The Iodide Transport Defect-Causing Y348D Mutation in the Na+/I- Symporter Renders the Protein Intrinsically Inactive and Impairs Its Targeting to the Plasma Membrane.

Background: The sodium/iodide (Na+/I-) symporter (NIS) mediates active transport of I- into the thyroid gland. Mutations in the SLC5A5 gene, which encodes NIS, cause I- transport defects (ITDs)-which, if left untreated, lead to congenital hypothyroidism and consequent cognitive and developmental deficiencies. The ITD-causing NIS mutation Y348D, located in transmembrane segment (TMS) 9, was reported in three Sudanese patients. Methods: We generated cDNAs coding for Y348D NIS and mutants with other hydrophilic and hydrophobic amino acid substitutions at position 348 and transfected them into cells. The activity of the resulting mutants was quantitated by radioiodide transport assays. NIS glycosylation was investigated by Western blotting after endoglycosidase H (Endo H) and PNGase-F glycosidase treatment. Subcellular localization of the mutant proteins was ascertained by flow cytometry analysis, cell surface biotinylation, and immunofluorescence. The intrinsic activity of Y348D was studied by measuring radioiodide transport in membrane vesicles prepared from Y348D-NIS-expressing cells. Our NIS homology models and molecular dynamics simulations were used to identify residues that interact with Y348 and investigate possible interactions between Y348 and the membrane. The sequences of several Slc5 family transporters were aligned, and a phylogenetic tree was generated in ClustalX. Results: Cells expressing Y348D NIS transport no I-. Furthermore, Y348D NIS is only partially glycosylated, is retained intracellularly, and is intrinsically inactive. Hydrophilic residues other than Asp at position 348 also yield NIS proteins that fail to be targeted to the plasma membrane (PM), whereas hydrophobic residues at this position, which we show do not interact with the membrane, rescue PM targeting and function. Conclusions: Y348D NIS does not reach the PM and is intrinsically inactive. Hydrophobic amino acid substitutions at position 348, however, preserve NIS activity. Our findings are consistent with our homology model's prediction that Y348 should face the side opposite the TMS9 residues that coordinate Na+ and participate in Na+ transport, and with the notion that Y348 interacts only with hydrophobic residues. Hydrophilic or charged residues at position 348 have deleterious effects on NIS PM targeting and activity, whereas a hydrophobic residue at this position rescues NIS activity.

The paradoxical lean phenotype of hypothyroid mice is marked by increased adaptive thermogenesis in the skeletal muscle.

Obesity is a major health problem worldwide, given its growing incidence and its association with a variety of comorbidities. Weight gain results from an increase in energy intake without a concomitant increase in energy expenditure. To combat the obesity epidemic, many studies have focused on the pathways underlying satiety and hunger signaling, while other studies have concentrated on the mechanisms involved in energy expenditure, most notably adaptive thermogenesis. Hypothyroidism in humans is typically associated with a decreased basal metabolic rate, lower energy expenditure, and weight gain. However, hypothyroid mouse models have been reported to have a leaner phenotype than euthyroid controls. To elucidate the mechanism underlying this phenomenon, we used a drug-free mouse model of hypothyroidism: mice lacking the sodium/iodide symporter (NIS), the plasma membrane protein that mediates active iodide uptake in the thyroid. In addition to being leaner than euthyroid mice, owing in part to reduced food intake, these hypothyroid mice show signs of compensatory up-regulation of the skeletal-muscle adaptive thermogenic marker sarcolipin, with an associated increase in fatty acid oxidation (FAO). Neither catecholamines nor thyroid-stimulating hormone (TSH) are responsible for sarcolipin expression or FAO stimulation; rather, thyroid hormones are likely to negatively regulate both processes in skeletal muscle. Our findings indicate that hypothyroidism in mice results in a variety of metabolic changes, which collectively lead to a leaner phenotype. A deeper understanding of these changes may make it possible to develop new strategies against obesity.

Nationally representative household survey data for studying the interaction between district-level development and individual-level socioeconomic gradients of cardiovascular disease risk factors in India.

In this article, we describe the dataset used in our study entitled "The interaction between district-level development and individual-level socioeconomic gradients of cardiovascular disease risk factors in India: A cross-sectional study of 2.4 million adults", recently published in Social Science & Medicine, and present supplementary analyses. We used data from three different household surveys in India, which are representative at the district level. Specifically, we analyzed pooled data from the District-Level Household Survey 4 (DLHS-4) and the second update of the Annual Health Survey (AHS), and separately analyzed data from the National Family Health Survey (NFHS-4). The DLHS-4 and AHS sampled adults aged 18 years or older between 2012 and 2014, while the NFHS-4 sampled women aged 15-49 years and - in a subsample of 15% of households - men aged 15-54 years in 2015 and 2016. The measures of individual-level socio-economic status that we used in both datasets were educational attainment and household wealth quintiles. The measures of district-level development, which we calculated from these data, were i) the percentage of participants living in an urban area, ii) female literacy rate, and iii) the district-level median of the continuous household wealth index. An additional measure of district-level development that we used was Gross Domestic Product per capita, which we obtained from the Planning Commission of the Government of India for 2004/2005. Our outcome variables were diabetes, hypertension, obesity, and current smoking. The data were analyzed using both district-level regressions and multilevel modelling.

The interaction between district-level development and individual-level socioeconomic gradients of cardiovascular disease risk factors in India: A cross-sectional study of 2.4 million adults.

BACKGROUND: Diabetes, hypertension, and obesity tend to be positively associated with socio-economic status in low- and middle-income countries (LMICs). It has been hypothesized that these positive socio-economic gradients will reverse as LMICs continue to undergo economic development. We use population-based cross-sectional data in India to examine how a district's economic development is associated with socio-economic differences in cardiovascular disease (CVD) risk factor prevalence between individuals. METHODS: We separately analyzed two nationally representative household survey datasets - the NFHS-4 and the DLHS-4/AHS - that are representative at the district level in India. Diabetes was defined based on a capillary blood glucose measurement, hypertension on blood pressure measurements, obesity on measurements of height and weight, and current smoking on self-report. Five different measures of a district's economic development were used. We analyzed the data using district-level regressions (plotting the coefficient comparing high to low socio-economic status against district-level economic development) and multilevel modeling. RESULTS: 757,655 and 1,618,844 adults participated in the NFHS-4 and DLHS-4/AHS, respectively. Higher education and household wealth were associated with a higher probability of having diabetes, hypertension, and obesity, and a lower probability of being a current smoker. For diabetes, hypertension, and obesity, we found that a higher economic development of a district was associated with a less positive (or even negative) association between the CVD risk factor and education. For smoking, the association with education tended to become less negative as districts had a higher level of economic development. In general, these associations did not show clear trends when household wealth quintile was used as the measure of socio-economic status instead of education. CONCLUSIONS: While this study provides some evidence for the "reversal hypothesis", large-scale longitudinal studies are needed to determine whether LMICs should expect a likely reversal of current positive socioeconomic gradients in diabetes, hypertension, and obesity as their countries continue to develop economically.