Biology subjects

Brown, C. R.

Publications and source records attributed to Brown, C. R..

At least 19 recordsLinked to original sources

bioRxiv2025

The evolution lifecycle of ribosome hibernation factors

Bacteria defend against hostile environments through a variety of molecular mechanisms, including ribosome hibernation. Previously, bacteria were shown to initiate ribosome hibernation by activating protective proteins known as hibernation factors. It was demonstrated that hibernation factors prevent ribosome degradation by nucleases, which allows bacteria to safely store their inactive ribosomes and survive under starvation or persistent stress. Because homologs of hibernation factors were found in diverse lineages of bacteria, it is currently assumed that the mechanism of ribosome hibernation is highly conserved across species. Here, we assess 46,015 complete bacterial genomes to reveal the principles underlying the origin and evolution of these essential proteins in bacterial cells. We find that hibernation factors emerged in ancient bacteria as relatively large proteins that then gradually reduced in size and have undergone complete extinction in over 10% of studied bacteria. We then demonstrate that the degeneration of ancient hibernation factors is often accompanied by "borrowing" hibernation factors from other species via gene transfers, de novo gene birth or fusion of truncated hibernation factors with fragments from other stress-response proteins. These findings reveal a unique evolutionary pathway in which bacteria respond to the reductive evolution of hibernation machinery by inventing novel hibernation mechanisms, thus restoring their capacity to survive starvation and stress. This model implies that most ribosome hibernation factors are yet to be discovered and predicts the organisms that rely on currently unknown hibernation mechanisms.

microbiology↗

bioRxiv2025

Transient Suppression of Dopamine Transporter Palmitoylation by Methamphetamine: Implications for Transport Regulation

The dopamine transporter (DAT) exerts temporal and spatial control over dopaminergic neurotransmission through reuptake of extracellular dopamine (DA). The functional capacity of DAT is under the control of signaling inputs and post-translational modifications that confer acute presynaptic regulation of reuptake in response to physiological needs, and dysregulation of these processes may contribute to DA imbalances in mood disorders and drug addiction. A key modification of DAT is palmitoylation, a lipid adduction that enhances transport velocity, is suppressed by protein kinase C, and opposes protein kinase C-mediated down-regulation. Here we now show in rat striatum and heterologous cells that transporter palmitoylation is also linked to methamphetamine (METH), undergoing rapid and transient reductions in response to the drug. The time course and other characteristics of palmitoylation reduction parallel those of METH-induced transport down-regulation, and a palmitoylation-deficient DAT mutant shows enhanced down-regulation to METH, supporting a mechanistic link between reduction of the modification and reduced reuptake activity. Recovery rates differed, however, with palmitoylation returning to starting levels more rapidly than reuptake, indicating that down-regulation mechanisms remain engaged with transporters that have undergone repalmitoylation. These results support palmitoylation as a rapid response mechanism that modulates DAT entry into METH-induced down-regulation states and suggest a broader role for the modification in control of reuptake in additional physiological and pathophysiological conditions.

neuroscience↗

bioRxiv2025

Modulation of autism-associated serotonin transporters by palmitoylation: Insights into the molecular pathogenesis and targeted therapies for autism spectrum disorder

BackgroundAutism spectrum disorder (ASD) is a developmental disorder of the nervous system characterized by a deficiency in interpersonal communication skills, a pathologic tendency for repetitive behaviors, and highly restrictive interests. The spectrum is a gradient-based construct used to categorize the widely varying degrees of ASD phenotypes, and has been linked to a genetic etiology in 25% of cases. Prior studies have revealed that 30% of ASD patients exhibit hyperserotonemia, or elevated whole blood serotonin, implicating the serotonergic system in the pathogenesis of ASD. Likewise, escitalopram, a selective-serotonin reuptake inhibitor (SSRI), has been demonstrated to improve aberrant behavior and irritability in ASD patients, potentially by modulating abnormal brain activation. Prior studies have uncovered proband patients with rare mutations in the human serotonin transporter (hSERT) that manifest enhanced surface expression and transport capacity, suggesting that abnormal enhancement of hSERT function may be involved in the pathogenesis of ASD. MethodsHEK-293 cells stably expressing WT, C109A, I425L, F465L, L550V, or K605N hSERT were subject to analysis for palmitoylation via Acyl-Biotin Exchange followed with hSERT immunoblotting. F465L functional enhancement was confirmed by surface analysis via biotinylation and saturation analysis via 5HT transport. F465L palmitoylation, surface expression and transport capacity were then assessed following treatment with 2-bromopalmitate or escitalopram. ResultsHere, we reveal that palmitoylation is enhanced in the ASD hSERT F465L and L550V coding variants, and confirm prior reports of enhanced kinetic activity and surface expression of F465L. Subsequently, treatment of F465L with the irreversible palmitoyl acyl-transferase inhibitor, 2-bromopalmitate (2BP), or escitalopram, rectified enhanced F465L palmitoylation, surface expression, and transport capacity to basal WT levels. LimitationsTests assessing L550V for surface expression, transport capacity, and reactivity to inhibition of palmitoylation was not assessed. In addition, further characterization is necessary for internalization rates, degradative mechanisms, the impact of cysteine-mediated substitutions, and other SSRIs on these processes. ConclusionsOverall, our results implicate disordered hSERT palmitoylation in the pathogenesis of serotonergic ASD subtypes, with basal recovery of these processes following escitalopram providing insight into its molecular utility as an ASD therapeutic.

neuroscience↗

bioRxiv2024

Natural variation of the drug-binding residues in eukaryotic ribosomes

Drugs that target eukaryotic ribosomes are becoming increasingly important as research tools and potential therapies against cancer and pathogenic eukaryotes. However, in the absence of comparative studies, we currently do not know how many eukaryotes possess ribosomal drug-binding sites identical to those in humans, and how many significantly differ from humans. To address this, we traced the evolutionary history of individual ribosomal drug-binding residues from the emergence of eukaryotes to the present day. We found that ribosomal drug-binding sites are divergent across eukaryotic clades, with some of the clades exhibiting more substitutions in their ribosomal drug-binding sites compared to humans than humans do compared to bacteria. Overall, our work provides a resource for understanding the evolutionary divergence of drug-binding sites in eukaryotic ribosomes, which may inform the use of ribosome inhibitors as research tools and lineage-specific drugs against eukaryotic parasites.

microbiology↗

bioRxiv2024

Evolutionary divergence of drug-binding sites in bacterial ribosomes

Ribosomes from certain bacteria possess divergent drug-binding sites compared to those of Escherichia coli, leading to natural evasion or hypersensitivity to antibiotics. However, in the absence of systematic studies, it is unknown whether this observed divergence is a rare exception or a common occurrence among bacterial species. Here, we address this question by reconstructing the evolutionary history of drug-binding residues of the ribosome from the origin of bacteria to the present day. This analysis reveals the extent of natural diversity of ribosomal drug-binding sites between bacterial species, which may inform the development of species-specific antimicrobials and a more accurate and personalized choice of ribosome-targeting drugs for a given pathogen.

microbiology↗

bioRxiv2024

Identification of In Vivo Internalizing Cardiac-Specific RNA Aptamers

BackgroundThe pursuit of selective therapeutic delivery to target tissue types represents a key goal in the treatment of a range of adverse health issues, including diseases afflicting the heart. The development of new cardiac-specific ligands is a crucial step towards effectively targeting therapeutics to the heart. MethodsUtilizing an ex vivo and in vivo SELEX approaches, we enriched a library of 2-fluoro modified aptamers for ventricular cardiomyocyte specificity. Lead candidates were identified from this library, and their binding and internalization into cardiomyocytes was evaluated in both ex vivo and in vivo mouse studies. ResultsThe ex vivo and in vivo SELEX processes generated an aptamer library with significant cardiac specificity over non-cardiac tissues such as liver and skeletal muscle. Our lead candidate aptamer from this library, CA1, demonstrates selective in vivo targeting and delivery of a fluorophore cargo to ventricular cardiomyocytes within the murine heart, while minimizing off-target localization to non-cardiac tissues, including the liver. By employing a novel RNase-based assay to evaluate aptamer interactions with cardiomyocytes, we discovered that CA1 predominantly internalizes into ventricular cardiomyocytes; conversely, another candidate CA41 primarily binds to the cardiomyocyte cell surface. ConclusionsThese findings suggest that CA1 and CA41 have the potential to be promising candidates for targeted drug delivery and imaging applications in cardiac diseases.

bioengineering↗

bioRxiv2024

Palmitoylation regulates norepinephrine transporter trafficking and expression and is potentially involved in the pathogenesis of postural orthostatic tachycardia syndrome

Postural orthostatic tachycardia syndrome (POTS) is an adrenergic signaling disorder characterized by excessive plasma norepinephrine, postural tachycardia, and syncope. The norepinephrine transporter (NET) modulates adrenergic homeostasis via reuptake of extracellular catecholamines and is implicated in the pathogenesis of adrenergic and neurological disorders. Previous research has outlined that NET activity and trafficking is modulated via reversible post-translational modifications like phosphorylation and ubiquitylation. S-palmitoylation, or the addition of a 16-carbon saturated fatty acid, is another post-translational modification responsible for numerous biological mechanisms. In this study, we reveal that NET is dynamically palmitoylated and inhibition of this modification with the palmitoyl acyltransferase (DHHC) inhibitor, 2-bromopalmitate (2BP), results in decreased NET palmitoylation within 90 min of treatment. This result was followed closely with a reduction in transport capacity, cell surface, and total cellular NET expression after 120 min of treatment. Increasing 2BP concentrations and treatment time revealed a nearly complete loss of total NET protein. Co-expression with individual DHHCs revealed a single DHHC enzyme, DHHC1, promoted WT hNET palmitoylation and elevated NET protein levels. The POTS associated NET mutant, A457P, exhibits dramatically decreased transport capacity and cell surface levels which we have confirmed in the current study. In an attempt to recover A457P NET expression we co-expressed the A457P variant with DHHC1 to drive expression as seen with the WT protein but instead saw an increase in NET N-terminal immuno-detectable fragments. Further investigation of A457P NET palmitoylation and surface expression is necessary, but our preliminary novel findings reveal palmitoylation as a mechanism of NET regulation and suggest that dysregulation of this process may contribute to the pathogenesis of POTS.

neuroscience↗

bioRxiv2023

Palmitoylation regulates human serotonin transporter activity, trafficking, and expression and is modulated by escitalopram

In the central nervous system, serotonergic signaling modulates sleep, mood, and cognitive control. During neuronal transmission, the synaptic concentration of serotonin is tightly controlled in a spatial and temporal manner by the serotonin transporter (SERT). Dysregulation of serotonergic signaling is implicated in the pathogenesis of major-depressive, obsessive-compulsive, and autism-spectrum disorders, which makes SERT a primary target for prescription therapeutics, most notably selective-serotonin reuptake inhibitors (SSRIs). S-palmitoylation is an increasingly recognized dynamic post-translational modification, regulating protein kinetics, trafficking, and localization patterns upon physiologic/cellular stimuli. In this study, we reveal that human SERTs are a target for palmitoylation, and using the irreversible palmitoyl acyl-transferase inhibitor, 2-bromopalmitate (2BP) we have identified several associated functions. Using a lower dose of 2BP in shorter time frames, inhibition of palmitoylation was associated with reductions in SERT Vmax, without changes in Km or surface expression. With higher doses of 2BP for longer time intervals, inhibition of palmitoylation was consistent with the loss of cell surface and total SERT protein, suggesting palmitoylation is an important mechanism in regulating SERT trafficking and maintenance of SERT protein through biogenic or anti-degradative processes. Additionally, we have identified that treatment with the SSRI escitalopram decreases SERT palmitoylation analogous to 2BP, reducing SERT surface expression and transport capacity. Ultimately, these results reveal palmitoylation is a major regulatory mechanism for SERT kinetics and trafficking and may be the mechanism responsible for escitalopram-induced internalization and loss of total SERT protein.

neuroscience↗

bioRxiv2023

Environmental context, parameter sensitivity and structural sensitivity impact predictions of annual-plant coexistence

Predicting the outcome of interactions between species is central to our current understanding of diversity maintenance. However, we have limited information about the robustness of many model-based predictions of species coexistence. This limitation is partly because several sources of uncertainty are often ignored when making predictions. Here, we introduce a framework to simultaneously explore how different mathematical models, different environmental contexts, and parameter uncertainty impact the probability of predicting species coexistence. Using a set of pairwise competition experiments on annual plants, we provide direct evidence that subtle differences between models lead to contrasting predictions of both coexistence and competitive exclusion. We also show that the effects of environmental context-dependency and parameter uncertainty on predictions of species coexistence are not independent of the model used to describe population dynamics. Our work suggests that predictions of species coexistence and extrapolations thereof may be particularly vulnerable to these underappreciated founts of uncertainty.

ecology↗

bioRxiv2022

Structure of dormant bacterial ribosomes reveals an elusive translation factor with evolutionary connections to eukaryotic protein synthesis factors

During starvation and stress, virtually all organisms arrest protein synthesis to conserve energy. Inactive ribosomes are converted into a dormant state, in which they are protected from damage by hibernation factor proteins. In bacteria, two major families of hibernation factors have been described, but the low conservation of these proteins and the huge diversity of species, habitats, and environmental stressors has confounded their discovery. In this study, using proteomics and cryo-EM, we identify a new dormancy factor from the psychrophilic bacterium Psychrobacter urativorans. By isolating ribosomes under cold-shock conditions, we observe a previously unknown protein bound to the ribosomal A site, protecting critical elements of both the decoding and peptidyl transferase centers. We show that this new factor, which we term Balon, is a homolog of the archaeo-eukaryotic translation factor aeRF1, providing a long-predicted evolutionary "missing link" between the eukaryotic and bacterial translation machinery. Our structures reveal that Balon is delivered to both vacant and actively translating ribosomes by EF-Tu, highlighting an unexpected and previously unknown role for this elongation factor in the bacterial stress response. We describe several unique structural motifs that allow Balon to bind ribosomes in an mRNA-independent manner, initiating a new mode of ribosome dormancy that can commence while ribosomes are still engaged in protein synthesis. Our bioinformatic analysis shows that putative Balon-encoding genes can be found within stress-response operons in nearly 20 % of all known bacterial species, including many human pathogens. Taken together, our work suggests that Balon/EF-Tu regulated ribosome dormancy is likely to be a ubiquitous stress-response mechanism throughout the bacterial kingdom. These findings call for a revision of our model of bacterial translation inferred from common model organisms and hold numerous implications for how we understand and study ribosome dormancy.

molecular biology↗

bioRxiv2022

RNAi-mediated rheostat for dynamic control of AAV-delivered transgenes

Adeno-associated virus (AAV)-based gene therapy could be facilitated by the development of molecular switches to control the magnitude and timing of expression of therapeutic transgenes. RNA interference (RNAi)-based approaches hold unique potential as a clinically proven modality to pharmacologically regulate AAV gene dosage in a sequence-specific manner. We present a generalizable RNAi-based rheostat wherein AAV transgene expression is silenced using the clinically validated modality of chemically modified short interfering RNA (siRNA) conjugates or vectorized co-expression of short hairpin RNA (shRNA). For transgene induction, we employ REVERSIR technology, a synthetic high-affinity oligonucleotide complementary to the siRNA or shRNA guide strand to reverse RNAi activity and rapidly recover transgene expression. For potential clinical development, we report potent and specific siRNA sequences that may allow selective regulation of transgenes while minimizing unintended off-target effects. Our results establish a conceptual framework for RNAi-based regulatory switches with potential for infrequent dosing in clinical settings to dynamically modulate expression of virally-delivered gene therapies.

genomics↗

bioRxiv2022

Ribosomal protein with conserved function has entirely different structures in different organisms

Ribosomes from different species can markedly differ in their composition by including dozens of ribosomal proteins that are unique to specific lineages but absent in others. However, it remains unknown how ribosomes acquire and specialize new proteins throughout evolution. Here, to help answer this question, we describe the evolution of the ribosomal protein msL1/msL2 that was recently found in ribosomes from the parasitic microorganism clade, microsporidia. We first show that this protein has a conserved location in the ribosome but entirely dissimilar structures in different organisms: in each of the analyzed species, msL1/msL2 exhibits an altered secondary structure, an inverted orientation of the N- and C-termini on the ribosomal binding surface, and a completely transformed three-dimensional fold. We then show that this evolutionary fold switching is likely caused by changes in the msL1/msL2-binding site in the ribosome; specifically, by variations in microsporidian rRNA. These observations allow us to infer an evolutionary scenario in which a small, positively-charged, de novo-born unfolded protein was first captured by rRNA to become part of the ribosome and subsequently underwent complete fold switching to optimize its binding to its evolving ribosomal binding site. Overall, our work provides a striking example of how a protein can switch its fold in the context of a complex biological assembly while retaining its specificity for its molecular partner. This finding will help us better understand the origin and evolution of new protein components of complex molecular assemblies - thereby enhancing our ability to engineer biological molecules, identify protein homologs, and peer into the history of life on Earth.

evolutionary biology↗

bioRxiv2022

Ribosomes as molecular thermometers: metal-binding sites in ribosomal proteins are robust indicators of bacterial adaptation to heat and cold

AO_SCPLOWBSTRACTC_SCPLOWRibosomal genes are widely used as "molecular clocks" to infer the evolutionary relatedness of species. It is unclear, however, whether these genes can also serve as "molecular thermometers" to precisely estimate an organisms optimal growth temperature. Previously, some estimations were made using the average nucleotide content in ribosomal RNA, but the universal application of this approach was prevented by numerous outliers. Here, seeking to bypass this problem, we asked whether ribosomal genes contain additional markers of thermal adaptations, aside from their nucleotide composition. To answer this, we analyzed site-specific variations in sequences of ribosomal proteins from 2,021 bacteria with known optimal growth conditions. We found that ribosomal proteins comprise a few "mutational hotspots"--residues that vary in a temperature-dependent manner and distinguish heat- and cold-adapted bacteria. Most of these residues coordinate metal ions that support protein folding at high temperatures. Using these residues, we then showed that the upper and lower limits of an organisms optimal growth temperatures can be estimated using just 0.001% of the genome sequence or just two amino residues in the cellular proteome. This finding illustrates that laboratory-independent estimation of optimal growth temperatures can be simplified if we abandon the traditional use of rRNA and protein sequences to assess their content and instead focus on those few residues that are most critical for protein structure. This finding may simplify the analysis of unculturable and extinct species by helping bypass the need for laborious, costly, and at times impossible laboratory experiments.

evolutionary biology↗

bioRxiv2022

A Telltale Sign of Irreversibility in Transcriptional Regulation

Transcription occurs in stochastic bursts, i.e., transcription events are temporally clustered. The clustering does not ensue from environmental fluctuations but springs from the intrinsically stochastic behavior of the regulatory process that controls transcription. Based on microscopic observations of transcription at a single gene copy of yeast, we show that the regulatory process is cyclic and irreversible, i.e., the process violates the detailed balance conditions for thermodynamic equilibrium. The theoretical significance of this finding is discussed.

molecular biology↗

bioRxiv2022

Robust and durable prophylactic protection conferred by RNA interference in preclinical models of SARS-CoV-2

RNA interference is a natural antiviral mechanism that could be harnessed to combat SARS-CoV-2 infection by targeting and destroying the viral genome. We screened lipophilic small-interfering RNA (siRNA) conjugates targeting highly conserved regions of the SARS-CoV-2 genome and identified leads targeting outside of the spike-encoding region capable of achieving [≥]3-log viral reduction. Serial passaging studies demonstrated that a two-siRNA combination prevented development of resistance compared to a single-siRNA approach. A two-siRNA combination delivered intranasally protected Syrian hamsters from weight loss and lung pathology by viral infection upon prophylactic administration but not following onset of infection. Together, the data support potential utility of RNAi as a prophylactic approach to limit SARS-CoV-2 infection that may help combat emergent variants, complement existing interventions, or protect populations where vaccines are less effective. Most importantly, this strategy has implications for developing medicines that may be valuable in protecting against future coronavirus pandemics.

pharmacology and toxicology↗

bioRxiv2021

Genome sequences hot and cold: a database of organisms with defined optimal growth temperatures

Currently, we are witnessing an explosive accumulation of genomic sequences for organisms across all branches of life. However, typically the genomic data lack the information about optimal growth conditions of corresponding organisms. As a result, it becomes challenging to use the genomic data for studying the adaptations of organisms and biological molecules to diverse environments. To address this problem, we have created a database Gosha, available at http://melnikovlab.com/gshc. This database brings together information about the genomic sequences and optimal growth temperatures for 25,324 species, including [~]89% of the bacterial species with known genome sequences. Using this database, one can annotate genomic sequences from thousands of species and correlate variations in genes and genomes with optimal growth temperatures. The database interface allows users to retrieve optimal growth temperatures for bacteria, eukaryotes and archaea, providing a tool to explore how organisms, genomes, and individual proteins and nucleic acids adapt to certain temperatures. We hope that this database will contribute to medicine and biotechnology by helping to create a better understanding of molecular adaptations to heat and cold, leading to new ways to preserve biological samples, engineer useful enzymes, and develop biological materials and organisms with the desired tolerance to heat and cold. GRAPHICAL ABSTRACTGosha (available at www.melnikovlab.com/gshc) is a database that collects information about the optimal growth temperatures of living species. This database aims to facilitate studies of molecular adaptation to specific temperatures. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/473645v2_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@17b949dorg.highwire.dtl.DTLVardef@5a0271org.highwire.dtl.DTLVardef@1566cccorg.highwire.dtl.DTLVardef@100e590_HPS_FORMAT_FIGEXP M_FIG C_FIG

evolutionary biology↗

bioRxiv2021

'Lose-to-gain' adaptation to genome decayin the structure of the smallest eukaryotic ribosomes

AO_SCPLOWBSTRACTC_SCPLOWThe evolution of microbial parasites involves the interplay of two opposing forces. On the one hand, the pressure to survive drives parasites to improve through Darwinian natural selection. On the other, frequent genetic drifts result in genome decay, an evolutionary process in which an ever-increasing burden of deleterious mutations leads to gene loss and gradual genome reduction. Here, seeking to understand how this interplay occurs at the scale of individual macromolecules, we describe cryo-EM and evolutionary analyses of ribosomes from Encephalitozoon cuniculi, a eukaryote with one of the most reduced genomes in nature. We show that E. cuniculi ribosomes, the smallest eukaryotic cytoplasmic ribosomes to be structurally characterized, employ unparalleled structural innovations that allow extreme rRNA reduction without loss of ribosome integrity. These innovations include the evolution of previously unknown rRNA features such as molten rRNA linkers and bulgeless rRNA. Furthermore, we show that E. cuniculi ribosomes withstand the loss of rRNA and protein segments by evolving a unique ability to effectively trap small molecules and use them as ribosomal building-blocks and structural mimics of degenerated rRNA and protein segments. Overall, our work reveals a recurrent evolutionary pattern, which we term "lose-to-gain" evolution, where it is only through the loss of rRNA and protein segments that E. cuniculi ribosomes evolve their major innovations. Our study shows that the molecular structures of intracellular parasites long viewed as reduced, degenerated, and suffering from various debilitating mutations instead possess an array of systematically overlooked and extraordinary structural features. These features allow them to not only adapt to molecular reduction but evolve new activities that parasites can possibly use to their advantage.

evolutionary biology↗

bioRxiv2020

Inhibition and down regulation of the serotonin transporter contribute to the progression of degenerative mitral regurgitation

AimsHeart valve disease attributed to serotonin (5HT) has been observed with 5HT-secreting carcinoid tumors and in association with medications, such as the diet drug, Dexfenfluoramine, a serotonin transporter (SLC6A4) inhibitor and 5HT receptor (HTR) 2B agonist. HTR2B signaling upregulates TGF{beta}-1 resulting in increased production of extracellular matrix proteins. SLC6A4 internalizes 5HT, limiting HTR signaling. Selective 5HT reuptake inhibitors (SSRI), widely used antidepressants, target SLC6A4, thus enhancing HTR signaling. However, 5HT and SLC6A4 mechanisms have not been previously associated with degenerative mitral regurgitation (MR). The present studies investigated the hypothesis that both dysregulation of SLC6A4 and inhibition of SLC6A4 contribute to the pathophysiology of MR. Methods and ResultsHere we report SLC6A4 related studies of 225 patients with MR requiring surgery. A multivariate analysis showed that SSRI use in MR patients was associated with surgery at a younger age, indicating more rapidly progressive MR (p=0.0183); this was confirmed in a national dataset (p<0.001). Aspirin use by MR patients was associated with surgery at an older age (p=0.0055). Quantitative reverse transcriptase PCR of MR leaflet RNA from 44 patients, and 20 normal mitral leaflets from heart transplant recipients, demonstrated down regulation in MR of both SLC6A4 and vesicular monoamine transporter-2 (SLC18A2), that packages 5HT (p<0.001). Human mitral valve interstitial cells cultivated with Fluoxetine, a SSRI, demonstrated down regulation of SLC6A4 and upregulation of HTR2B, compared to untreated, in cells from both normal and MR leaflets. Platelet 5HT studies in healthy subjects without heart disease used ADP-induced activation to model MR-associated activation. Fluoxetine significantly increased platelet activation and plasma 5HT levels, while Aspirin inhibited ADP platelet activation. ConclusionsDown regulation and inhibition of SLC6A4 influences MR through enhanced HTR signaling. SSRI may further influence MR through inhibition and down regulation of SLC6A4, upregulation of HTR2B, and increased platelet release of 5HT. Translational PerspectiveDegenerative mitral valve regurgitation (MR) affects millions, and there is no medical therapy for this disease. MR becomes progressively worse, and for severe MR, the only option is cardiac surgery. Serotonin (5HT) is best known as a neurotransmitter. However, 5HT secreting carcinoid tumors cause a cardiac valve disorder in many cases, and 5HT related medications, such as the diet drug Fenfluoramine, have been associated with the development of cardiac valve disease. The present paper presents evidence that diminished serotonin transporter (SLC6A4) expression and inhibition, lead to increased 5HT receptor signaling, contributing to the progression of MR.

physiology↗