Elucidation of an mTORC2-PKC-NRF2 pathway that sustains the ATF4 stress response and identification of Sirt5 as a key ATF4 effector

Muscle mTOR controls iron homeostasis and ferritinophagy via NRF2, HIFs and AKT/PKB signaling pathways

Balanced mTOR activity and iron levels are crucial for muscle integrity, with evidence suggesting mTOR regulates cellular iron homeostasis. In this study, we investigated iron metabolism in muscle-specific mTOR knockout mice (mTORmKO) and its relation to their myopathy. The mTORmKO mice exhibited distinct iron content patterns across muscle types and ages. Slow-twitch soleus muscles initially showed reduced iron levels in young mice, which increased with the dystrophy progression but remained within control ranges. In contrast, the less affected fast-twitch muscles maintained near-normal iron levels from a young age. Interestingly, both mTORmKO muscle types exhibited iron metabolism markers indicative of iron excess, including decreased transferrin receptor 1 (TFR1) and increased levels of ferritin (FTL) and ferroportin (FPN) proteins. Paradoxically, these changes were accompanied by downregulated Ftl and Fpn mRNA levels, indicating post-transcriptional regulation. This discordant regulation resulted from disruption of key iron metabolism pathways, including NRF2/NFE2L2, HIFs, and AKT/PKB signaling. Mechanistically, mTOR deficiency impaired transcriptional regulation of iron-related genes mediated by NRF2 and HIFs. Furthermore, it triggered ferritin accumulation through two NRF2 mechanisms: (1) derepression of ferritin translation via suppression of the FBXL5-IRP axis, and (2) autophagosomal sequestration driven by NCOA4-dependent ferritin targeting to autophagosomes, coupled with age-related impairments of autophagy linked to chronic AKT/PKB activation. Three-week spermidine supplementation in older mTORmKO mice was associated with normalized AKT/PKB-FOXO signaling, increased endolysosomal FTL and reduced total FTL levels in the dystrophic soleus muscle. These findings underscore mTOR's crucial role in skeletal muscle iron metabolism and suggest spermidine as a potential strategy to address impaired ferritinophagy due to autophagy blockade in dystrophic muscle.

Mechanisms coupling the mTOR pathway to chronic obstructive pulmonary disease (COPD) pathogenesis

Chronic Obstructive Pulmonary Disease (COPD) is a poorly reversible respiratory disorder distinguished by dyspnea, cough, expectoration and exacerbations due to abnormality of airways or emphysema. In this review, we consider the therapeutic potential of targeting Mammalian target of Rapamycin (mTOR) for treating COPD. The mTOR is a highly conserved serine-threonine protein kinase that integrates signals from growth factors and nutrients to control protein synthesis, lipid biogenesis and metabolism. Dysregulated mTOR pathway signaling due to genetic factors or cigarette smoking impairs autophagy, driving the buildup of abnormal cells and damaged proteins, resulting in inflammation and oxidative stress. Persistent mTOR activation also contributes to pulmonary vascular cell proliferation, facilitating the development of pulmonary resistance in COPD. Rapamycin, an inhibitor of mTOR, prevents the buildup of senescent cells in the lungs of COPD patients and inhibits the release of lung tissue-damaging proteases. mTOR also impacts the corticosteroid sensitivity in COPD patients by regulating the levels of histone deacetylases. The emerging role of gut-lung axis dysbiosis in the progression of COPD and its influence on mTOR further highlights the relevance of the mTOR pathway in COPD pathophysiology.

Network-Based Bioinformatics Highlights Broad Importance of Human Milk Hyaluronan

Human milk (HM) is rich in bioactive factors promoting postnatal small intestinal development and maturation of the microbiome. HM is also protective against necrotizing enterocolitis (NEC), a devastating inflammatory condition predominantly affecting preterm infants. The HM glycosaminoglycan, hyaluronan (HA), is present at high levels in colostrum and early milk. Our group has demonstrated that HA with a molecular weight of 35 kDa (HA35) promotes maturation of the murine neonatal intestine and protects against two distinct models of NEC. However, the molecular mechanisms underpinning HA35-induced changes in the developing ileum are unclear. CD-1 mouse pups were treated with HA35 or vehicle control daily, from P7 to P14, and we used network and functional analyses of bulk RNA-seq ileal transcriptomes to further characterize molecular mechanisms through which HA35 likely influences intestinal maturation. HA35-treated pups separated well by principal component analysis, and cell deconvolution revealed increases in stromal, Paneth, and mature enterocyte and progenitor cells in HA35-treated pups. Gene set enrichment and pathway analyses demonstrated upregulation in key processes related to antioxidant and growth pathways, such as nuclear factor erythroid 2-related factor-mediated oxidative stress response, hypoxia inducible factor-1 alpha, mechanistic target of rapamycin, and downregulation of apoptotic signaling. Collectively, pro-growth and differentiation signals induced by HA35 may present novel mechanisms by which this HM bioactive factor may protect against NEC.

Targeting sirtuins for cancer therapy: epigenetics modifications and beyond

Sirtuins (SIRTs) are well-known as nicotinic adenine dinucleotide+(NAD+)-dependent histone deacetylases, which are important epigenetic enzymes consisting of seven family members (SIRT1-7). Of note, SIRT1 and SIRT2 are distributed in the nucleus and cytoplasm, while SIRT3, SIRT4 and SIRT5 are localized in the mitochondria. SIRT6 and SIRT7 are distributed in the nucleus. SIRTs catalyze the deacetylation of various substrate proteins, thereby modulating numerous biological processes, including transcription, DNA repair and genome stability, metabolism, and signal transduction. Notably, accumulating evidence has recently underscored the multi-faceted roles of SIRTs in both the suppression and progression of various types of human cancers. Crucially, SIRTs have been emerging as promising therapeutic targets for cancer therapy. Thus, in this review, we not only present an overview of the molecular structure and function of SIRTs, but elucidate their intricate associations with oncogenesis. Additionally, we discuss the current landscape of small-molecule activators and inhibitors targeting SIRTs in the contexts of cancer and further elaborate their combination therapies, especially highlighting their prospective utility for future cancer drug development.

NRF2 signaling and amino acid metabolism in cancer

Alterations in amino acid metabolism have emerged as a critical component in cancer biology, influencing various aspects of tumor initiation, progression, and metastasis. This review explores how amino acids, beyond their role as protein building blocks, are essential for redox balance, cell proliferation, metastasis, signaling/epigenetic regulation, and tumor microenvironment modulation in cancer. We particularly focus on the intricate relationship between amino acid metabolism and nuclear factor erythroid 2-related factor 2 (NRF2) signaling, a master regulator of oxidative stress response that frequently hyperactivated in cancer. Increasing evidence indicates that NRF2 is a key player in amino acid metabolism, orchestrating metabolism of cysteine, glutamine, and serine/glycine to promote cancer cell survival and growth. This comprehensive analysis provides insights into potential therapeutic strategies targeting the NRF2-amino acid metabolism axis, offering new avenues for cancer treatment that address multiple aspects of tumor biology.

Molecular mechanisms and therapeutic strategies for ferroptosis and cuproptosis in ischemic stroke

Ischemic stroke, as one of the most severe and prevalent neurological disorders, poses a significant threat to the health and quality of life of affected individuals. Stemming from the obstruction of blood flow, ischemic stroke, leads to cerebral tissue hypoxia and ischemia, instigating a cascade of pathophysiological changes that markedly exacerbate neuronal damage and may even culminate in cell death. In recent years, emerging research has increasingly focused on novel cell death mechanisms such as ferroptosis and cuproptosis. Mounting evidence underscores the independent roles of ferroptosis and cuproptosis in ischemic stroke. This review aims to elucidate potential cross-regulatory mechanisms between ferroptosis and cuproptosis, exploring their regulatory roles in ischemic stroke. The objective is to provide targeted therapeutic intervention strategies.

Targeting cellular adaptive responses to glutaminolysis perturbation for cancer therapy

Metabolic aberrations, notably deviations in glutamine metabolism, are crucial in the oncogenic process, offering vital resources for the unlimited proliferation and enhanced survival capabilities of cancer cells. The dependency of malignant cells on glutamine metabolism has led to the proposition of targeted therapeutic strategies. However, the capability of cancer cells to initiate adaptive responses undermines the efficacy of these therapeutic interventions. This review meticulously examines the multifaceted adaptive mechanisms that cancer cells deploy to sustain survival and growth following the disruption of glutamine metabolism. Emphasis is placed on the roles of transcription factors, alterations in metabolic pathways, the mechanistic target of rapamycin complex 1 signaling axis, autophagy, macropinocytosis, nucleotide biosynthesis, and the scavenging of ROS. Thus, the delineation and subsequent targeting of these adaptive responses in the context of therapies aimed at glutamine metabolism offer a promising avenue for circumventing drug resistance in cancer treatment.

Interplay between mTOR and Purine Metabolism Enzymes and Its Relevant Role in Cancer

Tumor cells reprogram their metabolism to meet the increased demand for nucleotides and other molecules necessary for growth and proliferation. In fact, cancer cells are characterized by an increased "de novo" synthesis of purine nucleotides. Therefore, it is not surprising that specific enzymes of purine metabolism are the targets of drugs as antineoplastic agents, and a better knowledge of the mechanisms underlying their regulation would be of great help in finding new therapeutic approaches. The mammalian target of the rapamycin (mTOR) signaling pathway, which is often activated in cancer cells, promotes anabolic processes and is a major regulator of cell growth and division. Among the numerous effects exerted by mTOR, noteworthy is its empowerment of the "de novo" synthesis of nucleotides, accomplished by supporting the formation of purinosomes, and by increasing the availability of necessary precursors, such as one-carbon formyl group, bicarbonate and 5-phosphoribosyl-1-pyrophosphate. In this review, we highlight the connection between purine and mitochondrial metabolism, and the bidirectional relation between mTOR signaling and purine synthesis pathways.

ReCorDE: a framework for identifying drug classes targeting shared vulnerabilities with applications to synergistic drug discovery

Cancer is typically treated with combinatorial therapy, and such combinations may be synergistic. However, discovery of these combinations has proven difficult as brute force combinatorial screening approaches are both logistically complex and resource-intensive. Therefore, computational approaches to augment synergistic drug discovery are of interest, but current approaches are limited by their dependencies on combinatorial drug screening training data or molecular profiling data. These dataset dependencies can limit the number and diversity of drugs for which these approaches can make inferences. Herein, we describe a novel computational framework, ReCorDE (Recurrent Correlation of Drugs with Enrichment), that uses publicly-available cell line-derived monotherapy cytotoxicity datasets to identify drug classes targeting shared vulnerabilities across multiple cancer lineages; and we show how these inferences can be used to augment synergistic drug combination discovery. Additionally, we demonstrate in preclinical models that a drug class combination predicted by ReCorDE to target shared vulnerabilities (PARP inhibitors and Aurora kinase inhibitors) exhibits class-class synergy across lineages. ReCorDE functions independently of combinatorial drug screening and molecular profiling data, using only extensive monotherapy cytotoxicity datasets as its input. This allows ReCorDE to make robust inferences for a large, diverse array of drugs. In conclusion, we have described a novel framework for the identification of drug classes targeting shared vulnerabilities using monotherapy cytotoxicity datasets, and we showed how these inferences can be used to aid discovery of novel synergistic drug combinations.

Aldehyde-mediated inhibition of asparagine biosynthesis has implications for diabetes and alcoholism

Patients with alcoholism and type 2 diabetes manifest altered metabolism, including elevated aldehyde levels and unusually low asparagine levels. We show that asparagine synthetase B (ASNS), the only human asparagine-forming enzyme, is inhibited by disease-relevant reactive aldehydes, including formaldehyde and acetaldehyde. Cellular studies show non-cytotoxic amounts of reactive aldehydes induce a decrease in asparagine levels. Biochemical analyses reveal inhibition results from reaction of the aldehydes with the catalytically important N-terminal cysteine of ASNS. The combined cellular and biochemical results suggest a possible mechanism underlying the low asparagine levels in alcoholism and diabetes. The results will stimulate research on the biological consequences of the reactions of aldehydes with nucleophilic residues.

Cyclovirobuxine D alleviates aldosterone-induced myocardial hypertrophy by protecting mitochondrial function depending on the mutual regulation of Nrf2-SIRT3

BACKGROUND

Cyclovirobuxine D (CVB-D) is a natural alkaloid that exhibits multiple pharmacological activities, such as anti-inflammatory, anti-oxidative stress, and anti-cancer properties. However, its specific protective mechanism of action for myocardial hypertrophy remains unresolved.

PURPOSE

This work was to investigate the ameliorative impact of CVB-D in myocardial hypertrophy, and to elucidate aldosterone (ALD)-induced myocardial hypertrophy by inhibiting the SIRT3 mediated Nrf2 activation.

METHODS

The myocardial hypertrophy model was reproduced by ALD both in vitro and in vivo, and the protective effect of CVB-D on myocardium and mitochondria was evaluated by TEM, H&E, qPCR, Western blot and ChIP. An immunoprecipitation experiment was adopted to evaluate the acetylation level of Nrf2 and the binding between SIRT3 and Nrf2. Additionally, bardoxolone-methyl (BAR, an Nrf2 agonist), ML385 (an Nrf2 inhibitor), resveratrol (RES, a SIRT3 agonist), and 3-TYP (a SIRT3 inhibitor) were used to confirm the molecular mechanism of CVB-D. Lastly, a molecular docking technique was employed to predict the binding site of SIRT3 and Nrf2 proteins.

RESULTS

Our findings suggested that CVB-D improved mitochondrial function, leading to a reduction in ALD-induced cardiomyocyte hypertrophy. By CVB-D treatment, there was an activation of mutual regulation between Nrf2 and SIRT3. Specifically, CVB-D resulted in the increase of Nrf2 protein in the nucleus and activated Nrf2 signaling pathway, thus up-regulating SIRT3. The activation of SIRT3 and the protective action of mitochondrion disappeared because of the intervention of ML385. After CVB-D activated SIRT3, the acetylation level of Nrf2 decreased, followed by activating the Nrf2 pathway. The activation of Nrf2 and mitochondrial protection by CVB-D were reversed by 3-TYP. Our results are also supported by Co-IP and molecular docking analysis, revealing that CVB-D promotes SIRT3-mediated Nrf2 activation.

CONCLUSION

Thus, CVB-D ameliorates ALD-induced myocardial hypertrophy by recovering mitochondrial function by activating the mutual regulation of Nrf2 and SIRT3. Thus, CVB-D could be a beneficial drug for myocardial hypertrophy.

Identification of ATF3 as a novel protective signature of quiescent colorectal tumor cells

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of death in the world. In most cases, drug resistance and tumor recurrence are ultimately inevitable. One obstacle is the presence of chemotherapy-insensitive quiescent cancer cells (QCCs). Identification of unique features of QCCs may facilitate the development of new targeted therapeutic strategies to eliminate tumor cells and thereby delay tumor recurrence. Here, using single-cell RNA sequencing, we classified proliferating and quiescent cancer cell populations in the human colorectal cancer spheroid model and identified ATF3 as a novel signature of QCCs that could support cells living in a metabolically restricted microenvironment. RNA velocity further showed a shift from the QCC group to the PCC group indicating the regenerative capacity of the QCCs. Our further results of epigenetic analysis, STING analysis, and evaluation of TCGA COAD datasets build a conclusion that ATF3 can interact with DDIT4 and TRIB3 at the transcriptional level. In addition, decreasing the expression level of ATF3 could enhance the efficacy of 5-FU on CRC MCTS models. In conclusion, ATF3 was identified as a novel marker of QCCs, and combining conventional drugs targeting PCCs with an option to target QCCs by reducing ATF3 expression levels may be a promising strategy for more efficient removal of tumor cells.

Metformin combined with glucose starvation synergistically suppress triple-negative breast cancer by enhanced unfolded protein response

Metformin (MET) is a well-documented drug used in the treatment of type II diabetes. Recent studies have revealed its potential anti-tumor effects in various types of cancer. However, the dosage of MET required to exhibit anti-tumor activity is considerably higher than the clinically recommended dosage. In this study, we investigated the synergistical anti-tumor effect of glucose deprivation and MET in MDA-MB-231 cells, which represents a triple-negative breast cancer subtype (TNBC). Our findings demonstrate that glucose deprivation significantly enhances the anti-tumor activity of MET by reducing cell proliferation and increasing cell apoptosis. RNA-seq was performed to identify the key molecules involved in this process. Our results indicate that unfolded protein response of endoplasmic reticulum (UPRER) was significantly activated upon glucose starvation combining with MET compared to glucose starvation alone. Notably, the combined treatment significantly activated UPRER signaling pathway through ATF4/ATF3/CHOP axis, due to enhanced UPRER stress. In conclusion, our study suggests that the synergistic effects of MET and glucose deprivation suppress cell proliferation in TNBC by activating pro-apoptotic molecules through UPRER stress. These findings have potential implications for the anti-tumor application of MET in TNBC.

Role of SIRT5 in cancer. Friend or Foe?

Cancer is one of the main diseases currently afflicting mankind, being difficult to treat and generating thousands of deaths per year. As a result, researchers around the world are constantly searching for new therapeutic strategies to increase the survival rate of patients. In this regard, SIRT5 may be a promising therapeutic target due to its involvement in many metabolic pathways. Notably, SIRT5 has a dual role in the context of cancer, being able to act as a tumor suppressor in some types of cancer and behaving as an oncogene in others. Interestingly, the performance of SIRT5 is not specific and is highly dependent on the cellular context. As a tumor suppressor, SIRT5 prevents the Warburg effect, increases protection against ROS and reduces cell proliferation and metastasis, while as an oncogene it has the opposite effects as well as increasing resistance to chemotherapeutics and/or radiation. In this way, the aim of this work was to identify in which cancers SIRT5 has beneficial effects and in which deleterious ones based on their molecular characteristics. Furthermore, it was analyzed whether it is feasible to use this protein as a therapeutic target, either enhancing its activity or inhibiting it as appropriate.