mTORC2: a multifaceted regulator of autophagy

Manipulation of signaling pathways in bone tissue engineering and regenerative medicine: Current knowledge, novel strategies, and future directions

During osteogenesis, a large number of bioactive molecules, macromolecules, cells, and cellular signals are activated to induce bone growth and development. The activation of molecular pathways leads to the occurrence of cellular events, ultimately resulting in observable changes. Therefore, in the studies of bone tissue engineering and regenerative medicine, it is essential to target fundamental events to exploit the mechanisms involved in osteogenesis. In this context, signaling pathways are activated during osteogenesis and trigger the activation of numerous other processes involved in osteogenesis. Direct influence of signaling pathways should allow to manipulate the signaling pathways themselves and impact osteogenesis. A combination of sequential cascades takes place to drive the progression of osteogenesis. Also, the occurrence of these processes and, more generally, cellular and molecular processes related to osteogenesis necessitate the presence of transcription factors and their activity. The present review focuses on outlining several signaling pathways and transcription factors influencing the development of osteogenesis, and describes various methods of their manipulation to induce and enhance bone formation.

The autophagy paradox: A new hypothesis in neurodegenerative disorders

A recent study showed that while autophagy is usually tied to protein and organelle turnover, it can also play dual roles in neurodegenerative diseases. Traditionally, autophagy was seen as protective since it removes damaged proteins and organelles. but new data suggests autophagy can sometimes promote neuron death. and This review tackles autophagy's seemingly contradictory effects in neurodegeneration, or the "autophagy paradox. " It offers a framework for understanding autophagy in neurodegenerative research and the cellular processes involved. In short, our data uncovers a harmful autophagy role in certain situations, conflicting the view that it's always beneficial. We describe the distinct, disease-specific autophagy pathways functioning in various neurodegenerative diseases. Part two concerns potential therapeutic implications of manipulating autophagy and current strategies targeting the autophagic system, suggesting interesting areas for future research into tailored modulators. This could eventually enable activating or controlling specific autophagy pathways and aid in developing more effective treatments. Researchers believe more molecular-level research is needed so patient-tailored autophagy-modulating therapeutics can be developed given this dilemma. Moreover, research must translate faster into effective neurodegenerative disease treatment options. This article aims to provide a wholly new perspective on autophagy's classically described role in these severe diseases, challenging current dogma and opening new therapeutic avenue options.

RNA-binding protein GIGYF2 orchestrates hepatic insulin resistance through STAU1/PTEN-mediated disruption of the PI3K/AKT signaling cascade

BACKGROUND

Obesity is well-established as a significant contributor to the development of insulin resistance (IR) and diabetes, partially due to elevated plasma saturated free fatty acids like palmitic acid (PA). Grb10-interacting GYF Protein 2 (GIGYF2), an RNA-binding protein, is widely expressed in various tissues including the liver, and has been implicated in diabetes-induced cognitive impairment. Whereas, its role in obesity-related IR remains uninvestigated.

METHODS

In this study, we employed palmitic acid (PA) exposure to establish an in vitro IR model in the human liver cancer cell line HepG2 with high-dose chronic PA treatment. The cells were stained with fluorescent dye 2-NBDG to evaluate cell glucose uptake. The mRNA expression levels of genes were determined by real-time qRT-PCR (RT-qPCR). Western blotting was employed to examine the protein expression levels. The RNA immunoprecipitation (RIP) was used to investigate the binding between protein and mRNA. Lentivirus-mediated gene knockdown and overexpression were employed for gene manipulation. In mice, an IR model induced by a high-fat diet (HFD) was established to validate the role and action mechanisms of GIGYF2 in the modulation of HFD-induced IR in vivo.

RESULTS

In hepatocytes, high levels of PA exposure strongly trigger the occurrence of hepatic IR evidenced by reduced glucose uptake and elevated extracellular glucose content, which is remarkably accompanied by up-regulation of GIGYF2. Silencing GIGYF2 ameliorated PA-induced IR and enhanced glucose uptake. Conversely, GIGYF2 overexpression promoted IR, PTEN upregulation, and AKT inactivation. Additionally, PA-induced hepatic IR caused a notable increase in STAU1, which was prevented by depleting GIGYF2. Notably, silencing STAU1 prevented GIGYF2-induced PTEN upregulation, PI3K/AKT pathway inactivation, and IR. STAU1 was found to stabilize PTEN mRNA by binding to its 3'UTR. In liver cells, tocopherol treatment inhibits GIGYF2 expression and mitigates PA-induced IR. In the in vivo mice model, GIGYF2 knockdown and tocopherol administration alleviate high-fat diet (HFD)-induced glucose intolerance and IR, along with the suppression of STAU1/PTEN and restoration of PI3K/AKT signaling.

CONCLUSIONS

Our study discloses that GIGYF2 mediates obesity-related IR by disrupting the PI3K/AKT signaling axis through the up-regulation of STAU1/PTEN. Targeting GIGYF2 may offer a potential strategy for treating obesity-related metabolic diseases, including type 2 diabetes.

Targeting a mTOR/autophagy axis: a double-edged sword of rapamycin in spontaneous miscarriage

Immune dysfunction is a primary culprit behind spontaneous miscarriage (SM). To address this, immunosuppressive agents have emerged as a novel class of tocolytic drugs, modulating the maternal immune system's tolerance towards the embryo. Rapamycin (PubChem CID:5284616), a dual-purpose compound, functions as an immunosuppressive agent and triggers autophagy by targeting the mTOR pathway. Its efficacy in treating SM has garnered significant research interest in recent times. Autophagy, the cellular process of self-degradation and recycling, plays a pivotal role in numerous health conditions. Research indicates that autophagy is integral to endometrial decidualization, trophoblast invasion, and the proper functioning of decidual immune cells during a healthy pregnancy. Yet, in cases of SM, there is a dysregulation of the mTOR/autophagy axis in decidual stromal cells or immune cells at the maternal-fetal interface. Both in vitro and in vivo studies have highlighted the potential benefits of low-dose rapamycin in managing SM. However, given mTOR's critical role in energy metabolism, inhibiting it could potentially harm the pregnancy. Moreover, while low-dose rapamycin has been deemed safe for treating recurrent implant failure, its potential teratogenic effects remain uncertain due to insufficient data. In summary, rapamycin represents a double-edged sword in the treatment of SM, balancing its impact on autophagy and immune regulation. Further investigation is warranted to fully understand its implications.

Autophagy alterations in obesity, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease: the evidence from human studies

Autophagy is an evolutionarily conserved process that plays a pivotal role in the maintenance of cellular homeostasis and its impairment has been implicated in the pathogenesis of various metabolic diseases including obesity, type 2 diabetes (T2D), and metabolic dysfunction-associated steatotic liver disease (MASLD). This review synthesizes the current evidence from human studies on autophagy alterations under these metabolic conditions. In obesity, most data point to autophagy upregulation during the initiation phase of autophagosome formation, potentially in response to proinflammatory conditions in the adipose tissue. Autophagosome formation appears to be enhanced under hyperglycemic or insulin-resistant conditions in patients with T2D, possibly acting as a compensatory mechanism to eliminate damaged organelles and proteins. Other studies have proposed that prolonged hyperglycemia and disrupted insulin signaling hinder autophagic flux, resulting in the accumulation of dysfunctional cellular components that can contribute to β-cell dysfunction. Evidence from patients with MASLD supports autophagy inhibition in disease progression. Nevertheless, given the available data, it is difficult to ascertain whether autophagy is enhanced or suppressed in these conditions because the levels of autophagy markers depend on the overall metabolism of specific organs, tissues, experimental conditions, or disease duration. Owing to these constraints, determining whether the observed shifts in autophagic activity precede or result from metabolic diseases remains challenging. Additionally, autophagy-modulating strategies are shortly discussed. To conclude, more studies investigating autophagy impairment are required to gain a more comprehensive understanding of its role in the pathogenesis of obesity, T2D, and MASLD and to unveil novel therapeutic strategies for these conditions.

The cellular adaptor GULP1 interacts with ATG14 to potentiate autophagy and APP processing

Autophagy is a highly conserved catabolic mechanism by which unnecessary or dysfunctional cellular components are removed. The dysregulation of autophagy has been implicated in various neurodegenerative diseases, including Alzheimer's disease (AD). Understanding the molecular mechanism(s)/molecules that influence autophagy may provide important insights into developing therapeutic strategies against AD and other neurodegenerative disorders. Engulfment adaptor phosphotyrosine-binding domain-containing protein 1 (GULP1) is an adaptor that interacts with amyloid precursor protein (APP) to promote amyloid-β peptide production via an unidentified mechanism. Emerging evidence suggests that GULP1 has a role in autophagy. Here, we show that GULP1 is involved in autophagy through an interaction with autophagy-related 14 (ATG14), which is a regulator of autophagosome formation. GULP1 potentiated the stimulatory effect of ATG14 on autophagy by modulating class III phosphatidylinositol 3-kinase complex 1 (PI3KC3-C1) activity. The effect of GULP1 is attenuated by a GULP1 mutation (GULP1m) that disrupts the GULP1-ATG14 interaction. Conversely, PI3KC3-C1 activity is enhanced in cells expressing APP but not in those expressing an APP mutant that does not bind GULP1, which suggests a role of GULP1-APP in regulating PI3KC3-C1 activity. Notably, GULP1 facilitates the targeting of ATG14 to the endoplasmic reticulum (ER). Moreover, the levels of both ATG14 and APP are elevated in the autophagic vacuoles (AVs) of cells expressing GULP1, but not in those expressing GULP1m. APP processing is markedly enhanced in cells co-expressing GULP1 and ATG14. Hence, GULP1 alters APP processing by promoting the entry of APP into AVs. In summary, we unveil a novel role of GULP1 in enhancing the targeting of ATG14 to the ER to stimulate autophagy and, consequently, APP processing.

Autophagy: A Silent Protagonist in Kidney Transplantation

Autophagy is a lysosome-dependent regulated mechanism that recycles unnecessary cytoplasmic components. It is now known that autophagy dysfunction may have a pathogenic role in several human diseases and conditions, including kidney transplantation. Both defective and excessive autophagy may induce or aggravate several complications of kidney transplantation, such as ischemia-reperfusion injury, alloimmune response, and immunosuppressive treatment and side effects. Although it is still complicated to measure autophagy levels in clinical practice, more attention should be paid to the factors that may influence autophagy. In kidney transplantation, the association of low doses of a mammalian target of rapamycin inhibitor with low doses of a calcineurin inhibitor may be of benefit for autophagy modulation. However, further studies are needed to explore the role of other autophagy regulators.

The "Road" to Malignant Transformation from Endometriosis to Endometriosis-Associated Ovarian Cancers (EAOCs): An mTOR-Centred Review

Ovarian cancer is an umbrella term covering a number of distinct subtypes. Endometrioid and clear-cell ovarian carcinoma are endometriosis-associated ovarian cancers (EAOCs) frequently arising from ectopic endometrium in the ovary. The mechanistic target of rapamycin (mTOR) is a crucial regulator of cellular homeostasis and is dysregulated in both endometriosis and endometriosis-associated ovarian cancer, potentially favouring carcinogenesis across a spectrum from benign disease with cancer-like characteristics, through an atypical phase, to frank malignancy. In this review, we focus on mTOR dysregulation in endometriosis and EAOCs, investigating cancer driver gene mutations and their potential interaction with the mTOR pathway. Additionally, we explore the complex pathogenesis of transformation, considering environmental, hormonal, and epigenetic factors. We then discuss postmenopausal endometriosis pathogenesis and propensity for malignant transformation. Finally, we summarize the current advancements in mTOR-targeted therapeutics for endometriosis and EAOCs.

Trophoblast-specific overexpression of the LAT1 increases transplacental transport of essential amino acids and fetal growth in mice

Placental System L amino acid transporter activity is decreased in pregnancies complicated by intrauterine growth restriction (IUGR) and increased in fetal overgrowth. However, it is unknown if changes in the expression/activity of placental Large Neutral Amino Acid Transporter Small Subunit 1 (Slc7a5/LAT1) are mechanistically linked to placental function and fetal growth. We hypothesized that trophoblast-specific Slc7a5 overexpression increases placental transport of essential amino acids, activates the placental mechanistic target of rapamycin (mTOR) signaling, and promotes fetal growth in mice. Using lentiviral transduction of blastocysts with a Slc7a5 transgene, we achieved trophoblast-specific overexpression of Slc7a5 (Slc7a5 OX) with increased fetal (+27%) and placental weights (+10%). Trophoblast-specific Slc7a5 overexpression increased trophoblast plasma membrane (TPM) LAT1 protein abundance and TPM System L transporter (+53%) and System A transporter activity (+ 21%). Slc7a5 overexpression also increased transplacental transport of leucine (+ 85%) but not of the System A tracer, 14C-methylamino isobutyric acid, in vivo. Trophoblast-specific overexpression of Slc7a5 activated placental mTORC1, as assessed by increased (+44%) phosphorylation of S6 ribosomal protein (Ser 235/236), and mTORC2 as indicated by phosphorylation of PKCα-Tyr-657 (+47%) and Akt-Ser 473 (+96%). This is the first demonstration that placental transport of essential amino acids is mechanistically linked to fetal growth. The decreased placental System L activity in human IUGR and the increased placental activity of this transporter in some cases of fetal overgrowth may directly contribute to the development of these pregnancy complications.

Dietary restriction and life-history trade-offs: insights into mTOR pathway regulation and reproductive investment in Japanese quail

Resources are needed for growth, reproduction and survival, and organisms must trade off limited resources among competing processes. Nutritional availability in organisms is sensed and monitored by nutrient-sensing pathways that can trigger physiological changes or alter gene expression. Previous studies have proposed that one such signalling pathway, the mechanistic target of rapamycin (mTOR), underpins a form of adaptive plasticity when individuals encounter constraints in their energy budget. Despite the fundamental importance of this process in evolutionary biology, how nutritional limitation is regulated through the expression of genes governing this pathway and its consequential effects on fitness remain understudied, particularly in birds. We used dietary restriction to simulate resource depletion and examined its effects on body mass, reproduction and gene expression in Japanese quails (Coturnix japonica). Quails were subjected to feeding at 20%, 30% and 40% restriction levels or ad libitum for 2 weeks. All restricted groups exhibited reduced body mass, whereas reductions in the number and mass of eggs were observed only under more severe restrictions. Additionally, dietary restriction led to decreased expression of mTOR and insulin-like growth factor 1 (IGF1), whereas the ribosomal protein S6 kinase 1 (RPS6K1) and autophagy-related genes (ATG9A and ATG5) were upregulated. The pattern in which mTOR responded to restriction was similar to that for body mass. Regardless of the treatment, proportionally higher reproductive investment was associated with individual variation in mTOR expression. These findings reveal the connection between dietary intake and the expression of mTOR and related genes in this pathway.

Role of protein degradation systems in colorectal cancer

Protein degradation is essential for maintaining protein homeostasis. The ubiquitin‒proteasome system (UPS) and autophagy-lysosome system are the two primary pathways responsible for protein degradation and directly related to cell survival. In malignant tumors, the UPS plays a critical role in managing the excessive protein load caused by cancer cells hyperproliferation. In this review, we provide a comprehensive overview of the dual roles played by the UPS and autolysosome system in colorectal cancer (CRC), elucidating their impact on the initiation and progression of this disease while also highlighting their compensatory relationship. Simultaneously targeting both protein degradation pathways offers new promise for enhancing treatment efficacy against CRC. Additionally, apoptosis is closely linked to ubiquitination and autophagy, and caspases degrade proteins. A thorough comprehension of the interplay between various protein degradation pathways is highly important for clarifying the mechanism underlying the onset and progression of CRC.

The Role of Mechanotransduction in Contact Inhibition of Locomotion and Proliferation

Contact inhibition (CI) represents a crucial tumor-suppressive mechanism responsible for controlling the unbridled growth of cells, thus preventing the formation of cancerous tissues. CI can be further categorized into two distinct yet interrelated components: CI of locomotion (CIL) and CI of proliferation (CIP). These two components of CI have historically been viewed as separate processes, but emerging research suggests that they may be regulated by both distinct and shared pathways. Specifically, recent studies have indicated that both CIP and CIL utilize mechanotransduction pathways, a process that involves cells sensing and responding to mechanical forces. This review article describes the role of mechanotransduction in CI, shedding light on how mechanical forces regulate CIL and CIP. Emphasis is placed on filamin A (FLNA)-mediated mechanotransduction, elucidating how FLNA senses mechanical forces and translates them into crucial biochemical signals that regulate cell locomotion and proliferation. In addition to FLNA, trans-acting factors (TAFs), which are proteins or regulatory RNAs capable of directly or indirectly binding to specific DNA sequences in distant genes to regulate gene expression, emerge as sensitive players in both the mechanotransduction and signaling pathways of CI. This article presents methods for identifying these TAF proteins and profiling the associated changes in chromatin structure, offering valuable insights into CI and other biological functions mediated by mechanotransduction. Finally, it addresses unanswered research questions in these fields and delineates their possible future directions.

Rictor-A Mediator of Progression and Metastasis in Lung Cancer

Lung carcinoma is one of the most common cancer types for both men and women. Despite recent breakthroughs in targeted therapy and immunotherapy, it is characterized by a high metastatic rate, which can significantly affect quality of life and prognosis. Rictor (encoded by the RICTOR gene) is known as a scaffold protein for the multiprotein complex mTORC2. Among its diverse roles in regulating essential cellular functions, mTORC2 also facilitates epithelial-mesenchymal transition and metastasis formation. Amplification of the RICTOR gene and subsequent overexpression of the Rictor protein can result in the activation of mTORC2, which promotes cell survival and migration. Based on recent studies, RICTOR amplification or Rictor overexpression can serve as a marker for mTORC2 activation, which in turn provides a promising druggable target. Although selective inhibitors of Rictor and the Rictor-mTOR association are only in a preclinical phase, they seem to be potent novel approaches to reduce tumor cell migration and metastasis formation. Here, we summarize recent advances that support an important role for Rictor and mTORC2 as potential therapeutic targets in the treatment of lung cancer. This is a traditional (narrative) review based on Pubmed and Google Scholar searches for the following keywords: Rictor, RICTOR amplification, mTORC2, Rictor complexes, lung cancer, metastasis, progression, mTOR inhibitors.

miR-221 and Parkinson's disease: A biomarker with therapeutic potential

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra, leading to various motor and non-motor symptoms. Several cellular and molecular mechanisms such as alpha-synuclein (α-syn) accumulation, mitochondrial dysfunction, oxidative stress and neuroinflammation are involved in the pathogenesis of this disease. MicroRNAs (miRNAs) play important roles in post-transcriptional gene regulation. They are typically about 21-25 nucleotides in length and are involved in the regulation of gene expression by binding to the messenger RNA (mRNA) molecules. miRNAs like miR-221 play important roles in various biological processes, including development, cell proliferation, differentiation and apoptosis. miR-221 promotes neuronal survival against oxidative stress and neurite outgrowth and neuronal differentiation. Additionally, the role of miR-221 in PD has been investigated in several studies. According to the results of these studies, (1) miR-221 protects PC12 cells against oxidative stress induced by 6-hydroxydopamine; (2) miR-221 prevents Bax/caspase-3 signalling activation by stopping Bim; (3) miR-221 has moderate predictive power for PD; (4) miR-221 directly targets PTEN, and PTEN over-expression eliminates the protective action of miR-221 on p-AKT expression in PC12 cells; and (5) miRNA-221 controls cell viability and apoptosis by manipulating the Akt signalling pathway in PD. This review study suggested that miR-221 has the potential to be used as a clinical biomarker for PD diagnosis and stage assignment.

A historical perspective of macroautophagy regulation by biochemical and biomechanical stimuli

Macroautophagy is a lysosomal degradative pathway for intracellular macromolecules, protein aggregates, and organelles. The formation of the autophagosome, a double membrane-bound structure that sequesters cargoes before their delivery to the lysosome, is regulated by several stimuli in multicellular organisms. Pioneering studies in rat liver showed the importance of amino acids, insulin, and glucagon in controlling macroautophagy. Thereafter, many studies have deciphered the signaling pathways downstream of these biochemical stimuli to control autophagosome formation. Two signaling hubs have emerged: the kinase mTOR, in a complex at the surface of lysosomes which is sensitive to nutrients and hormones; and AMPK, which is sensitive to the cellular energetic status. Besides nutritional, hormonal, and energetic fluctuations, many organs have to respond to mechanical forces (compression, stretching, and shear stress). Recent studies have shown the importance of mechanotransduction in controlling macroautophagy. This regulation engages cell surface sensors, such as the primary cilium, in order to translate mechanical stimuli into biological responses.

New ruthenium-xanthoxylin complex eliminates colorectal cancer stem cells by targeting the heat shock protein 90 chaperone

In this work, we describe a novel ruthenium-xanthoxylin complex, [Ru(phen)2(xant)](PF6) (RXC), that can eliminate colorectal cancer (CRC) stem cells by targeting the chaperone Hsp90. RXC exhibits potent cytotoxicity in cancer cell lines and primary cancer cells, causing apoptosis in HCT116 CRC cells, as observed by cell morphology, YO-PRO-1/PI staining, internucleosomal DNA fragmentation, mitochondrial depolarization, and PARP cleavage (Asp214). Additionally, RXC can downregulate the HSP90AA1 and HSP90B1 genes and the expression of HSP90 protein, as well as the expression levels of its downstream/client elements Akt1, Akt (pS473), mTOR (pS2448), 4EBP1 (pT36/pT45), GSK-3β (pS9), and NF-κB p65 (pS529), implying that these molecular chaperones can be molecular targets for RXC. Moreover, this compound inhibited clonogenic survival, the percentage of the CRC stem cell subpopulation, and colonosphere formation, indicating that RXC can eliminate CRC stem cells. RXC reduced cell migration and invasion, decreased vimentin and increased E-cadherin expression, and induced an autophagic process that appeared to be cytoprotective, as autophagy inhibitors enhanced RXC-induced cell death. In vivo studies showed that RXC inhibits tumor progression and experimental metastasis in mice with CRC HCT116 cell xenografts. Taken together, these results highlight the potential of the ruthenium complex RXC in CRC therapy with the ability to eliminate CRC stem cells by targeting the chaperone Hsp90.

Bisphenol A induced neuronal apoptosis and enhanced autophagy in vitro through Nrf2/HO-1 and Akt/mTOR pathways

Bisphenol A (BPA) was traditionally used in epoxy resins and polycarbonate plastics, but it was found to be harmful to human health due to its endocrine-disrupting effects. It can affect various biological functions of human beings and interfere with brain development. However, the neurotoxic mechanisms of BPA on brain development and associated neurodegeneration remain poorly understood. Here, we reported that BPA (100, 250, 500 μM) inhibited cell viability of neural cells PC12, SH-SY5Y and caused dose-dependent cell death. In addition, BPA exposure increased intracellular reactive oxygen species (ROS) and mitochondrial ROS (mtROS) levels, decreased mitochondrial membrane potential, reduced the expression of cytochrome c oxidase IV (COX4), downregulated Bcl-2, and initiated apoptosis. Moreover, BPA treatment resulted in the accumulation of intracellular acidic vacuoles and increased the autophagy marker LC3 II to LC3 I ratio. Furthermore, BPA exposure inhibited Nrf2/ HO-1 and AKT/mTOR pathways and mediated cellular oxidative stress, apoptosis, and excessive autophagy, leading to neuronal degeneration. The interactions between oxidative stress, autophagy, and apoptosis during BPA-induced neurotoxicity remain unclear and require further in vivo confirmation.

S-Nitrosylation at the intersection of metabolism and autophagy: Implications for cancer

Metabolic plasticity, which determines tumour growth and metastasis, is now understood to be a flexible and context-specific process in cancer metabolism. One of the major pathways contributing to metabolic adaptations in eucaryotic cells is autophagy, a cellular degradation and recycling process that is activated during periods of starvation or stress to maintain metabolite and biosynthetic intermediate levels. Consequently, there is a close association between the metabolic adaptive capacity of tumour cells and autophagy-related pathways in cancer. Additionally, nitric oxide regulates protein function and signalling through S-nitrosylation, a post-translational modification that can also impact metabolism and autophagy. The primary objective of this review is to provide an up-to-date overview of the role of S-nitrosylation at the intersection of metabolism and autophagy in cancer. First, we will outline the involvement of S-nitrosylation in the metabolic adaptations that occur in tumours. Then, we will discuss the multifaceted role of autophagy in cancer, the interplay between metabolism and autophagy during tumour progression, and the contribution of S-nitrosylation to autophagic dysregulation in cancer. Finally, we will present insights into relevant therapeutic aspects and discuss prospects for the future.

Aging, oxidative stress and degenerative diseases: mechanisms, complications and emerging therapeutic strategies

Aging accompanied by several age-related complications, is a multifaceted inevitable biological progression involving various genetic, environmental, and lifestyle factors. The major factor in this process is oxidative stress, caused by an abundance of reactive oxygen species (ROS) generated in the mitochondria and endoplasmic reticulum (ER). ROS and RNS pose a threat by disrupting signaling mechanisms and causing oxidative damage to cellular components. This oxidative stress affects both the ER and mitochondria, causing proteopathies (abnormal protein aggregation), initiation of unfolded protein response, mitochondrial dysfunction, abnormal cellular senescence, ultimately leading to inflammaging (chronic inflammation associated with aging) and, in rare cases, metastasis. RONS during oxidative stress dysregulate multiple metabolic pathways like NF-κB, MAPK, Nrf-2/Keap-1/ARE and PI3K/Akt which may lead to inappropriate cell death through apoptosis and necrosis. Inflammaging contributes to the development of inflammatory and degenerative diseases such as neurodegenerative diseases, diabetes, cardiovascular disease, chronic kidney disease, and retinopathy. The body's antioxidant systems, sirtuins, autophagy, apoptosis, and biogenesis play a role in maintaining homeostasis, but they have limitations and cannot achieve an ideal state of balance. Certain interventions, such as calorie restriction, intermittent fasting, dietary habits, and regular exercise, have shown beneficial effects in counteracting the aging process. In addition, interventions like senotherapy (targeting senescent cells) and sirtuin-activating compounds (STACs) enhance autophagy and apoptosis for efficient removal of damaged oxidative products and organelles. Further, STACs enhance biogenesis for the regeneration of required organelles to maintain homeostasis. This review article explores the various aspects of oxidative damage, the associated complications, and potential strategies to mitigate these effects.

A Toxoplasma gondii putative arginine transporter localizes to the plant-like vacuolar compartment and controls parasite extracellular survival and stage differentiation

Toxoplasma gondii is a protozoan parasite that infects a broad spectrum of hosts and can colonize many organs and cell types. The ability to reside within a wide range of different niches requires substantial adaptability to diverse microenvironments. Very little is known about how this parasite senses various milieus and adapts its metabolism to survive, replicate during the acute stage, and then differentiate to the chronic stage. Most eukaryotes, from yeast to mammals, rely on a nutrient sensing machinery involving the TORC complex as master regulator of cell growth and cell cycle progression. The lysosome functions as a signaling hub where TORC complex assembles and is activated by transceptors, which both sense and transport amino acids, including the arginine transceptor SLC38A9. While most of the TORC components are lost in T. gondii , indicating the evolution of a distinct nutrient sensing mechanism, the parasite's lysosomal plant-like vacuolar compartment (PLVAC) may still serve as a sensory platform for controlling parasite growth and differentiation. Using SLC38A9 to query the T. gondii proteome, we identified four putative amino acid transporters, termed TgAAT1-4, that structurally resemble the SLC38A9 arginine transceptor. Assessing their expression and sub-cellular localization, we found that one of them, TgAAT1, localized to the PLVAC and is necessary for normal parasite extracellular survival and bradyzoite differentiation. Moreover, we show that TgAAT1 is involved in the PLVAC efflux of arginine, an amino acid playing a key role in T. gondii differentiation, further supporting the hypothesis that TgAAT1 might play a role in nutrient sensing.

IMPORTANCE

T. gondii is a highly successful parasite infecting a broad range of warm-blood organisms including about one third of all humans. Although Toxoplasma infections rarely result in symptomatic disease in individuals with a healthy immune system, the incredibly high number of persons infected along with the risk of severe infection in immunocompromised patients and the potential link of chronic infection to mental disorders make this infection a significant public health concern. As a result, there is a pressing need for new treatment approaches that are both effective and well-tolerated. The limitations in understanding how Toxoplasma gondii manages its metabolism to adapt to changing environments and triggers its transformation into bradyzoites have hindered the discovery of vulnerabilities in its metabolic pathways or nutrient acquisition mechanisms to identify new therapeutic targets. In this work, we have shown that the lysosome-like organelle PLVAC, acting through the putative arginine transporter TgAAT1, plays a pivotal role in regulating the parasite's extracellular survival and differentiation into bradyzoites.

mTOR pathway: Insights into an established pathway for brain mosaicism in epilepsy

The mechanistic target of rapamycin (mTOR) signaling pathway is an essential regulator of numerous cellular activities such as metabolism, growth, proliferation, and survival. The mTOR cascade recently emerged as a critical player in the pathogenesis of focal epilepsies and cortical malformations. The 'mTORopathies' comprise a spectrum of cortical malformations that range from whole brain (megalencephaly) and hemispheric (hemimegalencephaly) abnormalities to focal abnormalities, such as focal cortical dysplasia type II (FCDII), which manifest with drug-resistant epilepsies. The spectrum of cortical dysplasia results from somatic brain mutations in the mTOR pathway activators AKT3, MTOR, PIK3CA, and RHEB and from germline and somatic mutations in mTOR pathway repressors, DEPDC5, NPRL2, NPRL3, TSC1 and TSC2. The mTORopathies are characterized by excessive mTOR pathway activation, leading to a broad range of structural and functional impairments. Here, we provide a comprehensive literature review of somatic mTOR-activating mutations linked to epilepsy and cortical malformations in 292 patients and discuss the perspectives of targeted therapeutics for personalized medicine.

The Protective Effect of (-)-Tetrahydroalstonine against OGD/R-Induced Neuronal Injury via Autophagy Regulation

Here, (-)-Tetrahydroalstonine (THA) was isolated from Alstonia scholaris and investigated for its neuroprotective effect towards oxygen-glucose deprivation/re-oxygenation (OGD/R)-induced neuronal damage. In this study, primary cortical neurons were pre-treated with THA and then subjected to OGD/R induction. The cell viability was tested by the MTT assay, and the states of the autophagy-lysosomal pathway and Akt/mTOR pathway were monitored by Western blot analysis. The findings suggested that THA administration increased the cell viability of OGD/R-induced cortical neurons. Autophagic activity and lysosomal dysfunction were found at the early stage of OGD/R, which were significantly ameliorated by THA treatment. Meanwhile, the protective effect of THA was significantly reversed by the lysosome inhibitor. Additionally, THA significantly activated the Akt/mTOR pathway, which was suppressed after OGD/R induction. In summary, THA exhibited promising protective effects against OGD/R-induced neuronal injury by autophagy regulation through the Akt/mTOR pathway.