Genetic variants in taste genes play a role in oral microbial composition and severe early childhood caries.

Severe early childhood caries (S-ECC) is a multifactorial disease with strong evidence of genetic inheritance. Previous studies suggest that variants in taste genes are associated with dental caries due to the role of taste proteins in mediating taste preferences, oral innate immunity, and important host-microbial interactions. However, few taste genes have been investigated in caries studies. Therefore, the associations of genetic variants in sweet, bitter, umami, salt, sour, carbonation, and fat taste-related genes with S-ECC and plaque microbial composition (16S and ITS1 rRNA sequencing) were evaluated. The results showed that sixteen variants in seven taste genes (SCNN1D, CA6, TAS2R3, OTOP1, TAS2R5, TAS2R60, and TAS2R4) were associated with S-ECC. Twenty-one variants in twelve taste genes were correlated with relative abundances of bacteria or fungi. These results suggest that S-ECC risk and composition of the plaque microbiome can be partially influenced by genetic variants in genes related to taste sensation.

Extraoral expression and characterization of bitter taste receptors in Astyanax mexicanus (Mexican tetra fish).

The chemical senses of olfaction and taste are well developed in fish and play a vital role in its various activities such as navigation, mate recognition, and food detection. The small teleost fish Astyanax mexicanus consists of interfertile river-dwelling and cave-dwelling populations, referred to as "surface fish" and "cavefish" respectively. An important anatomical feature of cavefish is the lack of eyes leading them to be referred to as blind fish and suggesting an enhanced functional role for other senses such as taste. In this study, we characterize the expression of bitter taste receptors (T2Rs or Tas2Rs) in A. mexicanus and investigate their functionality in a heterologous expression system. The genome database of A. mexicanus (ensemble and NCBI) showed 7 Tas2Rs, among these Tas2R1, Tas2R3, Tas2R4, and Tas2R114 are well characterized in humans and mice but not in A. mexicanus. Therefore, the 4 Tas2Rs were selected for further analysis and their expression in A. mexicanus was confirmed by in situ hybridization and RT-PCR in early developmental stages. These Tas2Rs are expressed in various oral and extraoral organs (liver, fins, jaws, and gills) in A. mexicanus, and Tas2R1 has maximum expression and is localized throughout the fish body. Using the heterologous expression of A. mexicanus T2Rs in HEK293T cells coupled with cell-based calcium mobilization assays, we show that A. mexicanus T2Rs are activated by commonly used fish food and known bitter agonists, including quinine. This study provides novel insights into the extraoral expression of T2Rs in A. mexicanus and suggests their importance in extraoral food detection.

Association between Downstream Taste Signaling Genes, Oral Microbiome, and Severe Early Childhood Caries.

Polymorphisms in taste receptor genes have been shown to play a role in early childhood caries (ECC), a multifactorial, biofilm-mediated disease. This study aimed to evaluate associations between severe-ECC (S-ECC), the oral microbiome, and variants in genes that encode components of the G protein-coupled receptor (GPCR) signaling cascade involved in taste sensation. A total of 176 children (88 caries-free; 88 with S-ECC) were recruited. Analyses of 16S and ITS1 rRNA microbial genes and seven (GNAQ, GNAS, GNAT3, GNAI2, RAC1, RALB, and PLCB2) human genes were pursued using next-generation sequencing. Regression analyses were performed to evaluate associations between genetic variants, S-ECC, and the supragingival plaque microbiome. Results suggest that PLCB2 rs2305645 (T), rs1869901 (G), and rs2305649 (G) alleles had a protective effect on S-ECC (rs2305645, odds ratio (OR) = 0.27 (95% confidence interval (CI): 0.14-0.51); rs1869901, OR = 0.34 (95% CI: 0.20-0.58); and rs2305649, OR = 0.43 (95% CI: 0.26-0.71)). Variants in GNAQ, GNAS, GNAT3, PLCB2, RALB, and RAC1 were associated with oral fungal and bacterial community composition. This study revealed that three loci at PLCB2 are significantly associated with S-ECC. Variants in multiple genes were associated with the composition of dental biofilm. These findings contribute to the current knowledge about the role of genetics in S-ECC.

Association of Bitter Taste Receptor T2R38 Polymorphisms, Oral Microbiota, and Rheumatoid Arthritis.

The association of taste genetics and the oral microbiome in autoimmune diseases such as rheumatoid arthritis (RA) has not been reported. We explored a novel oral mucosal innate immune pathway involving the bitter taste G protein-coupled receptor T2R38. This case-control study aimed to evaluate whether T2R38 polymorphisms associate with the buccal microbial composition in RA. Genomic DNA was obtained from buccal swabs of 35 RA patients and 64 non-RA controls. TAS2R38 genotypes were determined by Sanger sequencing. The buccal microbiome was assessed by Illumina MiSeq sequencing of the V4-16S rRNA gene. Bacterial community differences were analyzed with alpha and beta diversity measures. Linear discriminant analysis effect size identified taxa discriminating between RA versus non-RA and across TAS2R38 genotypes. TAS2R38 genotype frequency was similar between RA and non-RA controls (PAV/PAV; PAV/AVI; AVI/AVI: RA 42.9%; 45.7%; 11.4% versus controls 32.8%; 48.4%; 18.8%, chi-square (2, N = 99) = 2.1, p = 0.35). The relative abundance of Porphyromonas, among others, differed between RA and non-RA controls. The relative abundance of several bacterial species also differed across TAS2R38 genotypes. These findings suggest an association between T2R38 polymorphisms and RA buccal microbial composition. However, further research is needed to understand the impact of T2R38 in oral health and RA development.

Characterization of Supragingival Plaque and Oral Swab Microbiomes in Children With Severe Early Childhood Caries.

The human oral cavity harbors one of the most diverse microbial communities with different oral microenvironments allowing the colonization of unique microbial species. This study aimed to determine which of two commonly used sampling sites (dental plaque vs. oral swab) would provide a better prediction model for caries-free vs. severe early childhood caries (S-ECC) using next generation sequencing and machine learning (ML). In this cross-sectional study, a total of 80 children (40 S-ECC and 40 caries-free) < 72 months of age were recruited. Supragingival plaque and oral swab samples were used for the amplicon sequencing of the V4-16S rRNA and ITS1 rRNA genes. The results showed significant differences in alpha and beta diversity between dental plaque and oral swab bacterial and fungal microbiomes. Differential abundance analyses showed that, among others, the cariogenic species Streptococcus mutans was enriched in the dental plaque, compared to oral swabs, of children with S-ECC. The fungal species Candida dubliniensis and C. tropicalis were more abundant in the oral swab samples of children with S-ECC compared to caries-free controls. They were also among the top 20 most important features for the classification of S-ECC vs. caries-free in oral swabs and for the classification of dental plaque vs. oral swab in the S-ECC group. ML approaches revealed the possibility of classifying samples according to both caries status and sampling sites. The tested site of sample collection did not change the predictability of the disease. However, the species considered to be important for the classification of disease in each sampling site were slightly different. Being able to determine the origin of the samples could be very useful during the design of oral microbiome studies. This study provides important insights into the differences between the dental plaque and oral swab bacteriome and mycobiome of children with S-ECC and those caries-free.

Role of Maternal Infections and Inflammatory Responses on Craniofacial Development.

Pregnancy is a tightly regulated immunological state. Mild environmental perturbations can affect the developing fetus significantly. Infections can elicit severe immunological cascades in the mother's body as well as the developing fetus. Maternal infections and resulting inflammatory responses can mediate epigenetic changes in the fetal genome, depending on the developmental stage. The craniofacial development begins at the early stages of embryogenesis. In this review, we will discuss the immunology of pregnancy and its responsive mechanisms on maternal infections. Further, we will also discuss the epigenetic effects of pathogens, their metabolites and resulting inflammatory responses on the fetus with a special focus on craniofacial development. Understanding the pathophysiological mechanisms of infections and dysregulated inflammatory responses during prenatal development could provide better insights into the origins of craniofacial birth defects.

Chemosensory bitter taste receptors (T2Rs) are activated by multiple antibiotics.

Many medications including antibiotics taste bitter. The potency of these antibiotics on the 25 bitter taste receptors (T2Rs) in humans remains poorly understood. Here we characterize by sensory and structure-function analyses how antibiotics frequently used to treat airway infections in cystic fibrosis activate multiple human T2Rs. The potency of the broad-spectrum antibiotics, tobramycin, levofloxacin, and azithromycin on the highly expressed T2Rs in airways, T2R4, T2R14, and T2R20 was pursued. The amino acids and structural features of T2R4, T2R14, and T2R20 important for antibiotic binding were characterized by mutational analysis in heterologous cell-based assays. Strikingly, extracellular loop 2 in T2Rs performs a key function in binding to antibiotics with contribution from residues in transmembrane helices. Our results suggest that different antibiotics activate multiple T2Rs with different potencies. An understanding of the nonantibiotic and physiologic effects mediated through T2Rs on the host cells is much needed.-Jaggupilli, A., Singh, N., De Jesus, V. C., Gounni, M. S., Dhanaraj, P., Chelikani, P. Chemosensory bitter taste receptors (T2Rs) are activated by multiple antibiotics.

Influence of laser photobiomodulation (GaAlAs) on salivary flow rate and histomorphometry of the submandibular glands of hypothyroid rats.

The aim of this study was to analyze the influence of laser photobiomodulation in salivary flow, weight, and histomorphometry of the submandibular glands of hypothyroid rats. Fifty-six male Wistar albino rats were divided in euthyroid group and hypothyroid group, treated with propylthiouracil (PTU) to induce hypothyroidism. Each group was divided into control (without laser) and laser groups (GaAlAs): λ660 nm (40 mW), λ780 nm (40 mW), and λ780 nm (70 mW). The laser application on the submandibular gland occurred after 2 weeks of PTU treatment and repeatedly during 2 weeks every 48 h. The rats were anesthetized, tracheostomized, and the evaluation of the salivary flow rate (µL/min/100 g body weight) was made by the weight of the saliva collected for 15 min from the first drop. After the animals' death, the glands were dissected and processed for histological analysis. There was an evident reduction of the salivary flow of hypothyroid rats in all groups in comparison to euthyroid group (Mann-Whitney test, p < 0.05). No significant difference was found in the salivary flow of rats that received laser photobiomodulation compared with their control groups. Histological analysis revealed a decrease in the parenchyma of the salivary glands of hypothyroid rats, but the laser was not able to reverse this process. Hypothyroid rats irradiated or not with laser showed acini and acinar cells with significantly smaller areas than euthyroid groups. The laser photobiomodulation protocol used was not able to change salivary flow or reverse the acinar atrophy process in the submandibular glands of hypothyroid rats.