Sodium Imbalance in Mice Results Primarily in Compensatory Gene Regulatory Responses in Kidney and Colon, but Not in Taste Tissue

LRBA, a BEACH protein mutated in human immune deficiency, is widely expressed in epithelia, exocrine and endocrine glands, and neurons

Mutations in LRBA, a BEACH domain protein, cause severe immune deficiency in humans. LRBA is expressed in many tissues and organs according to biochemical analysis, but little is known about its cellular and subcellular localization, and its deficiency phenotype outside the immune system. By LacZ histochemistry of Lrba gene-trap mice, we performed a comprehensive survey of LRBA expression in numerous tissues, detecting it in many if not all epithelia, in exocrine and endocrine cells, and in subpopulations of neurons. Immunofluorescence microscopy of the exocrine and endocrine pancreas, salivary glands, and intestinal segments, confirmed these patterns of cellular expression and provided information on the subcellular localizations of the LRBA protein. Immuno-electron microscopy demonstrated that in neurons and endocrine cells, which co-express LRBA and its closest relative, neurobeachin, both proteins display partial association with endomembranes in complementary, rather than overlapping, subcellular distributions. Prominent manifestations of human LRBA deficiency, such as inflammatory bowel disease or endocrinopathies, are believed to be primarily due to immune dysregulation. However, as essentially all affected tissues also express LRBA, it is possible that LRBA deficiency enhances their vulnerability and contributes to the pathogenesis.

A gut-brain axis mediates sodium appetite via gastrointestinal peptide regulation on a medulla-hypothalamic circuit

Salt homeostasis is orchestrated by both neural circuits and peripheral endocrine factors. The colon is one of the primary sites for electrolyte absorption, while its potential role in modulating sodium intake remains unclear. Here, we revealed that a gastrointestinal hormone, secretin, is released from colon endocrine cells under body sodium deficiency and is indispensable for inducing salt appetite. As the neural substrate, circulating secretin activates specific receptors in the nucleus of the solitary tracts, which further activates the downstream paraventricular nucleus of the hypothalamus, resulting in enhanced sodium intake. These results demonstrated a previously unrecognized gut-brain pathway for the timely regulation of sodium homeostasis.

Relationship between ENaC Regulators and SARS-CoV-2 Virus Receptor (ACE2) Expression in Cultured Adult Human Fungiform (HBO) Taste Cells

In addition to the α, β, and γ subunits of ENaC, human salt-sensing taste receptor cells (TRCs) also express the δ-subunit. At present, it is not clear if the expression and function of the ENaC δ-subunit in human salt-sensing TRCs is also modulated by the ENaC regulatory hormones and intracellular signaling effectors known to modulate salt responses in rodent TRCs. Here, we used molecular techniques to demonstrate that the G-protein-coupled estrogen receptor (GPER1), the transient receptor potential cation channel subfamily V member 1 (TRPV1), and components of the renin-angiotensin-aldosterone system (RAAS) are expressed in δ-ENaC-positive cultured adult human fungiform (HBO) taste cells. Our results suggest that RAAS components function in a complex with ENaC and TRPV1 to modulate salt sensing and thus salt intake in humans. Early, but often prolonged, symptoms of COVID-19 infection are the loss of taste, smell, and chemesthesis. The SARS-CoV-2 spike protein contains two subunits, S1 and S2. S1 contains a receptor-binding domain, which is responsible for recognizing and binding to the ACE2 receptor, a component of RAAS. Our results show that the binding of a mutated S1 protein to ACE2 decreases ACE2 expression in HBO cells. We hypothesize that changes in ACE2 receptor expression can alter the balance between the two major RAAS pathways, ACE1/Ang II/AT1R and ACE2/Ang-(1-7)/MASR1, leading to changes in ENaC expression and responses to NaCl in salt-sensing human fungiform taste cells.

Potential Effects of Prolonged Water-Only Fasting Followed by a Whole-Plant-Food Diet on Salty and Sweet Taste Sensitivity and Perceived Intensity, Food Liking, and Dietary Intake

The overconsumption of calorie-dense foods high in added salt, sugar, and fat is a major contributor to current rates of obesity, and methods to reduce consumption are needed. Prolonged water-only fasting followed by an exclusively whole-plant-food diet free of added salt, oil, and sugar may reduce the consumption of these hyper-palatable foods, but such effects have not been quantified. Therefore, we conducted a preliminary study to estimate the effects of this intervention on salty and sweet taste detection and recognition thresholds and perceived taste intensity after at least five days of fasting and at refeed day three. We also assessed the effects on sweet, salty, and fatty food preference and overall dietary consumption 30 days after the day three refeed visit. Based on this data, we estimated that 10 days after the start of the fasting, salty taste recognition, sweet taste detection, and sweet taste recognition thresholds decreased significantly, salty taste intensity ratings increased significantly, and sweet taste intensity ratings decreased significantly. We also have preliminary data that prolonged water-only fasting followed by refeeding on an exclusively whole-food-plant diet may reduce salty/fatty and sweet/fatty food liking, reduce sugar intake, and increase vegetable intake. These results support further research into the effects of fasting and diet on taste function and food likability and consumption.

Association between preeclampsia and prostasin polymorphism in Pakistani females

Objectives:

To investigate the relationship between a prostasin gene variations and the development of preeclampsia in a Pakistani female population.

Methods:

This was a case-control study carried out at University of Karachi, Karachi, Pakistan between May 2018 and 2019. A single nucleotide polymorphism (SNP) at rs12597511 locus was examined with polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses in 76 preeclamptic and 74 normotensive expecting mothers.

Results:

We observed significantly increased risk of preeclampsia associated with the CC genotype of rs12597511 polymorphism as compared to TT (p<0.001, OR=8.08, 95% CI:1.28-31.19) and TT/TC (p<0.001, OR=14.66 and 95% CI: 3.31-65.07) genotypes carriers. Calculation of the allelic distribution revealed a higher frequency of the T allele (82%) among controls; however, the C allele was more prevalent in the preeclamptic group (36%) significantly.

Conclusion:

The significantly higher C allele frequency in the prostasin gene at the rs12597511 locus in the preeclamptic group indicates that the distribution of the C allele of the prostasin gene is a potential risk factor contributing to the development of preeclampsia.

Optogenetic Stimulation of Type I GAD65+ Cells in Taste Buds Activates Gustatory Neurons and Drives Appetitive Licking Behavior in Sodium-Depleted Mice

Mammalian taste buds are comprised of specialized neuroepithelial cells that act as sensors for molecules that provide nutrition (e.g., carbohydrates, amino acids, and salts) and those that are potentially harmful (e.g., certain plant compounds and strong acids). Type II and III taste bud cells (TBCs) detect molecules described by humans as "sweet," "bitter," "umami," and "sour." TBCs that detect metallic ions, described by humans as "salty," are undefined. Historically, type I glial-like TBCs have been thought to play a supportive role in the taste bud, but little research has been done to explore their role in taste transduction. Some evidence implies that type I cells may detect sodium (Na⁺) via an amiloride-sensitive mechanism, suggesting they play a role in Na⁺ taste transduction. We used an optogenetic approach to study type I TBCs by driving the expression of the light-sensitive channelrhodopsin-2 (ChR2) in type I GAD65⁺ TBCs of male and female mice. Optogenetic stimulation of GAD65⁺ TBCs increased chorda tympani nerve activity and activated gustatory neurons in the rostral nucleus tractus solitarius. "N neurons," whose NaCl responses were blocked by the amiloride analog benzamil, responded robustly to light stimulation of GAD65⁺ TBCs on the anterior tongue. Two-bottle preference tests were conducted under Na⁺-replete and Na⁺-deplete conditions to assess the behavioral impact of optogenetic stimulation of GAD65⁺ TBCs. Under Na⁺-deplete conditions GAD65-ChR2-EYFP mice displayed a robust preference for H₂O illuminated with 470 nm light versus nonilluminated H₂O, suggesting that type I glial-like TBCs are sufficient for driving a behavior that resembles Na⁺ appetite.SIGNIFICANCE STATEMENT This is the first investigation on the role of type I GAD65⁺ taste bud cells (TBCs) in taste-mediated physiology and behavior via optogenetics. It details the first definitive evidence that selective optogenetic stimulation of glial-like GAD65⁺ TBCs evokes neural activity and modulates behavior. Optogenetic stimulation of GAD65⁺ TBCs on the anterior tongue had the strongest effect on gustatory neurons that responded best to NaCl stimulation through a benzamil-sensitive mechanism. Na⁺-depleted mice showed robust preferences to "light taste" (H₂O illuminated with 470 nm light vs nonilluminated H₂O), suggesting that the activation of GAD65⁺ cells may generate a salt-taste sensation in the brain. Together, our results shed new light on the role of GAD65⁺ TBCs in gustatory transduction and taste-mediated behavior.

Optogenetic Stimulation of Type I GAD65+ Cells in Taste Buds Activates Gustatory Neurons and Drives Appetitive Licking Behavior in Sodium-Depleted Mice

Mammalian taste buds are comprised of specialized neuroepithelial cells that act as sensors for molecules that provide nutrition (e.g., carbohydrates, amino acids, and salts) and those that are potentially harmful (e.g., certain plant compounds and strong acids). Type II and III taste bud cells (TBCs) detect molecules described by humans as "sweet," "bitter," "umami," and "sour." TBCs that detect metallic ions, described by humans as "salty," are undefined. Historically, type I glial-like TBCs have been thought to play a supportive role in the taste bud, but little research has been done to explore their role in taste transduction. Some evidence implies that type I cells may detect sodium (Na⁺) via an amiloride-sensitive mechanism, suggesting they play a role in Na⁺ taste transduction. We used an optogenetic approach to study type I TBCs by driving the expression of the light-sensitive channelrhodopsin-2 (ChR2) in type I GAD65⁺ TBCs of male and female mice. Optogenetic stimulation of GAD65⁺ TBCs increased chorda tympani nerve activity and activated gustatory neurons in the rostral nucleus tractus solitarius. "N neurons," whose NaCl responses were blocked by the amiloride analog benzamil, responded robustly to light stimulation of GAD65⁺ TBCs on the anterior tongue. Two-bottle preference tests were conducted under Na⁺-replete and Na⁺-deplete conditions to assess the behavioral impact of optogenetic stimulation of GAD65⁺ TBCs. Under Na⁺-deplete conditions GAD65-ChR2-EYFP mice displayed a robust preference for H₂O illuminated with 470 nm light versus nonilluminated H₂O, suggesting that type I glial-like TBCs are sufficient for driving a behavior that resembles Na⁺ appetite.SIGNIFICANCE STATEMENT This is the first investigation on the role of type I GAD65⁺ taste bud cells (TBCs) in taste-mediated physiology and behavior via optogenetics. It details the first definitive evidence that selective optogenetic stimulation of glial-like GAD65⁺ TBCs evokes neural activity and modulates behavior. Optogenetic stimulation of GAD65⁺ TBCs on the anterior tongue had the strongest effect on gustatory neurons that responded best to NaCl stimulation through a benzamil-sensitive mechanism. Na⁺-depleted mice showed robust preferences to "light taste" (H₂O illuminated with 470 nm light vs nonilluminated H₂O), suggesting that the activation of GAD65⁺ cells may generate a salt-taste sensation in the brain. Together, our results shed new light on the role of GAD65⁺ TBCs in gustatory transduction and taste-mediated behavior.