Age-related hearing loss (ARHL) is the most common sensory deficit in the elderly. The disease has a multifactorial etiology with both environmental and genetic factors involved being largely ...unknown. SLC7A8/SLC3A2 heterodimer is a neutral amino acid exchanger. Here, we demonstrated that SLC7A8 is expressed in the mouse inner ear and that its ablation resulted in ARHL, due to the damage of different cochlear structures. These findings make SLC7A8 transporter a strong candidate for ARHL in humans. Thus, a screening of a cohort of ARHL patients and controls was carried out revealing several variants in
, whose role was further investigated by in vitro functional studies. Significant decreases in SLC7A8 transport activity was detected for patient's variants (p.Val302Ile, p.Arg418His, p.Thr402Met and p.Val460Glu) further supporting a causative role for SLC7A8 in ARHL. Moreover, our preliminary data suggest that a relevant proportion of ARHL cases could be explained by SLC7A8 mutations.
Cystinuria is a primary inherited aminoaciduria caused by mutations in the genes that encode the two subunits (neutral and basic amino acid transport protein rBAT and b(0,+)-type amino acid ...transporter 1) of the amino acid transport system b(0,+). This autosomal recessive disorder (in which few cases show dominant inheritance) causes a failure in the reabsorption of filtered cystine and dibasic amino acids in the proximal tubule. The clinical symptoms of this disease are caused by the loss of poorly soluble cystine, which precipitates to form stones. Although rare, the prevalence of cystinuria is sufficiently high that the disease results in a substantial contribution to pediatric renal lithiasis. A thorough understanding of cystine transport processes over the past 15 years and the genetic abnormalities responsible for the disease has led to a new classification of cystinuria and recognition that some cases result from an autosomal dominant etiology with incomplete penetrance. This Review examines the molecular and mechanistic effects of some of the mutations that cause cystinuria based on our current understanding of the structural and cellular biology of system b(0,+). This Review also describes the current treatments to prevent recurrent cystine lithiasis.
Thyroid hormone entry into cells is facilitated by transmembrane transporters. Mutations of the specific thyroid hormone transporter, MCT8 (Monocarboxylate Transporter 8, SLC16A2) cause an X-linked ...syndrome of profound neurological impairment and altered thyroid function known as the Allan-Herndon-Dudley syndrome. MCT8 deficiency presumably results in failure of thyroid hormone to reach the neural target cells in adequate amounts to sustain normal brain development. However during the perinatal period the absence of Mct8 in mice induces a state of cerebral cortex hyperthyroidism, indicating increased brain access and/or retention of thyroid hormone. The contribution of other transporters to thyroid hormone metabolism and action, especially in the context of MCT8 deficiency is not clear. We have analyzed the role of the heterodimeric aminoacid transporter Lat2 (Slc7a8), in the presence or absence of Mct8, on thyroid hormone concentrations and on expression of thyroid hormone-dependent cerebral cortex genes. To this end we generated Lat2-/-, and Mct8-/yLat2-/- mice, to compare with wild type and Mct8-/y mice during postnatal development. As described previously the single Mct8 KO neonates had a transient increase of 3,5,3'-triiodothyronine concentration and expression of thyroid hormone target genes in the cerebral cortex. Strikingly the absence of Lat2 in the double Mct8Lat2 KO prevented the effect of Mct8 inactivation in newborns. The Lat2 effect was not observed from postnatal day 5 onwards. On postnatal day 21 the Mct8 KO displayed the typical pattern of thyroid hormone concentrations in plasma, decreased cortex 3,5,3'-triiodothyronine concentration and Hr expression, and concomitant Lat2 inactivation produced little to no modifications. As Lat2 is expressed in neurons and in the choroid plexus, the results support a role for Lat2 in the supply of thyroid hormone to the cerebral cortex during early postnatal development.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Inactivating mutations in the BCKDK gene, which codes for the kinase responsible for the negative regulation of the branched‐chain α‐keto acid dehydrogenase complex (BCKD), have recently ...been associated with a form of autism in three families. In this work, two novel exonic BCKDK mutations, c.520C>G/p.R174G and c.1166T>C/p.L389P, were identified at the homozygous state in two unrelated children with persistently reduced body fluid levels of branched‐chain amino acids (BCAAs), developmental delay, microcephaly, and neurobehavioral abnormalities. Functional analysis of the mutations confirmed the missense character of the c.1166T>C change and showed a splicing defect r.520c>g;521_543del/p.R174Gfs1*, for c.520C>G due to the presence of a new donor splice site. Mutation p.L389P showed total loss of kinase activity. Moreover, patient‐derived fibroblasts showed undetectable (p.R174Gfs1*) or barely detectable (p.L389P) levels of BCKDK protein and its phosphorylated substrate (phospho‐E1α), resulting in increased BCKD activity and the very rapid BCAA catabolism manifested by the patients’ clinical phenotype. Based on these results, a protein‐rich diet plus oral BCAA supplementation was implemented in the patient homozygous for p.R174Gfs1*. This treatment normalized plasma BCAA levels and improved growth, developmental and behavioral variables. Our results demonstrate that BCKDK mutations can result in neurobehavioral deficits in humans and support the rationale for dietary intervention.
Cystinuria is an aminoaciduria caused by mutations in the genes that encode the two subunits of the amino acid transport system b0,+, responsible for the renal reabsorption of cystine and dibasic ...amino acids. The clinical symptoms of cystinuria relate to nephrolithiasis, due to the precipitation of cystine in urine. Mutations in SLC3A1, which codes for the heavy subunit rBAT, cause cystinuria type A, whereas mutations in SLC7A9, which encodes the light subunit b0,+AT, cause cystinuria type B. By crossing Slc3a1-/- with Slc7a9-/- mice we generated a type AB cystinuria mouse model to test digenic inheritance of cystinuria. The 9 genotypes obtained have been analyzed at early (2- and 5-months) and late stage (8-months) of the disease. Monitoring the lithiasic phenotype by X-ray, urine amino acid content analysis and protein expression studies have shown that double heterozygous mice (Slc7a9+/-Slc3a1+/-) present lower expression of system b0,+ and higher hyperexcretion of cystine than single heterozygotes (Slc7a9+/-Slc3a1+/+ and Slc7a9+/+Slc3a1+/-) and give rise to lithiasis in 4% of the mice, demonstrating that cystinuria has a digenic inheritance in this mouse model. Moreover in this study it has been demonstrated a genotype/phenotype correlation in type AB cystinuria mouse model providing new insights for further molecular and genetic studies of cystinuria patients.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Cystinuria is an autosomal recessive disease caused by mutations in SLC3A1 (rBAT) and SLC7A9 (b(0,+)AT). Gene targeting of the catalytic subunit (Slc7a9) in mice leads to excessive excretion of ...cystine, lysine, arginine, and ornithine. Here, we studied this non-type I cystinuria mouse model using gene expression analysis, Western blotting, clearance, and brush-border membrane vesicle (BBMV) uptake experiments to further characterize the renal and intestinal consequences of losing Slc7a9 function. The electrogenic and BBMV flux studies in the intestine suggested that arginine and ornithine are transported via other routes apart from system b(0,+). No remarkable gene expression changes were observed in other amino acid transporters and the peptide transporters in the intestine and kidney. Furthermore, the glomerular filtration rate (GFR) was reduced by 30% in knockout animals compared with wild-type animals. The fractional excretion of arginine was increased as expected (∼100%), but fractional excretions of lysine (∼35%), ornithine (∼16%), and cystine (∼11%) were less affected. Loss of function of b(0,+)AT reduced transport of cystine and arginine in renal BBMVs and completely abolished the exchanger activity of dibasic amino acids with neutral amino acids. In conclusion, loss of Slc7a9 function decreases the GFR and increases the excretion of several amino acids to a lesser extent than expected with no clear regulation at the mRNA and protein level of alternative transporters and no increased renal epithelial uptake. These observations indicate that transporters located in distal segments of the kidney and/or metabolic pathways may partially compensate for Slc7a9 loss of function.
Heteromeric amino acid transporters (HATs) are composed of a heavy (SLC3 family) and a light (SLC7 family) subunit. Mutations in system b(0,+) (rBAT-b(0,+)AT) and in system y(+)L (4F2hc-y(+)LAT1) ...cause the primary inherited aminoacidurias (PIAs) cystinuria and lysinuric protein intolerance, respectively. Recent developments including the identification of the first Hartnup disorder gene (B0AT1; SLC6A19) and knockout mouse models have begun to reveal the basis of renal and intestinal reabsorption of amino acids in mammals.
Lysinuric Protein Intolerance (LPI, MIM 222700) is a recessive aminoaciduria caused by defective cationic amino acid transport in epithelial cells of intestine and kidney. SLC7A7, the gene mutated in ...LPI, codifies for the y+LAT1 subunit of system y+L amino acid transporter. LPI patients frequently display severe complications, such as pulmonary disease, haematological abnormalities and disorders of the immune response. The transport defect may explain only a part of the clinical aspects of the disease, while the mechanisms linking the genetic defect to the clinical features of the patients remain thus far obscure. The aim of the study is to investigate the consequences of SLC7A7 mutations on specific macrophage functions, so as to evaluate if a macrophage dysfunction may have a role in the development of pulmonary and immunological complications of LPI.
The results presented 1) confirm previous data obtained in one LPI patient, demonstrating that arginine influx through system y+L is markedly compromised in LPI macrophages; 2) demonstrate that also system y+L-mediated arginine efflux is significantly lower in LPI macrophages than in normal cells and 3) demonstrate that the phagocytic activity of LPI macrophages is severely impaired.
In conclusion, SLC7A7/y+LAT1 mutations lead to a defective phenotype of macrophages, supporting the pathogenetic role of these cells in the development of LPI-associated complications.
► Arginine influx/efflux through system y+L is compromised in LPI macrophages. ► LPI macrophages display a significant impairment of the phagocytic activity. ► An altered macrophage phenotype may underlie the pathogenesis of LPI complications.
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