TAAR1 levels and sub-cellular distribution are cell line but not breast cancer subtype specific

The Expression of Trace Amine-Associated Receptors (TAARs) in Breast Cancer Is Coincident with the Expression of Neuroactive Ligand-Receptor Systems and Depends on Tumor Intrinsic Subtype

Currently, the contribution of trace amine-associated receptors (TAARs) to breast cancer (BC) is recognized, but their associations with various pathological characteristics are not yet understood. There is accumulated transcriptomic data for BC tumors, which are represented in publicly accessible databases. We estimated TAARs' (including TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) associations with BC stage, grade, and molecular subtypes in these data and identified that the expression of all TAARs was associated with more unfavorable cancer subtypes, including basal-like and HER2-positive tumors. Also, the significant upregulation of all TAARs was demonstrated in circulating tumor cells compared to the metastatic lesions. Considering that co-expressed genes are more likely to be involved in the same biologic processes, we analyzed genes that are co-expressed with TAARs in BC. These gene sets were enriched with the genes of the olfactory transduction pathway and neuroactive ligand-receptor interaction participants. TAARs are co-expressed with G-protein-coupled receptors of monoamine neurotransmitters including dopamine, norepinephrine, and serotonin as well as with other neuroactive ligand-specific receptors. Since TAAR1 is able to modulate the activity of monoamine receptors that are involved in the regulation of BC growth, TAAR1 and potentially other TAARs may be regarded as prospective therapeutic targets for breast cancer.

The breast cancer microenvironment and lipoprotein lipase: Another negative notch for a beneficial enzyme?

The energy demand of breast cancers is in part met through the β-oxidation of exogenous fatty acids. Fatty acids may also be used to aid in cell signaling and toward the construction of new membranes for rapidly proliferating tumor cells. A significant quantity of fatty acids comes from the hydrolysis of lipoprotein triacylglycerols and phospholipids by lipoprotein lipase (LPL). The lipid obtained via LPL in the breast tumor microenvironment may thus promote breast tumor growth and development. In this hypothesis article, we introduce LPL, provide a meta-analysis of RNAseq data showing that LPL is associated with poor prognosis, and explain how LPL might play a role in breast cancer prognosis over time.

Gut Microbiota Alterations in Trace Amine-Associated Receptor 9 (TAAR9) Knockout Rats

Trace amine-associated receptors (TAAR1-TAAR9) are a family of G-protein-coupled monoaminergic receptors which might have great pharmacological potential. It has now been well established that TAAR1 plays an important role in the central nervous system. Interestingly, deletion of TAAR9 in rats leads to alterations in the periphery. Previously, we found that knockout of TAAR9 in rats (TAAR9-KO rats) decreased low-density lipoprotein cholesterol levels in the blood. TAAR9 was also identified in intestinal tissues, and it is known that it responds to polyamines. To elucidate the role of TAAR9 in the intestinal epithelium, we analyzed TAAR9-co-expressed gene clusters in public data for cecum samples. As identified by gene ontology enrichment analysis, in the intestine, TAAR9 is co-expressed with genes involved in intestinal mucosa homeostasis and function, including cell organization, differentiation, and death. Additionally, TAAR9 was co-expressed with genes implicated in dopamine signaling, which may suggest a role for this receptor in the regulation of peripheral dopaminergic transmission. To further investigate how TAAR9 might be involved in colonic mucosal homeostasis, we analyzed the fecal microbiome composition in TAAR9-KO rats and their wild-type littermates. We identified a significant difference in the number of observed taxa between the microbiome of TAAR9-KO and wild-type rats. In TAAR9-KO rats, the gut microbial community became more variable compared with the wild-type rats. Furthermore, it was found that the family Saccharimonadaceae, which is one of the top 10 most abundant families in TAAR9-KO rat feces, is almost completely absent in wild-type animal fecal samples. Taken together, these data indicate a role of TAAR9 in intestinal function.

Modelling of p-tyramine transport across human intestinal epithelial cells predicts the presence of additional transporters

p-Tyramine (TYR) is an endogenous trace amine, which can also be synthesized by intestinal microbiota, and is present in commonly consumed diets. TYR is an agonist for the intracellular trace amine-associated receptor 1, which has been implicated in psychiatric, metabolic, and immune-related disorders. We have previously demonstrated TYR readily diffuses across lipid bilayers, while transport across Caco-2 cell membranes involves Organic Cation Transporter 2 (OCT2) and a Na⁺-dependent active transporter. Here we developed mathematical models to determine whether known kinetics for these processes are sufficient to explain observed transcellular TYR passage. Ordinary differential equations were developed for known TYR transport processes to predict concentration-time relationships. Michaelis-Menten kinetics were assumed for all transporter-mediated processes and a one phase exponential function used for simple diffusion. Modelled concentration-time plots were compared to published experimental results. Additional transporter functions were sequentially added to models to improve consistency, and a least squares error minimization approach utilized to determine added transporter kinetics. Finally, possible TYR compartmentalization was also modelled. Following apical loading, transport across the apical, but not the basolateral, membrane was modelled without additional transporters, suggesting a basolateral transporter was missing. Consistent with this, models of basolateral compartment loading did not match experimental observations, indicating missing basolateral transporters were bidirectional. Addition of a transporter with the kinetic characteristics of OCT2 did not improve models. Varying the kinetic parameters of the added transporter improved models of basolateral, but worsened apical, loading models, suggesting the need for either a directional preference in transporters, or intracellular TYR compartmentalization. Experimental parameters were recapitulated by introducing asymmetry into the apical OCT2 (K_{t_OCT2_apicaltocell} = 110.4 nM, K_{t_OCT2_celltoapical} = 1,227.9 nM), and a symmetric basolateral facilitated diffusion transporter (V_max = 6.0 nM/s, K_t = 628.3 nM). The apparent directionality of OCT2 may reflect altered TYR ionization due to known pH differences between compartments. Models for asymmetry and compartmentalization were compared by root mean square deviation from experimental data, and it was found that TYR compartmentalization could only partially replace the need for asymmetry of OCT2. In conclusion, modelling indicates that known TYR transport processes are insufficient to explain experimental concentration-time profiles and that asymmetry of the apical membrane OCT2 combined with additional, low affinity, basolateral membrane facilitated diffusion transporters are required.

TAAR1 regulates drug-induced reinstatement of cocaine-seeking via negatively modulating CaMKIIα activity in the NAc

Relapse remains a major challenge to the treatment of cocaine addiction. Recent studies suggested that the trace amine-associated receptor 1 (TAAR1) could be a promising target to treat cocaine addiction and relapse; however, the underlying mechanism remains unclear. Here, we aimed to investigate the neural mechanism underlying the role of TAAR1 in the drug priming-induced reinstatement of cocaine-seeking behavior in rats, an animal model of cocaine relapse. We focused on the shell subregion of nucleus accumbens (NAc), a key brain region of the brain reward system. We found that activation of TAAR1 by systemic and intra-NAc shell administration of the selective TAAR1 agonist RO5166017 attenuated drug-induced reinstatement of cocaine-seeking and prevented drug priming-induced CaMKIIα activity in the NAc shell. Activation of TAAR1 dampened the CaMKIIα/GluR1 signaling pathway in the NAc shell and reduced AMPAR-EPSCs on the NAc slice. Microinjection of the selective TAAR1 antagonist EPPTB into the NAc shell enhanced drug-induced reinstatement as well as potentiated CaMKIIα activity in the NAc shell. Furthermore, viral-mediated expression of CaMKIIα in the NAc shell prevented the behavioral effects of TAAR1 activation. Taken together, our findings indicate that TAAR1 regulates drug-induced reinstatement of cocaine-seeking by negatively regulating CaMKIIα activity in the NAc. Our findings elucidate a novel mechanism of TAAR1 in regulating drug-induced reinstatement of cocaine-seeking and further suggests that TAAR1 is a promising target for the treatment of cocaine relapse.

Therapeutic Potential of TAAR1 Agonists in Schizophrenia: Evidence from Preclinical Models and Clinical Studies

Trace amine-associated receptor 1 (TAAR1) has emerged as a promising therapeutic target for neuropsychiatric disorders due to its ability to modulate monoaminergic and glutamatergic neurotransmission. In particular, agonist compounds have generated interest as potential treatments for schizophrenia and other psychoses due to TAAR1-mediated regulation of dopaminergic tone. Here, we review unmet needs in schizophrenia, the current state of knowledge in TAAR1 circuit biology and neuropharmacology, including preclinical behavioral, imaging, and cellular evidence in glutamatergic, dopaminergic and genetic models linked to the pathophysiology of psychotic, negative and cognitive symptoms. Clinical trial data for TAAR1 drug candidates are reviewed and contrasted with antipsychotics. The identification of endogenous TAAR1 ligands and subsequent development of small-molecule agonists has revealed antipsychotic-, anxiolytic-, and antidepressant-like properties, as well as pro-cognitive and REM-sleep suppressing effects of TAAR1 activation in rodents and non-human primates. Ulotaront, the first TAAR1 agonist to progress to randomized controlled clinical trials, has demonstrated efficacy in the treatment of schizophrenia, while another, ralmitaront, is currently being evaluated in clinical trials in schizophrenia. Coupled with the preclinical findings, this provides a rationale for further investigation and development of this new pharmacological class for the treatment of schizophrenia and other psychiatric disorders.

TAAR1 Expression in Human Macrophages and Brain Tissue: A Potential Novel Facet of MS Neuroinflammation

TAAR1 is a neuroregulator with emerging evidence suggesting a role in immunomodulation. Multiple sclerosis (MS) is an immune-mediated demyelinating disease of the central nervous system. Here, we investigate TAAR1 expression in human primary monocytes, peripherally-derived macrophages, and MS brain tissue. RT-qPCR was used to assess TAAR1 levels in MS monocytes. Using a previously validated anti-human TAAR1 antibody and fluorescence microscopy, TAAR1 protein was visualized in lipopolysaccharide-stimulated or basal human macrophages, as well as macrophage/microglia populations surrounding, bordering, and within a mixed active/inactive MS lesion. In vivo, TAAR1 mRNA expression was significantly lower in MS monocytes compared to age- and sex-matched healthy controls. In vitro, TAAR1 protein showed a predominant nuclear localization in quiescent/control macrophages with a shift to a diffuse intracellular distribution following lipopolysaccharide-induced activation. In brain tissue, TAAR1 protein was predominantly expressed in macrophages/microglia within the border region of mixed active/inactive MS lesions. Considering that TAAR1-mediated anti-inflammatory effects have been previously reported, decreased mRNA in MS patients suggests possible pathophysiologic relevance. A shift in TAAR1 localization following pro-inflammatory activation suggests its function is altered in pro-inflammatory states, while TAAR1-expressing macrophages/microglia bordering an MS lesion supports TAAR1 as a novel pharmacological target in cells directly implicated in MS neuroinflammation.

Biomolecular Evaluation of Piceatannol's Effects in Counteracting the Senescence of Mesenchymal Stromal Cells: A New Candidate for Senotherapeutics?

Several investigations on senescence and its causative role in aging have underscored the importance of developing senotherapeutics, a field focused on killing senescent cells and/or preventing their accumulation within tissues. Using polyphenols in counteracting senescence may facilitate the development of senotherapeutics given their presence in the human diet, their confirmed tolerability and absence of severe side effects, and their role in preventing senescence and inducing the death of senescent cells. Against that background, we evaluated the effect of piceatannol, a natural polyphenol, on the senescence of mesenchymal stromal cells (MSCs), which play a key role in the body's homeostasis. Among our results, piceatannol reduced the number of senescent cells both after genotoxic stress that induced acute senescence and in senescent replicative cultures. Such senotherapeutics activity, moreover, promoted the recovery of cell proliferation and the stemness properties of MSCs. Altogether, our findings demonstrate piceatannol's effectiveness in counteracting senescence by targeting its associated pathways and detecting and affecting P53-dependent and P53-independent senescence. Our study thus suggests that, given piceatannol's various mechanisms to accomplish its pleiotropic activities, it may be able to counteract any senescent phenotypes.

Involvement of Organic Cation Transporter 2 and a Na+-dependent active transporter in p-tyramine transport across Caco-2 intestinal cells

AIMS

We have previously demonstrated that p-tyramine (TYR), an endogenous trace amine-associated receptor 1 agonist, passage across neuronal membranes involves a transporter exhibiting the pharmacological profile of Organic Cation Transporter 2 (OCT2). Since TYR is also a constituent of foodstuffs and produced by the intestinal microbiota, here we have investigated whether similar processes are involved in the passage of 100 nM TYR across apical and basolateral membranes of the Caco-2 human intestinal epithelial cell line.

MATERIALS AND METHODS

[³H]TYR transport across apical and basolateral membranes of Caco-2 cell monolayers was measured in the presence of inhibitors of TYR metabolizing enzymes. Cellular, apical, and basolateral compartments were collected at various timepoints, TYR concentrations calculated, and transport properties pharmacologically characterized.

KEY FINDINGS

Apical transport resulted in equimolar accumulation of TYR within cells. Pentamidine (OCT1/OCT2 inhibitor) decreased apical transport (P = 0.001) while atropine (OCT1 inhibitor) had no effect, suggesting apical transport involved OCT2. In contrast, basolateral transport resulted in 500-1000 nM cellular concentrations (P < 0.0001) indicating the presence of an active transporter. Replacement of Na⁺ on an equimolar basis with choline resulted in loss of TYR transport (P = 0.017). Unexpectedly, this active transport was also atropine-sensitive (P = 0.020). Kinetic analysis of the active transporter revealed V_max = 43.0 nM/s with a K_t = 33.1 nM.

SIGNIFICANCE

We have demonstrated for the first time that TYR is transported across Caco-2 apical membranes via facilitated diffusion by OCT2, whereas transport across basolateral membranes is by a Na⁺-dependent, atropine-sensitive, active transporter.

Trastuzumab-Coated Nanoparticles Loaded With Docetaxel for Breast Cancer Therapy

Docetaxel (DTX) is commonly used for breast cancer treatment. Tween 80 used for DTX dissolution in its clinical formulation causes severe hypersensitivity and other adverse reactions. In this study, trastuzumab (Tmab)-coated lipid-polymer hybrid nanoparticles (PLNs) were prepared, composed of poly (d, l-lactide-co-glycolide), PLGA; polyethylenimine (PEI); and lipids. The PLGA/PEI/lipid formed a hydrophobic core, while Tmab was electrostatically adsorbed on the surface of the PLNs as a ligand that targets human epidermal growth factor receptor 2 (HER2)-positive breast cancer cells. The resulting PLNs, electrostatically adsorbed Tmab-bearing PLGA/PEI/lipid nanoparticles (eTmab-PPLNs), had a mean particle size of 217.4 ± 13.36 nm, a ζ potential of 0.056 ± 0.315 mV, and good stability. In vitro, the eTmab-PPLNs showed increased cytotoxicity in HER2-postive BT474 cells but not in HER2-negative MCF7 cells. Studies of the ability of eTmab-PPLNs to target HER2 were performed. The uptake of eTmab-PPLNs was shown to be dependent on HER2 expression level. Therefore, eTmab-PPLNs provide a promising therapeutic for the treatment of breast cancer.