Altered Metabolic Flexibility in Inherited Metabolic Diseases of Mitochondrial Fatty Acid Metabolism

Thorough examination of the potential biological implications of the cuproptosis-related gene LIPT2 in the prognosis and immunotherapy in pan-cancer

OBJECTIVES

To elucidate the expression levels and prognostic value of the Lipoyltransferase 2 (LIPT2) gene in a pan-cancer view.

METHODOLOGY

Our study comprehensively investigated the role of LIPT2 in pan-cancer, combining bioinformatics analyses with experimental validations.

RESULTS

Analysis of LIPT2 mRNA expression across various cancers revealed a significant up-regulation in 18 tumor types and down-regulation in 8 types, indicating its diverse involvement. Prognostic assessment demonstrated a correlation between elevated LIPT2 expression and poorer outcomes in Overall Survival (OS) and Disease-Free Survival (DFS), particularly in Glioblastoma Multiforme (GBM), Liver Hepatocellular Carcinoma (LIHC), and Pheochromocytoma and Paraganglioma (PCPG). Protein expression analysis in GBM, LIHC, and PCPG affirmed a consistent increase in LIPT2 levels compared to normal tissues. Examining the methylation status in GBM, LIHC, and PCPG, we found reduced promoter methylation levels in tumor samples, suggesting a potential influence on LIPT2 function. Genetic mutation analysis using cBioPortal indicated a low mutation frequency (< 2%) in LIPT2 across GBM, LIHC, and PCPG. Immune correlation analysis unveiled a positive association between LIPT2 expression and infiltration levels of immune cells in GBM, LIHC, and PCPG. Single-cell analysis illustrated LIPT2's positive correlation with functional states, including angiogenesis and inflammation. Enrichment analysis identified LIPT2-associated processes and pathways, providing insights into its potential molecular mechanisms. Drug sensitivity analysis demonstrated that elevated LIPT2 expression conferred resistance to multiple compounds, while lower expression increased sensitivity. Finally, RT-qPCR validation in HCC cell lines confirmed the heightened expression of LIPT2 compared to a control cell line, reinforcing the bioinformatics findings.

CONCLUSION

Overall, our study highlights LIPT2 as a versatile player in cancer, influencing diverse aspects from molecular processes to clinical outcomes across different cancer types.

Comprehensive analysis of the potential biological significance of cuproptosis-related gene LIPT2 in pan-cancer prognosis and immunotherapy

Lipoyltransferase 2 (LIPT2) acts as a key enzyme involved in fatty acid metabolism and cell membrane synthesis. However, the biological function of LIPT2 in various cancer types and its potential significance in prognosis continue to be unresolved. For this analysis, we evaluated the expression levels and the significance of prognosis of LIPT2 gene in all cancers by various bioinformatics methods. The results found that LIPT2 was dramatically overexpressed in the vast majority of cancers. The upregulated LIPT2 was related to bad prognosis in Brain Lower Grade Glioma (LGG), Glioma (GBMLGG), Glioblastoma multiforme (GBM), Kidney Chromophobe (KICH), and High-Risk Wilms Tumor (WT), while it had a favorable prognosis in Kidney renal clear cell carcinoma (KIRC), and Ovarian serous cystadenocarcinoma (OV), Pan-kidney cohort (KIPAN). Furthermore, we assessed the mutation status, methylation levels, and immune status of LIPT2 in pan-cancer. Single-cell sequencing results revealed the correlation of LIPT2 expression with various biological characteristics such as DNA lesion, tumor angiogenesis, cell apoptosis, metastasis, and invasion. Enrichment analysis unveiled potential molecular regulatory mechanisms. In conclusion, our research reveals a detailed key role of LIPT2 in the progression, prognosis, and immune efficacy of various forms of cancer. Therefore, we have reason to believe that LIPT2 has the potential to be a candidate biomarker for tumors.

Heptanoate Improves Compensatory Mechanism of Glucose Homeostasis in Mitochondrial Long-Chain Fatty Acid Oxidation Defect

Defects in mitochondrial fatty acid β-oxidation (FAO) impair metabolic flexibility, which is an essential process for energy homeostasis. Very-long-chain acyl-CoA dehydrogenase (VLCADD; OMIM 609575) deficiency is the most common long-chain mitochondrial FAO disorder presenting with hypoglycemia as a common clinical manifestation. To prevent hypoglycemia, triheptanoin-a triglyceride composed of three heptanoates (C7) esterified with a glycerol backbone-can be used as a dietary treatment, since it is metabolized into precursors for gluconeogenesis. However, studies investigating the effect of triheptanoin on glucose homeostasis are limited. To understand the role of gluconeogenesis in the pathophysiology of long-chain mitochondrial FAO defects, we injected VLCAD-deficient (VLCAD-/-) mice with 13C3-glycerol in the presence and absence of heptanoate (C7). The incorporation of 13C3-glycerol into blood glucose was higher in VLCAD-/- mice than in WT mice, whereas the difference disappeared in the presence of C7. The result correlates with 13C enrichment of liver metabolites in VLCAD-/- mice. In contrast, the C7 bolus significantly decreased the 13C enrichment. These data suggest that the increased contribution of gluconeogenesis to the overall glucose production in VLCAD-/- mice increases the need for gluconeogenesis substrate, thereby avoiding hypoglycemia. Heptanoate is a suitable substrate to induce glucose production in mitochondrial FAO defect.

Protein posttranslational modifications in health and diseases: Functions, regulatory mechanisms, and therapeutic implications

Protein posttranslational modifications (PTMs) refer to the breaking or generation of covalent bonds on the backbones or amino acid side chains of proteins and expand the diversity of proteins, which provides the basis for the emergence of organismal complexity. To date, more than 650 types of protein modifications, such as the most well-known phosphorylation, ubiquitination, glycosylation, methylation, SUMOylation, short-chain and long-chain acylation modifications, redox modifications, and irreversible modifications, have been described, and the inventory is still increasing. By changing the protein conformation, localization, activity, stability, charges, and interactions with other biomolecules, PTMs ultimately alter the phenotypes and biological processes of cells. The homeostasis of protein modifications is important to human health. Abnormal PTMs may cause changes in protein properties and loss of protein functions, which are closely related to the occurrence and development of various diseases. In this review, we systematically introduce the characteristics, regulatory mechanisms, and functions of various PTMs in health and diseases. In addition, the therapeutic prospects in various diseases by targeting PTMs and associated regulatory enzymes are also summarized. This work will deepen the understanding of protein modifications in health and diseases and promote the discovery of diagnostic and prognostic markers and drug targets for diseases.

Investigation of the Association between the Energy Metabolism of the Insect Vector Laodelphax striatellus and Rice Stripe Virus (RSV)

Viruses, as intracellular parasites, rely on the host organism to complete their life cycle. Although over 70% of plant viruses are transmitted by insect vectors, the role of vector energy metabolism on the infection process of insect-borne plant viruses is unclear. In this study, full-length cDNAs of three energy metabolism-related genes (LsATPase, LsMIT13 and LsNADP-ME) were obtained from the small brown planthopper (SBPH, Laodelphax striatellus), which transmits the Rice stripe virus (RSV). Expression levels of LsATPase, LsMIT13 and LsNADP-ME increased by 105%, 1120% and 259%, respectively, due to RSV infection. The repression of LsATPase, LsMIT13 or LsNADP-ME by RNAi had no effect on RSV nucleocapsid protein (NP) transcripts or protein levels. The repression of LsATPase caused a significant increase in LsMIT13 and LsNADP-ME transcript levels by 230% and 217%, respectively, and the repression of LsMIT13 caused a significant increase in LsNADP-ME mRNA levels. These results suggested that the silencing of LsATPase induced compensatory upregulation of LsMIT13 and LsNADP-ME, and silencing LsMIT13 induced compensatory upregulation of LsNADP-ME. Further study indicated that the co-silencing of LsATPase, LsMIT13 and LsNADP-ME in viruliferous SBPHs increased ATP production and RSV loads by 182% and 117%, respectively, as compared with nonviruliferous SBPHs. These findings indicate that SBPH energy metabolism is involved in RSV infection and provide insight into the association between plant viruses and energy metabolism in the insect vector.

In vivo metabolic imaging identifies lipid vulnerability in a preclinical model of Her2+/Neu breast cancer residual disease and recurrence

Recurrent cancer cells that evade therapy is a leading cause of death in breast cancer patients. This risk is high for women showing an overexpression of human epidermal growth factor receptor 2 (Her2). Cells that persist can rely on different substrates for energy production relative to their primary tumor counterpart. Here, we characterize metabolic reprogramming related to tumor dormancy and recurrence in a doxycycline-induced Her2+/Neu model of breast cancer with varying times to recurrence using longitudinal fluorescence microscopy. Glucose uptake (2-NBDG) and mitochondrial membrane potential (TMRE) imaging metabolically phenotype mammary tumors as they transition to regression, dormancy, and recurrence. “Fast-recurrence” tumors (time to recurrence ~55 days), transition from glycolysis to mitochondrial metabolism during regression and this persists upon recurrence. “Slow-recurrence” tumors (time to recurrence ~100 days) rely on both glycolysis and mitochondrial metabolism during recurrence. The increase in mitochondrial activity in fast-recurrence tumors is attributed to a switch from glucose to fatty acids as the primary energy source for mitochondrial metabolism. Consequently, when fast-recurrence tumors receive treatment with a fatty acid inhibitor, Etomoxir, tumors report an increase in glucose uptake and lipid synthesis during regression. Treatment with Etomoxir ultimately prolongs survival. We show that metabolic reprogramming reports on tumor recurrence characteristics, particularly at time points that are essential for actionable targets. The temporal characteristics of metabolic reprogramming will be critical in determining the use of an appropriate timing for potential therapies; namely, the notion that metabolic-targeted inhibition during regression reports long-term therapeutic benefit.

Mitochondrial hepatopathy: Anticipated difficulties in management of fatty acid oxidation defects and urea cycle defects

Fatty acid oxidation defects (FAOD) and urea cycle defects (UCD) are among the most common metabolic liver diseases. Management of these disorders is dotted with challenges as the strategies differ based on the type and severity of the defect. In those with FAOD the cornerstone of management is avoiding hypoglycemia which in turn prevents the triggering of fatty acid oxidation. In this review, we discuss the role of carnitine supplementation, dietary interventions, newer therapies like triheptanoin, long-term treatment and approach to positive newborn screening. In UCD the general goal is to avoid excessive protein intake and indigenous protein breakdown. However, one size does not fit all and striking the right balance between avoiding hyperammonemia and preventing deficiencies of essential nutrients is a formidable task. Practical issues during the acute presentation including differential diagnosis of hyperammonemia, dietary dilemmas, the role of liver transplantation, management of the asymptomatic individual and monitoring are described in detail. A multi-disciplinary team consisting of hepatologists, metabolic specialists and dieticians is required for optimum management and improvement in quality of life for these patients.

Phospholipids: Identification and Implication in Muscle Pathophysiology

Phospholipids (PLs) are amphiphilic molecules that were essential for life to become cellular. PLs have not only a key role in compartmentation as they are the main components of membrane, but they are also involved in cell signaling, cell metabolism, and even cell pathophysiology. Considered for a long time to simply be structural elements of membranes, phospholipids are increasingly being viewed as sensors of their environment and regulators of many metabolic processes. After presenting their main characteristics, we expose the increasing methods of PL detection and identification that help to understand their key role in life processes. Interest and importance of PL homeostasis is growing as pathogenic variants in genes involved in PL biosynthesis and/or remodeling are linked to human diseases. We here review diseases that involve deregulation of PL homeostasis and present a predominantly muscular phenotype.

Short-Term Effect of a Low-Protein High-Carbohydrate Diet on Mature Female and Male, and Neomale Rainbow Trout

Rainbow trout are considered as a poor user of dietary carbohydrates, displaying persistent postprandial hyperglycaemia when fed a diet containing high amounts of carbohydrates. While this phenotype is well-described in juveniles, less attention was given to broodstock. Our objective was to assess for the first time the short-term consequences of feeding mature female and male, and neomale trout with a low-protein high-carbohydrate diet on glucose and lipid metabolism. Fish were fed for two days with a diet containing either no or 32% of carbohydrates. We analysed plasma metabolites, mRNA levels and enzymatic activities of glycolysis, gluconeogenesis, de novo lipogenesis and β-oxidation in the liver. Results demonstrated that the glucose and lipid metabolism were regulated by the nutritional status in all sexes, irrespective of the carbohydrate intake. These data point out that carbohydrate intake during a short period (5 meals) at 8 °C did not induce specific metabolic changes in broodstock. Finally, we demonstrated, for the first time, sex differences regarding the consequences of two days of feeding on glucose and lipid metabolism.