No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Friedreich’s Ataxia (FRDA) is a rare and poorly understood autosomal recessive disease caused by a pathological deficiency of the mitochondrial protein frataxin. Patients suffer neurodegeneration, ataxia, diabetes, and heart failure. In an effort to understand the mechanisms of heart failure in FRDA, we investigated the role of the protein modification acetylation, which is highly abundant on mitochondrial proteins and has been implicated in regulating intermediary metabolism. Using mouse models of FRDA, we found that cardiac frataxin deficiency causes progressive hyperacetylation of mitochondrial proteins which is correlated with loss of respiratory chain subunits and an altered mitochondrial redox state. Mitochondrial protein hyperacetylation could be reversed by the mitochondria-localized deacetylase SIRT3 in vitro, suggesting a defect in endogenous SIRT3 activity. Consistently, frataxin-deficient cardiac mitochondria showed significantly decreased rates of fatty acid oxidation and complete oxidation to carbon dioxide. However, the degree of protein hyperacetylation in FRDA could not be fully explained by SIRT3 loss. Our data suggested that intermediary metabolites and perhaps acetyl-CoA, which is required for protein acetylation, are accumulating in frataxin-deficient mitochondria. Upon testing the hypothesis that mitochondrial protein acetylation is non-enzymatic, we found that the minimal chemical conditions of the mitochondrial matrix are sufficient to cause widespread non-enzymatic protein acetylation in vitro. These data suggest that mitochondrial protein hyperacetylation in FRDA cardiomyopathy mediates progressive post-translational suppression of mitochondrial oxidative pathways which is caused by a combination of SIRT3 deficiency and, likely, an accumulation of unoxidized acetyl-CoA capable of initiating non-enzymatic protein acetylation. These findings provide novel insight into the mechanisms underlying a poorly understood and fatal cardiomyopathy and highlight a fundamental biochemical mechanism that had been previously overlooked in biological systems.

No description available.

Cette étude pilote vise à développer une méthode d'analyse intégrative qui permet d'augmenter le taux de réussite du diagnostic clinique des mutations génétiques rares. De plus, l'identification de nouveaux gènes associés à l'ataxie épisodique (EA) et l'évaluation de nouveaux algorithmes de prédiction, pour un examen de variants plus robuste, découleront de l'enquête. Caractérisé par une perte sporadique de la coordination des mouvements volontaires, l'EA se manifeste généralement tardivement, avec une hétérogénéité clinique et génétique élevée, compliquant largement l’obtention d’un diagnostic précis. Alors que quatre gènes ont été liés aux huit sous-types d'EA, de nombreux patients demeurent sans diagnostic moléculaire dû aux limites des méthodes de séquençage d’ADN. Ces lacunes accentuent l’intérêt d’implanter le séquençage de l’ARN en milieu clinique, afin d’obtenir l’information fonctionnelle offerte par l’approche. Des patients atteints d’EA, sans diagnostic moléculaire malgré un examen approfondi, ont été recrutés à Montréal. Le séquençage du génome entier (WGS) et de l'ARN a été effectué sur des échantillons de sang pour identifier les variants nucléotidiques, l'expression différentielle, les événements d'épissage ainsi que les expansions de microsatellites. Plusieurs algorithmes de prédiction de la pathogénicité récents ont été choisis pour être testés parallèlement aux algorithmes standard. Des données WGS provenant d’un trio familial atteint de pathologies neurologiques ont également été soumises au pipeline génomique développé pour la cohorte EA. Des variants candidats ont été identifiés pour chaque patient en fonction des scores de pathogénicité, de la rareté des événements génétiques et des informations fonctionnelles et cliniques connues pour un gène altéré donné. Parmi les découvertes figurent des mutations non-sens, des faux-sens, de l'épissage alternatif ainsi que des expansions nucléotidiques dans des gènes associés aux ataxies spinocérébelleuses ou aux paraplégies spastiques. En plus d'être présents dans les ensembles de données de séquençage disponibles pour chaque patient, les événements génomiques ont été vérifiés par séquençage Sanger de l'ADN et de l'ARN lorsque possible. Les effets fonctionnels potentiels, prédits principalement à partir du RNA-seq et suggérant une expression anormale de l'ARNm, ont également été évalués par amplification PCR et qPCR traditionnelle. À ce jour, quatre des dix patients ont reçu ou sont en voie de recevoir un diagnostic clinique, et quatre autres présentent d’excellents candidats moléculaires pour expliquer une pathologie ataxique. Ce projet devrait permettre un diagnostic mieux défini, conduisant à une meilleure qualité de vie, une meilleure évaluation du pronostic et une meilleure prise en charge des patients. L’identification de modulateurs génétiques chez certains d’entre eux devrait également permettre une meilleure caractérisation clinique des conditions rapportées, bénéficiant les évaluations symptomatiques futures. De plus, la méta-analyse des données RNA-seq offre le potentiel de découvrir des régulateurs de pathogenèse communs à l’EA. Il favorisera également l'approche intégrative pour un plus large éventail de troubles et pourrait éventuellement conduire à de nouvelles stratégies thérapeutiques. / This pilot study aims to develop an integrative analysis method that allows for an increased diagnosis success rate of rare genetic mutations. Moreover, identification of novel genes associated with Episodic Ataxia (EA) and evaluation of new AI-generated prediction algorithms, for a more robust variant examination, will ensue from the investigation. Characterized by sporadic loss of voluntary movement coordination, EA typically manifest with a late onset as well as high-clinical and genetic heterogeneity, setting additional hurdles to diagnosis. While four genes have been linked to the eight subtypes of EA, many patients are left without molecular diagnosis due to the limitations of individual DNA-sequencing methods, which can be mitigated by the functional overview that RNA sequencing (RNA-seq) offers. EA patients, lacking molecular diagnosis despite in-depth examination, were recruited in Montreal. Whole-Genome sequencing (WGS) and RNA-seq were performed on blood samples to identify single nucleotide variants, differential expression, splicing events, structural variants and repeat expansions. Multiple recent pathogenicity prediction algorithms were chosen for testing concurrently to standard ones, in order to evaluate their performance and potential for clinical pipelines integration. WGS data of a family trio from France, in which the father and the daughter present neurologic pathologies, were also processed through the genomic pipeline that was developed for the EA cohort in order to identify the cause of their disorder. Candidate variants were identified for each patient according to pathogenicity scores, rarity of genetic events, and known functional as well as clinical information for a given altered gene. Among the findings are truncations, missenses, alternative splicing, and repeat expansions in genes already associated to either spinocerebellar ataxia or spastic paraplegia. In addition to being present in both datasets when available, validation of these interesting genomic events has been performed through Sanger Sequencing of both DNA and RNA when feasible. For strong candidates where the available functional information from RNA-seq suggests abnormal mRNA expression, validation includes PCR amplification as well as a traditional qPCR to support effects on transcripts. To this day, four out of ten patients have received or are on the verge of receiving a diagnosis, and four others are carrying excellent molecular candidates requiring further validation to explain their ataxic pathologies. This project should provide more defined diagnosis, leading to better quality of life, better evaluation of prognosis and better management of care for patients. Identification of genetic modifier in some of them should also allow for a better clinical characterization of the reported conditions, benefiting future patient examinations. A meta-analysis of our patients’ transcriptomic profiles could also uncover commonly affected pathways in EA development. It will also promote the integrative approach for a larger spectrum of disorders and might eventually lead to new therapeutic strategies.

Type I interferons (IFNs) as part of the innate immune system have an outstanding importance as antiviral defense cytokines that stimulate innate and adaptive immune responses. Upon sensing of pattern recognition particles (PRPs) such as nucleic acids, IFN secretion is activated and induces the expression of interferon stimulated genes (ISGs). Uncontrolled constitutive activation of the type I IFN system can lead to autoinflammation and autoimmunity, which is observed in autoimmune disorders such as systemic lupus erythematodes and in monogenic interferonopathies. They are caused by mutations in genes which are involved in sensing or metabolism of intracellular nucleic acids and DNA repair. Many authors described mechanisms of type I IFN secretion upon increased DNA damage, including the formation of micronuclei, cytosolic chromatin fragments and destabilization of DNA binding proteins. Hereditary cutaneous DNA damage syndromes, which are caused by mutations in proteins of the DNA repair, share laboratory and clinical features also seen in autoimmune disorders and interferonopathies; hence a potential role of DNA-damage-induced type I IFN secretion seems likely. Here, we aim to summarize possible mechanisms of IFN induction in cutaneous DNA damage syndromes with defects in the DNA double-strand repair and nucleotide excision repair. We review recent publications referring to Ataxia teleangiectasia, Bloom syndrome, Rothmund–Thomson syndrome, Werner syndrome, Huriez syndrome, and Xeroderma pigmentosum. Furthermore, we aim to discuss the role of type I IFN in cancer and these syndromes.

Friedreich's ataxia (FRDA) is the most prevalent inherited ataxia, affecting one in every 50,000 individuals in the United States. This hereditary condition is caused by an abnormal GAA trinucleotide repeat expansion within the first intron of the frataxin gene resulting in decreased levels of the frataxin protein (FXN). Insufficient cellular frataxin levels results in iron accumulation, increased reactive oxygen species production and mitochondrial dysfunction. Tissues most heavily impacted are those most dependent on oxidative phosphorylation as an energy source and include the nervous system and muscle tissue. This is evident in the clinical phenotype which includes muscle weakness, ataxia, neurodegeneration and cardiomyopathy. However, there has been a lack of data regarding the cell type specific contributions in FRDA pathogenesis. We generated a cohort of induced pluripotent stem cells (iPSCs) consisting of FRDA patient lines, CRISPR-Cas9 edited controls, carriers and non-related controls. Our preliminary data identified a hyperinflammatory microglial phenotype with extensive defects in mitochondrial function; since microglia are the primary innate immune cell of the brain, we hypothesized microglia may decrease neuronal viability which contributes to FRDA pathology. To investigate this, the iPSC cohort was utilized to generate microglia (iMGs) and neurons to better understand microglia-mediated neurodegeneration and how this contributes to pathology. An in vitro co-culture model composed of neurons, astrocytes and microglia was employed to better understand microglia-neuronal communication in FRDA. Healthy neurons co-cultured with FRDA iMG or with FRDA iMG-conditioned media demonstrated higher incidences of caspase-3 mediated apoptosis. These findings were recapitulated in vivo as xenotransplantation of FRDA microglia progenitors into a murine model resulted in reduced Purkinje cell survival in the cerebellum. Previous research has demonstrated the therapeutic potential of wildtype microglia to rescue the FRDA phenotype in the Y8GR mouse model of FRDA. To further explore the potential mechanisms behind this rescue, the delivery of mitochondria and FXN to FRDA microglia and neurons was investigated. CRISPR-Cas9 edited microglia demonstrated transfer of healthy mitochondria to FRDA microglia and neurons in an in vitro co-culture model. To investigate the transfer of frataxin protein, an FRDA iPSC line was transduced with an FXN-GFP lentivirus. Restoring FXN expression was demonstrated to rescue the FRDA microglial morphological phenotype. FXN-GFP microglia demonstrated transfer of frataxin protein to FRDA microglia suggesting the potential role of microglia as a therapeutic vehicle in FRDA. Together these findings show that FRDA microglia have a deleterious effect on neuronal viability, while healthy microglia may work as a therapeutic vehicle through the delivery of mitochondria and frataxin to FRDA cells.

Yes / Despite significant preclinical promise as anticancer agents, vascular-disrupting agents have yet to fulfil their clinical potential due to systemic toxicities. ICT2588 is a tumour-selective MT1-MMP-targeted prodrug of azademethylcolchicine, ICT2552. We investigate activation of ICT2588 and subsequent release of ICT2552 in tumour cells, and examine its ability to induce G2/M cell cycle arrest. We also explore synergism between ICT2588 and ATR inhibition, since colchicine, in addition to its vascular-disrupting properties, is known to induce G2/M arrest, DNA damage, and trigger apoptosis. Several ATR inhibitors are currently undergoing clinical evaluation. The cellular activation of ICT2588 was observed to correlate with MT1-MMP expression, with selective release of ICT2552 not compromised by cellular uptake and prodrug activation mechanisms. ICT2588 induced G2/M arrest, and triggered apoptosis in MT1-MMP-expressing cells, but not in cells lacking MT1-MMP expression, while ICT2552 itself induced G2/M arrest and triggered apoptosis in both cell lines. Interestingly, we uncovered that the intracellular release and accumulation dynamics of ICT2552 subsequent to prodrug activation provided synergism with an ATR inhibitor in a way not observed with direct administration of ICT2552. These findings have important potential implications for clinical combinations of ICT2588 and DNA repair inhibitors.

Résumé : Introduction : L’ataxie récessive spastique de Charlevoix-Saguenay (ARSCS) est une maladie héréditaire dégénérative présentant un taux élevé de porteurs (1/22) au Saguenay-Lac-Saint-Jean, mais aussi retrouvée à l’échelle mondiale. Les personnes atteintes présentent des atteintes cérébelleuses (ataxie), neuropathiques (amyotrophie) et pyramidales (spasticité). L’ARSCS présente un portrait différent des autres types d’ataxies et il n’existe pas d’échelle de gravité spécifique pour évaluer la progression de la maladie ou évaluer l’efficacité d’un traitement. Méthodologie : Les objectifs de ce projet sont de développer et documenter les qualités métrologiques des items de la section pyramidale de l’échelle de gravité de l’ARSCS (Disease Severity Index for Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay, DSI-ARSACS). La section pyramidale a été élaborée à l’aide du modèle de développement de Streiner et Norman (2008). La planification et la construction ont été réalisées à l’aide d’une recension systématique des écrits et d’une consultation Delphi. La validité de construit (convergente et discriminatoire) et la fidélité (intraévaluateur et interévaluateurs [n=2]) ont été documentées. Vingt-huit (28) participants âgés de 18 à 59 ans ont été recrutés, selon un échantillonnage stratifié pour l’âge et le sexe. Le diagnostic devait être confirmé génétiquement. La validité convergente a été documentée avec des outils évaluant le contrôle moteur aux membres inférieurs (LEMOCOT), la gravité de la spasticité (SPRS), la mobilité (6MWT, 10mWT, échelle de Berg), le fonctionnement dans les activités quotidiennes (Index de Barthel), la participation sociale (MHAVIE) et la qualité de vie (SF-12v2). La validité discriminatoire a été documentée selon le sexe, le groupe d’âge et le stade de la maladie. La section pyramidale a été administrée à trois reprises par deux physiothérapeutes, à deux semaines d’intervalle, pour évaluer la fidélité intra/interévaluateurs. Résultats : La validité de contenu a été jugée adéquate par les experts du domaine. La validité de construit convergente est soutenue par des corrélations élevées avec les outils mesurant des concepts apparentés (r > 0,7, p = 0,00), à l’exception du SF-12v2 (r = 0,09-0,33). La validité de construit discriminatoire est appuyée par la capacité de distinguer les personnes atteintes en fonction des groupes d’âge et des stades de la maladie. La fidélité intra/interévaluateurs est excellente pour les items individuels (κ[indice inférieur w] = 0,68-0,96/0,60-0,95 sauf pour deux items κ[indice inférieur w] = 0,12 et 0,47) et pour le sous-total pyramidal (CCI = 0,94/0,88, p = 0,000). La cohérence interne (α = 0,85) témoigne de l’homogénéité des items pyramidaux. Conclusion : Le sous-total pyramidal du DSI-ARSACS a démontré une excellente validité de construit convergente et discriminatoire et une bonne fidélité. L’échelle de gravité permettra de mieux documenter l’évolution naturelle de la maladie. / Abstract : Introduction: Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a hereditary and degenerative illness that has a high carrier rate (1/22) in Saguenay-Lac-St-Jean (Quebec, Canada) but that is also found elsewhere around the world. Individuals with ARSACS have cerebellar impairments (ataxia), neuropathic impairments (amyotrophy) and pyramidal impairments (spasticity). ARSACS does not have the same characteristics as other forms of ataxia and there is currently no specific disease severity index (DSI) for it. Method: This project aimed to develop the items of the pyramidal section of the DSI-ARSACS and document their metrological properties. A literature review was conducted to identify ARSACS’ related impairments and existing scales measuring pyramidal impairments. Both items from known scales and new items were used to build a new scale that would assess the pyramidal impairments associated with ARSACS. The scale’s content validation was based on expert opinion. A consensus on the final scale composition was reached. Two physiotherapists administered the newly developed scale to 28 participants with a genetically confirmed ARSACS diagnosis in order to document the reliability of the pyramidal section of the DSI. Existing scales related to pyramidal impairments, mobility, social participation and quality of life were administered to assess convergent construct validity. The contrasting group method (age group, disease stage, gender) was used to assess discriminant validity. Results: Content validity was considered adequate by an expert panel that completed a Delphi process. The pyramidal section’s subscore was distributed normally and did not show a ceiling/floor effect. Convergent construct validity was supported by strong correlations with existing scales measuring related constructs (r > 0.7, p = 0.00), excluding SF-12 v2 (r = 0.09-0.33). Discriminant construct validity was supported by the scale’s ability to distinguish subjects according to age and disease stage. Intra/inter-rater reliability was excellent for individual items (κ[subscript w] = 0.68-0.96/0.60-0.95), except for two items (κ[subscript w] = 0.12 and 0.47), and also excellent for the section’s subscore (CCI = 0.94/0.88, p = 0.000). Internal consistency (α = 0.85) reflected the homogeneity of the pyramidal items. Conclusion: The pyramidal section’s subscore of DSI-ARSACS displayed excellent metrological properties (discriminative and convergent validity, reliability) during this initial validation. The index will lead to a better understanding of ARSACS’ natural history while also allowing for the categorization of subjects participating in future clinical trials.

Résumé : Introduction : L’ataxie récessive spastique de Charlevoix-Saguenay (ARSCS) est une maladie neuromusculaire héréditaire rare qui affecte notamment les voies spinocérébelleuses. Elle est caractérisée par une triple composante de signes et symptômes incluant l’ataxie et la dysarthrie (atteintes cérébelleuses), la spasticité aux membres inférieurs (atteintes pyramidales) et une faiblesse distale qui engendre des difficultés de préhension (atteintes neuropathiques). Des avancées récentes permettent de croire que des essais thérapeutiques seront bientôt possibles. Dans ce contexte, il est nécessaire de développer une échelle de gravité de la maladie pour permettre la sélection des patients et la documentation de l’histoire naturelle. But : L’objectif de ce projet était de développer les items de la section cérébelleuse du Disease Severity Index for Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (DSI-ARSACS) et de documenter ses qualités métrologiques. Méthode : La section cérébelleuse a été élaborée à l’aide du modèle de développement de Streiner et Norman (2008) qui comprend trois grandes étapes : planification, construction et validation. La planification et la construction ont été réalisées à l’aide de consultations d’experts par la méthode Delphi et d’une recension systématique des écrits. La validité de construit (convergente et discriminatoire) et la fidélité (intra-évaluateur et inter-évaluateur) ont été documentées. Vingt-huit participants ont été recrutés selon un échantillonnage stratifié pour l’âge et le sexe. Ils devaient avoir un diagnostic confirmé génétiquement et être âgés entre 18 ans et 59 ans. La validité convergente a été documentée avec des outils évaluant les aptitudes motrices des membres supérieurs (9HPT, PPT, TDNS), la gravité de l’ataxie (SARA), la mobilité (6MWT, 10mWT, échelle de Berg), le fonctionnement dans les activités quotidiennes (Index de Barthel), la participation sociale (MHAVIE) et la qualité de vie (SF-12v2). La validité discriminante a été documentée selon le sexe, le groupe d’âge et le stade de la maladie. La section cérébelleuse a été appliquée à trois reprises par deux physiothérapeutes à deux semaines d’intervalle pour évaluer la fidélité intra et inter-évaluateurs. Résultats : La section cérébelleuse comporte 6 items d’évaluation liés aux fonctions motrices du cervelet. Le sous total de la section cérébelleuse est fortement corrélé avec la majorité des outils d’évaluation (r ≥ 0,69, p = 0,00), à l’exception du SF-12v2 (r ≤ 0,36, p ≥ 0,06). Une différence significative (p < 0,00) a été démontrée entre chaque groupe d’âge pour la majorité des items et le sous-total de la section cérébelleuse de l’échelle. Le résultat de chaque item et le sous-total de la section cérébelleuse augmentent significativement avec le stade de la maladie (p < 0,00). La fidélité intra et inter-évaluateurs correspond à un accord fort (κ ≥ 0,69) pour la majorité des items et le sous-total. Conclusion : Ce projet a permis de développer la section cérébelleuse de l’échelle de gravité DSI-ARSACS avec de bonnes qualités psychométriques (validité et fidélité). L’échelle pourra être utilisée dans le processus de catégorisation et d’évaluation des participants pour de futurs essais thérapeutiques. / Abstract : Introduction: Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) is a rare hereditary neuromuscular disease that mainly affects the spinocerebellar tract. It is characterized by a triad of signs and symptoms, including ataxia and dysarthria (cerebellum impairment), spasticity in the lower limbs (pyramidal impairment) and a distal weakness leading to prehension difficulties (neuropathic impairment). Recent research advances suggest that clinical trials may soon become possible. In this context, it is necessary to develop a disease severity index in order to select patients and document natural history of disease. Objective: The project aimed to develop the items of the cerebellar section of the Disease Severity Index for Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay DSI-ARSACS and document their metrological properties. Method: The cerebellar section was developed using the Streiner and Norman (2008) model, which involves three stages: planning, construction and validation. The planning and construction stages were conducted by carrying out a literature review, obtaining expert opinions and completing a Delphi process. Construct validity (convergent and discriminant) and reliability (intra- and inter-raters) were documented. Twenty-eight participants between the ages of 18 and 59 were recruited using a stratified sampling method based on age and gender. All of them had a genetically confirmed diagnosis of ARSACS. Convergent validity was documented with measurements of upper limbs motor abilities (9HPT, PPT, TDNS), ataxia severity (SARA), mobility (6MWT, 10mWT, Berg scale), functional status in activities of daily living (Barthel index), social participation (MHAVIE) and quality of life (SF-12v2). Discriminant validity was documented according to gender, age group and disease stage. The cerebellar section was administered three times, two weeks apart, by two physiotherapists to assess intra- and inter-rater reliability. Results: The cerebellar section includes 6 assessment items linked to cerebellum motor functions. The cerebellar section subscore was strongly correlated with the majority of assessment tools (r ≥ 0.69, p = 0.00), excluding SF 12v2 (r ≤ 0,36, p ≥ 0,06). A significant difference (p < 0.00) was observed between each age group for most items and the subscore of the cerebellar section. Results on each item and the subscore significantly increase with disease stage (p < 0.00). Intra- and inter-rater reliability reflects a strong level of agreement (κ ≥ 0.69) on the majority of items and the subscore. Conclusion: The cerebellar section of the DSI-ARSACS shows good psychometric properties (validity and reliability). The index can be used to categorize and assess future participants in clinical trials.

Malignant cutaneous melanoma is the deadliest form of skin cancer, and a majority of melanoma diagnoses are a result of exposure to ultraviolet (UV) radiation. UV radiation causes DNA damage, which if not repaired correctly via nucleotide excision repair (NER) can result in mutations and melanomagenesis. The melanocortin 1 receptor (MC1R) is a Gs protein coupled receptor located on melanocyte plasma membranes and is involved in protecting the skin from UV induced damage. MC1R signaling results in the activation of two protective pathways: 1) induction of eumelanin synthesis downstream of micropthalmia-associated transcription factor (MITF) and 2) acceleration of NER downstream of ataxia telangiectaseia mutated and Rad3 related (ATR). MC1R signaling, however, also promotes melanocyte proliferation, therefore, the activation of the MC1R pathway must be regulated. The overall hypothesis of this dissertation is that the pathways downstream of MC1R can be manipulated to protect against UV induced damage. Chapter 2 investigates the regulation of the MC1R neutral antagonist human β-defensin 3 (βD3). UV damage did not induce βD3 mRNA expression in ex vivo human skin explants. The induction of βD3 expression instead correlated with inflammatory cytokines including TNF. Chapter 3 investigates the interdependence and cross talk between the two protective pathways downstream of MC1R. We directly tested the effect of MITF on the acceleration of NER and the effect of ATR on the induction of eumelanin synthesis following MC1R activation. MITF was not required for the acceleration of NER as mediated by ATR, however, the induction of transcription of enzymes involved in eumelanin synthesis was dependent upon ATR kinase activity. Finally, Chapter 4 investigates the mechanism by which MC1R promoted proliferation and whether the two UV protective pathways downstream of MC1R could be selectively activated without the risk of melanocyte proliferation. MC1R signaling resulted in activation of the mechanistic target of rapamycin complex 1 (mTORC1), a major regulator of cell growth and proliferation. Inhibition of mTORC1 signaling via rapamycin prevented MC1R induced proliferation in vitro. Rapamycin, however, did not prevent MC1R induced eumelanin synthesis or the acceleration of NER in vitro or in vivo suggesting it is possible to selectively activate the beneficial signaling pathways without the risk of melanocyte proliferation. The results of this dissertation suggest that MC1R signaling could be augmented in individuals to prevent UV induced damage.