Defects in the peripheral taste structure and function in the MRL/lpr mouse model of autoimmune disease

Chronic social defeat stress broadly inhibits gene expression in the peripheral taste system and alters taste responses in mice

Human studies have linked stress exposure to unhealthy eating behavior. However, the mechanisms that drive stress-associated changes in eating behavior remain incompletely understood. The sense of taste plays important roles in food preference and intake. In this study, we use a chronic social defeat stress (CSDS) model in mice to address whether chronic stress impacts taste sensation and gene expression in taste buds and the gut. Our results showed that CSDS significantly elevated circulating levels of corticosterone and acylated ghrelin while lowering levels of leptin, suggesting a change in metabolic hormones that promotes food consumption. Stressed mice substantially increased their intake of food and water 3-5 days after the stress onset and gradually gained more body weight than that of controls. Moreover, CSDS significantly decreased the expression of multiple taste receptors and signaling molecules in taste buds and reduced mRNA levels of several taste progenitor/stem cell markers and regulators. Stressed mice showed significantly reduced sensitivity and response to umami and sweet taste compounds in behavioral tests. In the small intestine, the mRNA levels of Gnat3 and Tas1r2 were elevated in CSDS mice. The increased Gnat3 was mostly localized in a type of Gnat3+ and CD45+ immune cells, suggesting changes of immune cell distribution in the gut of stressed mice. Together, our study revealed broad effects of CSDS on the peripheral taste system and the gut, which may contribute to stress-associated changes in eating behavior.

In Vitro Functional Characterization of Type-I Taste Bud Cells as Monocytes/Macrophages-like Which Secrete Proinflammatory Cytokines

The sense of taste determines the choice of nutrients and food intake and, consequently, influences feeding behaviors. The taste papillae are primarily composed of three types of taste bud cells (TBC), i.e., type I, type II, and type III. The type I TBC, expressing GLAST (glutamate--aspartate transporter), have been termed as glial-like cells. We hypothesized that these cells could play a role in taste bud immunity as glial cells do in the brain. We purified type I TBC, expressing F4/80, a specific marker of macrophages, from mouse fungiform taste papillae. The purified cells also express CD11b, CD11c, and CD64, generally expressed by glial cells and macrophages. We further assessed whether mouse type I TBC can be polarized toward M1 or M2 macrophages in inflammatory states like lipopolysaccharide (LPS)-triggered inflammation or obesity, known to be associated with low-grade inflammation. Indeed, LPS-treatment and obesity state increased TNFα, IL-1β, and IL-6 expression, both at mRNA and protein levels, in type I TBC. Conversely, purified type I TBC treated with IL-4 showed a significant increase in arginase 1 and IL-4. These findings provide evidence that type I gustatory cells share many features with macrophages and may be involved in oral inflammation.

Lipopolysaccharide increases bitter taste sensitivity via epigenetic changes in Tas2r gene clusters

T2R bitter receptors, encoded by Tas2r genes, are not only critical for bitter taste signal transduction but also important for defense against bacteria and parasites. However, little is known about whether and how Tas2r gene expression are regulated. Here, we show that in an inflammation model mimicking bacterial infection using lipopolysaccharide, the expression of many Tas2rs was significantly upregulated and mice displayed markedly increased neural and behavioral responses to bitter compounds. Using single-cell assays for transposase-accessible chromatin with sequencing (scATAC-seq), we found that the chromatin accessibility of Tas2rs was highly celltype specific and lipopolysaccharide increased the accessibility of many Tas2rs. scATAC-seq also revealed substantial chromatin remodeling in immune response genes in taste tissue stem cells, suggesting potential long-lasting effects. Together, our results suggest an epigenetic mechanism connecting inflammation, Tas2r gene regulation, and altered bitter taste, which may explain heightened bitter taste that can occur with infections and cancer treatments.

Inflammation induces bitter taste oversensitization via epigenetic changes in Tas2r gene clusters

T2R bitter receptors, encoded by Tas2r genes, are not only critical for bitter taste signal transduction but also important for defense against bacteria and parasites. However, little is known about whether and how Tas2r gene expression are regulated. Here we show that, in an inflammation model mimicking bacterial infection, the expression of many Tas2rs are significantly up-regulated and mice displayed markedly increased neural and behavioral responses to bitter compounds. Using single-cell assays for transposase-accessible chromatin with sequencing (scATAC-seq), we found that the chromatin accessibility of Tas2rs was highly cell type specific and inflammation increased the accessibility of many Tas2rs . scATAC-seq also revealed substantial chromatin remodeling in immune response genes in taste tissue stem cells, suggesting potential long-term effects. Together, our results suggest an epigenetic mechanism connecting inflammation, Tas2r gene regulation, and altered bitter taste, which may explain heightened bitter taste that can occur with infections and cancer treatments.

Smell and Taste Function and Their Disturbances in Sjögren's Syndrome

Chemosensory disorders are a possible disturbance in Sjögren's syndrome (SS). The aim of the study is to comprehensively present chemosensory disorders in SS and to indicate their possible causes. The possible causes of taste and smell disorders in SS are changes in the structure of exocrine glands and their dysfunction, damage to receptors and weakening of their ability to regenerate, and neurological changes in the form of peripheral neuropathy and impaired cognitive function. Other postulated causes of chemosensory disorders are autoimmune mechanisms, adverse effects of drugs used in SS, and primary potentially SS-triggering viral infections. They are multifactorial and may occur independently of each other. The time of their onset and correlation with other disease symptoms may facilitate the determination of their primary cause in each patient. Awareness of chemosensory disorders in SS may help to ease their progress and eliminate other factors responsible for their more severe manifestation. In the prevention and treatment of chemosensory disorders in SS, the most important thing is to alleviate xerostomia and dryness in the nasal cavity and their effects in the form of chronic local inflammations, counteract receptor atrophy, and an implementation of appropriate neurological diagnosis and treatment.

Chemosensory Functions in Patients with Inflammatory Bowel Disease and Their Association with Clinical Disease Activity

Purpose: Decreased olfactory and gustatory functions are present in various systemic autoimmune diseases. However, little is known about the chemosensory functions of patients with inflammatory bowel disease (IBD). The present study aimed to investigate olfactory and gustatory functions in patients with IBD and their correlation with clinical disease activity. Methods: A total of 103 patients with IBD were included (52 men, 51 women, mean age 40.3 ± 1.2 years) in the present study. Chemosensory functions were assessed utilizing the “Sniffin’ Sticks” olfactory function test and “taste sprays” gustatory function test. The clinical disease activity of patients was graded as remission, mild, and moderate−severe. In addition, inflammatory markers (fecal calprotectin, C-reactive protein and blood leucocyte count) were recorded. Results: In total, 70% of IBD patients were normosmic, 30% were hyposmic, and none of them was functionally anosmic; 6% of the patients showed signs of hypogeusia. Patients with moderate−severe IBD reached a higher olfactory threshold score compared with patients with remission (p = 0.011) and mild IBD (p < 0.001). The BMI of IBD patients was inversely correlated with their olfactory threshold (r = −0.25, p = 0.010). Olfactory and gustatory function in IBD patients did not correlate with duration of disease, blood leucocyte count, CRP level, or fecal calprotectin level. However, patients’ olfactory function significantly increased after 4 months of TNF-α inhibitor treatment (p = 0.038). Conclusions: IBD patients are more likely to present with hyposmia. Olfactory thresholds were mainly affected. They were significantly associated with clinical disease activity and BMI. As shown in a subgroup, treatment with TNF-α inhibitors appeared to improve olfactory function.

Dysgeusia: A review in the context of COVID-19

Background

Taste disorders in general, and dysgeusia in particular, are relatively common disorders that may be a sign of a more complex acute or chronic medical condition. During the COVID-19 pandemic, taste disorders have found their way into the realm of general as well as specialty dentistry, with significance in screening for patients who potentially may have the virus.

Types of Studies Reviewed

The authors searched electronic databases (PubMed, Embase, Web of Science, Google Scholar) for studies focused on dysgeusia, ageusia, and other taste disorders and their relationship to local and systemic causes.

Results

The authors found pertinent literature explaining the normal physiology of taste sensation, proposals for suggested new tastes, presence of gustatory receptors in remote tissues of the body, and etiology and pathophysiology of taste disorders, in addition to the valuable knowledge gained about gustatory disorders in the context of COVID-19. Along with olfactory disorders, taste disorders are one of the earliest suggestive symptoms of COVID-19 infection.

Conclusions

Gustatory disorders are the result of local or systemic etiology or both. Newer taste sensations, such as calcium and fat tastes, have been discovered, as well as taste receptors that are remote from the oropharyngeal area. Literature published during the COVID-19 pandemic to date reinforces the significance of early detection of potential patients with COVID-19 by means of screening for recent-onset taste disorders.

Practical Implications

Timely screening and identification of potential gustatory disorders are paramount for the dental care practitioner to aid in the early diagnosis of COVID-19 and other serious systemic disorders.

Do Gut Microbes Taste?

Gut microbiota has emerged as a major metabolically active organ with critical functions in both health and disease. The trillions of microorganisms hosted by the gastrointestinal tract are involved in numerous physiological and metabolic processes including modulation of appetite and regulation of energy in the host spanning from periphery to the brain. Indeed, bacteria and their metabolic byproducts are working in concert with the host chemosensory signaling pathways to affect both short- and long-term ingestive behavior. Sensing of nutrients and taste by specialized G protein-coupled receptor cells is important in transmitting food-related signals, optimizing nutrition as well as in prevention and treatment of several diseases, notably obesity, diabetes and associated metabolic disorders. Further, bacteria metabolites interact with specialized receptors cells expressed by gut epithelium leading to taste and appetite response changes to nutrients. This review describes recent advances on the role of gut bacteria in taste perception and functions. It further discusses how intestinal dysbiosis characteristic of several pathological conditions may alter and modulate taste preference and food consumption via changes in taste receptor expression.

To Detect and Reject, Parallel Roles for Taste and Immunity

PURPOSE OF REVIEW

From single cells to entire organisms, biological entities are in constant communication with their surroundings, deciding what to 'allow' in, and what to reject. In very different ways, the immune and taste systems both fulfill this function, with growing evidence suggesting a relationship between the two, through shared signaling pathways, receptors, and feedback loops. The purpose of this review was to explore recent reports on taste and immunity in model animals and in humans to explore our understanding of the interplay between these systems.

RECENT FINDINGS

Acute infections in the upper airway, as with SARS-CoV-2, are associated with a proinflammatory state, and blunted taste perception. Further, recent findings highlight taste receptors working as immune sentinels throughout the body. Work in humans and mice also points to inflammation from obesity impacting taste, altering taste bud abundance and composition. There is accumulating evidence that taste cells, and particularly their receptors, play a role in airway and gut immunity, responsive to invading organisms. Inflammation itself may further act on taste buds and other taste receptor expressing cells throughout the body as a form of homeostatic control.

Identification of biological pathways specific to phases preceding rheumatoid arthritis development through gene expression profiling

The etiopathogenesis of rheumatoid arthritis is partially understood; however, it is believed to result from a multi-step process. The immune onset followed by pre-clinical phases will eventually lead to the development of symptomatic disease. We aim at identifying differentially expressed genes in order to highlight pathways involved in the pre-clinical stages of rheumatoid arthritis development. The study population consisted of first-degree relatives of patients with rheumatoid arthritis, known to have an increased risk of developing disease as compared to the general population. Whole transcriptome analysis was performed in four groups: asymptomatic without autoantibodies or symptoms associated with possible rheumatoid arthritis (controls); having either clinically suspect arthralgias, undifferentiated arthritis or autoimmunity associated with RA (pre-clinical stages of RA: Pcs-RA); having subsequently developed classifiable RA (pre-RA); and early untreated rheumatoid arthritis patients (RA). Differentially expressed genes were determined, and enrichment analysis was performed. Functional enrichment analysis revealed 31 pathways significantly enriched in differentially expressed genes for Pcs-RA, pre-RA and RA compared to the controls. Osteoclast pathway is among the seven pathways specific for RA. In Pcs-RA and in pre-RA, several enriched pathways include TP53 gene connections, such as P53 and Wnt signalling pathways. Analysis of whole transcriptome for phenotypes related to rheumatoid arthritis allows highlighting which pathways are requested in the pre-clinical stages of disease development. After validation in replication studies, molecules belonging to some of these pathways could be used to identify new specific biomarkers for individuals with impending rheumatoid arthritis.

COVID-19 and the Chemical Senses: Supporting Players Take Center Stage

The main neurological manifestation of COVID-19 is loss of smell or taste. The high incidence of smell loss without significant rhinorrhea or nasal congestion suggests that SARS-CoV-2 targets the chemical senses through mechanisms distinct from those used by endemic coronaviruses or other common cold-causing agents. Here we review recently developed hypotheses about how SARS-CoV-2 might alter the cells and circuits involved in chemosensory processing and thereby change perception. Given our limited understanding of SARS-CoV-2 pathogenesis, we propose future experiments to elucidate disease mechanisms and highlight the relevance of this ongoing work to understanding how the virus might alter brain function more broadly.

Lipopolysaccharide-Induced Inflammatory Cytokine Expression in Taste Organoids

Inflammatory cytokines are signaling molecules that regulate numerous physiological processes, from tissue homeostasis to metabolism and food intake. Expression of certain cytokines can be markedly induced in subsets of taste bud cells under acute and chronic inflammation. This may contribute to altered taste perception and preference associated with many diseases. Although the pathways of cytokine induction are well studied in immune cells, they remain poorly characterized in taste cells, in part due to the difficulties of performing biochemical analyses with a limited number of taste cells. The recently developed taste organoid model provides an opportunity to carry out these mechanistic studies in vitro. However, it was unknown whether taste organoids respond to inflammatory stimuli as do in vivo native taste buds. Here we analyze lipopolysaccharide (LPS)-induced expression and secretion of two inflammatory cytokines, tumor necrosis factor (TNF), and interleukin-6 (IL-6). We show that, similarly to native mouse taste epithelia, organoids derived from mouse circumvallate stem cells express several toll-like receptors (TLRs), including TLR4-the primary receptor for LPS. Organoids and native taste epithelia express all five genes in the nuclear factor-κb (Nfkb) family that encode the transcription factor NF-κB, a critical regulator of inflammatory responses. LPS stimulates fast induction of TNF and IL-6 with similar induction kinetics in organoids and native taste epithelia. These results show that taste epithelial cells possess necessary components for inflammatory cytokine induction and secretion and suggest that the organoid model can be a useful tool to dissect the underlying mechanisms.

Immune Responses Alter Taste Perceptions: Immunomodulatory Drugs Shape Taste Signals during Treatments

Considering that nutrients are required in health and diseases, the detection and ingestion of food to meet the requirements is attributable to the sense of taste. Altered taste sensations lead to a decreased appetite, which is usually one of the frequent causes of malnutrition in patients with diseases. Ongoing taste research has identified a variety of drug pathways that cause changes in taste perceptions in cancer, increasing our understanding of taste disturbances attributable to aberrant mechanisms of taste sensation. The evidence discussed in this review, which addresses the implications of innate immune responses in the modulation of taste functions, focuses on the adverse effects on taste transmission from taste buds by immune modulators responsible for alterations in the perceived intensity of some taste modalities. Another factor, damage to taste progenitor cells that directly results in local effects on taste buds, must also be considered in relation to taste disturbances in patients with cancer. Recent discoveries discussed have provided new insights into the pathophysiology of taste dysfunctions associated with the specific treatments. SIGNIFICANCE STATEMENT: The paradigm that taste signals transmitted to the brain are determined only by tastant-mediated activation via taste receptors has been challenged by the immune modification of taste transmission through drugs during the processing of gustatory information in taste buds. This article reports the findings in a model system (mouse taste buds) that explain the basis for the taste dysfunctions in patients with cancer that has long been observed but never understood.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.

Neurolocalization of taste disorders

Neurolocalization of taste disorders requires a knowledge of the functional anatomy involved in mediating taste information from the peripheral mucosal surfaces through numerous peripheral cranial nerves to complex subcortical and cortical brain regions. Our understanding of this functional anatomy has advanced in recent years. Taste is an experience that is both innate and learned, and the "taste" experience involves the integration of information from other sensory modalities, such as olfaction and somatosensation. Normal taste perception is influenced by different neurophysiologic states, which involve endocrine function, emotions, and even attitudes and expectations toward eating. At its core, the normal effective ability to taste is a reflection of the proper function of many organ systems within the body and may be considered a marker for good health. Clinical taste disorders, on the other hand, involve the dysfunction of the normal neural taste pathways and/or aberrant influences on multisensory integration and cortical taste processing. The number of disease processes, which can adversely affect taste, are numerous and quite varied in their presentation. There may be contributory involvement of other organ systems within the body, and the appropriate management of taste disorders often requires a multidisciplinary approach to fully understand the disorder. Depending on the underlying cause, taste disorders can be effectively managed when identified. Treatments may include correcting underlying metabolic disturbances, eliminating infections, changing offending medications, replenishing nutritional deficiencies, operating on structural impairments, calming autoimmune processes, and even stabilizing electrochemical interactions.

Decreased hippocampal cell proliferation in mice with experimental antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of antiphospholipid antibodies, which may trigger vascular thrombosis with consecutive infarcts. However, cognitive dysfunctions representing one of the most commonest neuropsychiatric symptoms are frequently present despite the absence of any ischemic brain lesions. Data on the structural and functional basis of the neuropsychiatric symptoms are sparse. To examine the effect of APS on hippocampal neurogenesis and on white matter, we induced experimental APS (eAPS) in adult female Balb/C mice by immunization with β2-glycoprotein 1. To investigate cell proliferation in the dentate gyrus granular cell layer (DG GCL), eAPS and control mice (n = 5, each) were injected with 5-bromo-2'-deoxyuridine (BrdU) once a day for 10 subsequent days. Sixteen weeks after immunization, eAPS resulted in a significant reduction of BrdU-positive cells in the DG GCL compared to control animals. However, double staining with doublecortin and NeuN revealed a largely preserved neurogenesis. Ultrastructural analysis of corpus callosum (CC) axons in eAPS (n = 6) and control mice (n = 7) revealed no significant changes in CC axon diameter or g-ratio. In conclusion, decreased cellular proliferation in the hippocampus of eAPS mice indicates a limited regenerative potential and may represent one neuropathological substrate of cognitive changes in APS while evidence for alterations of white matter integrity is lacking.

Gli3 is a negative regulator of Tas1r3-expressing taste cells

Mouse taste receptor cells survive from 3-24 days, necessitating their regeneration throughout adulthood. In anterior tongue, sonic hedgehog (SHH), released by a subpopulation of basal taste cells, regulates transcription factors Gli2 and Gli3 in stem cells to control taste cell regeneration. Using single-cell RNA-Seq we found that Gli3 is highly expressed in Tas1r3-expressing taste receptor cells and Lgr5+ taste stem cells in posterior tongue. By PCR and immunohistochemistry we found that Gli3 was expressed in taste buds in all taste fields. Conditional knockout mice lacking Gli3 in the posterior tongue (Gli3CKO) had larger taste buds containing more taste cells than did control wild-type (Gli3WT) mice. In comparison to wild-type mice, Gli3CKO mice had more Lgr5+ and Tas1r3+ cells, but fewer type III cells. Similar changes were observed ex vivo in Gli3CKO taste organoids cultured from Lgr5+ taste stem cells. Further, the expression of several taste marker and Gli3 target genes was altered in Gli3CKO mice and/or organoids. Mirroring these changes, Gli3CKO mice had increased lick responses to sweet and umami stimuli, decreased lick responses to bitter and sour taste stimuli, and increased glossopharyngeal taste nerve responses to sweet and bitter compounds. Our results indicate that Gli3 is a suppressor of stem cell proliferation that affects the number and function of mature taste cells, especially Tas1r3+ cells, in adult posterior tongue. Our findings shed light on the role of the Shh pathway in adult taste cell regeneration and may help devise strategies for treating taste distortions from chemotherapy and aging.

Sustained Immunosuppression Alters Olfactory Function in the MRL Model of CNS Lupus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that is frequently accompanied by diverse neuropsychiatric manifestations. An increased frequency of olfactory deficits has been recently reported as another marker of CNS involvement in SLE patients. Similarly, we observed that spontaneous development of lupus-like disease in MRL/lpr mice is accompanied by altered olfaction-related behaviors. However, it remained unclear whether the behavioral deficits are due to systemic autoimmunity, or the distinct genetic make-up. To address this question, we presently examine whether prolonged treatment with the immunosuppressive drug cyclophosphamide (CY) restores odor-guided behaviors in MRL/lpr mice. Over 12 weekends, MRL/lpr and control MRL +/+ males were given ad lib access to a sweetened CY solution or a vehicle. Their responsiveness to different scents was assessed at ages corresponding to mild, modest, and severe disease. Odor-guided exploratory behavior was further examined in the novel object test at 21 weeks of age, shortly before terminal assessment of immunopathology. In comparison to control groups, MRL/lpr mice exposed to CY exhibited normal spleen size and antibody levels, as well as increased responsiveness to an attractant and a novel object. However, CY treatment also exacerbated their aberrant response to a repellent, suggesting a dual mode of action on brain olfactory systems. The present results reveal that generalized immunosuppression modulates odor-guided behaviors in lupus-prone animals. Although key pathogenic mechanisms are not clear, the findings strengthen the construct validity of the MRL model by supporting the hypothesis that onset of systemic autoimmunity alters the activity of olfactory circuits.

Alteration in Taste Perception in Cancer: Causes and Strategies of Treatment

The sense of taste is responsible for the detection and ingestion of food to cover energetic requirements in health and disease. The change in taste perception might lead to malnutrition that is usually one of the frequent causes of morbidity and mortality in patients with cancer. In this review, we summarize the mechanisms of taste perception and how they are altered in cancer. We also address the question of the implication of inflammation, responsible for the alterations in taste modalities. We highlight the role of radio- and chemotherapy in the modulation of taste physiology. Other several factors like damage to taste progenitor cells and disruption of gut microbiota are also dealt with relation to taste perception in cancer. We further shed light on how to restore taste acuity, by using different preventive methods, dietary modifications and pharmacotherapy in subjects with advanced cancer state.

The effect of imiquimod on taste bud calcium transients and transmitter secretion

BACKGROUND AND PURPOSE

Imiquimod is an immunomodulator approved for the treatment of basal cell carcinoma and has adverse side effects, including taste disturbances. Paracrine transmission, representing cell-cell communication within taste buds, has the potential to shape the final signals that taste buds transmit to the brain. Here, we tested the underlying assumption that imiquimod modifies taste transmitter secretion in taste buds of mice.

EXPERIMENTAL APPROACH

Taste buds were isolated from C57BL/6J mice. The effects of imiquimod on transmitter release in taste buds were measured using calcium imaging with cellular biosensors, and examining the net effect of imiquimod on taste-evoked ATP secretion from mouse taste buds.

KEY RESULTS

Up to 72% of presynaptic (Type III) taste cells responded to 100 μM imiquimod with an increase in intracellular Ca²⁺ concentrations. These Ca²⁺ responses were inhibited by thapsigargin, an inhibitor of the sarco/endoplasmic reticulum Ca²⁺ -ATPase, and by U73122, a PLC inhibitor, suggesting that the Ca²⁺ mobilization elicited by imiquimod was dependent on release from internal Ca²⁺ stores. Moreover, combining studies of Ca²⁺ imaging with cellular biosensors showed that imiquimod evoked secretion of 5-HT, which then provided negative feedback onto receptor (Type II) cells to reduce taste-evoked ATP secretion.

CONCLUSION AND IMPLICATIONS

Our results provide evidence that there is a subset of taste cells equipped with a range of intracellular mechanisms that respond to imiquimod. The findings are also consistent with a role of imiquimod as an immune response modifier, which shapes peripheral taste responses via 5-HT signalling.

Inflammatory stimuli acutely modulate peripheral taste function

Inflammation-mediated changes in taste perception can affect health outcomes in patients, but little is known about the underlying mechanisms. In the present work, we hypothesized that proinflammatory cytokines directly modulate Na(+) transport in taste buds. To test this, we measured acute changes in Na(+) flux in polarized fungiform taste buds loaded with a Na(+) indicator dye. IL-1β elicited an amiloride-sensitive increase in Na(+) transport in taste buds. In contrast, TNF-α dramatically and reversibly decreased Na(+) flux in polarized taste buds via amiloride-sensitive and amiloride-insensitive Na(+) transport systems. The speed and partial amiloride sensitivity of these changes in Na(+) flux indicate that IL-1β and TNF-α modulate epithelial Na(+) channel (ENaC) function. A portion of the TNF-mediated decrease in Na(+) flux is also blocked by the TRPV1 antagonist capsazepine, although TNF-α further reduced Na(+) transport independently of both amiloride and capsazepine. We also assessed taste function in vivo in a model of infection and inflammation that elevates these and additional cytokines. In rats administered systemic lipopolysaccharide (LPS), CT responses to Na(+) were significantly elevated between 1 and 2 h after LPS treatment. Low, normally preferred concentrations of NaCl and sodium acetate elicited high response magnitudes. Consistent with this outcome, codelivery of IL-1β and TNF-α enhanced Na(+) flux in polarized taste buds. These results demonstrate that inflammation elicits swift changes in Na(+) taste function, which may limit salt consumption during illness.

Neuropsychiatric systemic lupus erythematosus persists despite attenuation of systemic disease in MRL/lpr mice

Background

Systemic lupus erythematosus (SLE) is a prototypical autoimmune disease marked by both B and T cell hyperactivity which commonly affects the joints, skin, kidneys, and brain. Neuropsychiatric disease affects about 40 % of SLE patients, most frequently manifesting as depression, memory deficits, and general cognitive decline. One important and yet unresolved question is whether neuropsychiatric SLE (NPSLE) is a complication of systemic autoimmunity or whether it is primarily driven by brain-intrinsic factors.

Methods

To dissect the relative contributions of the central nervous system from those of the hematopoietic compartment, we generated bone marrow chimeras between healthy control (MRL/+) and lupus-prone MRL/Tnfrsf6^lpr/lpr mice (MRL/+ → MRL/lpr), as well as control chimeras. After bone marrow reconstitution, mice underwent extensive behavioral testing, analysis of brain tissue, and histological assessment.

Results

Despite transfer of healthy MRL/+ bone marrow and marked attenuation of systemic disease, we found that MRL/+ → MRL/lpr mice had a behavioral phenotype consisting of depressive-like behavior and visuospatial memory deficits, comparable to MRL/lpr → MRL/lpr control transplanted mice and the behavioral profile previously established in MRL/lpr mice. Moreover, MRL/+ → MRL/lpr chimeric mice displayed increased brain RANTES expression, neurodegeneration, and cellular infiltration in the choroid plexus, as well as blood brain barrier disruption, all in the absence of significant systemic autoimmunity.

Conclusions

Chimeric MRL/+ → MRL/lpr mice displayed no attenuation of the behavioral phenotype found in MRL/lpr mice, despite normalized serum autoantibodies and conserved renal function. Therefore, neuropsychiatric disease in the MRL/lpr lupus-prone strain of mice can occur absent any major contributions from systemic autoimmunity.

Arecoline Alters Taste Bud Cell Morphology, Reduces Body Weight, and Induces Behavioral Preference Changes in Gustatory Discrimination in C57BL/6 Mice

Arecoline, a major alkaloid in areca nuts, is involved in the pathogenesis of oral diseases. Mammalian taste buds are the structural unit for detecting taste stimuli in the oral cavity. The effects of arecoline on taste bud morphology are poorly understood. Arecoline was injected intraperitoneally (IP) into C57BL/6 mice twice daily for 1-4 weeks. After arecoline treatment, the vallate papillae were processed for electron microscopy and immunohistochemistry analysis of taste receptor proteins (T1R2, T1R3, T1R1, and T2R) and taste associated proteins (α-gustducin, PLCβ2, and SNAP25). Body weight, food intake and water consumption were recorded. A 2-bottle preference test was also performed. The results demonstrated that 1) arecoline treatment didn't change the number and size of the taste buds or taste bud cells, 2) electron microscopy revealed the change of organelles and the accumulation of autophagosomes in type II cells, 3) immunohistochemistry demonstrated a decrease of taste receptor T1R2- and T1R3-expressing cells, 4) the body weight and food intake were markedly reduced, and 5) the sweet preference behavior was reduced. We concluded that the long-term injection of arecoline alters the morphology of type II taste bud cells, retards the growth of mice, and affects discrimination competencies for sweet tastants.

Regulation of bitter taste responses by tumor necrosis factor

Inflammatory cytokines are important regulators of metabolism and food intake. Over production of inflammatory cytokines during bacterial and viral infections leads to anorexia and reduced food intake. However, it remains unclear whether any inflammatory cytokines are involved in the regulation of taste reception, the sensory mechanism governing food intake. Previously, we showed that tumor necrosis factor (TNF), a potent proinflammatory cytokine, is preferentially expressed in a subset of taste bud cells. The level of TNF in taste cells can be further induced by inflammatory stimuli. To investigate whether TNF plays a role in regulating taste responses, in this study, we performed taste behavioral tests and gustatory nerve recordings in TNF knockout mice. Behavioral tests showed that TNF-deficient mice are significantly less sensitive to the bitter compound quinine than wild-type mice, while their responses to sweet, umami, salty, and sour compounds are comparable to those of wild-type controls. Furthermore, nerve recording experiments showed that the chorda tympani nerve in TNF knockout mice is much less responsive to bitter compounds than that in wild-type mice. Chorda tympani nerve responses to sweet, umami, salty, and sour compounds are similar between TNF knockout and wild-type mice, consistent with the results from behavioral tests. We further showed that taste bud cells express the two known TNF receptors TNFR1 and TNFR2 and, therefore, are potential targets of TNF. Together, our results suggest that TNF signaling preferentially modulates bitter taste responses. This mechanism may contribute to taste dysfunction, particularly taste distortion, associated with infections and some chronic inflammatory diseases.

Diagnostic utility of Acoustic Radiation Force Impulse (ARFI) imaging in primary Sjoegren`s syndrome

OBJECTIVES

The purpose of the study was to assess the diagnostic utility of acoustic radiation force impulse (ARFI) imaging in primary Sjögren's syndrome (pSS).

METHODS

One hundred fifty-seven patients with sicca symptoms and/or salivary gland swelling were included. Sicca symptoms, Schirmer test, unstimulated whole saliva (UWS), SS-A/B antibodies, and histology were assessed according to American-European Consensus group (AECG) criteria. All patients underwent high-resolution ultrasound and ARFI imaging of the parotid (PG) and submandibular glands (SMG).

RESULTS

Seventy patients were classified as having pSS. The remaining 87 patients suffered from idiopathic sicca (n = 24), rheumatoid arthritis (n = 12), sarcoidosis (n = 9), cutaneous/systemic lupus erythematosus (n = 7), scleroderma (n = 2), dermatomyositis (n = 1), HBV/HCV (n = 2), and panarteritis nodosa (n = 1), and disorders in 29 patients were classified as not otherwise specified. ARFI values of the PG were significantly higher in the pSS versus non-pSS groups (2.86 ± 0.07 m/s vs. 2.15 ± 0.11 m/s, p < 0.0001). ARFI imaging demonstrated diagnostic sensitivity and specificity of 81 % and 67 %, respectively.

CONCLUSIONS

In addition to histology, ARFI imaging was the most important diagnostic tool for identifying early pSS.

KEY POINTS

• Early stages in Sjögren's syndrome become apparent with major salivary gland enlargements. • Schirmer and unstimulated whole saliva tests demonstrated insufficient sensitivity/specificity for early-stage diagnosis. • Acoustic radiation force impulse imaging is a reliable tool for diagnosing early disease stages.

Zoopharmacognosy in diseased laboratory mice: conflicting evidence

Zoopharmacognosy denotes a constellation of learned ingestive responses that promote healing and survival of infected or poisoned animals. A similar self-medication phenomenon was reported in diseased laboratory rodents. In particular, a series of studies revealed that autoimmune MRL/lpr mice readily consume solutions paired or laced with cyclophosphamide (CY), an immunosuppressive drug that prevents inflammatory damage to internal organs. However, due to design limitations, it could not be elucidated whether such a response reflects the learned therapeutic effect of CY, or a deficit in sensory input. We presently assess the behavioural effects of prolonged consumption of CY-laced, 16% sucrose solution in a continuous choice paradigm, with tap water available ad lib. Contrary to overall expectation, MRL/lpr mice did not increase their intake of CY with disease progression. Moreover, they ingested lower doses of CY and preferred less CY-laced sucrose solution than age-matched controls. The results obtained could not confirm zoopharmacognosy in diseased MRL/lpr mice, likely due to impaired responsiveness to palatable stimulation, or attenuated survival mechanisms after prolonged inbreeding in captivity. However, by revealing the effectiveness of unrestricted drinking of drug-laced sucrose solution on behavior and immunity, the current study supports broader use of such an administration route in behavioural studies sensitive to external stressors.

Sweet taste loss in myasthenia gravis: more than a coincidence?

Sweet dysgeusia, a rare taste disorder, may be encountered in severe anti-acetylcholine receptor antibody (AChRAb)-myasthenia gravis (MG). A 42 year-old man reported progressive loss of sweet taste evolving for almost 10 weeks, revealing an AChRAb-positive MG with thymoma. Improvement of sweet perception paralleled reduction of the MG composite score during the 15 months follow up period, with immunosuppressive and surgical treatments. We suggest that sweet dysgeusia is a non-motor manifestation of MG that may result from a thymoma-dependent autoimmune mechanism targeting gustducin-positive G-protein-coupled taste receptor cells, in line with recent data from MRL/MpJ-Fas^lpr/ (MRL/lpr) transgenic mice with autoimmune disease.

Interleukin-10 is produced by a specific subset of taste receptor cells and critical for maintaining structural integrity of mouse taste buds

Although inflammatory responses are a critical component in defense against pathogens, too much inflammation is harmful. Mechanisms have evolved to regulate inflammation, including modulation by the anti-inflammatory cytokine interleukin-10 (IL-10). Previously we have shown that taste buds express various molecules involved in innate immune responses, including the proinflammatory cytokine tumor necrosis factor (TNF). Here, using a reporter mouse strain, we show that taste cells also express the anti-inflammatory cytokine IL-10. Remarkably, IL-10 is produced by only a specific subset of taste cells, which are different from the TNF-producing cells in mouse circumvallate and foliate taste buds: IL-10 expression was found exclusively in the G-protein gustducin-expressing bitter receptor cells, while TNF was found in sweet and umami receptor cells as reported previously. In contrast, IL-10R1, the ligand-binding subunit of the IL-10 receptor, is predominantly expressed by TNF-producing cells, suggesting a novel cellular hierarchy for regulating TNF production and effects in taste buds. In response to inflammatory challenges, taste cells can increase IL-10 expression both in vivo and in vitro. These findings suggest that taste buds use separate populations of taste receptor cells that coincide with sweet/umami and bitter taste reception to modulate local inflammatory responses, a phenomenon that has not been previously reported. Furthermore, IL-10 deficiency in mice leads to significant reductions in the number and size of taste buds, as well as in the number of taste receptor cells per taste bud, suggesting that IL-10 plays critical roles in maintaining structural integrity of the peripheral gustatory system.

Taste bud homeostasis in health, disease, and aging

The mammalian taste bud is an onion-shaped epithelial structure with 50-100 tightly packed cells, including taste receptor cells, supporting cells, and basal cells. Taste receptor cells detect nutrients and toxins in the oral cavity and transmit the sensory information to gustatory nerve endings in the buds. Supporting cells may play a role in the clearance of excess neurotransmitters after their release from taste receptor cells. Basal cells are precursor cells that differentiate into mature taste cells. Similar to other epithelial cells, taste cells turn over continuously, with an average life span of about 8-12 days. To maintain structural homeostasis in taste buds, new cells are generated to replace dying cells. Several recent studies using genetic lineage tracing methods have identified populations of progenitor/stem cells for taste buds, although contributions of these progenitor/stem cell populations to taste bud homeostasis have yet to be fully determined. Some regulatory factors of taste cell differentiation and degeneration have been identified, but our understanding of these aspects of taste bud homoeostasis remains limited. Many patients with various diseases develop taste disorders, including taste loss and taste distortion. Decline in taste function also occurs during aging. Recent studies suggest that disruption or alteration of taste bud homeostasis may contribute to taste dysfunction associated with disease and aging.

Expression and secretion of TNF-α in mouse taste buds: a novel function of a specific subset of type II taste cells

Taste buds are chemosensory structures widely distributed on the surface of the oral cavity and larynx. Taste cells, exposed to the oral environment, face great challenges in defense against potential pathogens. While immune cells, such as T-cells and macrophages, are rarely found in taste buds, high levels of expression of some immune-response-associated molecules are observed in taste buds. Yet, the cellular origins of these immune molecules such as cytokines in taste buds remain to be determined. Here, we show that a specific subset of taste cells selectively expresses high levels of the inflammatory cytokine tumor necrosis factor-α (TNF-α). Based on immuno-colocalization experiments using taste-cell-type markers, the TNF-α-producing cells are predominantly type II taste cells expressing the taste receptor T1R3. These cells can rapidly increase TNF-α production and secretion upon inflammatory challenges, both in vivo and in vitro. The lipopolysaccharide (LPS)-induced TNF-α expression in taste cells was completely eliminated in TLR2^−/−/TLR4^−/− double-gene-knockout mice, which confirms that the induction of TNF-α in taste buds by LPS is mediated through TLR signaling pathways. The taste-cell-produced TNF-α may contribute to local immune surveillance, as well as regulate taste sensation under normal and pathological conditions.