1 5631 156 SENESCENCE-INFLAMMATORY REGULATION OF REPARATIVE CELLULAR REPROGRAMMING IN AGING AND CANCER. THE INABILITY OF ADULT TISSUES TO TRANSITORILY GENERATE CELLS WITH FUNCTIONAL STEM CELL-LIKE PROPERTIES IS A MAJOR OBSTACLE TO TISSUE SELF-REPAIR. NUCLEAR REPROGRAMMING-LIKE PHENOMENA THAT INDUCE A TRANSIENT ACQUISITION OF EPIGENETIC PLASTICITY AND PHENOTYPE MALLEABILITY MAY CONSTITUTE A REPARATIVE ROUTE THROUGH WHICH HUMAN TISSUES RESPOND TO INJURY, STRESS, AND DISEASE. HOWEVER, TISSUE REJUVENATION SHOULD INVOLVE NOT ONLY THE TRANSIENT EPIGENETIC REPROGRAMMING OF DIFFERENTIATED CELLS, BUT ALSO THE COMMITTED RE-ACQUISITION OF THE ORIGINAL OR ALTERNATIVE COMMITTED CELL FATE. CHRONIC OR UNRESTRAINED EPIGENETIC PLASTICITY WOULD DRIVE AGING PHENOTYPES BY IMPAIRING THE REPAIR OR THE REPLACEMENT OF DAMAGED CELLS; SUCH UNCONTROLLED PHENOMENA OF IN VIVO REPROGRAMMING MIGHT ALSO GENERATE CANCER-LIKE CELLULAR STATES. WE HEREIN PROPOSE THAT THE ABILITY OF SENESCENCE-ASSOCIATED INFLAMMATORY SIGNALING TO REGULATE IN VIVO REPROGRAMMING CYCLES OF TISSUE REPAIR OUTLINES A THRESHOLD MODEL OF AGING AND CANCER. THE DEGREE OF SENESCENCE/INFLAMMATION-ASSOCIATED DEVIATION FROM THE HOMEOSTATIC STATE MAY DELINEATE A TYPE OF THRESHOLDING ALGORITHM DISTINGUISHING BENEFICIAL FROM DELETERIOUS EFFECTS OF IN VIVO REPROGRAMMING. FIRST, TRANSIENT ACTIVATION OF NF-KAPPAB-RELATED INNATE IMMUNITY AND SENESCENCE-ASSOCIATED INFLAMMATORY COMPONENTS (E.G., IL-6) MIGHT FACILITATE REPARATIVE CELLULAR REPROGRAMMING IN RESPONSE TO ACUTE INFLAMMATORY EVENTS. SECOND, PARA-INFLAMMATION SWITCHES MIGHT PROMOTE LONG-LASTING BUT REVERSIBLE REFRACTORINESS TO REPARATIVE CELLULAR REPROGRAMMING. THIRD, CHRONIC SENESCENCE-ASSOCIATED INFLAMMATORY SIGNALING MIGHT LOCK CELLS IN HIGHLY PLASTIC EPIGENETIC STATES DISABLED FOR REPARATIVE DIFFERENTIATION. THE CONSIDERATION OF A CELLULAR REPROGRAMMING-CENTERED VIEW OF EPIGENETIC PLASTICITY AS A FUNDAMENTAL ELEMENT OF A TISSUE'S CAPACITY TO UNDERGO SUCCESSFUL REPAIR, AGING DEGENERATION OR MALIGNANT TRANSFORMATION SHOULD PROVIDE CHALLENGING STOCHASTIC INSIGHTS INTO THE CURRENT DETERMINISTIC GENETIC PARADIGM FOR MOST CHRONIC DISEASES, THEREBY INCREASING THE SPECTRUM OF THERAPEUTIC APPROACHES FOR PHYSIOLOGICAL AGING AND CANCER. 2017 2 601 30 BETA-GLUCAN "TRAINED IMMUNITY" IMMUNOMODULATORY PROPERTIES POTENTIATE TISSUE WOUND MANAGEMENT AND ACCELERATE FITNESS RECOVER. INTRODUCTION: IT IS WELL ESTABLISHED THAT MODERATE PHYSICAL ACTIVITY CAN IMPROVE THE IMMUNE STATUS, RATHER EXCESS OR HIGH-INTENSITY PHYSICAL EXERCISE CAN CAUSE DAMAGE TO THE IMMUNE SYSTEM. IN ADDITION, MUSCLE INJURIES RESULTING FROM INCREASED FREQUENCY AND INTENSITY OF EXERCISES COMPROMISE INNATE IMMUNE ACTIVITY AND MAY DECREASE TISSUE REGENERATION. THUS, BETA-GLUCANS, A NATURAL COMPOUND, MAY REPRESENT AN IMPORTANT SUBSTANCE WITH STRONG IMMUNOMODULATORY PROPERTIES ACTING AS AN IMMUNOSTIMULANT THERAPY KNOWN AS "TRAINED IMMUNITY". THIS IMMUNE STIMULATING THERAPEUTIC IS AN IMMUNOLOGICAL MEMORY PHENOMENON LINKED TO THE INNATE IMMUNE SYSTEM, TRIGGERING CELLULAR CHANGES AT EPIGENETIC, TRANSCRIPTIONAL, AND FUNCTIONAL LEVELS, TO REGULATE THE IMMUNE SYSTEM AND RECOVER ITS HOMEOSTASIS WITH CLINICAL BENEFITS. CONCLUSION: THIS NARRATIVE REVIEW WORKS WITH THE CURRENT EVIDENCE REGARDING BETA-GLUCANS AS A POSSIBLE ALTERNATIVE THERAPY FOR WOUND HEALING AND ITS SAFETY AND EFFICACY IN THE TREATMENT OF MUSCLE INJURIES AND PHYSICAL RECOVERY INCLUDING OTHER CHRONIC CONDITIONS AND DISEASES. 2022 3 6503 30 TRAINED IMMUNITY: REPROGRAMMING INNATE IMMUNITY IN HEALTH AND DISEASE. TRADITIONALLY, THE INNATE AND ADAPTIVE IMMUNE SYSTEMS ARE DIFFERENTIATED BY THEIR SPECIFICITY AND MEMORY CAPACITY. IN RECENT YEARS, HOWEVER, THIS PARADIGM HAS SHIFTED: CELLS OF THE INNATE IMMUNE SYSTEM APPEAR TO BE ABLE TO GAIN MEMORY CHARACTERISTICS AFTER TRANSIENT STIMULATION, RESULTING IN AN ENHANCED RESPONSE UPON SECONDARY CHALLENGE. THIS PHENOMENON HAS BEEN CALLED TRAINED IMMUNITY. TRAINED IMMUNITY IS CHARACTERIZED BY NONSPECIFIC INCREASED RESPONSIVENESS, MEDIATED VIA EXTENSIVE METABOLIC AND EPIGENETIC REPROGRAMMING. TRAINED IMMUNITY EXPLAINS THE HETEROLOGOUS EFFECTS OF VACCINES, WHICH RESULT IN INCREASED PROTECTION AGAINST SECONDARY INFECTIONS. HOWEVER, IN CHRONIC INFLAMMATORY CONDITIONS, TRAINED IMMUNITY CAN INDUCE MALADAPTIVE EFFECTS AND CONTRIBUTE TO HYPERINFLAMMATION AND PROGRESSION OF CARDIOVASCULAR DISEASE, AUTOINFLAMMATORY SYNDROMES, AND NEUROINFLAMMATION. IN THIS REVIEW WE SUMMARIZE THE CURRENT STATE OF THE FIELD OF TRAINED IMMUNITY, ITS MECHANISMS, AND ITS ROLES IN BOTH HEALTH AND DISEASE. 2021 4 1711 38 DYSFUNCTIONAL STATE OF T CELLS OR EXHAUSTION DURING CHRONIC VIRAL INFECTIONS AND COVID-19: A REVIEW. CORONAVIRUS DISEASE 2019 (COVID-19) CONTINUOUSLY AFFECTING THE LIVES OF MILLIONS OF PEOPLE. THE VIRUS IS SPREAD THROUGH THE RESPIRATORY ROUTE TO AN UNINFECTED PERSON, CAUSING MILD-TO-MODERATE RESPIRATORY DISEASE-LIKE SYMPTOMS THAT SOMETIMES PROGRESS TO SEVERE FORM AND CAN BE FATAL. WHEN THE HOST IS INFECTED WITH THE VIRUS, BOTH INNATE AND ADAPTIVE IMMUNITY COMES INTO PLAY. THE EFFECTOR T CELLS ACT AS THE MASTER PLAYER OF ADAPTIVE IMMUNE RESPONSE IN ERADICATING THE VIRUS FROM THE SYSTEM. BUT DURING CANCER AND CHRONIC VIRAL INFECTIONS, THE FATE OF AN EFFECTOR T CELL IS ALTERED, AND THE T CELL MAY ENTERS A STATE OF EXHAUSTION, WHICH IS MARKED BY LOSS OF EFFECTOR FUNCTION, DEPLETED PROLIFERATIVE CAPACITY AND CYTOTOXIC EFFECT ACCOMPLISHED BY AN INCREASED EXPRESSION OF NUMEROUS INHIBITORY RECEPTORS SUCH AS PROGRAMMED CELL DEATH PROTEIN 1 (PD-1), LYMPHOCYTE-ACTIVATION PROTEIN 3 (LAG-3), AND CYTOTOXIC T LYMPHOCYTE-ASSOCIATED ANTIGEN 4 (CTLA-4) ON THEIR SURFACE. VARIOUS OTHER TRANSCRIPTIONAL AND EPIGENETIC CHANGES TAKE PLACE INSIDE THE T CELL WHEN IT ENTERS INTO AN EXHAUSTED STATE. LATEST STUDIES POINT TOWARD THE INDUCTION OF AN ABNORMAL IMMUNE RESPONSE SUCH AS LYMPHOPENIA, CYTOKINE STORM, AND T CELL EXHAUSTION DURING SARS-COV-2 (SEVERE ACUTE RESPIRATORY SYNDROME CORONAVIRUS 2) INFECTION. THIS REVIEW SHEDS LIGHT ON THE DYSFUNCTIONAL STATE OF T CELLS DURING CHRONIC VIRAL INFECTION AND COVID-19. UNDERSTANDING THE CAUSE AND THE EFFECT OF T CELL EXHAUSTION OBSERVED DURING COVID-19 MAY HELP RESOLVE NEW THERAPEUTIC POTENTIALS FOR TREATING CHRONIC INFECTIONS AND OTHER DISEASES. 2022 5 4543 28 MUSCLE DYSFUNCTION IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE: UPDATE ON CAUSES AND BIOLOGICAL FINDINGS. RESPIRATORY AND/OR LIMB MUSCLE DYSFUNCTION, WHICH ARE FREQUENTLY OBSERVED IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) PATIENTS, CONTRIBUTE TO THEIR DISEASE PROGNOSIS IRRESPECTIVE OF THE LUNG FUNCTION. MUSCLE DYSFUNCTION IS CAUSED BY THE INTERACTION OF LOCAL AND SYSTEMIC FACTORS. THE KEY DELETERIOUS ETIOLOGIC FACTORS ARE PULMONARY HYPERINFLATION FOR THE RESPIRATORY MUSCLES AND DECONDITIONING SECONDARY TO REDUCED PHYSICAL ACTIVITY FOR LIMB MUSCLES. NONETHELESS, CIGARETTE SMOKE, SYSTEMIC INFLAMMATION, NUTRITIONAL ABNORMALITIES, EXERCISE, EXACERBATIONS, ANABOLIC INSUFFICIENCY, DRUGS AND COMORBIDITIES ALSO SEEM TO PLAY A RELEVANT ROLE. ALL THESE FACTORS MODIFY THE PHENOTYPE OF THE MUSCLES, THROUGH THE INDUCTION OF SEVERAL BIOLOGICAL PHENOMENA IN PATIENTS WITH COPD. WHILE RESPIRATORY MUSCLES IMPROVE THEIR AEROBIC PHENOTYPE (PERCENTAGE OF OXIDATIVE FIBERS, CAPILLARIZATION, MITOCHONDRIAL DENSITY, ENZYME ACTIVITY IN THE AEROBIC PATHWAYS, ETC.), LIMB MUSCLES EXHIBIT THE OPPOSITE PHENOTYPE. IN ADDITION, BOTH MUSCLE GROUPS SHOW OXIDATIVE STRESS, SIGNS OF DAMAGE AND EPIGENETIC CHANGES. HOWEVER, FIBER ATROPHY, INCREASED NUMBER OF INFLAMMATORY CELLS, ALTERED REGENERATIVE CAPACITY; SIGNS OF APOPTOSIS AND AUTOPHAGY, AND AN IMBALANCE BETWEEN PROTEIN SYNTHESIS AND BREAKDOWN ARE RATHER CHARACTERISTIC FEATURES OF THE LIMB MUSCLES, MOSTLY IN PATIENTS WITH REDUCED BODY WEIGHT. DESPITE THAT SIGNIFICANT PROGRESS HAS BEEN ACHIEVED IN THE LAST DECADES, FULL ELUCIDATION OF THE SPECIFIC ROLES OF THE TARGET BIOLOGICAL MECHANISMS INVOLVED IN COPD MUSCLE DYSFUNCTION IS STILL REQUIRED. SUCH AN ACHIEVEMENT WILL BE CRUCIAL TO ADEQUATELY TACKLE WITH THIS RELEVANT CLINICAL PROBLEM OF COPD PATIENTS IN THE NEAR-FUTURE. 2015 6 5798 38 STEM CELLS AND LUNG REGENERATION. THE ABILITY TO REPLACE DEFECTIVE CELLS IN AN AIRWAY WITH CELLS THAT CAN ENGRAFT, INTEGRATE, AND RESTORE A FUNCTIONAL EPITHELIUM COULD POTENTIALLY CURE A NUMBER OF LUNG DISEASES. PROGRESS TOWARD THE DEVELOPMENT OF STRATEGIES TO REGENERATE THE ADULT LUNG BY EITHER IN VIVO OR EX VIVO TARGETING OF ENDOGENOUS STEM CELLS OR PLURIPOTENT STEM CELL DERIVATIVES IS LIMITED BY OUR FUNDAMENTAL LACK OF UNDERSTANDING OF THE MECHANISMS CONTROLLING HUMAN LUNG DEVELOPMENT, THE PRECISE IDENTITY AND FUNCTION OF HUMAN LUNG STEM AND PROGENITOR CELL TYPES, AND THE GENETIC AND EPIGENETIC CONTROL OF HUMAN LUNG FATE. IN THIS REVIEW, WE INTEND TO DISCUSS THE KNOWN STEM/PROGENITOR CELL POPULATIONS, THEIR RELATIVE DIFFERENCES BETWEEN RODENTS AND HUMANS, THEIR ROLES IN CHRONIC LUNG DISEASE, AND THEIR THERAPEUTIC PROSPECTS. ADDITIONALLY, WE HIGHLIGHT THE RECENT BREAKTHROUGHS THAT HAVE INCREASED OUR UNDERSTANDING OF THESE CELL TYPES. THESE ADVANCEMENTS INCLUDE NOVEL LINEAGE-TRACED ANIMAL MODELS AND SINGLE-CELL RNA SEQUENCING OF HUMAN AIRWAY CELLS, WHICH HAVE PROVIDED CRITICAL INFORMATION ON THE STEM CELL SUBTYPES, TRANSITION STATES, IDENTIFYING CELL MARKERS, AND INTRICATE PATHWAYS THAT COMMIT A STEM CELL TO DIFFERENTIATE OR TO MAINTAIN PLASTICITY. AS OUR CAPACITY TO MODEL THE HUMAN LUNG EVOLVES, SO WILL OUR UNDERSTANDING OF LUNG REGENERATION AND OUR ABILITY TO TARGET ENDOGENOUS STEM CELLS AS A THERAPEUTIC APPROACH FOR LUNG DISEASE. 2020 7 295 31 AGING INDUCES B CELL DEFECTS AND DECREASED ANTIBODY RESPONSES TO INFLUENZA INFECTION AND VACCINATION. BACKGROUND: AGING IS CHARACTERIZED BY A PROGRESSIVE DECLINE IN THE CAPACITY OF THE IMMUNE SYSTEM TO FIGHT INFLUENZA VIRUS INFECTION AND TO RESPOND TO VACCINATION. AMONG THE SEVERAL FACTORS INVOLVED, IN ADDITION TO INCREASED FRAILTY AND HIGH-RISK CONDITIONS, THE AGE-ASSOCIATED DECREASE IN CELLULAR AND HUMORAL IMMUNE RESPONSES PLAYS A RELEVANT ROLE. THIS IS IN LARGE PART DUE TO INFLAMMAGING, THE CHRONIC LOW-GRADE INFLAMMATORY STATUS OF THE ELDERLY, ASSOCIATED WITH INTRINSIC INFLAMMATION OF THE IMMUNE CELLS AND DECREASED IMMUNE FUNCTION. RESULTS: AGING IS USUALLY ASSOCIATED WITH REDUCED INFLUENZA VIRUS-SPECIFIC AND INFLUENZA VACCINE-SPECIFIC ANTIBODY RESPONSES BUT SOME ELDERLY INDIVIDUALS WITH HIGHER PRE-EXPOSURE ANTIBODY TITERS, DUE TO A PREVIOUS INFECTION OR VACCINATION, HAVE LESS PROBABILITY TO GET INFECTED. EXAMPLES OF THIS EXCEPTION ARE THE ELDERLY INDIVIDUALS INFECTED DURING THE 2009 PANDEMIC SEASON WHO MADE ANTIBODIES WITH BROADER EPITOPE RECOGNITION AND HIGHER AVIDITY THAN THOSE MADE BY YOUNGER INDIVIDUALS. SEVERAL STUDIES HAVE ALLOWED THE IDENTIFICATION OF B CELL INTRINSIC DEFECTS ACCOUNTING FOR SUB-OPTIMAL ANTIBODY RESPONSES OF ELDERLY INDIVIDUALS. THESE DEFECTS INCLUDE 1) REDUCED CLASS SWITCH RECOMBINATION, RESPONSIBLE FOR THE GENERATION OF A SECONDARY RESPONSE OF CLASS SWITCHED ANTIBODIES, 2) REDUCED DE NOVO SOMATIC HYPERMUTATION OF THE ANTIBODY VARIABLE REGION, 3) REDUCED BINDING AND NEUTRALIZATION CAPACITY, AS WELL AS BINDING SPECIFICITY, OF THE SECRETED ANTIBODIES, 4) INCREASED EPIGENETIC MODIFICATIONS THAT ARE ASSOCIATED WITH LOWER ANTIBODY RESPONSES, 5) INCREASED FREQUENCIES OF INFLAMMATORY B CELL SUBSETS, AND 6) SHORTER TELOMERES. CONCLUSIONS: ALTHOUGH INFLUENZA VACCINATION REPRESENTS THE MOST EFFECTIVE WAY TO PREVENT INFLUENZA INFECTION, VACCINES WITH GREATER IMMUNOGENICITY ARE NEEDED TO IMPROVE THE RESPONSE OF ELDERLY INDIVIDUALS. RECENT ADVANCES IN TECHNOLOGY HAVE MADE POSSIBLE A BROAD APPROACH TO BETTER UNDERSTAND THE AGE-ASSOCIATED CHANGES IN IMMUNE CELLS, NEEDED TO DESIGN TAILORED VACCINES AND EFFECTIVE THERAPEUTIC STRATEGIES THAT WILL BE ABLE TO IMPROVE THE IMMUNE RESPONSE OF VULNERABLE INDIVIDUALS. 2020 8 2770 39 EXTENDING INJURY- AND DISEASE-RESISTANT CNS PHENOTYPES BY REPETITIVE EPIGENETIC CONDITIONING. SIGNIFICANT REDUCTIONS IN THE EXTENT OF ACUTE INJURY IN THE CNS CAN BE ACHIEVED BY EXPOSURE TO DIFFERENT PRECONDITIONING STIMULI, BUT THE DURATION OF THE INDUCED PROTECTIVE PHENOTYPE IS TYPICALLY SHORT-LASTING, AND THUS IS DEEMED AS LIMITING ITS CLINICAL APPLICABILITY. EXTENDING THE PERIOD OVER WHICH SUCH ADAPTIVE EPIGENETIC CHANGES PERSIST - IN EFFECT, EXPANDING CONDITIONING'S "THERAPEUTIC WINDOW" - WOULD SIGNIFICANTLY BROADEN THE POTENTIAL APPLICATIONS OF SUCH A TREATMENT APPROACH IN PATIENTS. THE FREQUENCY OF THE CONDITIONING STIMULUS MAY HOLD THE KEY. WHILE TRANSIENT (1-3 DAYS) PROTECTION AGAINST CNS ISCHEMIC INJURY IS WELL ESTABLISHED PRECLINICALLY FOLLOWING A SINGLE PRECONDITIONING STIMULUS, REPETITIVELY PRESENTING PRECONDITIONING STIMULI EXTENDS THE DURATION OF ISCHEMIC TOLERANCE BY MANY WEEKS. MOREOVER, REPETITIVE INTERMITTENT POSTCONDITIONING ENHANCES POST-ISCHEMIC RECOVERY METRICS AND IMPROVES LONG-TERM SURVIVAL. INTERMITTENT CONDITIONING IS ALSO EFFICACIOUS FOR PREVENTING OR DELAYING INJURY IN PRECLINICAL MODELS OF CHRONIC NEURODEGENERATIVE DISEASE, AND FOR PROMOTING LONG-LASTING FUNCTIONAL IMPROVEMENTS IN A NUMBER OF OTHER PATHOLOGIES AS WELL. ALTHOUGH THE DETAILED MECHANISMS UNDERLYING THESE PROTRACTED KINDS OF NEUROPLASTICITY REMAIN LARGELY UNSTUDIED, ACCUMULATING EMPIRICAL EVIDENCE SUPPORTS THE CONTENTION THAT ALL OF THESE ADAPTIVE PHENOTYPES ARE EPIGENETICALLY MEDIATED. GOING FORWARD, ADDITIONAL PRECLINICAL DEMONSTRATIONS OF THE ABILITY TO INDUCE SUSTAINED BENEFICIAL PHENOTYPES THAT REDUCE THE BURDEN OF ACUTE AND CHRONIC NEURODEGENERATION, AND EXPERIMENTAL INTERROGATIONS OF THE REGULATORY CONSTRUCTS RESPONSIBLE FOR THESE EPIGENETIC RESPONSES, WILL ACCELERATE THE IDENTIFICATION OF NOT ONLY EFFICACIOUS BUT ALSO PRACTICAL, ADAPTIVE EPIGENETICS-BASED TREATMENTS FOR INDIVIDUALS WITH NEUROLOGICAL DISEASE. 2015 9 4386 34 MITOCHONDRIAL STRESS INDUCED BY CONTINUOUS STIMULATION UNDER HYPOXIA RAPIDLY DRIVES T CELL EXHAUSTION. CANCER AND CHRONIC INFECTIONS INDUCE T CELL EXHAUSTION, A HYPOFUNCTIONAL FATE CARRYING DISTINCT EPIGENETIC, TRANSCRIPTOMIC AND METABOLIC CHARACTERISTICS. HOWEVER, DRIVERS OF EXHAUSTION REMAIN POORLY UNDERSTOOD. AS INTRATUMORAL EXHAUSTED T CELLS EXPERIENCE SEVERE HYPOXIA, WE HYPOTHESIZED THAT METABOLIC STRESS ALTERS THEIR RESPONSES TO OTHER SIGNALS, SPECIFICALLY, PERSISTENT ANTIGENIC STIMULATION. IN VITRO, ALTHOUGH CD8(+) T CELLS EXPERIENCING CONTINUOUS STIMULATION OR HYPOXIA ALONE DIFFERENTIATED INTO FUNCTIONAL EFFECTORS, THE COMBINATION RAPIDLY DROVE T CELL DYSFUNCTION CONSISTENT WITH EXHAUSTION. CONTINUOUS STIMULATION PROMOTED BLIMP-1-MEDIATED REPRESSION OF PGC-1ALPHA-DEPENDENT MITOCHONDRIAL REPROGRAMMING, RENDERING CELLS POORLY RESPONSIVE TO HYPOXIA. LOSS OF MITOCHONDRIAL FUNCTION GENERATED INTOLERABLE LEVELS OF REACTIVE OXYGEN SPECIES (ROS), SUFFICIENT TO PROMOTE EXHAUSTED-LIKE STATES, IN PART THROUGH PHOSPHATASE INHIBITION AND THE CONSEQUENT ACTIVITY OF NUCLEAR FACTOR OF ACTIVATED T CELLS. REDUCING T CELL-INTRINSIC ROS AND LOWERING TUMOR HYPOXIA LIMITED T CELL EXHAUSTION, SYNERGIZING WITH IMMUNOTHERAPY. THUS, IMMUNOLOGIC AND METABOLIC SIGNALING ARE INTRINSICALLY LINKED: THROUGH MITIGATION OF METABOLIC STRESS, T CELL DIFFERENTIATION CAN BE ALTERED TO PROMOTE MORE FUNCTIONAL CELLULAR FATES. 2021 10 6502 24 TRAINED IMMUNITY: LONG-TERM ADAPTATION IN INNATE IMMUNE RESPONSES. ADAPTIVE IMMUNE RESPONSES ARE CHARACTERIZED BY ANTIGEN SPECIFICITY AND INDUCTION OF LIFELONG IMMUNOLOGIC MEMORY. RECENTLY, IT HAS BEEN REPORTED THAT INNATE IMMUNE CELLS CAN ALSO BUILD IMMUNE MEMORY CHARACTERISTICS-A PROCESS TERMED TRAINED IMMUNITY. TRAINED IMMUNITY DESCRIBES THE PERSISTENT HYPERRESPONSIVE PHENOTYPE THAT INNATE IMMUNE CELLS CAN DEVELOP AFTER BRIEF STIMULATION. PATHOGENIC STIMULI SUCH AS MICROORGANISMS, AND ALSO ENDOGENOUS MOLECULES INCLUDING URIC ACID, OXIDIZED LDL (LOW-DENSITY LIPOPROTEIN), AND CATECHOLAMINES, ARE CAPABLE OF INDUCING MEMORY IN MONOCYTES AND MACROPHAGES. WHILE TRAINED IMMUNITY PROVIDES FAVORABLE CROSS-PROTECTION IN THE CONTEXT OF INFECTIOUS DISEASES, THE HEIGHTENED IMMUNE RESPONSE CAN BE MALADAPTIVE IN DISEASES DRIVEN BY CHRONIC SYSTEMIC INFLAMMATION, SUCH AS ATHEROSCLEROSIS. TRAINED IMMUNITY IS MAINTAINED BY DISTINCT EPIGENETIC AND METABOLIC MECHANISMS AND PERSISTS FOR AT LEAST SEVERAL MONTHS IN VIVO DUE TO REPROGRAMMING OF MYELOID PROGENITOR CELLS. ADDITIONALLY, CERTAIN NONIMMUNE CELLS ARE ALSO FOUND TO EXHIBIT TRAINED IMMUNITY CHARACTERISTICS. THUS, TRAINED IMMUNITY PRESENTS AN EXCITING FRAMEWORK TO DEVELOP NEW APPROACHES TO VACCINATION AND ALSO NOVEL PHARMACOLOGICAL TARGETS IN THE TREATMENT OF INFLAMMATORY DISEASES. 2021 11 6494 30 TRAINED IMMUNITY AS A NOVEL THERAPEUTIC STRATEGY. RECENT STUDIES HAVE SHOWN THAT UPON CERTAIN VACCINATIONS OR INFECTIONS HUMAN INNATE IMMUNE CELLS CAN UNDERGO EXTENSIVE METABOLIC AND EPIGENETIC REPROGRAMMING, WHICH RESULTS IN ENHANCED IMMUNE RESPONSES UPON HETEROLOGOUS RE-INFECTION, A PROCESS TERMED TRAINED IMMUNITY. TRAINED IMMUNITY HAS ALSO BEEN SHOWN TO BE INAPPROPRIATELY ACTIVATED IN INFLAMMATORY DISEASES. THIS PROVIDES THE POTENTIAL FOR IDENTIFYING NOVEL THERAPEUTIC TARGETS: POTENTIATION OF TRAINED IMMUNITY COULD PROTECT FROM SECONDARY INFECTIONS AND REVERSE IMMUNOTOLERANT STATES, WHILE INHIBITION OF TRAINED IMMUNITY MIGHT REDUCE EXCESSIVE IMMUNE ACTIVATION IN CHRONIC INFLAMMATORY CONDITIONS. BY TARGETING SPECIFIC MECHANISMS OF TRAINED IMMUNITY ON EITHER IMMUNOLOGIC, METABOLIC OR EPIGENETIC LEVEL, NOVEL THERAPEUTIC APPROACHES COULD BE DEVELOPED. 2018 12 5489 32 REVERSING POST-INFECTIOUS EPIGENETIC-MEDIATED IMMUNE SUPPRESSION. THE IMMUNE RESPONSE MUST BALANCE THE PRO-INFLAMMATORY, CELL-MEDIATED CYTOTOXICITY WITH THE ANTI-INFLAMMATORY AND WOUND REPAIR RESPONSE. EPIGENETIC MECHANISMS MEDIATE THIS BALANCE AND LIMIT HOST IMMUNITY FROM INDUCING EXUBERANT COLLATERAL DAMAGE TO HOST TISSUE AFTER SEVERE AND CHRONIC INFECTIONS. HOWEVER, FOLLOWING TREATMENT FOR THESE INFECTIONS, INCLUDING SEPSIS, PNEUMONIA, HEPATITIS B, HEPATITIS C, HIV, TUBERCULOSIS (TB) OR SCHISTOSOMIASIS, DETRIMENTAL EPIGENETIC SCARS PERSIST, AND RESULT IN LONG-LASTING IMMUNE SUPPRESSION. THIS IS HYPOTHESIZED TO BE ONE OF THE CONTRIBUTING MECHANISMS EXPLAINING WHY SURVIVORS OF INFECTION HAVE INCREASED ALL-CAUSE MORTALITY AND INCREASED RATES OF UNRELATED SECONDARY INFECTIONS. THE MECHANISMS THAT INDUCE EPIGENETIC-MEDIATED IMMUNE SUPPRESSION HAVE BEEN DEMONSTRATED IN-VITRO AND IN ANIMAL MODELS. MODULATION OF THE AMP-ACTIVATED PROTEIN KINASE (AMPK)-MAMMALIAN TARGET OF RAPAMYCIN (MTOR), NUCLEAR FACTOR OF ACTIVATED T CELLS (NFAT) OR NUCLEAR RECEPTOR (NR4A) PATHWAYS IS ABLE TO BLOCK OR REVERSE THE DEVELOPMENT OF DETRIMENTAL EPIGENETIC SCARS. SIMILARLY, DRUGS THAT DIRECTLY MODIFY EPIGENETIC ENZYMES, SUCH AS THOSE THAT INHIBIT HISTONE DEACETYLASES (HDAC) INHIBITORS, DNA HYPOMETHYLATING AGENTS OR MODIFIERS OF THE NUCLEOSOME REMODELING AND DNA METHYLATION (NURD) COMPLEX OR POLYCOMB REPRESSIVE COMPLEX (PRC) HAVE DEMONSTRATED CAPACITY TO RESTORE HOST IMMUNITY IN THE SETTING OF CANCER-, LCMV- OR MURINE SEPSIS-INDUCED EPIGENETIC-MEDIATED IMMUNE SUPPRESSION. A THIRD CLINICALLY FEASIBLE STRATEGY FOR REVERSING DETRIMENTAL EPIGENETIC SCARS INCLUDES BIOENGINEERING APPROACHES TO EITHER DIRECTLY REVERSE THE DETRIMENTAL EPIGENETIC MARKS OR TO MODIFY THE EPIGENETIC ENZYMES OR TRANSCRIPTION FACTORS THAT INDUCE DETRIMENTAL EPIGENETIC SCARS. EACH OF THESE APPROACHES, ALONE OR IN COMBINATION, HAVE ABLATED OR REVERSED DETRIMENTAL EPIGENETIC MARKS IN IN-VITRO OR IN ANIMAL MODELS; TRANSLATIONAL STUDIES ARE NOW REQUIRED TO EVALUATE CLINICAL APPLICABILITY. 2021 13 5900 31 T-CELL EXHAUSTION IN ORGAN TRANSPLANTATION. EXHAUSTION OF T CELLS OCCURS IN RESPONSE TO LONG-TERM EXPOSURE TO SELF AND FOREIGN ANTIGENS. IT LIMITS T CELL CAPACITY TO PROLIFERATE AND PRODUCE CYTOKINES, LEADING TO AN IMPAIRED ABILITY TO CLEAR CHRONIC INFECTIONS OR ERADICATE TUMORS. T-CELL EXHAUSTION IS ASSOCIATED WITH A SPECIFIC TRANSCRIPTIONAL, EPIGENETIC, AND METABOLIC PROGRAM AND CHARACTERISTIC CELL SURFACE MARKERS' EXPRESSION. RECENT STUDIES HAVE BEGUN TO ELUCIDATE THE ROLE OF T-CELL EXHAUSTION IN TRANSPLANT. HIGHER LEVELS OF EXHAUSTED T CELLS HAVE BEEN ASSOCIATED WITH BETTER GRAFT FUNCTION IN KIDNEY TRANSPLANT RECIPIENTS. IN CONTRAST, REINVIGORATING EXHAUSTED T CELLS BY IMMUNE CHECKPOINT BLOCKADE THERAPIES, WHILE PROMOTING TUMOR CLEARANCE, INCREASES THE RISK OF ACUTE REJECTION. LYMPHOCYTE DEPLETION AND HIGH ALLOANTIGEN LOAD HAVE BEEN IDENTIFIED AS MAJOR DRIVERS OF T-CELL EXHAUSTION. THIS COULD ACCOUNT, AT LEAST IN PART, FOR THE REDUCED RATES OF ACUTE REJECTION IN ORGAN TRANSPLANT RECIPIENTS INDUCED WITH THYMOGLOBULIN AND FOR THE PRO-TOLEROGENIC EFFECTS OF A LARGE ORGAN SUCH AS THE LIVER. AMONG THE DRUGS THAT ARE WIDELY USED FOR MAINTENANCE IMMUNOSUPPRESSION, CALCINEURIN INHIBITORS HAVE A CONTRASTING INHIBITORY EFFECT ON EXHAUSTION OF T CELLS, WHILE THE INFLUENCE OF MTOR INHIBITORS IS STILL UNCLEAR. HARNESSING OR ENCOURAGING THE NATURAL PROCESSES OF EXHAUSTION MAY PROVIDE A NOVEL STRATEGY TO PROMOTE GRAFT SURVIVAL AND TRANSPLANTATION TOLERANCE. 2022 14 2617 40 EPIGENOME TARGETING BY PROBIOTIC METABOLITES. BACKGROUND: THE INTESTINAL MICROBIOTA PLAYS AN IMPORTANT ROLE IN IMMUNE DEVELOPMENT AND HOMEOSTASIS. A DISTURBED MICROBIOTA DURING EARLY INFANCY IS ASSOCIATED WITH AN INCREASED RISK OF DEVELOPING INFLAMMATORY AND ALLERGIC DISEASES LATER IN LIFE. THE MECHANISMS UNDERLYING THESE EFFECTS ARE POORLY UNDERSTOOD BUT ARE LIKELY TO INVOLVE ALTERATIONS IN MICROBIAL PRODUCTION OF FERMENTATION-DERIVED METABOLITES, WHICH HAVE POTENT IMMUNE MODULATING PROPERTIES AND ARE REQUIRED FOR MAINTENANCE OF HEALTHY MUCOSAL IMMUNE RESPONSES. PROBIOTICS ARE BENEFICIAL BACTERIA THAT HAVE THE CAPACITY TO ALTER THE COMPOSITION OF BACTERIAL SPECIES IN THE INTESTINE THAT CAN IN TURN INFLUENCE THE PRODUCTION OF FERMENTATION-DERIVED METABOLITES. PRINCIPAL AMONG THESE METABOLITES ARE THE SHORT-CHAIN FATTY ACIDS BUTYRATE AND ACETATE THAT HAVE POTENT ANTI-INFLAMMATORY ACTIVITIES IMPORTANT IN REGULATING IMMUNE FUNCTION AT THE INTESTINAL MUCOSAL SURFACE. THEREFORE STRATEGIES AIMED AT RESTORING THE MICROBIOTA PROFILE MAY BE EFFECTIVE IN THE PREVENTION OR TREATMENT OF ALLERGIC AND INFLAMMATORY DISEASES. PRESENTATION OF THE HYPOTHESIS: PROBIOTIC BACTERIA HAVE DIVERSE EFFECTS INCLUDING ALTERING MICROBIOTA COMPOSITION, REGULATING EPITHELIAL CELL BARRIER FUNCTION AND MODULATING OF IMMUNE RESPONSES. THE PRECISE MOLECULAR MECHANISMS MEDIATING THESE PROBIOTIC EFFECTS ARE NOT WELL UNDERSTOOD. SHORT-CHAIN FATTY ACIDS SUCH AS BUTYRATE ARE A CLASS OF HISTONE DEACETYLASE INHIBITORS IMPORTANT IN THE EPIGENETIC CONTROL OF HOST CELL RESPONSES. IT IS HYPOTHESIZED THAT THE BIOLOGICAL FUNCTION OF PROBIOTICS MAY BE A RESULT OF EPIGENETIC MODIFICATIONS THAT MAY EXPLAIN THE WIDE RANGE OF EFFECTS OBSERVED. STUDIES DELINEATING THE EFFECTS OF PROBIOTICS ON SHORT-CHAIN FATTY ACID PRODUCTION AND THE EPIGENETIC ACTIONS OF SHORT-CHAIN FATTY ACIDS WILL ASSIST IN UNDERSTANDING THE ASSOCIATION BETWEEN MICROBIOTA AND ALLERGIC OR AUTOIMMUNE DISORDERS. TESTING THE HYPOTHESIS: WE PROPOSE THAT TREATMENT WITH SPECIFIC PROBIOTIC BACTERIA UNDER IN VIVO CONDITIONS WOULD OFFER THE IDEAL CONDITIONS TO EXAMINE THE MICROBIOLOGICAL, IMMUNOLOGICAL AND EPIGENETIC MECHANISMS OF ACTION. ADVANCES IN EPIGENETIC TECHNOLOGY NOW ALLOW INVESTIGATORS TO BETTER UNDERSTAND THE COMPLEX BIOLOGICAL PROPERTIES OF PROBIOTICS AND THEIR METABOLITES. IMPLICATIONS OF THE HYPOTHESIS: DETERMINING THE PRECISE MECHANISMS OF PROBIOTIC ACTION WILL LEAD TO MORE SPECIFIC AND EFFICACIOUS THERAPEUTIC STRATEGIES IN THE PREVENTION OR TREATMENT OF CHRONIC INFLAMMATORY CONDITIONS. 2010 15 5816 33 STRESS AND STEM CELLS. THE UNIQUE PROPERTIES AND FUNCTIONS OF STEM CELLS MAKE THEM PARTICULARLY SUSCEPTIBLE TO STRESSES AND ALSO LEAD TO THEIR REGULATION BY STRESS. STEM CELL DIVISION MUST RESPOND TO THE DEMAND TO REPLENISH CELLS DURING NORMAL TISSUE TURNOVER AS WELL AS IN RESPONSE TO DAMAGE. OXIDATIVE STRESS, MECHANICAL STRESS, GROWTH FACTORS, AND CYTOKINES SIGNAL STEM CELL DIVISION AND DIFFERENTIATION. MANY OF THE CONSERVED PATHWAYS REGULATING STEM CELL SELF-RENEWAL AND DIFFERENTIATION ARE ALSO STRESS-RESPONSE PATHWAYS. THE LONG LIFE SPAN AND DIVISION POTENTIAL OF STEM CELLS CREATE A PROPENSITY FOR TRANSFORMATION (CANCER) AND SPECIFIC STRESS RESPONSES SUCH AS APOPTOSIS AND SENESCENCE ACT AS ANTITUMOR MECHANISMS. QUIESCENCE REGULATED BY CDK INHIBITORS AND A HYPOXIC NICHE REGULATED BY FOXO TRANSCRIPTION FACTOR FUNCTION TO REDUCE STRESS FOR SEVERAL TYPES OF STEM CELLS TO FACILITATE LONG-TERM MAINTENANCE. AGING IS A PARTICULARLY RELEVANT STRESS FOR STEM CELLS, BECAUSE REPEATED DEMANDS ON STEM CELL FUNCTION OVER THE LIFE SPAN CAN HAVE CUMULATIVE CELL-AUTONOMOUS EFFECTS INCLUDING EPIGENETIC DYSREGULATION, MUTATIONS, AND TELOMERE EROSION. IN ADDITION, AGING OF THE ORGANISM IMPAIRS FUNCTION OF THE STEM CELL NICHE AND SYSTEMIC SIGNALS, INCLUDING CHRONIC INFLAMMATION AND OXIDATIVE STRESS. 2012 16 2703 28 EXERCISE ADAPTATIONS: MOLECULAR MECHANISMS AND POTENTIAL TARGETS FOR THERAPEUTIC BENEFIT. EXERCISE IS FUNDAMENTAL FOR GOOD HEALTH, WHEREAS PHYSICAL INACTIVITY UNDERPINS MANY CHRONIC DISEASES OF MODERN SOCIETY. IT IS WELL APPRECIATED THAT REGULAR EXERCISE IMPROVES METABOLISM AND THE METABOLIC PHENOTYPE IN A NUMBER OF TISSUES. THE PHENOTYPIC ALTERATIONS OBSERVED IN SKELETAL MUSCLE ARE PARTLY MEDIATED BY TRANSCRIPTIONAL RESPONSES THAT OCCUR FOLLOWING EACH INDIVIDUAL BOUT OF EXERCISE. THIS ADAPTIVE RESPONSE INCREASES OXIDATIVE CAPACITY AND INFLUENCES THE FUNCTION OF MYOKINES AND EXTRACELLULAR VESICLES THAT SIGNAL TO OTHER TISSUES. OUR UNDERSTANDING OF THE EPIGENETIC AND TRANSCRIPTIONAL MECHANISMS THAT MEDIATE THE SKELETAL MUSCLE GENE EXPRESSION RESPONSE TO EXERCISE AS WELL AS OF THEIR UPSTREAM SIGNALLING PATHWAYS HAS ADVANCED SUBSTANTIALLY IN THE PAST 10 YEARS. WITH THIS KNOWLEDGE ALSO COMES THE OPPORTUNITY TO DESIGN NEW THERAPEUTIC STRATEGIES BASED ON THE BIOLOGY OF EXERCISE FOR A VARIETY OF CHRONIC CONDITIONS WHERE REGULAR EXERCISE MIGHT BE A CHALLENGE. THIS REVIEW PROVIDES AN OVERVIEW OF THE BENEFICIAL ADAPTIVE RESPONSES TO EXERCISE AND DETAILS THE MOLECULAR MECHANISMS INVOLVED. THE POSSIBILITY OF DESIGNING THERAPEUTIC INTERVENTIONS BASED ON THESE MOLECULAR MECHANISMS IS ADDRESSED, USING RELEVANT EXAMPLES THAT HAVE EXPLOITED THIS APPROACH. 2020 17 4974 32 PATHOPHYSIOLOGICAL MECHANISMS LEADING TO MUSCLE LOSS IN CHRONIC KIDNEY DISEASE. LOSS OF MUSCLE PROTEINS IS A DELETERIOUS CONSEQUENCE OF CHRONIC KIDNEY DISEASE (CKD) THAT CAUSES A DECREASE IN MUSCLE STRENGTH AND FUNCTION, AND CAN LEAD TO A REDUCTION IN QUALITY OF LIFE AND INCREASED RISK OF MORBIDITY AND MORTALITY. THE EFFECTIVENESS OF CURRENT TREATMENT STRATEGIES IN PREVENTING OR REVERSING MUSCLE PROTEIN LOSSES IS LIMITED. THE LIMITATIONS LARGELY STEM FROM THE SYSTEMIC NATURE OF DISEASES SUCH AS CKD, WHICH STIMULATE SKELETAL MUSCLE PROTEIN DEGRADATION PATHWAYS WHILE SIMULTANEOUSLY ACTIVATING MECHANISMS THAT IMPAIR MUSCLE PROTEIN SYNTHESIS AND REPAIR. STIMULI THAT INITIATE MUSCLE PROTEIN LOSS INCLUDE METABOLIC ACIDOSIS, INSULIN AND IGF1 RESISTANCE, CHANGES IN HORMONES, CYTOKINES, INFLAMMATORY PROCESSES AND DECREASED APPETITE. A GROWING BODY OF EVIDENCE SUGGESTS THAT SIGNALLING MOLECULES SECRETED FROM MUSCLE CAN ENTER THE CIRCULATION AND SUBSEQUENTLY INTERACT WITH RECIPIENT ORGANS, INCLUDING THE KIDNEYS, WHILE CONVERSELY, PATHOLOGICAL EVENTS IN THE KIDNEY CAN ADVERSELY INFLUENCE PROTEIN METABOLISM IN SKELETAL MUSCLE, DEMONSTRATING THE EXISTENCE OF CROSSTALK BETWEEN KIDNEY AND MUSCLE. TOGETHER, THESE SIGNALS, WHETHER DIRECT OR INDIRECT, INDUCE CHANGES IN THE LEVELS OF REGULATORY AND EFFECTOR PROTEINS VIA ALTERATIONS IN MRNAS, MICRORNAS AND CHROMATIN EPIGENETIC RESPONSES. ADVANCES IN OUR UNDERSTANDING OF THE SIGNALS AND PROCESSES THAT MEDIATE MUSCLE LOSS IN CKD AND OTHER MUSCLE WASTING CONDITIONS WILL SUPPORT THE FUTURE DEVELOPMENT OF THERAPEUTIC STRATEGIES TO REDUCE MUSCLE LOSS. 2022 18 4340 30 MIGRATION OF STEM-LIKE CD8 T CELLS BETWEEN TISSUE MICROENVIRONMENTS UNDERPINS SUCCESSFUL ANTI-TUMOUR IMMUNE RESPONSES. THE CLINICAL SUCCESS OF IMMUNE CHECKPOINT BLOCKADE IN SOME PATIENTS HAS TRANSFORMED TREATMENT APPROACHES IN CANCER AND OFFERS THE HOPE OF DURABLE CURATIVE RESPONSES. BUILDING FROM STUDIES OF CHRONIC INFECTION, THE COMPOSITION OF TUMOUR INFILTRATING LYMPHOCYTES AND IN PARTICULAR, THE SPECTRUM OF EXHAUSTED CD8 T CELLS HAS NOW BEEN CHARACTERIZED IN DETAIL, PROFILING THE PHENOTYPE, FUNCTION, TRANSCRIPTIONAL REGULATION AND EVEN THE EPIGENETIC CHANGES. HOWEVER, WHAT REMAINS LESS CLEAR IS HOW INTRATUMOURAL IMMUNE CELLS INTERFACE WITH POPULATIONS IN THE PERIPHERY, BOTH IN TERMS OF SUSTAINING THE RESPONSE IN CANCER, BUT ALSO IN ESTABLISHING SYSTEMIC MEMORY RESPONSES THAT CAN PROVIDE LONG-TERM PROTECTION. HERE WE WILL SUCCINCTLY REVIEW THE CURRENT UNDERSTANDING OF THE ANTI-TUMOUR RESPONSE, CONSIDER THE TISSUE MICROENVIRONMENTS THAT SUPPORT KEY CELLULAR SUBSETS AND THE EXTENT TO WHICH CELLULAR MIGRATION BETWEEN THESE SITES IMPACTS THE RESPONSE. 2023 19 1066 31 CLINICAL USE OF AMINO ACIDS AS DIETARY SUPPLEMENT: PROS AND CONS. NITROGEN SUPPLY IS PIVOTAL FOR THE MAINTENANCE OF LIFE. AMINO ACIDS CAN BE UTILIZED TO SYNTHESIZE BOTH GLUCOSE AND LIPIDS. THE OPPOSITE, I.E., PRODUCTION OF AMINO ACIDS FROM EITHER ONE OF THEM, IS NOT POSSIBLE IN THE ABSENCE OF OTHER AMINO ACIDS AS DONORS OF NITROGEN. THE QUALITY OF AMINO ACID CONTENT IN PROTEIN HAS BEEN RE-EVALUATED RECENTLY, AND THE RELEVANCE OF ESSENTIAL AMINO ACIDS HAS BEEN REPEATEDLY UNDERLINED. ESSENTIAL AMINO ACID REQUIREMENTS IN DIFFERENT MAMMALS ARE NOT IDENTICAL, AND RATIOS AMONG THEM SHOULD BE TAKEN INTO ACCOUNT WHEN PROJECTING AN EFFICIENT FORMULATION. RECENT RESEARCH HAS DEMONSTRATED THAT GENES RESPOND TO DIFFERENT QUALITIES AND QUANTITIES OF NUTRITIONAL SUPPLY, AND INCREASED PROVISION OF ESSENTIAL AMINO ACIDS INCREASES LIFESPAN IN ANIMAL EXPERIMENTS THROUGH MITOCHONDRIOGENESIS AND MAINTENANCE OF ELEVATED RATES OF SYNTHESIS OF ANTI-OXIDANT MOLECULES. MOREOVER, GENETIC EXPRESSION OF KEY CONTROLLERS OF SYNTHESIS, LIKE MTOR, MAY BE PARTICULARLY IMPORTANT FOR UNDERSTANDING SKELETAL MUSCLE MAINTENANCE. LOSSES OF MUSCLE MASS AND IMPAIRED IMMUNE FUNCTION ARE RELATED TO REDUCED PROTEIN SUPPLY, AND THERE IS INCREASING EVIDENCE THAT REGULAR ESSENTIAL AMINO ACID INTAKE AS PART OF AN ORAL DIET IS EFFECTIVE IN REVERSING MUSCLE CATABOLISM, PROMOTING MUSCLE ANABOLISM, AND RESTORING IMMUNOLOGICAL FUNCTION. THEREFORE, THE USE OF AMINO ACIDS AS SUPPLEMENTS TO DIET WOULD BE EXPANDING IN THE NEAR FUTURE. IS THIS SAFE? FEW DATA ARE AVAILABLE ON AMINO ACID TOXICITY, AND ONLY ONE ESSENTIAL AMINO ACID MAY BE CONSIDERED TO HAVE CLINICALLY RELEVANT TOXICITY: METHIONINE, BECAUSE IT IS TRANSFORMED INTO A TOXIC INTERMEDIATE, HOMOCYSTEINE, WHEN CYSTEINE SYNTHESIS IS REQUIRED BY METABOLIC NEEDS. MATCHING OF STOICHIOMETRIC RATIOS BETWEEN METHIONINE AND CYSTEINE MAY SOLVE THE PROBLEM OF SUPPLYING SUFFICIENT AMOUNTS OF SULFUR TO THE BODY. ARGININE AND GLUTAMINE ARE TWO NON-ESSENTIAL AMINO ACIDS THAN CAN BECOME "CONDITIONALLY ESSENTIAL" BECAUSE OF ELEVATED NEEDS DURING PATHOLOGICAL CONDITIONS, AND METABOLISM MAY NOT BE ABLE TO MAINTAIN THEIR CONCENTRATIONS AT SUFFICIENT LEVELS TO MATCH METABOLIC REQUIREMENTS. CHRONIC EXOGENOUS ARGININE SUPPLEMENTATION HAS NOT PROVEN TO EXERT POSITIVE CLINICAL EFFECTS IN DIFFERENT TRIALS, AND SEQUENTIAL ARTICULATION OF THE KNOWLEDGE OF INTRODUCTION OF ARGININE-DRIVEN TRANSCRIPTIONAL, TRANSLATIONAL, AND EPIGENETIC ADAPTATIONS MAY GIVE US A KEY FOR INTERPRETING THOSE PUZZLING RESULTS. 2011 20 737 46 CANCER STEM CELLS. THERE IS AN INCREASING EVIDENCE SUPPORTING THE CANCER STEM CELL HYPOTHESIS. NORMAL STEM CELLS IN THE ADULT ORGANISM ARE RESPONSIBLE FOR TISSUE RENEWAL AND REPAIR OF AGED OR DAMAGED TISSUE. A SUBSTANTIAL CHARACTERISTIC OF STEM CELLS IS THEIR ABILITY FOR SELF-RENEWAL WITHOUT LOSS OF PROLIFERATION CAPACITY WITH EACH CELL DIVISION. THE STEM CELLS ARE IMMORTAL, AND RATHER RESISTANT TO ACTION OF DRUGS. THEY ARE ABLE TO DIFFERENTIATE AND FORM SPECIFIC TYPES OF TISSUE DUE TO THE INFLUENCE OF MICROENVIRONMENTAL AND SOME OTHER FACTORS. STEM CELLS DIVIDE ASYMMETRICALLY PRODUCING TWO DAUGHTER CELLS -- ONE IS A NEW STEM CELL AND THE SECOND IS PROGENITOR CELL, WHICH HAS THE ABILITY FOR DIFFERENTIATION AND PROLIFERATION, BUT NOT THE CAPABILITY FOR SELF-RENEWAL. CANCER STEM CELLS ARE IN MANY ASPECTS SIMILAR TO THE STEM CELLS. IT HAS BEEN PROVEN THAT TUMOR CELLS ARE HETEROGENEOUS COMPRISING RARE TUMOR INITIATING CELLS AND ABUNDANT NON-TUMOR INITIATING CELLS. TUMOR INITIATING CELLS -- CANCER STEM CELLS HAVE THE ABILITY OF SELF-RENEWAL AND PROLIFERATION, ARE RESISTANT TO DRUGS, AND EXPRESS TYPICAL MARKERS OF STEM CELLS. IT IS NOT CLEAR WHETHER CANCER STEM CELLS ORIGINATE FROM NORMAL STEM CELLS IN CONSEQUENCE OF GENETIC AND EPIGENETIC CHANGES AND/OR BY REDIFFERENTIATION FROM SOMATIC TUMOR CELLS TO THE STEM-LIKE CELLS. PROBABLY BOTH MECHANISMS ARE INVOLVED IN THE ORIGIN OF CANCER STEM CELLS. DYSREGULATION OF STEM CELL SELF-RENEWAL IS A LIKELY REQUIREMENT FOR THE DEVELOPMENT OF CANCER. ISOLATION AND IDENTIFICATION OF CANCER STEM CELLS IN HUMAN TUMORS AND IN TUMOR CELL LINES HAS BEEN SUCCESSFUL. TO DATE, THE EXISTENCE OF CANCER STEM CELLS HAS BEEN PROVEN IN ACUTE AND CHRONIC MYELOID LEUKEMIA, IN BREAST CANCER, IN BRAIN TUMORS, IN LUNG CANCER AND GASTROINTESTINAL TUMORS. CANCER STEM CELL MODEL IS ALSO CONSISTENT WITH SOME CLINICAL OBSERVATIONS. ALTHOUGH STANDARD CHEMOTHERAPY KILLS MOST CELLS IN A TUMOR, CANCER STEM CELLS REMAIN VIABLE. DESPITE THE SMALL NUMBER OF SUCH CELLS, THEY MIGHT BE THE CAUSE OF TUMOR RECURRENCE, SOMETIMES MANY YEARS AFTER THE "SUCCESSFUL" TREATMENT OF PRIMARY TUMOR. GROWTH OF METASTASES IN DISTINCT AREAS OF BODY AND THEIR CELLULAR HETEROGENEITY MIGHT BE CONSEQUENCE OF CANCER STEM CELL DIFFERENTIATION AND/OR DEDIFFERENTIATION AND ASYMMETRIC DIVISION OF CANCER STEM CELLS. FURTHER CHARACTERIZATION OF CANCER STEM CELLS IS NEEDED IN ORDER TO FIND WAYS TO DESTROY THEM, WHICH MIGHT CONTRIBUTE SIGNIFICANTLY TO THE THERAPEUTIC MANAGEMENT OF MALIGNANT TUMORS. 2005