Tissue-specific deletion of mouse basolateral uniporter LAT4 (Slc43a2) reveals its crucial role in small intestine and kidney amino acid transport

Alcohol-induced C/EBP β-driven VIRMA decreases oxidative stress and promotes pancreatic ductal adenocarcinoma growth and metastasis via the m6A/YTHDF2/SLC43A2 pathway

N6-methyladenosine (m6A) plays a role in the development of tumors. However, the specific role of VIRMA, an RNA methyltransferase, in pancreatic ductal adenocarcinoma (PDAC) remains unclear. This study shows that VIRMA expression is elevated in PDAC. Increased VIRMA levels promoted PDAC growth and spread, while reducing VIRMA expression slowed these processes. VIRMA facilitated SLC43A2 mRNA degradation through an m6A-YTHDF2 pathway. The resulting decrease in SLC43A2 reduced phenylalanine absorption and oxidative stress, further driving PDAC progression. Furthermore, alcohol increased C/EBP β expression, which bound to VIRMA's promoter, enhancing its transcription. These findings suggest a connection between alcohol consumption, m6A modifications, and phenylalanine absorption in PDAC progression, offering a new approach to combat this disease.

Blood-Based Epigenetic Biomarkers Associated With Incident Chronic Kidney Disease in Individuals With Type 2 Diabetes

There is an increasing need for new biomarkers to improve prediction of chronic kidney disease (CKD) in individuals with type 2 diabetes (T2D). We aimed to identify blood-based epigenetic biomarkers associated with incident CKD and develop a methylation risk score (MRS) predicting CKD in individuals with newly diagnosed T2D. DNA methylation was analyzed epigenome wide in blood from 487 individuals with newly diagnosed T2D, of whom 88 developed CKD during an 11.5-year follow-up. Weighted Cox regression was used to associate methylation with incident CKD. Weighted logistic models and cross-validation (k = 5) were performed to test whether the MRS could predict CKD. Methylation at 37 sites was associated with CKD development based on a false discovery rate of <5% and absolute methylation differences of ≥5% between individuals with incident CKD and those free of CKD during follow-up. Notably, 15 genes annotated to these sites, e.g., TGFBI, SHISA3, and SLC43A2 (encoding LAT4), have been linked to CKD or related risk factors, including blood pressure, BMI, and estimated glomerular filtration rate. Using an MRS including 37 sites and cross-validation for prediction of CKD, we generated receiver operating characteristic (ROC) curves with an area under the curve (AUC) of 0.82 for the MRS and AUC of 0.87 for the combination of MRS and clinical factors. Importantly, ROC curves including the MRS had significantly better AUCs versus the one only including clinical factors (AUC = 0.72). The combined epigenetic biomarker had high accuracy in identifying individuals free of future CKD (negative predictive value of 94.6%). We discovered a high-performance epigenetic biomarker for predicting CKD, encouraging its potential role in precision medicine, risk stratification, and targeted prevention in T2D.

ARTICLE HIGHLIGHTS

There is an increasing need for new biomarkers to improve the prediction and prevention of chronic kidney disease (CKD) in individuals with type 2 diabetes (T2D), a leading cause of morbidity and mortality in this population. We investigated whether new blood-based epigenetic biomarkers predict incident CKD in individuals with newly diagnosed T2D. We discovered a novel blood-based epigenetic biomarker, composed of a combination of a methylation risk score and clinical factors, capable of predicting CKD during an 11.5-year follow-up (area under the curve of 0.87, negative predictive value of 94.6%) in individuals with newly diagnosed T2D. The epigenetic biomarker could provide a valuable tool for early risk stratification and prevention of CKD in individuals with newly diagnosed T2D, supporting its future use for precision medicine.

Comprehensive review of amino acid transporters as therapeutic targets

The solute carrier (SLC) family, with more than 400 membrane-bound proteins, facilitates the transport of a wide array of substrates such as nutrients, ions, metabolites, and drugs across biological membranes. Amino acid transporters (AATs) are membrane transport proteins that mediate transfer of amino acids into and out of cells or cellular organelles. AATs participate in many important physiological functions including nutrient supply, metabolic transformation, energy homeostasis, redox regulation, and neurological regulation. Several AATs have been found to significantly impact the progression of human malignancies, and dysregulation of AATs results in metabolic reprogramming affecting tumor growth and progression. However, current clinical therapies that directly target AATs have not been developed. The purpose of this review is to highlight the structural and functional diversity of AATs, the molecular mechanisms in human diseases such as tumors, kidney diseases, and emerging therapeutic strategies for targeting AATs.

Intestinal Amino Acid Transport and Metabolic Health

Amino acids derived from protein digestion are important nutrients for the growth and maintenance of organisms. Approximately half of the 20 proteinogenic amino acids can be synthesized by mammalian organisms, while the other half are essential and must be acquired from the nutrition. Absorption of amino acids is mediated by a set of amino acid transporters together with transport of di- and tripeptides. They provide amino acids for systemic needs and for enterocyte metabolism. Absorption is largely complete at the end of the small intestine. The large intestine mediates the uptake of amino acids derived from bacterial metabolism and endogenous sources. Lack of amino acid transporters and peptide transporter delays the absorption of amino acids and changes sensing and usage of amino acids by the intestine. This can affect metabolic health through amino acid restriction, sensing of amino acids, and production of antimicrobial peptides.

Dynamic cellular changes in acute kidney injury caused by different ischemia time

Ischemia reperfusion injury (IRI), often related to surgical procedures, is one of the important causes of acute kidney injury (AKI). To decipher the dynamic process of AKI caused by IRI (with prolonged ischemia phase), we performed single-cell RNA sequencing (scRNA-seq) of clinically relevant IRI murine model with different ischemic intervals. We discovered that Slc5a2^hi proximal tubular cells were susceptible to AKI and highly expressed neutral amino acid transporter gene Slc6a19, which was dramatically decreased over the time course. With the usage of mass spectrometry-based metabolomic analysis, we detected that the level of neutral amino acid isoleucine dropped off in AKI mouse plasma metabolites. And the reduction of plasma isoleucine was also verified in patients with cardiac surgery-associated acute kidney injury (CSA-AKI). The findings advanced the understanding of dynamic process of AKI and introduced reduction of isoleucine as a potential biomarker for CSA-AKI.

Impact of Inhibition of Glutamine and Alanine Transport on Cerebellar Glial and Neuronal Metabolism

The cerebellum, or “little brain”, is often overlooked in studies of brain metabolism in favour of the cortex. Despite this, anomalies in cerebellar amino acid homeostasis in a range of disorders have been reported. Amino acid homeostasis is central to metabolism, providing recycling of carbon backbones and ammonia between cell types. Here, we examined the role of cerebellar amino acid transporters in the cycling of glutamine and alanine in guinea pig cerebellar slices by inhibiting amino acid transporters and examining the resultant metabolism of [1-¹³C]d-glucose and [1,2-¹³C]acetate by NMR spectroscopy and LCMS. While the lack of specific inhibitors of each transporter makes interpretation difficult, by viewing results from experiments with multiple inhibitors we can draw inferences about the major cell types and transporters involved. In cerebellum, glutamine and alanine transfer is dominated by system A, blockade of which has maximum effect on metabolism, with contributions from System N. Inhibition of neural system A isoform SNAT1 by MeAIB resulted in greatly decreased metabolite pools and reduced net fluxes but showed little effect on fluxes from [1,2-¹³C]acetate unlike inhibition of SNAT3 and other glutamine transporters by histidine where net fluxes from [1,2-¹³C]acetate are reduced by ~50%. We interpret the data as further evidence of not one but several glutamate/glutamine exchange pools. The impact of amino acid transport inhibition demonstrates that the cerebellum has tightly coupled cells and that glutamate/glutamine, as well as alanine cycling, play a major role in that part of the brain.

GPRC6A Mediates Glucose and Amino Acid Homeostasis in Mice

GPRC6A, an important member of the G-protein-coupled receptor superfamily, has been widely studied in body health maintenance and related diseases. However, it is still controversial whether GPRC6A plays a vital role in glucose homeostasis, and the role of GPRC6A on amino acid homeostasis has not been reported. In this study, GPRC6A was knocked out in C57BL6 mice, and we found that GPRC6A plays an important role in the glucose metabolism, mainly affecting the glucose clearance capacity and gluconeogenesis in mice. GPRC6A plays an important role in maintaining amino acid homeostasis under dietary restrictions, and this may be realized by participating in the regulation of autophagy. Since a large amount of amino acid is lost from urine in aged GPRC6A^−/− mice, it is possible that GPRC6A regulates amino acid homeostasis by affecting the integrity of tissue structure. GPRC6A is involved in the regulation of mTORC1 activation but is not necessary for mTORC1 activation under sufficient nutritional supply. In the absence of exogenous amino acids, the loss of GPRC6A induces the GCN2 pathway activation and excessive autophagy of cells, leading to the overactivation of mTORC1, which may be detrimental to body health and cell survival. In summary, this study provides a theoretical and experimental basis for the metabolic process of GPRC6A in body growth and health.

Analysis of L-leucine amino acid transporter species activity and gene expression by human blood brain barrier hCMEC/D3 model reveal potential LAT1, LAT4, B0AT2 and y+LAT1 functional cooperation

In the CNS, amino acid (AA) neurotransmitters and neurotransmitter precursors are subject to tight homeostatic control mediated by blood-brain barrier (BBB) solute carrier amino acid transporters (AATs). Since the BBB is composed of multiple closely apposed cell types and opportunities for human in vivo studies are limited, we used in vitro and computational approaches to investigate human BBB AAT activity and regulation. Quantitative real-time PCR (qPCR) of the human BBB endothelial cell model hCMEC/D3 (D3) was used to determine expression of selected AAT, tight junction (TJ), and signal transduction (ST) genes under various culture conditions. L-leucine uptake data were interrogated with a computational model developed by our group for calculating AAT activity in complex cell cultures. This approach is potentially applicable to in vitro cell culture drug studies where multiple "receptors" may mediate observed responses. Of 7 Leu AAT genes expressed by D3 only the activity of SLC7A5-SLC3A2/LAT1-4F2HC (LAT1), SLC43A2/LAT4 (LAT4) and sodium-dependent AATs, SLC6A15/B⁰AT2 (B⁰AT2), and SLC7A7/y⁺LAT1 (y⁺LAT1) were calculated to be required for Leu uptake. Therefore, D3 Leu transport may be mediated by a potentially physiologically relevant functional cooperation between the known BBB AAT, LAT1 and obligatory exchange (y⁺LAT1), facilitative diffusion (LAT4), and sodium symporter (B⁰AT2) transporters.

Proteomic Analysis of the Intestinal Resistance to Thyroid Hormone Mouse Model With Thyroid Hormone Receptor Alpha Mutations

Thyroid hormone is critical during the development of vertebrates and affects the function of many organs and tissues, especially the intestine. Triiodothyronine (T₃) is the active form and can bind to thyroid hormone nuclear receptors (TRs) to play a vital role in the development of vertebrates. The resistance to thyroid hormone α, as seen in patients, has been mimicked by the Thra^E403X mutation. To investigate the mechanisms underlying the effect of TRα1 on intestinal development, the present study employed proteomic analysis to identify differentially expressed proteins (DEPs) in the distal ileum between homozygous Thra^E403X/E403X and wild-type Thra^+/+ mice. A total of 1,189 DEPs were identified, including 603 upregulated and 586 downregulated proteins. Proteomic analysis revealed that the DEPs were highly enriched in the metabolic process, the developmental process, the transporter of the nutrients, and the intestinal immune system-related pathway. Of these DEPs, 20 proteins were validated by parallel reaction monitoring analysis. Our intestinal proteomic results provide promising candidates for future studies, as they suggest novel mechanisms by which TRα1 may influence intestinal development, such as the transport of intestinal nutrients and the establishment of innate and adaptive immune barriers of the intestine.

Amino Acid Homeostasis in Mammalian Cells with a Focus on Amino Acid Transport

Amino acid homeostasis is maintained by import, export, oxidation, and synthesis of nonessential amino acids, and by the synthesis and breakdown of protein. These processes work in conjunction with regulatory elements that sense amino acids or their metabolites. During and after nutrient intake, amino acid homeostasis is dominated by autoregulatory processes such as transport and oxidation of excess amino acids. Amino acid deprivation triggers processes such as autophagy and the execution of broader transcriptional programs to maintain plasma amino acid concentrations. Amino acid transport plays a crucial role in the absorption of amino acids in the intestine, the distribution of amino acids across cells and organs, the recycling of amino acids in the kidney, and the recycling of amino acids after protein breakdown.

Differential expression of system L amino acid transporter subtypes in rat placenta and yolk sac

INTRODUCTION

Amino acid transport across the placenta is crucial for fetal growth. In rodent models, the visceral yolk sac (referred to as yolk sac hereafter) is also likely to contribute to fetal amino acid provision. System L amino acid transporters mediate the transport of essential amino acids. System L activity is mediated by light chains LAT1 (Slc7a5) and LAT2 (Slc7a8) which form functional complexes by heterodimeric linkage to CD98 (Slc3a2). LAT4 (Slc43a2) is monomeric, possessing overlapping amino acid substrate specificity with LAT1 and LAT2.

METHODS

This study investigates the expression of these LAT subtypes in fetus-matched rat placenta and yolk sac.

RESULTS

Slc7a5, Slc7a8 and Slc43a2 transcripts were expressed in placenta and yolk sac with similar expression patterns between sexes. LAT1 expression was significantly higher in placenta than yolk sac. Conversely, LAT2 and LAT4 expression was significantly higher in yolk sac than placenta; CD98 expression was comparable. LAT1, LAT2, LAT4 and CD98 were distributed to rat placental labyrinth zone (LZ) and junctional zone (JZ). LAT1 and LAT4 demonstrated higher expression in LZ, whilst LAT2 was more intensely distributed to JZ. LAT1, LAT2, LAT4 and CD98 were expressed in yolk sac, with punctate LAT1 staining to endodermal cell cytoplasm, contrasting with the intense LAT2, LAT4 and CD98 endodermal cell basolateral distribution, accounting for greater LAT2 and LAT4 expression in yolk sac compared to placenta.

CONCLUSION

LAT1, LAT2 and LAT4 are expressed in rat placenta and yolk sac implicating a combined role for these LAT subtypes in supporting fetal growth and development.