromosome 3 during the course of SAB. The effects of protective minor alleles may be mediated by increasing expression levels of SLC7A14 in valve tissues. We conclude that occurrence of SaIE may be the combination of a well-adapted bacterial genotype to a susceptible host.

Screening for SLC7A14 gene mutations in patients with autosomal recessive or sporadic retinitis pigmentosa.

PURPOSE: In this study, we aimed to detect mutations in the SLC7A14 cationic transporter gene, which has recently been reported as a causative gene for retinitis pigmentosa (RP), in Japanese patients with autosomal recessive (AR) or sporadic RP. MATERIALS AND METHODS: We included 146 unrelated Japanese patients with AR or sporadic RP who lacked mutations in genes known to be associated with RP despite next-generation sequencing-based screening. We sequenced the seven SLC7A14 coding exons along with their flanking intronic DNA using the Sanger method. The detected polymorphisms were assessed for their pathogenicity with in silico prediction tools. For those who had heterozygous, nonsynonymous variants, we performed multiplex ligation-dependent probe amplification (MLPA) to search for additional deletion/duplication. RESULTS: We detected four distinct SLC7A14 polymorphisms excluding synonymous polymorphisms. Two of these polymorphisms were assessed as detrimental by in silico prediction tools. However, all of the mutations were heterozygous. Neither homozygous polymorphisms nor compound heterozygous polymorphisms, which are considered detrimental variants, were detected. Neither deletion nor duplication was found with MLPA in patients with heterozygous variants. CONCLUSIONS: The four SLC7A14 mutations detected herein were unlikely to be pathogenic in this Japanese cohort. The frequency and pathogenicity of SLC7A14 mutations may vary depending on ethnicity, and these mutations may be rare in Japanese patients.