Phosphatidic acid-mediated mitogenic activation of mTOR signaling

Lipin1 depletion coordinates neuronal signaling pathways to promote motor and sensory axon regeneration after spinal cord injury

Adult central nervous system (CNS) neurons down-regulate growth programs after injury, leading to persistent regeneration failure. Coordinated lipids metabolism is required to synthesize membrane components during axon regeneration. However, lipids also function as cell signaling molecules. Whether lipid signaling contributes to axon regeneration remains unclear. In this study, we showed that lipin1 orchestrates mechanistic target of rapamycin (mTOR) and STAT3 signaling pathways to determine axon regeneration. We established an mTOR-lipin1-phosphatidic acid/lysophosphatidic acid-mTOR loop that acts as a positive feedback inhibitory signaling, contributing to the persistent suppression of CNS axon regeneration following injury. In addition, lipin1 knockdown (KD) enhances corticospinal tract (CST) sprouting after unilateral pyramidotomy and promotes CST regeneration following complete spinal cord injury (SCI). Furthermore, lipin1 KD enhances sensory axon regeneration after SCI. Overall, our research reveals that lipin1 functions as a central regulator to coordinate mTOR and STAT3 signaling pathways in the CNS neurons and highlights the potential of lipin1 as a promising therapeutic target for promoting the regeneration of motor and sensory axons after SCI.

Diacylglycerol kinase is a keystone regulator of signaling relevant to the pathophysiology of asthma

Signal transduction by G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and immunoreceptors converge at the activation of phospholipase C (PLC) for the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). This is a point for second-messenger bifurcation where DAG via protein kinase C (PKC) and IP3 via calcium activate distinct protein targets and regulate cellular functions. IP3 signaling is regulated by multiple calcium influx and efflux proteins involved in calcium homeostasis. A family of lipid kinases belonging to DAG kinases (DGKs) converts DAG to phosphatidic acid (PA), negatively regulating DAG signaling and pathophysiological functions. PA, through a series of biochemical reactions, is recycled to produce new molecules of PIP2. Therefore, DGKs act as a central switch in terminating DAG signaling and resynthesis of membrane phospholipids precursor. Interestingly, calcium and PKC regulate the activation of α and ζ isoforms of DGK that are predominantly expressed in airway and immune cells. Thus, DGK forms a feedback and feedforward control point and plays a crucial role in fine-tuning phospholipid stoichiometry, signaling, and functions. In this review, we discuss the previously underappreciated complex and intriguing DAG/DGK-driven mechanisms in regulating cellular functions associated with asthma, such as contraction and proliferation of airway smooth muscle (ASM) cells and inflammatory activation of immune cells. We highlight the benefits of manipulating DGK activity in mitigating salient features of asthma pathophysiology and shed light on DGK as a molecule of interest for heterogeneous diseases such as asthma.

PLD1 is a key player in cancer stemness and chemoresistance: Therapeutic targeting of cross-talk between the PI3K/Akt and Wnt/β-catenin pathways

The development of chemoresistance is a major challenge in the treatment of several types of cancers in clinical settings. Stemness and chemoresistance are the chief causes of poor clinical outcomes. In this context, we hypothesized that understanding the signaling pathways responsible for chemoresistance in cancers is crucial for the development of novel targeted therapies to overcome drug resistance. Among the aberrantly activated pathways, the PI3K-Akt/Wnt/β-catenin signaling pathway is clinically implicated in malignancies such as colorectal cancer (CRC) and glioblastoma multiforme (GBM). Aberrant dysregulation of phospholipase D (PLD) has been implicated in several malignancies, and oncogenic activation of this pathway facilitates tumor proliferation, stemness, and chemoresistance. Crosstalk involving the PLD and Wnt/β-catenin pathways promotes the progression of CRC and GBM and reduces the sensitivity of cancer cells to standard therapies. Notably, both pathways are tightly regulated and connected at multiple levels by upstream and downstream effectors. Thus, gaining deeper insights into the interactions between these pathways would help researchers discover unique therapeutic targets for the management of drug-resistant cancers. Here, we review the molecular mechanisms by which PLD signaling stimulates stemness and chemoresistance in CRC and GBM. Thus, the current review aims to address the importance of PLD as a central player coordinating cross-talk between the PI3K/Akt and Wnt/β-catenin pathways and proposes the possibility of targeting these pathways to improve cancer therapy and overcome drug resistance.

Rapamycin improves the survival of epilepsy model cells by blocking phosphorylation of mTOR base on computer simulations and cellular experiments

PURPOSE

Epilepsy is a chronic brain dysfunction characterized by recurrent epileptic seizures. Rapamycin is a naturally occurring macrolide from Streptomyces hygroscopicus, and rapamycin may provide a protective effect on the nervous system by affecting mTOR. Therefore, we investigated the pharmacologic mechanism of rapamycin treating epilepsy through bioinformatics analysis, cellular experiments and supercomputer simulation.

METHODS

Bioinformatics analysis was used to analyze targets of rapamycin treating epilepsy. We established epilepsy cell model by HT22 cells. RT-qPCR, WB and IF were used to verify the effects of rapamycin on mTOR at gene level and protein level. Computer simulations were used to model and evaluate the stability of rapamycin binding to mTOR protein.

RESULTS

Bioinformatics indicated mTOR played an essential role in signaling pathways of cell growth and cell metabolism. Cellular experiments showed that rapamycin could promote cell survival, and rapamycin did not have an effect on mRNA expression of mTOR. However, rapamycin was able to significantly inhibit the phosphorylation of mTOR at protein level. Computer simulations indicated that rapamycin was involved in the treatment of epilepsy through regulating phosphorylation of mTOR at protein level.

CONCLUSION

We found that rapamycin was capable of promoting the survival of epilepsy cells by inhibiting the phosphorylation of mTOR at protein level, and rapamycin did not have an effect on mRNA expression of mTOR. In addition to the traditional study that rapamycin affects mTORC1 complex by acting on FKBP12, this study found rapamycin could also directly block the phosphorylation of mTOR, therefore affecting the assembly of mTORC1 complex and mTOR signaling pathway.

Integrated Omics Analysis Uncovers the Culprit behind Exacerbated Atopic Dermatitis in a Diet-Induced Obesity Model

Atopic dermatitis (AD), a chronic inflammatory skin disease, is exacerbated by obesity, yet the precise linking mechanism remains elusive. This study aimed to elucidate how obesity amplifies AD symptoms. We studied skin samples from three mouse groups: sham control, AD, and high-fat (HF) + AD. The HF + AD mice exhibited more severe AD symptoms than the AD or sham control mice. Skin lipidome analysis revealed noteworthy changes in arachidonic acid (AA) metabolism, including increased expression of pla2g4, a key enzyme in AA generation. Genes for phospholipid transport (Scarb1) and acyltransferase utilizing AA as the acyl donor (Agpat3) were upregulated in HF + AD skin. Associations were observed between AA-containing phospholipids and skin lipids containing AA and its metabolites. Furthermore, imbalanced phospholipid metabolism was identified in the HF + AD mice, marked by excessive activation of the AA and phosphatidic acid (PA)-mediated pathway. This imbalance featured increased expression of Plcb1, Plcg1, and Dgk involved in PA generation, along with a decrease in genes converting PA into diglycerol (DG) and CDP-DG (Lpin1 and cds1). This investigation revealed imbalanced phospholipid metabolism in the skin of HF + AD mice, contributing to the heightened inflammatory response observed in HF + AD, shedding light on potential mechanisms linking obesity to the exacerbation of AD symptoms.

GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes

BACKGROUND

Glycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance.

OBJECTIVE

We asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur.

METHODS

Mouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined.

RESULTS

Overexpressing GPAT1 in mouse hepatocytes impaired insulin's suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects.

CONCLUSION

These data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin's ability to suppress hepatic glucose production in primary mouse hepatocytes.

mTORC1 accelerates osteosarcoma progression via m6A-dependent stabilization of USP7 mRNA

Osteosarcoma (OS) is considered a sex steroid hormone-dependent bone tumor. The development and progression of OS are regulated by 17β-estradiol (E2). However, the detailed mechanisms of E2-modulated OS progression remained to be elucidated. Here, we found that E2-activated mammalian target of rapamycin (mTOR) signaling promoted N6-methyladenosine (m6A) modification through regulating WTAP. Inhibition of mTOR complex 1 (mTORC1) reversed E2-activated WTAP expression. Meanwhile, inhibition of mTORC1 suppressed OS cell proliferation and migration. Deficiency of TSC2 activated mTORC1 signaling and enhanced OS cell proliferation and migration, while abrogated by Rapamycin. Interestingly, mTOMC1 promoted mRNA stability of ubiquitin-specific protease 7 (USP7) through m6A modification. Loss of USP7 suppressed the proliferation, migration, and ASC specks, while promoted apoptosis of OS cells. USP7 interacted with NLRP3 and deubiquitinated NLRP3 through K48-ubiquitination. USP7 was upregulated and positive correlation with NLRP3 in OS patients with high level of E2. Loss of USP7 suppressed the progression of OS via inhibiting NLRP3 inflammasome signaling pathway. Our results demonstrated that E2-activtated mTORC1 promoted USP7 stability, which promoted OS cell proliferation and migration via upregulating NLRP3 expression and enhancing NLRP3 inflammasome signaling pathway. These results discover a novel mechanism of E2 regulating OS progression and provide a promising therapeutic target for OS progression.

Dynamic changes in the mouse hepatic lipidome following warm ischemia reperfusion injury

Liver failure secondary to metabolic dysfunction-associated steatotic liver disease (MASLD) has become the most common cause for liver transplantation in many parts of the world. Moreover, the prevalence of MASLD not only increases the demand for liver transplantation, but also limits the supply of suitable donor organs because steatosis predisposes grafts to ischemia-reperfusion injury (IRI). There are currently no pharmacological interventions to limit hepatic IRI because the mechanisms by which steatosis leads to increased injury are unclear. To identify potential novel mediators of IRI, we used liquid chromatography and mass spectrometry to assess temporal changes in the hepatic lipidome in steatotic and non-steatotic livers after warm IRI in mice. Our untargeted analyses revealed distinct differences between the steatotic and non-steatotic response to IRI and highlighted dynamic changes in lipid composition with marked changes in glycerophospholipids. These findings enhance our knowledge of the lipidomic changes that occur following IRI and provide a foundation for future mechanistic studies. A better understanding of the mechanisms underlying such changes will lead to novel therapeutic strategies to combat IRI.

Multiomics analysis reveals metabolic subtypes and identifies diacylglycerol kinase α (DGKA) as a potential therapeutic target for intrahepatic cholangiocarcinoma

BACKGROUND

Intrahepatic cholangiocarcinoma (iCCA) is a highly heterogeneous and lethal hepatobiliary tumor with few therapeutic strategies. The metabolic reprogramming of tumor cells plays an essential role in the development of tumors, while the metabolic molecular classification of iCCA is largely unknown. Here, we performed an integrated multiomics analysis and metabolic classification to depict differences in metabolic characteristics of iCCA patients, hoping to provide a novel perspective to understand and treat iCCA.

METHODS

We performed integrated multiomics analysis in 116 iCCA samples, including whole-exome sequencing, bulk RNA-sequencing and proteome analysis. Based on the non-negative matrix factorization method and the protein abundance of metabolic genes in human genome-scale metabolic models, the metabolic subtype of iCCA was determined. Survival and prognostic gene analyses were used to compare overall survival (OS) differences between metabolic subtypes. Cell proliferation analysis, 5-ethynyl-2'-deoxyuridine (EdU) assay, colony formation assay, RNA-sequencing and Western blotting were performed to investigate the molecular mechanisms of diacylglycerol kinase α (DGKA) in iCCA cells.

RESULTS

Three metabolic subtypes (S1-S3) with subtype-specific biomarkers of iCCA were identified. These metabolic subtypes presented with distinct prognoses, metabolic features, immune microenvironments, and genetic alterations. The S2 subtype with the worst survival showed the activation of some special metabolic processes, immune-suppressed microenvironment and Kirsten rat sarcoma viral oncogene homolog (KRAS)/AT-rich interactive domain 1A (ARID1A) mutations. Among the S2 subtype-specific upregulated proteins, DGKA was further identified as a potential drug target for iCCA, which promoted cell proliferation by enhancing phosphatidic acid (PA) metabolism and activating mitogen-activated protein kinase (MAPK) signaling.

CONCLUSION

Via multiomics analyses, we identified three metabolic subtypes of iCCA, revealing that the S2 subtype exhibited the poorest survival outcomes. We further identified DGKA as a potential target for the S2 subtype.

Proteomic, Metabolomic, and Fatty Acid Profiling of Small Extracellular Vesicles from Glioblastoma Stem-Like Cells and Their Role in Tumor Heterogeneity

Glioblastoma is a deadly brain tumor for which there is no cure. The presence of glioblastoma stem-like cells (GSCs) contributes to the heterogeneous nature of the disease and makes developing effective therapies challenging. Glioblastoma cells have been shown to influence their environment by releasing biological nanostructures known as extracellular vesicles (EVs). Here, we investigated the role of GSC-derived nanosized EVs (<200 nm) in glioblastoma heterogeneity, plasticity, and aggressiveness, with a particular focus on their protein, metabolite, and fatty acid content. We showed that conditioned medium and small extracellular vesicles (sEVs) derived from cells of one glioblastoma subtype induced transcriptomic and proteomic changes in cells of another subtype. We found that GSC-derived sEVs are enriched in proteins playing a role in the transmembrane transport of amino acids, carboxylic acids, and organic acids, growth factor binding, and metabolites associated with amino acid, carboxylic acid, and sugar metabolism. This suggests a dual role of GSC-derived sEVs in supplying neighboring GSCs with valuable metabolites and proteins responsible for their transport. Moreover, GSC-derived sEVs were enriched in saturated fatty acids, while their respective cells were high in unsaturated fatty acids, supporting that the loading of biological cargos into sEVs is a highly regulated process and that GSC-derived sEVs could be sources of saturated fatty acids for the maintenance of glioblastoma cell metabolism. Interestingly, sEVs isolated from GSCs of the proneural and mesenchymal subtypes are enriched in specific sets of proteins, metabolites, and fatty acids, suggesting a molecular collaboration between transcriptionally different glioblastoma cells. In summary, this study revealed the complexity of GSC-derived sEVs and unveiled their potential contribution to tumor heterogeneity and critical cellular processes commonly deregulated in glioblastoma.

ATP13A2 (PARK9) and basal ganglia function

ATP13A2 is a lysosomal protein involved in polyamine transport with loss of function mutations associated with multiple neurodegenerative conditions. These include early onset Parkinson's disease, Kufor-Rakeb Syndrome, neuronal ceroid lipofuscinosis, hereditary spastic paraplegia, and amyotrophic lateral sclerosis. While ATP13A2 mutations may result in clinical heterogeneity, the basal ganglia appear to be impacted in the majority of cases. The basal ganglia is particularly vulnerable to environmental exposures such as heavy metals, pesticides, and industrial agents which are also established risk factors for many neurodegenerative conditions. Not surprisingly then, impaired function of ATP13A2 has been linked to heavy metal toxicity including manganese, iron, and zinc. This review discusses the role of ATP13A2 in basal ganglia function and dysfunction, potential common pathological mechanisms in ATP13A2-related disorders, and how gene x environment interactions may contribute to basal ganglia dysfunction.

Oleic acid stimulation of amino acid uptake in primary human trophoblast cells is mediated by phosphatidic acid and mTOR signaling

Normal fetal development is critically dependent on optimal nutrient supply by the placenta, and placental amino acid transport has been demonstrated to be positively associated with fetal growth. Mechanistic target of rapamycin (mTOR) is a positive regulator of placental amino acid transporters, such as System A. Oleic acid (OA) has been previously shown to have a stimulatory role on placental mTOR signaling and System A amino acid uptake in primary human trophoblast (PHT) cells. We investigated the mechanistic link between OA and System A activity in PHT. We found that inhibition of mTOR complex 1 or 2, using small interfering RNA to knock down raptor or rictor, prevented OA-stimulated System A amino acid transport indicating the interaction of OA with mTOR. Phosphatidic acid (PA) is a key intermediary for phospholipid biosynthesis and a known regulator of the mTOR pathway; however, phospholipid biosynthetic pathways have not been extensively studied in placenta. We identified placental isoforms of acyl transferase enzymes involved in de novo phospholipid synthesis. Silencing of 1-acylglycerol-3-phosphate-O-acyltransferase-4, an enzyme in this pathway, prevented OA mediated stimulation of mTOR and System A amino acid transport. These data indicate that OA stimulates mTOR and amino acid transport in PHT cells mediated through de novo synthesis of PA. We speculate that fatty acids in the maternal circulation, such as OA, regulate placental functions critical for fetal growth by interaction with mTOR and that late pregnancy hyperlipidemia may be critical for increasing nutrient transfer to the fetus.

Integrated Metabolomics and Transcriptomics Analyses Reveal the Candidate Genes Regulating the Meat Quality Change by Castration in Yudong Black Goats (Capra hircus)

Yudong black goats (YDGs) are a local breed in southwest China that possess unique meat qualities and produce a high meat yield, making them ideal models for studying goat meat quality. Castration may decrease off-odors, significantly change metabolites and improve meat quality. Using multi-omics techniques, this study focused on Yudong black goat wethers (YDW, n = 4) and Yudong black bucks (YDB, n = 4). The findings revealed that 33 differentially expressed genes (DEGs) and 279 significantly changed metabolites (SCMs) influenced goat meat quality by affecting fat accumulation and lipolysis regulatory processes. Herein, several candidate genes (IGF1, TNNT2, PPP2R2C, MAPK10 and VNN1, etc.) were identified that play a role in regulating meat quality, non-castrated and castrated, alongside a series of metabolites that may serve as potential meat quality biomarkers. Lipids (triglycerides, oxidized lipids_5-iso PGF2VI, ceramide (t18:1/36:2(2OH)) and Carnitine C20:5, etc.) were significantly higher in the castrated goats. These results revealed that lipids and hydrophilic metabolites were affected by castration, which might be beneficial in terms of goat meat quality. This study aimed to investigate the differences in meat quality between uncastrated and castrated male goats and the possible molecular regulatory mechanisms.

Lipocalin 2 regulates mitochondrial phospholipidome remodeling, dynamics, and function in brown adipose tissue in male mice

Mitochondrial function is vital for energy metabolism in thermogenic adipocytes. Impaired mitochondrial bioenergetics in brown adipocytes are linked to disrupted thermogenesis and energy balance in obesity and aging. Phospholipid cardiolipin (CL) and phosphatidic acid (PA) jointly regulate mitochondrial membrane architecture and dynamics, with mitochondria-associated endoplasmic reticulum membranes (MAMs) serving as the platform for phospholipid biosynthesis and metabolism. However, little is known about the regulators of MAM phospholipid metabolism and their connection to mitochondrial function. We discover that LCN2 is a PA binding protein recruited to the MAM during inflammation and metabolic stimulation. Lcn2 deficiency disrupts mitochondrial fusion-fission balance and alters the acyl-chain composition of mitochondrial phospholipids in brown adipose tissue (BAT) of male mice. Lcn2 KO male mice exhibit an increase in the levels of CLs containing long-chain polyunsaturated fatty acids (LC-PUFA), a decrease in CLs containing monounsaturated fatty acids, resulting in mitochondrial dysfunction. This dysfunction triggers compensatory activation of peroxisomal function and the biosynthesis of LC-PUFA-containing plasmalogens in BAT. Additionally, Lcn2 deficiency alters PA production, correlating with changes in PA-regulated phospholipid-metabolizing enzymes and the mTOR signaling pathway. In conclusion, LCN2 plays a critical role in the acyl-chain remodeling of phospholipids and mitochondrial bioenergetics by regulating PA production and its function in activating signaling pathways.

Activity-based directed evolution of a membrane editor in mammalian cells

Cellular membranes contain numerous lipid species, and efforts to understand the biological functions of individual lipids have been stymied by a lack of approaches for controlled modulation of membrane composition in situ. Here we present a strategy for editing phospholipids, the most abundant lipids in biological membranes. Our membrane editor is based on a bacterial phospholipase D (PLD), which exchanges phospholipid head groups through hydrolysis or transphosphatidylation of phosphatidylcholine with water or exogenous alcohols. Exploiting activity-dependent directed enzyme evolution in mammalian cells, we have developed and structurally characterized a family of 'superPLDs' with up to a 100-fold enhancement in intracellular activity. We demonstrate the utility of superPLDs for both optogenetics-enabled editing of phospholipids within specific organelle membranes in live cells and biocatalytic synthesis of natural and unnatural designer phospholipids in vitro. Beyond the superPLDs, activity-based directed enzyme evolution in mammalian cells is a generalizable approach to engineer additional chemoenzymatic biomolecule editors.

Predicting small molecule binding pockets on diacylglycerol kinases using chemoproteomics and AlphaFold

Diacylglycerol kinases (DGKs) are metabolic kinases involved in regulating cellular levels of diacylglycerol and phosphatidic lipid messengers. The development of selective inhibitors for individual DGKs would benefit from discovery of protein pockets available for inhibitor binding in cellular environments. Here we utilized a sulfonyl-triazole probe (TH211) bearing a DGK fragment ligand for covalent binding to tyrosine and lysine sites on DGKs in cells that map to predicted small molecule binding pockets in AlphaFold structures. We apply this chemoproteomics-AlphaFold approach to evaluate probe binding of DGK chimera proteins engineered to exchange regulatory C1 domains between DGK subtypes (DGKα and DGKζ). Specifically, we discovered loss of TH211 binding to a predicted pocket in the catalytic domain when C1 domains on DGKα were exchanged that correlated with impaired biochemical activity as measured by a DAG phosphorylation assay. Collectively, we provide a family-wide assessment of accessible sites for covalent targeting that combined with AlphaFold revealed predicted small molecule binding pockets for guiding future inhibitor development of the DGK superfamily.

AGK Potentiates Arterial Thrombosis by Affecting Talin-1 and αIIbβ3-Mediated Bidirectional Signaling Pathway

BACKGROUND

AGK (acylglycerol kinase) was first identified as a mitochondrial transmembrane protein that exhibits a lipid kinase function. Recent studies have established that AGK promotes cancer growth and metastasis, enhances glycolytic metabolism and function fitness of CD8+ T cells, or regulates megakaryocyte differentiation. However, the role of AGK in platelet activation and arterial thrombosis remains to be elaborated.

METHODS

We performed hematologic analysis using automated hematology analyzer and investigated platelets morphology by transmission electron microscope. We explored the role of AGK in platelet activation and arterial thrombosis utilizing transgenic mice, platelet functional experiments in vitro, and thrombosis models in vivo. We revealed the regulation effect of AGK on Talin-1 by coimmunoprecipitation, mass spectrometry, immunofluorescence, and Western blot. We tested the role of AGK on lipid synthesis of phosphatidic acid/lysophosphatidic acid and thrombin generation by specific Elisa kits.

RESULTS

In this study, we found that AGK depletion or AGK mutation had no effect on the platelet average volumes, the platelet microstructures, or the expression levels of the major platelet membrane receptors. However, AGK deficiency or AGK mutation conspicuously decreased multiple aspects of platelet activation, including agonists-induced platelet aggregation, granules secretion, JON/A binding, spreading on Fg (fibrinogen), and clot retraction. AGK deficiency or AGK mutation also obviously delayed arterial thrombus formation but had no effect on tail bleeding time and platelet procoagulant function. Mechanistic investigation revealed that AGK may promote Talin-1Ser425 phosphorylation and affect the αIIbβ3-mediated bidirectional signaling pathway. However, AGK does not affect lipid synthesis of phosphatidic acid/lysophosphatidic acid in platelets.

CONCLUSIONS

AGK, through its kinase activity, potentiates platelet activation and arterial thrombosis by promoting Talin-1 Ser425 phosphorylation and affecting the αIIbβ3-mediated bidirectional signaling pathway.

Phosphoinositide 3-kinase (PI3K) classes: From cell signaling to endocytic recycling and autophagy

Lipid signaling is defined as any biological signaling action in which a lipid messenger binds to a protein target, converting its effects to specific cellular responses. In this complex biological pathway, the family of phosphoinositide 3-kinase (PI3K) represents a pivotal role and affects many aspects of cellular biology from cell survival, proliferation, and migration to endocytosis, intracellular trafficking, metabolism, and autophagy. While yeasts have a single isoform of phosphoinositide 3-kinase (PI3K), mammals possess eight PI3K types divided into three classes. The class I PI3Ks have set the stage to widen research interest in the field of cancer biology. The aberrant activation of class I PI3Ks has been identified in 30-50% of human tumors, and activating mutations in PIK3CA is one of the most frequent oncogenes in human cancer. In addition to indirect participation in cell signaling, class II and III PI3Ks primarily regulate vesicle trafficking. Class III PI3Ks are also responsible for autophagosome formation and autophagy flux. The current review aims to discuss the original data obtained from international research laboratories on the latest discoveries regarding PI3Ks-mediated cell biological processes. Also, we unravel the mechanisms by which pools of the same phosphoinositides (PIs) derived from different PI3K types act differently.

The metabolic effects of APOL1 in humans

Harboring apolipoprotein L1 (APOL1) variants coded by the G1 or G2 alleles of the APOL1 gene increases the risk for collapsing glomerulopathy, focal segmental glomerulosclerosis, albuminuria, chronic kidney disease, and accelerated kidney function decline towards end-stage kidney disease. However, most subjects carrying APOL1 variants do not develop the kidney phenotype unless a second clinical condition adds to the genotype, indicating that modifying factors modulate the genotype-phenotype correlation. Subjects with an APOL1 high-risk genotype are more likely to develop essential hypertension or obesity, suggesting that carriers of APOL1 risk variants experience more pronounced insulin resistance compared to noncarriers. Likewise, arterionephrosclerosis (the pathological correlate of hypertension-associated nephropathy) and glomerulomegaly take place among carriers of APOL1 risk variants, and these pathological changes are also present in conditions associated with insulin resistance, such as essential hypertension, aging, and diabetes. Insulin resistance may contribute to the clinical features associated with the APOL1 high-risk genotype. Unlike carriers of wild-type APOL1, bearers of APOL1 variants show impaired formation of lipid droplets, which may contribute to inducing insulin resistance. Nascent lipid droplets normally detach from the endoplasmic reticulum into the cytoplasm, although the proteins that enable this process remain to be fully defined. Wild-type APOL1 is located in the lipid droplet, whereas mutated APOL1 remains sited at the endoplasmic reticulum, suggesting that normal APOL1 may participate in lipid droplet biogenesis. The defective formation of lipid droplets is associated with insulin resistance, which in turn may modulate the clinical phenotype present in carriers of APOL1 risk variants.

The phospholipid transporter PITPNC1 links KRAS to MYC to prevent autophagy in lung and pancreatic cancer

BACKGROUND

The discovery of functionally relevant KRAS effectors in lung and pancreatic ductal adenocarcinoma (LUAD and PDAC) may yield novel molecular targets or mechanisms amenable to inhibition strategies. Phospholipids availability has been appreciated as a mechanism to modulate KRAS oncogenic potential. Thus, phospholipid transporters may play a functional role in KRAS-driven oncogenesis. Here, we identified and systematically studied the phospholipid transporter PITPNC1 and its controlled network in LUAD and PDAC.

METHODS

Genetic modulation of KRAS expression as well as pharmacological inhibition of canonical effectors was completed. PITPNC1 genetic depletion was performed in in vitro and in vivo LUAD and PDAC models. PITPNC1-deficient cells were RNA sequenced, and Gene Ontology and enrichment analyses were applied to the output data. Protein-based biochemical and subcellular localization assays were run to investigate PITPNC1-regulated pathways. A drug repurposing approach was used to predict surrogate PITPNC1 inhibitors that were tested in combination with KRASG12C inhibitors in 2D, 3D, and in vivo models.

RESULTS

PITPNC1 was increased in human LUAD and PDAC, and associated with poor patients' survival. PITPNC1 was regulated by KRAS through MEK1/2 and JNK1/2. Functional experiments showed PITPNC1 requirement for cell proliferation, cell cycle progression and tumour growth. Furthermore, PITPNC1 overexpression enhanced lung colonization and liver metastasis. PITPNC1 regulated a transcriptional signature which highly overlapped with that of KRAS, and controlled mTOR localization via enhanced MYC protein stability to prevent autophagy. JAK2 inhibitors were predicted as putative PITPNC1 inhibitors with antiproliferative effect and their combination with KRASG12C inhibitors elicited a substantial anti-tumour effect in LUAD and PDAC.

CONCLUSIONS

Our data highlight the functional and clinical relevance of PITPNC1 in LUAD and PDAC. Moreover, PITPNC1 constitutes a new mechanism linking KRAS to MYC, and controls a druggable transcriptional network for combinatorial treatments.

A novel tumor suppressor encoded by a 1p36.3 lncRNA functions as a phosphoinositide-binding protein repressing AKT phosphorylation/activation and promoting autophagy

Peptides/small proteins, encoded by noncanonical open reading frames (ORF) of previously claimed non-coding RNAs, have recently been recognized possessing important biological functions, but largely uncharacterized. 1p36 is an important tumor suppressor gene (TSG) locus frequently deleted in multiple cancers, with critical TSGs like TP73, PRDM16, and CHD5 already validated. Our CpG methylome analysis identified a silenced 1p36.3 gene KIAA0495, previously thought coding long non-coding RNA. We found that the open reading frame 2 of KIAA0495 is actually protein-coding and translating, encoding a small protein SP0495. KIAA0495 transcript is broadly expressed in multiple normal tissues, but frequently silenced by promoter CpG methylation in multiple tumor cell lines and primary tumors including colorectal, esophageal and breast cancers. Its downregulation/methylation is associated with poor survival of cancer patients. SP0495 induces tumor cell apoptosis, cell cycle arrest, senescence and autophagy, and inhibits tumor cell growth in vitro and in vivo. Mechanistically, SP0495 binds to phosphoinositides (PtdIns(3)P, PtdIns(3,5)P2) as a lipid-binding protein, inhibits AKT phosphorylation and its downstream signaling, and further represses oncogenic AKT/mTOR, NF-κB, and Wnt/β-catenin signaling. SP0495 also regulates the stability of autophagy regulators BECN1 and SQSTM1/p62 through modulating phosphoinositides turnover and autophagic/proteasomal degradation. Thus, we discovered and validated a 1p36.3 small protein SP0495, functioning as a novel tumor suppressor regulating AKT signaling activation and autophagy as a phosphoinositide-binding protein, being frequently inactivated by promoter methylation in multiple tumors as a potential biomarker.

Doxorubicin downregulates autophagy to promote apoptosis-induced dilated cardiomyopathy via regulating the AMPK/mTOR pathway

The broad-spectrum antineoplastic drug doxorubicin (DOX) has one of the most serious chronic side effects on the heart, dilated cardiomyopathy, but the precise molecular mechanisms underlying disease progression subsequent to long latency periods remain puzzling. Here, we established a model of DOX-induced dilated cardiomyopathy. In a cardiac cytology exploration, we found that differentially expressed genes in the KEGG signaling pathway enrichment provided a novel complex network of mTOR bridging autophagy and oxidative stress. Validation results showed that DOX caused intracellular reactive oxygen species accumulation in cardiomyocytes, disrupted mitochondria, led to imbalanced intracellular energy metabolism, and triggered cardiomyocyte apoptosis. Apoptosis showed a negative correlation with DOX-regulated cardiomyocyte autophagy. To evaluate whether the inhibition of mTOR could upregulate autophagy to protect cardiomyocytes, we used rapamycin to restore autophagy depressed by DOX. Rapamycin increased cardiomyocyte survival by easing the autophagic flux blocked by DOX. In addition, rapamycin reduced oxidative stress, prevented mitochondrial damage, and restored energy metabolic homeostasis in DOX-treated cardiomyocytes. In vivo, we used metformin (Met) which is an AMPK activator to protect cardiac tissue to alleviate DOX-induced dilated cardiomyopathy. In this study, Met significantly attenuated the oxidative stress response of myocardial tissue caused by DOX and activated cardiomyocyte autophagy to maintain cardiomyocyte energy metabolism and reduce cardiomyocyte apoptosis by downregulating mTOR activity. Overall, our study revealed the role of autophagy and apoptosis in DOX-induced dilated cardiomyopathy and demonstrated the potential role of regulation of the AMPK/mTOR axis in the treatment of DOX-induced dilated cardiomyopathy.

Regulation of Autophagy via Carbohydrate and Lipid Metabolism in Cancer

Metabolic changes are an important component of tumor cell progression. Tumor cells adapt to environmental stresses via changes to carbohydrate and lipid metabolism. Autophagy, a physiological process in mammalian cells that digests damaged organelles and misfolded proteins via lysosomal degradation, is closely associated with metabolism in mammalian cells, acting as a meter of cellular ATP levels. In this review, we discuss the changes in glycolytic and lipid biosynthetic pathways in mammalian cells and their impact on carcinogenesis via the autophagy pathway. In addition, we discuss the impact of these metabolic pathways on autophagy in lung cancer.

Influence of mTOR-regulated anabolic pathways on equine skeletal muscle health

Skeletal muscle is a highly dynamic organ that is essential for locomotion as well as endocrine regulation in all populations of horses. However, despite the importance of adequate muscle development and maintenance, the mechanisms underlying protein anabolism in horses on different diets, exercise programs, and at different life stages remain obscure. Mechanistic target of rapamycin (mTOR) is a key component of the protein synthesis pathway and is regulated by biological factors such as insulin and amino acid availability. Providing a diet ample in vital amino acids, such as leucine and glutamine, is essential in activating sensory pathways that recruit mTOR to the lysosome and assist in the translation of important downstream targets. When the diet is well balanced, mitochondrial biogenesis and protein synthesis are activated in response to increased exercise bouts in the performing athlete. It is important to note that the mTOR kinase pathways are multi-faceted and very complex, with several binding partners and targets that lead to specific functions in protein turnover of the cell, and ultimately, the capacity to maintain or grow muscle mass. Further, these pathways are likely altered across the lifespan, with an emphasis of growth in young horses while decreases in musculature with aged horses appears to be attributable to degradation or other regulators of protein synthesis rather than alterations in the mTOR pathway. Previous work has begun to pinpoint ways in which the mTOR pathway is influenced by diet, exercise, and age; however, future research is warranted to quantify the functional outcomes related to changes in mTOR. Promisingly, this could provide direction on appropriate management techniques to support skeletal muscle growth and maximize athletic potential in differing equine populations.

Regulation of mTOR by phosphatidic acid

mTORC1, the mammalian target of rapamycin complex 1, is a key regulator of cellular physiology. The lipid metabolite phosphatidic acid (PA) binds to and activates mTORC1 in response to nutrients and growth factors. We review structural findings and propose a model for PA activation of mTORC1. PA binds to a highly conserved sequence in the α4 helix of the FK506 binding protein 12 (FKBP12)/rapamycin-binding (FRB) domain of mTOR. It is proposed that PA binding to two adjacent positively charged amino acids breaks and shortens the C-terminal region of helix α4. This has profound consequences for both substrate binding and the catalytic activity of mTORC1.

Autophagy: A Cellular Guardian against Hepatic Lipotoxicity

Lipotoxicity is a phenomenon of lipid-induced cellular injury in nonadipose tissue. Excess of free saturated fatty acids (SFAs) contributes to hepatic injury in nonalcoholic fatty liver disease (NAFLD), which has been growing at an unprecedented rate in recent years. SFAs and their derivatives such as ceramides and membrane phospholipids have been shown to induce intrahepatic oxidative damage and ER stress. Autophagy represents a cellular housekeeping mechanism to counter the perturbation in organelle function and activation of stress signals within the cell. Several aspects of autophagy, including lipid droplet assembly, lipophagy, mitophagy, redox signaling and ER-phagy, play a critical role in mounting a strong defense against lipotoxic lipid species within the hepatic cells. This review provides a succinct overview of our current understanding of autophagy-lipotoxicity interaction and its pharmacological and nonpharmacological modulation in treating NAFLD.

Nutrient-sensing mTORC1 and AMPK pathways in chronic kidney diseases

Nutrients such as glucose, amino acids and lipids are fundamental sources for the maintenance of essential cellular processes and homeostasis in all organisms. The nutrient-sensing kinases mechanistic target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) are expressed in many cell types and have key roles in the control of cell growth, proliferation, differentiation, metabolism and survival, ultimately contributing to the physiological development and functions of various organs, including the kidney. Dysregulation of these kinases leads to many human health problems, including cancer, neurodegenerative diseases, metabolic disorders and kidney diseases. In the kidney, physiological levels of mTOR and AMPK activity are required to support kidney cell growth and differentiation and to maintain kidney cell integrity and normal nephron function, including transport of electrolytes, water and glucose. mTOR forms two functional multi-protein kinase complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Hyperactivation of mTORC1 leads to podocyte and tubular cell dysfunction and vulnerability to injury, thereby contributing to the development of chronic kidney diseases, including diabetic kidney disease, obesity-related kidney disease and polycystic kidney disease. Emerging evidence suggests that targeting mTOR and/or AMPK could be an effective therapeutic approach to controlling or preventing these diseases.

Claspin is Required for Growth Recovery from Serum Starvation through Regulating the PI3K-PDK1-mTOR Pathway in Mammalian Cells

Claspin plays multiple important roles in regulation of DNA replication as a mediator for the cellular response to replication stress, an integral replication fork factor that facilitates replication fork progression and a factor that promotes initiation by recruiting Cdc7 kinase. Here, we report a novel role of Claspin in growth recovery from serum starvation, which requires the activation of PI3 kinase (PI3K)-PDK1-Akt-mTOR pathways. In the absence of Claspin, cells do not proceed into S phase and eventually die partially in a ROS- and p53-dependent manner. Claspin directly interacts with PI3K and mTOR, and is required for activation of PI3K-PDK1-mTOR and for that of mTOR downstream factors, p70S6K and 4EBP1, but not for p38 MAPK cascade during the recovery from serum starvation. PDK1 physically interacts with Claspin, notably with CKBD, in a manner dependent on phosphorylation of the latter protein, and is required for interaction of mTOR with Claspin. Thus, Claspin plays a novel role as a key regulator for nutrition-induced proliferation/survival signaling by activating the mTOR pathway. The results also suggest a possibility that Claspin may serve as a common mediator that receives signals from different PI3K-related kinases and transmit them to specific downstream kinases.

Drug discovery inspired by bioactive small molecules from nature

Natural products (NPs) have greatly contributed to the development of novel treatments for human diseases such as cancer, metabolic disorders, and infections. Compared to synthetic chemical compounds, primary and secondary metabolites from medicinal plants, fungi, microorganisms, and our bodies are promising resources with immense chemical diversity and favorable properties for drug development. In addition to the well-validated significance of secondary metabolites, endogenous small molecules derived from central metabolism and signaling events have shown great potential as drug candidates due to their unique metabolite-protein interactions. In this short review, we highlight the values of NPs, discuss recent scientific and technological advances including metabolomics tools, chemoproteomics approaches, and artificial intelligence-based computation platforms, and explore potential strategies to overcome the current challenges in NP-driven drug discovery.

Evaluation of the Timing of Use of Phosphatidic Acid in the Diet on Growth Performance and Breast Meat Yield in Broilers

With a growing increase in further processing of poultry, there has been an increased interest in factors, including feed additives, that may improve broiler performance, increase growth, and influence dressing percentage. Mammalian target of rapamycin (mTOR) is known to play vital roles in protein synthesis; mTOR controls the anabolic and catabolic signaling of skeletal muscle mass, resulting in the modulation of muscle hypertrophy. Exogenous phosphatidic acid (PA) can stimulate the mTOR pathway via its activation of the substrate S6 kinase. A study with 648 Cobb 500 male broilers, housed in 36 floor pens (1.11 m2) from 1 to 42 days of age was conducted to evaluate the timing of PA (Mediator® 50P, Chemi Nutra, Austin, TX, USA) supplementation on the growth performance and carcass yield of broilers. Dietary treatments included T1, Control (CON), T2, 5 mg/bird/day of PA for 42 days (d0−42, PAA); T3, 5 mg/bird/day of PA for 28 days (d15−42, PAGF); and T4, 5 mg/bird/day of PA for 14 days (d29−42, PAF). All birds were weighed on d14, 28, and 42 to obtain BW (body weight), FCR (feed conversion ratio), and MORT (mortality percentage). On d42, eight birds per pen were processed to determine carcass and breast meat yield. No differences were observed in BW at d14 or d28. At d42, birds fed PAA were heavier (3.73 ± 0.02, p < 0.05) than all dietary treatments (3.68 ± 0.02). From d0 to d28, birds fed PAA had the lowest FCR (1.423 ± 0.005, p < 0.05) compared to all dietary treatments (1.441 ± 0.005). From d0 to d42, birds fed PAA and PAGF had a lower FCR (1.545 ± 0.014, p < 0.05) when compared to the CON (1.609 ± 0.013). No differences were observed in MORT between treatments during growout. Increased BW observed in birds fed PAA translated to increased breast fillet weight (0.772 ± 0.009 kg, p < 0.05) when compared to the CON (0.743 ± 0.008 kg). Carcass yields were increased in birds fed PAA (77.48 ± 0.32 kg, p < 0.05) when compared to all dietary treatments (76.24 ± 0.16 kg). Utilizing PA for 42 days increased live weights, improved FCR, increased carcass yield, and increased breast fillet weight at processing. Results from this study indicate that supplementation of PA during all phases of growth may increase the production efficiency of broilers.

PPARγ-AGPAT6 signaling mediates acetate-induced mTORC1 activation and milk fat synthesis in mammary epithelial cells of dairy cows

This research communication investigated the role and the underlying mechanism of sn-1-acylglycerol-3-phosphate O-acyltransferase 6 (AGPAT6) in acetate-induced mTORC1 signaling activation and milk fat synthesis in dairy cow mammary epithelial cells. The data showed AGPAT6 knockdown significantly decreased acetate-induced phosphorylation of mTORC1 signaling molecules and intracellular triacylglycerol (TAG) content, whereas this inhibition effect was reversed after the addition of 16:0,18:1 phosphatidic acid (PA), suggesting that AGPAT6 could generate PA in response to acetate simulation, that in turn activates mTORC1 signaling. PPARγ is the upstream regulator of AGPAT6 upon acetate stimulation. Luciferase assay with clones containing various deletions and mutation in AGPAT6 promoter showed that there is a RXRα binding sequence located at -96 bp of AGPAT6 promoter. Acetate stimulation significantly increased the interaction between PPARγ and AGPAT6 via this RXRα binding site. Taken together, our data indicated that AGPAT6 could activate mTORC1 signaling by producing PA during acetate-induced milk fat synthesis, and PPARγ acts as a transcription factor to mediate the effect of acetate on AGPAT6 via RXRα.

Phosphatidic acid suppresses autophagy through competitive inhibition by binding GAPC (glyceraldehyde-3-phosphate dehydrogenase) and PGK (phosphoglycerate kinase) proteins

Macroautophagy/autophagy is a finely-regulated process in which cytoplasm encapsulated within transient organelles termed autophagosomes is delivered to lysosomes or vacuoles for degradation. Phospholipids, particularly phosphatidic acid (PA) that functions as a second messenger, play crucial and differential roles in autophagosome formation; however, the underlying mechanism remains largely unknown. Here we demonstrated that PA inhibits autophagy through competitive inhibition of the formation of ATG3 (autophagy-related)-ATG8e and ATG6-VPS34 (vacuolar protein sorting 34) complexes. PA bound to GAPC (glyceraldehyde-3-phosphate dehydrogenase) or PGK (phosphoglycerate kinase) and promoted their interaction with ATG3 or ATG6, which further attenuated the interactions of ATG3-ATG8e or ATG6-VPS34, respectively. Structural and mutational analyses revealed the mechanism of PA binding with GAPCs and PGK3, and that GAPCs or ATG8e competitively interacted with ATG3, and PGK3 or VPS34 competitively interacted with ATG6, at the same binding interface. These results elucidate the molecular mechanism of how PA inhibits autophagy through binding GAPC or PGK3 proteins and expand the understanding of the functional mode of PA, demonstrating the importance of phospholipids in plant autophagy and providing a new perspective for autophagy regulation by phospholipids.Abbreviation: ATG: autophagy-related; BiFC: bimolecular fluorescence complementation; co-IP: co-immunoprecipitation; Con A: concanamycin A; ER: endoplasmic reticulum; EZ: elongation zone; FRET-FLIM: fluorescence resonance energy transfer with fluorescence lifetime imaging microscopy; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GST: glutathione S-transferase; MDC: monodansylcadaverine; MZ: meristem zone; PA: phosphatidic acid; PAS: phagophore assembly site; PC: phosphatidylcholine; PE: phosphatidylethanolamine; PGK3: phosphoglycerate kinase; PtdIns3K: phosphatidylinositol 3-kinase; PLD: phospholipase D; TEM: transmission electron microscopy; TOR: target of rapamycin; VPS34: vacuolar protein sorting 34; WT: wild type; Y2H: yeast two-hybrid.

The Role of Diacylglycerol Kinase in the Amelioration of Diabetic Nephropathy

The drastic increase in the number of patients with diabetes and its complications is a global issue. Diabetic nephropathy, the leading cause of chronic kidney disease, significantly affects patients’ quality of life and medical expenses. Furthermore, there are limited drugs for treating diabetic nephropathy patients. Impaired lipid signaling, especially abnormal protein kinase C (PKC) activation by de novo-synthesized diacylglycerol (DG) under high blood glucose, is one of the causes of diabetic nephropathy. DG kinase (DGK) is an enzyme that phosphorylates DG and generates phosphatidic acid, i.e., DGK can inhibit PKC activation under diabetic conditions. Indeed, it has been proven that DGK activation ameliorates diabetic nephropathy. In this review, we summarize the involvement of PKC and DGK in diabetic nephropathy as therapeutic targets, and its mechanisms, by referring to our recent study.

Regulation of Airway Smooth Muscle Cell Proliferation by Diacylglycerol Kinase: Relevance to Airway Remodeling in Asthma

Airway remodeling in asthma involves the hyperproliferation of airway smooth muscle (ASM) cells. However, the molecular signals that regulate ASM growth are not completely understood. Gq-coupled G protein-coupled receptor and receptor tyrosine kinase signaling regulate ASM cell proliferation via activation of phospholipase C, generation of inositol triphosphate (IP3) and diacylglycerol (DAG). Diacylglycerol kinase (DGK) converts DAG into phosphatidic acid (PA) and terminates DAG signaling while promoting PA-mediated signaling and function. Herein, we hypothesized that PA is a pro-mitogenic second messenger in ASM, and DGK inhibition reduces the conversion of DAG into PA resulting in inhibition of ASM cell proliferation. We assessed the effect of pharmacological inhibition of DGK on pro-mitogenic signaling and proliferation in primary human ASM cells. Pretreatment with DGK inhibitor I (DGKI) significantly inhibited platelet-derived growth factor-stimulated ASM cell proliferation. Anti-mitogenic effect of DGKI was associated with decreased mTOR signaling and expression of cyclin D1. Exogenous PA promoted pro-mitogenic signaling and rescued DGKI-induced attenuation of ASM cell proliferation. Finally, house dust mite (HDM) challenge in wild type mice promoted airway remodeling features, which were attenuated in DGKζ-/- mice. We propose that DGK serves as a potential drug target for mitigating airway remodeling in asthma.

Phosphoproteomics of three exercise modalities identifies canonical signaling and C18ORF25 as an AMPK substrate regulating skeletal muscle function

Exercise induces signaling networks to improve muscle function and confer health benefits. To identify divergent and common signaling networks during and after different exercise modalities, we performed a phosphoproteomic analysis of human skeletal muscle from a cross-over intervention of endurance, sprint, and resistance exercise. This identified 5,486 phosphosites regulated during or after at least one type of exercise modality and only 420 core phosphosites common to all exercise. One of these core phosphosites was S67 on the uncharacterized protein C18ORF25, which we validated as an AMPK substrate. Mice lacking C18ORF25 have reduced skeletal muscle fiber size, exercise capacity, and muscle contractile function, and this was associated with reduced phosphorylation of contractile and Ca2+ handling proteins. Expression of C18ORF25 S66/67D phospho-mimetic reversed the decreased muscle force production. This work defines the divergent and canonical exercise phosphoproteome across different modalities and identifies C18ORF25 as a regulator of exercise signaling and muscle function.

Restoration of mitophagy ameliorates cardiomyopathy in Barth syndrome

Barth syndrome (BTHS) is an X-linked genetic disorder caused by mutations in the TAFAZZIN/Taz gene which encodes a transacylase required for cardiolipin remodeling. Cardiolipin is a mitochondrial signature phospholipid that plays a pivotal role in maintaining mitochondrial membrane structure, respiration, mtDNA biogenesis, and mitophagy. Mutations in the TAFAZZIN gene deplete mature cardiolipin, leading to mitochondrial dysfunction, dilated cardiomyopathy, and premature death in BTHS patients. Currently, there is no effective treatment for this debilitating condition. In this study, we showed that TAFAZZIN deficiency caused hyperactivation of MTORC1 signaling and defective mitophagy, leading to accumulation of autophagic vacuoles and dysfunctional mitochondria in the heart of Tafazzin knockdown mice, a rodent model of BTHS. Consequently, treatment of TAFAZZIN knockdown mice with rapamycin, a potent inhibitor of MTORC1, not only restored mitophagy, but also mitigated mitochondrial dysfunction and dilated cardiomyopathy. Taken together, these findings identify MTORC1 as a novel therapeutic target for BTHS, suggesting that pharmacological restoration of mitophagy may provide a novel treatment for BTHS.Abbreviations: BTHS: Barth syndrome; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CL: cardiolipin; EIF4EBP1/4E-BP1: eukaryotic translation initiation factor 4E binding protein 1; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; KD: knockdown; KO: knockout; LAMP1: lysosomal-associated membrane protein 1; LV: left ventricle; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MEFs: mouse embryonic fibroblasts; MTORC1: mechanistic target of rapamycin kinase complex 1; OCR: oxygen consumption rate; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced putative kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; qRT-PCR: quantitative real-time polymerase chain reaction; RPS6KB/S6K: ribosomal protein S6 kinase beta; SQSTM1/p62: sequestosome 1; TLCL: tetralinoleoyl cardiolipin; WT: wild-type.

Phosphatidic acid binds to and stimulates the activity of ARGAH2 from Arabidopsis

Phosphatidic acid (PA) has emerged as an important lipid signal during abiotic and biotic stress conditions such as drought, salinity, freezing, nutrient starvation, wounding and microbial elicitation. PA acts during stress responses primarily via binding and translocating target proteins or through modulating their activity. Owing to the importance of PA during stress signaling and developmental stages, it is imperative to identify PA interacting proteins and decipher their specific roles. In the present study, we have identified PA binding proteins from the leaves of Arabidopsis thaliana. Mass spectroscopy analysis led to the identification of 21 PA binding proteins with known roles in various cellular processes. One of the PA-binding proteins identified during this study, AtARGAH2, was further studied to unravel the role of PA interaction. Recombinant AtARGAH2 binding with immobilized PA on a solid support validated PA-AtARGAH2 binding invitro. PA binding to AtARGAH2 leads to the enhancement of arginase enzymatic activity in a dose dependent manner. Enzyme kinetics of recombinant AtARGAH2 demonstrated a lower K_m value in presence of PA, suggesting role of PA in efficient enzyme-substrate binding. This simple approach could systematically be applied to perform an inclusive study on lipid binding proteins to elucidate their role in physiology of plants.

Ceramide levels in blood plasma correlate with major depressive disorder severity and its neutralization abrogates depressive behavior in mice

Major depressive disorder (MDD) is a severe disease of unknown pathogenesis that will affect ∼10% of people during their lifetime. Therapy for MDD requires prolonged treatment and often fails, predicating a need for novel treatment strategies. Here, we report increased ceramide levels in the blood plasma of MDD patients and in murine stress-induced models of MDD. These blood plasma ceramide levels correlated with the severity of MDD in human patients and were independent of age, sex, or body mass index. In addition, intravenous injection of anti-ceramide antibodies or neutral ceramidase rapidly abrogated stress-induced MDD, and intravenous injection of blood plasma from mice with MDD induced depression-like behavior in untreated mice, which was abrogated by ex vivo pre-incubation of the plasma with anti-ceramide antibodies or ceramidase. Mechanistically, we demonstrate that ceramide accumulated in endothelial cells of the hippocampus of stressed mice, evidenced by the quantitative measurement of ceramide in purified hippocampus endothelial cells. We found ceramide inhibited the activity of phospholipase D (PLD) in endothelial cells in vitro and in the hippocampus in vivo and thereby decreased phosphatidic acid in the hippocampus. Finally, we show intravenous injection of PLD or phosphatidic acid abrogated MDD, indicating the significance of this pathway in MDD pathogenesis. Our data indicate that ceramide controls PLD activity and phosphatidic acid formation in hippocampal endothelial cells and thereby mediates MDD. We propose that neutralization of plasma ceramide could represent a rapid-acting targeted treatment for MDD.

Targeting mTOR in the Context of Diet and Whole-body Metabolism

The mechanistic target of the rapamycin (mTOR) signaling pathway is the central regulator of cell growth and proliferation by integrating growth factor and nutrient availability. Under healthy physiological conditions, this process is tightly coordinated and essential to maintain whole-body homeostasis. Not surprisingly, dysregulated mTOR signaling underpins several diseases with increasing incidence worldwide, including obesity, diabetes, and cancer. Consequently, there is significant clinical interest in developing therapeutic strategies that effectively target this pathway. The transition of mTOR inhibitors from the bench to bedside, however, has largely been marked with challenges and shortcomings, such as the development of therapy resistance and adverse side effects in patients. In this review, we discuss the current status of first-, second-, and third-generation mTOR inhibitors as a cancer therapy in both preclinical and clinical settings, with a particular emphasis on the mechanisms of drug resistance. We focus especially on the emerging role of diet as an important environmental determinant of therapy response, and posit a conceptual framework that links nutrient availability and whole-body metabolic states such as obesity with many of the previously defined processes that drive resistance to mTOR-targeted therapies. Given the role of mTOR as a central integrator of cell metabolism and function, we propose that modulating nutrient inputs through dietary interventions may influence the signaling dynamics of this pathway and compensatory nodes. In doing so, new opportunities for exploiting diet/drug synergies are highlighted that may unlock the therapeutic potential of mTOR inhibitors as a cancer treatment.

Mechanistic Target of Rapamycin Complex 1: From a Nutrient Sensor to a Key Regulator of Metabolism and Health

Mechanistic target of rapamycin complex 1 (mTORC1) is a multi-protein complex widely found in eukaryotes. It serves as a central signaling node to coordinate cell growth and metabolism by sensing diverse extracellular and intracellular inputs, including amino acid-, growth factor-, glucose-, and nucleotide-related signals. It is well documented that mTORC1 is recruited to the lysosomal surface, where it is activated and, accordingly, modulates downstream effectors involved in regulating protein, lipid, and glucose metabolism. mTORC1 is thus the central node for coordinating the storage and mobilization of nutrients and energy across various tissues. However, emerging evidence indicated that the overactivation of mTORC1 induced by nutritional disorders leads to the occurrence of a variety of metabolic diseases, including obesity and type 2 diabetes, as well as cancer, neurodegenerative disorders, and aging. That the mTORC1 pathway plays a crucial role in regulating the occurrence of metabolic diseases renders it a prime target for the development of effective therapeutic strategies. Here, we focus on recent advances in our understanding of the regulatory mechanisms underlying how mTORC1 integrates metabolic inputs as well as the role of mTORC1 in the regulation of nutritional and metabolic diseases.

FRB domain of human TOR protein induces compromised proliferation and mitochondrial dysfunction in Labrus donovani promastigotes

Visceral leishmaniasis (VL) or Kala-azar, the second-largest parasitic killer worldwide, is caused by Leishmania donovani. The drugs to treat VL are toxic and expensive. Moreover, their indiscriminate use gave rise to resistant strains. The high rate of parasite proliferation within the host macrophage cells causes pathogenesis. In the proliferative pathway, FRB domain of TOR protein is ubiquitously essential. Although orthologues of mTOR protein are reported in trypanosomatids and Leishmania but therein depth molecular characterization is yet to be done. Considerable protein sequence homology exists between the TOR of kinetoplastidas and mammals. Interestingly, exogenous human FRB domain was shown to block G1 to S transition in mammalian cancer cells. Thus, we hypothesized that expression of human FRB domain would inhibit the proliferation of Labrus donovani. Indeed, promastigotes stably expressing wild type human FRB domain show 4.7 and 1.5 folds less intra- and extra-cellular proliferations than that of untransfected controls. They also manifested 2.65 times lower rate of glucose stimulated oxygen consumption. The activities of all respiratory complexes were compromised in the hFRB expressing promastigotes. In these cells, depolarized mitochondria were 2-fold more than control cells. However, promastigotes expressing its mutant version (Trp²⁰²⁷-Phe) has shown similar characteristics like untransfected cells. Thus, this study reveals greater insights on the conserved role of TOR in the regulation of the respiratory complexes in L. donovani. The slow growing variant of FRB expressing promastigotes will have great potential to be exploited as a prophylactic agent against leishmaniasis.

Discovery of Phospholipase D Inhibitors with Improved Drug-like Properties and Central Nervous System Penetrance

Phospholipase D (PLD) is a phospholipase enzyme responsible for hydrolyzing phosphatidylcholine into the lipid signaling molecule, phosphatidic acid, and choline. From a therapeutic perspective, PLD has been implicated in human cancer progression as well as a target for neurodegenerative diseases, including Alzheimer's. Moreover, knockdown of PLD rescues the ALS phenotype in multiple Drosophila models of ALS (amyotrophic lateral sclerosis) and displays modest motor benefits in an SOD1 ALS mouse model. To further validate whether inhibiting PLD is beneficial for the treatment of ALS, a brain penetrant small molecule inhibitor with suitable PK properties to test in an ALS animal model is needed. Using a combination of ligand-based drug discovery and structure-based design, a dual PLD1/PLD2 inhibitor was discovered that is single digit nanomolar in the Calu-1 cell assay and has suitable PK properties for in vivo studies. To capture the in vivo measurement of PLD inhibition, a transphosphatidylation pharmacodynamic LC-MS assay was developed, in which a dual PLD1/PLD2 inhibitor was found to reduce PLD activity by 15-20-fold.

Self-transducible LRS-UNE-L peptide enhances muscle regeneration

BACKGROUND

Muscle regeneration includes proliferation and differentiation of muscle satellite cells, which involves the mammalian target of rapamycin (mTOR). We identified the C-terminal unique attached sequence motif (UNE) domain of leucyl-tRNA synthetase (LRS-UNE-L) as an mTORC1 (mTOR complex1)-activating domain that acts through Vps34 and phospholipase D1 (PLD1) when introduced in the form of a muscle-enhancing peptide.

METHODS

In vitro Vps34 lipid kinase assay, phosphatidylinositol 3-phosphate (PI(3)P) measurement, in vivo PLD1 assay, and western blot assay were performed in HEK293 cells to test the effect of the LRS-UNE-L on the Vps34-PLD1-mTOR pathway. Adeno-associated virus (AAV)-LRS-UNE-L was transduced in C2C12 cells in vitro, in BaCl₂ -injured tibialis anterior (TA) muscles, and in 18-month-old TA muscles to analyse its effect on myogenesis, muscle regeneration, and aged muscle, respectively. The muscle-specific cell-permeable peptide M12 was fused with LRS-UNE-L and tested for cell integration in C2C12 and HEK293 cells using FACS analysis and immunocytochemistry. Finally, M12-LRS-UNE-L was introduced into BaCl₂ -injured TA muscles of 15-week-old Pld1^+/+ or Pld1^-/- mice, and its effect was analysed by measurement of cross-sectional area of regenerating muscle fibres.

RESULTS

The LRS-UNE-L expression restored amino acid-induced S6K1 phosphorylation in LRS knockdown cells in a RagD GTPases-independent manner (421%, P = 0.007 vs. LRS knockdown control cells). The LRS-UNE-L domain was directly bound to Vps34; this interaction was accompanied by increases in Vps34 activity (166%, P = 0.0352), PI(3)P levels (146%, P = 0.0039), and PLD1 activity (228%, P = 0.0294) compared with amino acid-treated control cells, but it did not affect autophagic flux. AAV-delivered LRS-UNE-L domain augmented S6K1 phosphorylation (174%, P = 0.0013), mRNA levels of myosin heavy chain (MHC) (122%, P = 0.0282) and insulin-like growth factor 2 (IGF2) (146%, P = 0.008), and myogenic fusion (133%, P = 0.0479) in C2C12 myotubes. AAV-LRS-UNE-L increased the size of regenerating muscle fibres in BaCl₂ -injured TA muscles (124%, P = 0.0279) (n = 9-10), but it did not change the muscle fibre size of TA muscles in old mice. M12-LRS-UNE-L was preferentially delivered into C2C12 cells compared with HEK293 cells and augmented regeneration of BaCl₂ -injured TA muscles in a PLD1-dependent manner (116%, P = 0.0022) (n = 6).

CONCLUSIONS

Our results provide compelling evidence that M12-LRS-UNE-L could be a muscle-enhancing protein targeting mTOR.

Click chemistry and optogenetic approaches to visualize and manipulate phosphatidic acid signaling

The simple structure of phosphatidic acid (PA) belies its complex biological functions as both a key phospholipid biosynthetic intermediate and a potent signaling molecule. In the latter role, PA controls processes including vesicle trafficking, actin dynamics, cell growth, and migration. However, experimental methods to decode the pleiotropy of PA are sorely lacking. Because PA metabolism and trafficking are rapid, approaches to accurately visualize and manipulate its levels require high spatiotemporal precision. Here, we describe recent efforts to create a suite of chemical tools that enable imaging and perturbation of PA signaling. First, we describe techniques to visualize PA production by phospholipase D (PLD) enzymes, which are major producers of PA, called Imaging Phospholipase D Activity with Clickable Alcohols via Transphosphatidylation (IMPACT). IMPACT harnesses the ability of endogenous PLD enzymes to accept bioorthogonally tagged alcohols in transphosphatidylation reactions to generate functionalized reporter lipids that are subsequently fluorescently tagged via click chemistry. Second, we describe two light-controlled approaches for precisely manipulating PA signaling. Optogenetic PLDs use light-mediated heterodimerization to recruit a bacterial PLD to desired organelle membranes, and photoswitchable PA analogs contain azobenzene photoswitches in their acyl tails, enabling molecular shape and bioactivity to be controlled by light. We highlight select applications of these tools for studying GPCR-Gq signaling, discovering regulators of PLD signaling, tracking intracellular lipid transport pathways, and elucidating new oncogenic signaling roles for PA. We envision that these chemical tools hold promise for revealing many new insights into lipid signaling pathways.

Autophagy-related signaling pathways in non-small cell lung cancer

Lung cancer is one of the most prevalent causes of morbidity and mortality in both men and women across the globe. The disease has a quiet phenotype at first, which leads to chronic tumor development. Non-small cell lung cancer (NSCLC) is the most common kind of lung cancer, accounting for 85 percent of all lung malignancies. Autophagy has been described as an intracellular "recycle bin" where damaged proteins and molecules are degraded. Autophagy regulation is mainly dependent on signaling pathways such as phosphoinositide 3-kinases (PI3K), AKT, and the mammalian target of rapamycin (mTOR). In the context of NSCLC, studies on these signaling pathways are inconsistent, but our literature review suggests that the inhibition of mTOR, PI3K/AKT, and epidermal growth factor receptor signaling pathways by different medications can active autophagy and inhibit NSCLC progression. In conclusion, signaling pathways related to autophagy are effective therapeutic approaches for the treatment of NSCLC.

Sapienic Acid Metabolism Influences Membrane Plasticity and Protein Signaling in Breast Cancer Cell Lines

The importance of sapienic acid (6c-16:1), a monounsaturated fatty acid of the n-10 family formed from palmitic acid by delta-6 desaturase, and of its metabolism to 8c-18:1 and sebaleic acid (5c,8c-18:2) has been recently assessed in cancer. Data are lacking on the association between signaling cascades and exposure to sapienic acid comparing cell lines of the same cancer type. We used 50 μM sapienic acid supplementation, a non-toxic concentration, to cultivate MCF-7 and 2 triple-negative breast cancer cells (TNBC), MDA-MB-231 and BT-20. We followed up for three hours regarding membrane fatty acid remodeling by fatty acid-based membrane lipidome analysis and expression/phosphorylation of EGFR (epithelial growth factor receptor), mTOR (mammalian target of rapamycin) and AKT (protein kinase B) by Western blotting as an oncogenic signaling cascade. Results evidenced consistent differences among the three cell lines in the metabolism of n-10 fatty acids and signaling. Here, a new scenario is proposed for the role of sapienic acid: one based on changes in membrane composition and properties, and the other based on changes in expression/activation of growth factors and signaling cascades. This knowledge can indicate additional players and synergies in breast cancer cell metabolism, inspiring translational applications of tailored membrane lipid strategies to assist pharmacological interventions.

Interactome analysis of human phospholipase D and phosphatidic acid-associated protein network

Mammalian phospholipase D (PLD) enzyme family consists of six members. Among them, PLD1/2/6 catalyzes phosphatidic acid (PA) production, while PLD3/4/5 has no catalytic activities. Deregulation of the PLD-PA lipid signaling has been associated with various human diseases including cancer. However, a comprehensive analysis of the regulators and effectors for this crucial lipid metabolic pathway has not been fully achieved. Using a proteomic approach, we defined the protein interaction network for the human PLD family of enzymes and PA and revealed diverse cellular signaling events involving them. Through it, we identified PJA2 as a novel E3 ubiquitin ligase for PLD1 involved in control of the PLD1-mediated mammalian target of rapamycin signaling. Additionally, we showed that PA interacted with and positively regulated sphingosine kinase 1. Taken together, our study not only generates a rich interactome resource for further characterizing the human PLD-PA lipid signaling but also connects this important metabolic pathway with numerous biological processes.

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Defining the interactome of human phospholipase D enzymes and phosphatidic acid.

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PJA2 functions as an E3 ubiquitin ligase of phospholipase D1.

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Phosphatidic acid interacts with and positively regulates sphingosine kinase 1.

Circulating metabolites as a concept beyond tumor biology determining disease recurrence after resection of colorectal liver metastasis

BACKGROUND

Micro-metastatic growth is considered the main source of early cancer recurrence. Nutritional and microenvironmental components are increasingly recognized to play a significant role in the liver. We explored the predictive potential of preoperative plasma metabolites for postoperative disease recurrence in colorectal cancer liver metastasis (CRCLM) patients.

METHODS

All included patients (n = 71) had undergone R0 liver resection for colorectal cancer liver metastasis in the years between 2012 and 2018. Preoperative blood samples were collected and assessed for 180 metabolites using a preconfigured mass-spectrometry kit (Biocrates Absolute IDQ p180 kit). Postoperative disease-free (DFS) and overall survival (OS) were prospectively recorded. Patients that recurred within 6 months after surgery were defined as "high-risk" and, subsequently, a three-metabolite model was created which can assess DFS in our collective.

RESULTS

Multiple lysophosphatidylcholines (lysoPCs) and phosphatidylcholines (PCs) significantly predicted disease recurrence within 6 months (strongest: PC aa C36:1 AUC = 0.83, p = 0.003, PC ae C34:0 AUC = 0.83, p = 0.004 and lysoPC a C18:1 AUC = 0.8, p = 0.006). High-risk patients had a median DFS of 183 days versus 522 days in low-risk population (p = 0.016, HR = 1.98 95% CI 1.16-4.35) with a 6 months recurrence rate of 47.6% versus 4.7%, outperforming routine predictors of oncological outcome.

CONCLUSION

Circulating metabolites identified CRCLM patients at highest risk for 6 months disease recurrence after surgery. Our data also suggests that circulating metabolites might play a significant pathophysiological role in micro-metastatic growth and concomitant early tumor recurrences after liver resection. However, the clinical applicability and performance of this proposed metabolomic concept needs to be independently validated in future studies.

Chronic Exposure to Palmitic Acid Down-Regulates AKT in Beta-Cells through Activation of mTOR

High circulating lipids occurring in obese individuals and insulin-resistant patients are considered a contributing factor to type 2 diabetes. Exposure to high lipid concentration is proposed to both protect and damage beta-cells under different circumstances. Here, by feeding mice a high-fat diet (HFD) for 2 weeks to up to 14 months, the study showed that HFD initially causes the beta-cells to expand in population, whereas long-term exposure to HFD is associated with failure of beta-cells and the inability of animals to respond to glucose challenge. To prevent the failure of beta-cells and the development of type 2 diabetes, the molecular mechanisms that underlie this biphasic response of beta-cells to lipid exposure were explored. Using palmitic acid (PA) in cultured beta-cells and islets, the study demonstrated that chronic exposure to lipids leads to reduced viability and inhibition of cell cycle progression concurrent with down-regulation of a pro-growth/survival kinase AKT, independent of glucose. This AKT down-regulation by PA is correlated with the induction of mTOR/S6K activity. Inhibiting mTOR activity with rapamycin induced Raptor and restored AKT activity, allowing beta-cells to gain proliferation capacity that was lost after HFD exposure. In summary, a novel mechanism in which lipid exposure may cause the dipole effects on beta-cell growth was elucidated, where mTOR acts as a lipid sensor. These mechanisms can be novel targets for future therapeutic developments.