Impaired Adipocyte SLC7A10 Promotes Lipid Storage in Association With Insulin Resistance and Altered BCAA Metabolism

CONTEXT

The neutral amino acid transporter SLC7A10/ASC-1 is an adipocyte-expressed gene with reduced expression in insulin resistance and obesity. Inhibition of SLC7A10 in adipocytes was shown to increase lipid accumulation despite decreasing insulin-stimulated uptake of glucose, a key substrate for de novo lipogenesis. These data imply that alternative lipogenic substrates to glucose fuel continued lipid accumulation during insulin resistance in obesity.

OBJECTIVE

We examined whether increased lipid accumulation during insulin resistance in adipocytes may involve alter flux of lipogenic amino acids dependent on SLC7A10 expression and activity, and whether this is reflected by extracellular and circulating concentrations of marker metabolites.

METHODS

In adipocyte cultures with impaired SLC7A10, we performed RNA sequencing and relevant functional assays. By targeted metabolite analyses (GC-MS/MS), flux of all amino acids and selected metabolites were measured in human and mouse adipose cultures. Additionally, SLC7A10 mRNA levels in human subcutaneous adipose tissue (SAT) were correlated to candidate metabolites and adiposity phenotypes in 2 independent cohorts.

RESULTS

SLC7A10 impairment altered expression of genes related to metabolic processes, including branched-chain amino acid (BCAA) catabolism, lipogenesis, and glyceroneogenesis. In 3T3-L1 adipocytes, SLC7A10 inhibition increased fatty acid uptake and cellular content of glycerol and cholesterol. SLC7A10 impairment in SAT cultures altered uptake of aspartate and glutamate, and increased net uptake of BCAAs, while increasing the net release of the valine catabolite 3- hydroxyisobutyrate (3-HIB). In human cohorts, SLC7A10 mRNA correlated inversely with total fat mass, circulating triacylglycerols, BCAAs, and 3-HIB.

CONCLUSION

Reduced SLC7A10 activity strongly affects flux of BCAAs in adipocytes, which may fuel continued lipogenesis during insulin resistance, and be reflected in increased circulating levels of the valine-derived catabolite 3-HIB.

Liquid biopsies and patient-reported outcome measures for integrative monitoring of patients with early-stage breast cancer: a study protocol for the longitudinal observational Prospective Breast Cancer Biobanking (PBCB) study

INTRODUCTION

Breast cancer is still the most common malignancy among women worldwide. The Prospective Breast Cancer Biobank (PBCB) collects blood and urine from patients with breast cancer every 6 or 12 months for 11 years from 2011 to 2030 at two university hospitals in Western Norway. The project aims to identify new biomarkers that enable detection of systemic recurrences at the molecular level. As blood represents the biological interface between the primary tumour, the microenvironment and distant metastases, liquid biopsies represent the ideal medium to monitor the patient's cancer biology for identification of patients at high risk of relapse and for early detection systemic relapse.Including patient-reported outcome measures (PROMs) allows for a vast number of possibilities to compare PROM data with biological information, enabling the study of fatigue and Quality of Life in patients with breast cancer.

METHODS AND ANALYSIS

A total of 1455 patients with early-stage breast cancer are enrolled in the PBCB study, which has a one-armed prospective observational design. Participants consent to contribute liquid biopsies (i.e., peripheral blood and urine samples) every 6 or 12 months for 11 years. The liquid biopsies are the basis for detection of circulating tumour cells, circulating tumour DNA (ctDNA), exosomal micro-RNA (miRNA), miRNA in Tumour Educated Platelet and metabolomic profiles. In addition, participants respond to 10 PROM questionnaires collected annually. Moreover, a control group comprising 200 women without cancer aged 25-70 years will provide the same data.

ETHICS AND DISSEMINATION

The general research biobank PBCB was approved by the Ministry of Health and Care Services in 2007, by the Regional Ethics Committee (REK) in 2010 (#2010/1957). The PROM (#2011/2161) and the biomarker study PerMoBreCan (#2015/2010) were approved by REK in 2011 and 2015 respectively. Results will be published in international peer reviewed journals. Deidentified data will be accessible on request.

TRIAL REGISTRATION NUMBER

NCT04488614.

Role of the Neutral Amino Acid Transporter SLC7A10 in Adipocyte Lipid Storage, Obesity, and Insulin Resistance

Elucidation of mechanisms that govern lipid storage, oxidative stress, and insulin resistance may lead to improved therapeutic options for type 2 diabetes and other obesity-related diseases. Here, we find that adipose expression of the small neutral amino acid transporter SLC7A10, also known as alanine-serine-cysteine transporter-1 (ASC-1), shows strong inverse correlates with visceral adiposity, insulin resistance, and adipocyte hypertrophy across multiple cohorts. Concordantly, loss of Slc7a10 function in zebrafish in vivo accelerates diet-induced body weight gain and adipocyte enlargement. Mechanistically, SLC7A10 inhibition in human and murine adipocytes decreases adipocyte serine uptake and total glutathione levels and promotes reactive oxygen species (ROS) generation. Conversely, SLC7A10 overexpression decreases ROS generation and increases mitochondrial respiratory capacity. RNA sequencing revealed consistent changes in gene expression between human adipocytes and zebrafish visceral adipose tissue following loss of SLC7A10, e.g., upregulation of SCD (lipid storage) and downregulation of CPT1A (lipid oxidation). Interestingly, ROS scavenger reduced lipid accumulation and attenuated the lipid-storing effect of SLC7A10 inhibition. These data uncover adipocyte SLC7A10 as a novel important regulator of adipocyte resilience to nutrient and oxidative stress, in part by enhancing glutathione levels and mitochondrial respiration, conducive to decreased ROS generation, lipid accumulation, adipocyte hypertrophy, insulin resistance, and type 2 diabetes.

A novel SRC-2-dependent regulation of epithelial-mesenchymal transition in breast cancer cells

Steroid receptor coactivator 2 (SRC-2) is a nuclear receptor coactivator, important for the regulation of estrogen receptor alpha (ERα)-mediated transcriptional activity in breast cancer cells. However, the transcriptional role of SRC-2 in breast cancer is still ambiguous. Here we aimed to unravel a more precise transcriptional role of SRC-2 and uncover unique target genes in MCF-7 breast cancer cells, as opposed to the known oncogene SRC-3. Gene expression analyses of cells depleted of either SRC-2 or SRC-3 showed that they transcriptionally regulate mostly separate gene sets. However, individual unique gene sets were implicated in some of the same major gene ontology biological processes, such as cellular structure and development. This finding was supported by three-dimensional cell cultures, demonstrating that depletion of SRC-2 and SRC-3 changed the morphology of the cells into epithelial-like hollow acinar structures, indicating that both SRC proteins are involved in maintaining the hybrid E/M phenotype. In clinical ER-positive, HER2-negative breast cancer samples the expression of SRC-2 was negatively correlated with the expression of MCF-7-related luminal, cell cycle and cellular morphogenesis genes. Finally, elucidating SRC-2 unique transcriptional effects, we identified Lyn kinase (an EMT biomarker) to be upregulated exclusively after SRC-2 depletion. In conclusion, we show that both SRC-2 and SRC-3 are essential for the EMT in breast cancer cells, controlling different transcriptional niches.

Cyclin C interacts with steroid receptor coactivator 2 and upregulates cell cycle genes in MCF-7 cells

Steroid receptor coactivator 2 (SRC-2) is a coactivator that regulates nuclear receptor activity. We previously reported that SRC-2 protein is degraded through the action of cAMP-dependent protein kinase A (PKA) and cAMP response element binding protein (CREB). In the study presented here, we aimed to identify proteins that interact with and thereby regulate SRC-2. We isolated cyclin C (CCNC) as an interacting partner with the SRC-2 degradation domain aa 347-758 in a yeast two-hybrid assay and confirmed direct interaction in an in vitro assay. The protein level of SRC-2 was increased with CCNC overexpression in COS-1 cells and decreased with CCNC silencing in COS-1 and MCF-7 cells. In a pulse-chase assay, we further show that silencing of CCNC resulted in a different SRC-2 degradation pattern during the first 6 h after the pulse. Finally, we provide evidence that CCNC regulates expression of cell cycle genes upregulated by SRC-2. In conclusion, our results suggest that CCNC temporarily protects SRC-2 against degradation and this event is involved in the transcriptional regulation of SRC-2 cell cycle target genes.

The active tamoxifen metabolite endoxifen (4OHNDtam) strongly down-regulates cytokeratin 6 (CK6) in MCF-7 breast cancer cells

Introduction

Tamoxifen is an anti-estrogen drug used in treatment of Estrogen Receptor (ER) positive breast cancer. Effects and side effects of tamoxifen is the sum of tamoxifen and all its metabolites. 4-Hydroxytamoxifen (4OHtam) and 4-hydroxy-N-demethyltamoxifen (4OHNDtam, endoxifen) both have ER affinity exceeding that of the parent drug tamoxifen. 4OHNDtam is considered the main active metabolite of tamoxifen. Ndesmethyltamoxifen (NDtam) is the major tamoxifen metabolite. It has low affinity to the ER and is not believed to influence tumor growth. However, NDtam might mediate adverse effects of tamoxifen treatment. In this study we investigated the gene regulatory effects of the three metabolites of tamoxifen in MCF-7 breast cancer cells.

Material and Methods

Using concentrations that mimic the clinical situation we examined effects of 4OHtam, 4OHNDtam and NDtam on global gene expression in 17β-estradiol (E₂) treated MCF-7 cells. Transcriptomic responses were assessed by correspondence analysis, differential expression, gene ontology analysis and quantitative real time PCR (Q-rt-PCR). E₂ deprivation and knockdown of Steroid Receptor Coactivator-3 (SRC-3)/Amplified in Breast Cancer 1 (AIB1) mRNA in MCF-7 cells were performed to further characterize specific effects on gene expression.

Results

4OHNDtam and 4OHtam caused major changes in gene expression compared to treatment with E₂ alone, with a stronger effect of 4OHNDtam. NDtam had nearly no effect on the global gene expression profile. Treatment of MCF-7 cells with 4OHNDtam led to a strong down-regulation of the CytoKeratin 6 isoforms (KRT6A, KRT6B and KRT6C). The CytoKeratin 6 mRNAs were also down-regulated in MCF-7 cells after E₂ deprivation and after SRC-3/AIB1 knockdown.

Conclusion

Using concentrations that mimic the clinical situation we report global gene expression changes that were most pronounced with 4OHNDtam and minimal with NDtam. Genes encoding CytoKeratin 6, were highly down-regulated by 4OHNDtam, as well as after E₂ deprivation and knockdown of SRC-3/AIB1, indicating an estrogen receptor-dependent regulation.

Synovial inflammation in active rheumatoid arthritis and psoriatic arthritis facilitates trapping of a variety of oral bacterial DNAs

OBJECTIVE

To investigate the presence of oral bacterial DNAs in serum and synovial fluid (SF) of patients with active rheumatoid arthritis (RA) and psoriatic arthritis (PsA).

METHODS

Serum and SF samples from 16 RA patients, 14 PsA patients, and 9 osteoarthritis (controls) patients were extracted for oral bacterial DNA. This was used in a checkerboard DNA-DNA-hybridization set up, to identify 40 different bacteria.

RESULTS

Mean number +/- standard deviation (SD) of oral bacterial species in sera were 6.2 (3.2) in the RA group (p = 0.004) and 5.4 (2.7) in the PsA group (p = 0.009) compared to 2.1 (1.7) in the controls. Periodontitis associated species Porphyromonas gingivalis and Prevotella nigrescens were exclusively detected in RA and PsA. Mean number (+/- SD) of oral bacterial species in SF were 14.0 (6.8) in the RA (p = 0.001) and 19.4 (7.1) in the PsA group (p < 0.001) compared to 4.0 (1.7) in controls. P. gingivalis, Tannerella forsythensis and Prevotella intermedia were exclusively identified in RA and PsA SF. Higher means of DNAs were found in RA SF compared to RA serum (p < 0.001), and in PsA SF compared to PsA serum (p < 0.001). Higher concentrations of bacterial DNAs were found in RA and PsA compared to controls.

CONCLUSION

Higher variety and concentrations of oral bacterial DNAs were found in SF compared to serum of RA and PsA patients. These findings indicate that synovial inflammation in RA and PsA may favor trapping of oral bacterial DNAs, suggesting a perpetuating effect of oral pathogens in joint disease.

Radiopacity of glass ionomer materials

To facilitate the detection of overhangs and defects adjacent to a filling, restorative materials should have a radiographic density higher than or at least similar to that of enamel. In the present study the density of 21 glass ionomer materials was measured and compared with the density of enamel, dentine, amalgam and aluminium. Most materials were more radiopaque than enamel, thereby satisfying the requirements as proposed by several investigators. The materials with lower density were mainly types intended for use in anterior teeth where the entire filling can more easily be examined clinically. They should not be used as a base under approximal fillings in order to avoid a false positive diagnosis of recurrent caries.

Effect of fluoride in amalgam on secondary caries incidence

Caries incidence is falling in many developed countries but is believed to be increasing in developing countries. Insofar as treatment for caries is provided, ordinary amalgam restorations are usually the standard choice. These carry a risk of failing due to secondary caries. The aim of this study was to compare the occurrence of secondary caries adjacent to fluoride-containing amalgam with that adjacent to a conventional amalgam under field conditions in Bahrain. Children (n = 415) aged 6-14 yr who required occlusal restorations in two homologous contralateral permanent molar teeth were identified. Using the split-mouth design, one tooth received a fluoride-containing amalgam filling and the other a conventional amalgam restoration. A random method was used to determine which type of filling was placed on each side. After 4 yr, 357 children were still available for examination; of these 5 had to be eliminated from analysis for various reasons. Of the 704 teeth in the analysis, secondary caries had occurred in 135 (86 conventional amalgam, 49 fluoridated amalgam). By comparison with the conventional amalgam, the effectiveness of the fluoride amalgam was 43% (95% C.I. 24.4%, 57.1%) and the net gain 10.3% (95% C.I. 4.75%, 16.3%). The relative risk was 0.570 (95% C.I. 0.444%, 0.731%). Since fluoride amalgam has identical handling properties to conventional amalgam, performs similarly under clinical conditions and costs about the same, it should be the amalgam of choice for restorations in communities where the incidence of secondary caries is high.

Effect of fluoride amalgams on artificial recurrent enamel and root caries

The present study examined the effect of F-containing amalgams on recurrent caries in vitro. Four amalgams were tested: A - Conventional amalgam; B - Amalgam A with 1% SnF2; C - Non-gamma-2 amalgam; D - Amalgam C with 1% SnF2. Twenty fillings from each amalgam were placed at the cementoenamel junction in sound extracted human teeth. The teeth were covered with varnish except for a 2-mm-wide zone around the fillings and immersed in separate vials containing dialyzed 15% gelatin gel, pH 4.2, for 17 days. Longitudinal sections through the created enamel and root lesions were examined using polarized light microscopy with distilled water as imbibition medium. Lesion depth was measured adjacent to the fillings and at the midpoint of the lesions. In the amalgam D group, 14 enamel lesions and 15 root lesions showed no demineralization in the area closest to the fillings, and mean lesion depth was significantly smaller than adjacent to the F-free amalgams in enamel as well as in root surfaces. In the root lesions, protection was most evident in amalgam D. At the midpoint of the lesions, depths were not statistically different between groups A-D. This study suggests that fluoride amalgams have anticaries properties sufficient to inhibit recurrent caries.

Release of fluoride and metal ions from root surfaces after topical application of TiF4, SnF2, and NaF in vitro

Aqueous solutions of TiF4 cause a rapid uptake and a long-lasting retention of fluoride when applied to dentin. The aim of this study was therefore to investigate the pattern of fluoride release after TiF4 application in vitro, compared with SnF2 and NaF application. TiF4, SnF2, and NaF were applied for 4 min and 1 min to standardized areas of six groups of root surface specimens immersed in distilled water. Untreated specimens were used as controls. The water was changed daily for 30 days, and F concentrations measured by an ion-selective electrode. All test groups showed a rapid decline in F concentration. In the 4-min group F concentration more than double the detection limit of the F electrode could be registered the first 28 days for TiF4, 11 days for SnF2, and 7 days for NaF. In the 1-min group periods of F registration were shorter. Analysis of Sn by atomic absorption spectrophotometry showed decreasing concentrations in the first 12-day samples in the 1-min and 4-min groups. Traces of Ti were found in the first few samples, but no pattern of release could be observed.

Root surface reactions to TiF4 and SnF2 solutions in vitro. An ultrastructural study

Previous studies have indicated that TiF4 and SnF2 differ in their demineralizing effect when applied topically to root surfaces at the same acidity. The aim of this study was to examine in more detail the outermost layer of root surface specimens by transmission electron microscopy (TEM) after short-term exposure to these acidic fluoride solutions. Root surface specimens were exposed for 1 min and 4 min to equimolar (1.1 M F) solutions of a) TiF4, native pH 1.0; b) SnF2, acidified to pH 1.0; and c) SnF2, native pH 2.5. The specimens were then rinsed in saline and processed for TEM. Exposure to TiF4 resulted in a partly demineralized zone 8-10 microns deep after 1 min and 5-27 microns deep after 4 min of application. A 0.1-micron-thick, electron-dense coating was present in all TiF4-treated specimens. Acidified SnF2 resulted in a completely demineralized zone, 4-7 microns deep, when applied for 1 min and 4 min, whereas SnF2 at native pH produced a 0.5- to 1.0-micron-wide partially demineralized zone. Unevenly distributed crystalline deposits were a frequent finding on SnF2-treated surfaces. The results indicate that solutions of TiF4 and SnF2 at native pH will cause only slight demineralization when applied topically to root surfaces.

Caries-inhibitory effect of titanium tetrafluoride in rats

The purpose of this study was to evaluate the caries-inhibitory effect of TiF4 as compared with equimolar solutions of neutral and acidified NaF. Sixty Sprague-Dawley rats were weaned 19 days after birth and given a cariogenic diet. They were randomly divided into four groups and given a 1-min topical treatment of the molar teeth on day 1 and day 17 of the experiment with the following solutions: group 1: 1% TiF4, pH 1.5; group 2: 1.3% NaF, pH 7.0; group 3: 1.3% NaF, pH 1.5; and group 4: control, distilled water. From day 2 the rats were inoculated with Streptococcus mutans twice weekly. On day 55 the rats were killed, and caries scored in accordance with Keyes. Total caries scored were (mean +/- SD): group 1, 12.7 +/- 9.5; group 2, 17.4 +/- 8.6; group 3, 14.3 +/- 9.7; and group 4, 29.5 +/- 9.0. There were significantly (p less than 0.05) reduced caries scores for total caries and for buccal + lingual and sulcal areas for all test groups as compared with the control group. Differences between control and test groups in proximal surfaces and between fluoride groups were non-significant. The results showed that the caries-inhibitory effect of TiF4 is at least as good as that of NaF in rats.

Effect of TiF4 solutions on bacterial growth in vitro and on tooth surfaces

The purpose of this study was to assess the antimicrobial effect of TiF4 as compared with equimolar solutions of NaF, APF, and SnF2 and to evaluate the effect, if any, on bacterial growth on topically treated tooth surfaces. In an in vitro study, paper discs impregnated with 20 microliters of equimolar solutions of SnF2, NaF, APF, and TiF4 were placed on blood agar plates seeded with Streptococcus mutans and Bacteroides gingivalis. Sterile saline was used as control. Similar growth inhibition zones were found for all fluorides. In the second part of the study six volunteers carried intraoral appliances containing enamel and root surface specimens treated with 1% TiF4 and untreated specimens for 18 h. Scanning electron microscopic examination of the experimental tooth surfaces showed great variation in bacterial growth between subjects, but no systematic difference between fluoride-treated and untreated specimens. Bacteria from test and control specimens were grown under aerobic and anaerobic conditions on blood agar and on mitis salivarius agar. Colony-forming unit counts showed great interindividual variations, but no differences could be observed between treated and untreated enamel or root surfaces. Thus, the hypothesis that the presence of a Ti-rich coating may influence bacterial colonization on TiF4-treated tooth surfaces could not be substantiated.

In vivo fluoride uptake in enamel and dentin from fluoride-containing materials

The ability of fluoride-containing materials to deposit fluoride into the cavity walls could be a measure of their anticariogenic properties. Great penetration depths of fluoride were found in all groups in this study, with deeper penetration in dentin compared to enamel.

In vivo uptake and retention of fluoride after a brief application of TiF4 to dentin

The purpose of this study was to examine the long-term retention of F and Ti in dentin after a brief application of 1% TiF4. Six facets of exposed dentin in each of four beagle dogs were treated for 10 sec or 1 min with a 1% solution of TiF4. Four control facets in a fifth dog were left untreated and extracted after 12 weeks. The TiF4-treated teeth were harvested after 4, 8, and 22 weeks and analyzed for F and Ti with an electron microprobe. The F concentrations in dentin surfaces of specimens retained in the mouth for 4, 8, and 22 weeks were after the 10-sec treatment 0.48% +/- 0.24, 0.51% +/- 0.20, and 0.56% +/- 0.20, respectively, and after the 1-min treatment 0.64% +/- 0.20, 0.66% +/- 0.18, and 0.71% +/- 0.19. High concentrations of Ti were found at the specimen surfaces in all groups. None of the control specimens showed F or Ti contents above the detection limits for the method used. The results showed that a very brief application of 1% TiF4 deposited high concentrations of F and Ti which were retained for at least 22 weeks.

Effects of TiF4 solutions on root surfaces in vitro after different application periods

Topical application of aqueous solutions of TiF4 to root surfaces has been shown to result in a rapid uptake of fluoride. The purpose of this study was to assess whether the application period and/or the ionic strength of the TiF4 solution can be reduced without a corresponding reduction in the fluoride uptake. Root halves from human teeth were exposed to (a) 1% TiF4 for 10 sec and 1, 2, and 4 min, and (b) 3.4% TiF4 for the same application periods. Root surface areas protected by nail polish served as controls. Transverse ground sections through the treated root surface areas were then prepared and analyzed for F by electron microprobe analysis. Most treated specimens showed F concentrations in the 0.60-1.94% range, whereas control surfaces contained less than 0.30%. Similar F concentrations were found in the surfaces treated with the two solutions. Reducing the application period resulted in a shallower penetration of F into the hard tissue but only a slight reduction of the F concentration in the surface layer. High concentrations of Ti were found on the surface of all treated specimens. This shows that both the application period and the ionic strength of TiF4 solutions can be considerably reduced and still enable a high uptake of fluoride. The results indicate that TiF4 may be an efficacious agent for F application to root surfaces under clinical conditions.

Clinical assessment of a fluoride-containing amalgam

The aim of this study was to compare the marginal breakdown as a measure of clinical behavior of fillings made with two conventional amalgam alloys, one of which contained 1% stannous fluoride. Children requiring class II restorations in both mandibular molars received conventional amalgam (New True Dentalloy (R] in one molar and a fluoride-containing amalgam (Fluor Alloy (R)) in the other. Impressions of the filled teeth were taken just after polishing and at 1-yr intervals up to a 2-yr period. Plastic models were made and evaluated under a stereomicroscope. The results showed that the fluoride-containing amalgam presented slightly better margins than the conventional amalgam after 2 yr.

Fluoride release from a fluoride-containing amalgam in vivo

Six test subjects using a low fluoride diet collected saliva samples each morning for 1 wk to determine the normal fluoride concentration. During the following 8 wk an acrylic plate, containing amalgam "fillings" corresponding to 6 MOD amalgams in premolars, was worn each night. Saliva samples were collected every morning and analyzed with a fluoride-ion electrode. Normal fluoride values ranged from 1.22 microM to 0.57 microM. The first days after insertion of the plates the fluoride concentration ranged from 91.06 microM to 12.26 microM in the subjects. The following 25-30 days there was an exponential decline of the fluoride concentration in saliva with a half-life of 6 to 7 days. The fluoride level was significantly higher (P less than 0.01) than basal levels in all subjects during this period. The following 20-25 days the fluoride level decreased more slowly, approaching the basal level. One subject had a significantly higher fluoride level for all 8 wk. Since the saliva fluoride concentrations registered seem to be sufficient to enhance remineralization, it is concluded that restorations with this material may have a favorable effect not only on secondary caries, but on any initial demineralization in the mouth.