Kentaro Nagaoka

Diet is a key factor shaping gut microbiota in mammals, with herbivores and carnivores harboring distinct microbial communities. However, despite humans being highly omnivorous, it remains unclear whether their gut microbiota more closely resembles that of herbivores or carnivores or how individual-level variations along this spectrum are associated with human health status. We compared gut microbiota profiles of 858 samples from 109 mammalian species and constructed a Herbivore-Carnivore (HC) index based on bacterial groups characteristic of each diet. The HC-index positioned humans between herbivores and carnivores and showed that traditional hunter-gatherers and nonhuman apes retained herbivore-leaning profiles, whereas urbanized humans exhibited a shift toward a carnivore-leaning state. By applying the HC-index to >72,000 participants across multiple cohorts worldwide, we found that elevated HC-index values were associated with plant-based and fiber-rich diets, greater microbial diversity, enhanced potential to degrade plant-derived carbohydrates, favorable clinical measures, and lower prevalence of self-reported disease. We demonstrated that the HC balance of gut microbiota captures a conserved diet-related gradient across mammals and provides an interpretable framework linking human diet, microbial function, and health.

Pregnancy is accompanied by profound endocrine remodeling, yet the mechanisms by which maternal hormonal signals establish long-term tissue homeostasis remain largely unknown. Here we identify maternal progesterone signaling as a developmental cue that establishes lifelong oral homeostasis through a hormone–lipid–microbiome axis. We show that the membrane progesterone receptor mPRδ is selectively expressed in the developing and maternal submandibular glands, where it mediates non-genomic progesterone signaling to promote epithelial differentiation by driving the selective mobilization of docosahexaenoic acid (DHA). Loss of this pathway disrupts salivary gland maturation, reshapes the oral microbial ecosystem through the selective expansion of Pasteurellaceae, and causes local inflammation as well as systemic metabolic dysfunction. Mechanistically, antibiotic treatment abolishes these phenotypes, whereas transfer of the oral microbiota recapitulates disease, demonstrating that developmental defects in the host are translated into long-term pathology through the oral microbiome. Remarkably, maternal—but not adult—DHA supplementation restores salivary gland development and microbial homeostasis and prevents adult disease phenotypes, identifying a critical developmental window during which oral homeostasis is durably established. Collectively, these findings reveal a previously unrecognized maternal endocrine mechanism that establishes lifelong host–microbiome homeostasis and identify developmental programming as a fundamental principle linking maternal physiology to adult health.

Progesterone governs the establishment and maintenance of pregnancy in ruminants, acting through the nuclear progesterone receptor (PGR) and, potentially, through membrane progesterone receptors (mPRs) of the PAQR family. The cellular distribution of mPRs in ruminant reproductive tissues, however, remains undefined. We generated and validated rabbit polyclonal antibodies against the intracellular C-terminal peptides of bovine PAQR6 (mPRδ) and PAQR8 (mPRβ), and used them, with quantitative PCR of the uterus and conceptus, to map these receptors in the ovine uterus and conceptus and in the bovine ovary. Both antisera showed high ELISA titer against their immunizing peptides, negligible preimmune reactivity, and complete loss of tissue signal after peptide pre-absorption. By qPCR, PAQR6 , PAQR8 and PGR transcript levels did not change significantly across the peri-implantation period in either the conceptus or the endometrium; in contrast, the progesterone-responsive gene ZBTB16 increased markedly in the conceptus (up to ∼45-fold by day 21, p < 0.05 at days 17, 19 and 21), whereas FKBP5 showed a numerical increase without reaching statistical significance. Both genes remained relatively stable in the endometrium, indicating conceptus-specific changes in progesterone-responsive gene expression. At the protein level, PAQR6 and PAQR8 localized to the luminal and glandular epithelium of the endometrium across the cycle and early pregnancy, and to follicular (granulosa) and luteal cells of the ovary. Dual immunofluorescence in the ovine endometrium showed that both PAQR6 and PAQR8 are enriched at the apical surface of the luminal epithelium and are spatially distinct from the basolateral adherens-junction marker E-cadherin. These results provide a protein-level map of PAQR6 and PAQR8 in the ruminant reproductive tract, identify the apical epithelial surface as a site of receptor enrichment, and show that the endometrial epithelium retains membrane progesterone receptors while progesterone-responsive gene expression changes dynamically in the conceptus during the peri-implantation period. The validated ruminant-reactive antibodies provide a resource for future functional studies.

Progesterone is essential for the establishment and maintenance of pregnancy, primarily through the classical nuclear progesterone receptor (PGR). However, progesterone also exerts rapid, non-genomic effects through membrane progesterone receptors, including members of the progestin and adipoQ receptor (PAQR) family, whose cellular distribution and potential roles at the human maternal–fetal interface remain poorly understood. We therefore sought to define the cell-type-specific expression landscape of classical and membrane progesterone receptors during early human pregnancy. We analyzed publicly available single-cell RNA-sequencing datasets of the first-trimester human maternal–fetal interface to characterize the expression of PGR and PAQR family members across trophoblast, immune, stromal, and vascular cell populations. Major expression patterns were examined across independent datasets and further assessed using spatial transcriptomic data. PGR expression was predominantly localized to decidual stromal and perivascular populations, whereas individual PAQR family members showed distinct cellular distributions. PAQR6 was enriched in decidual natural killer cells, PAQR7 was broadly expressed in trophoblast populations, PAQR8 was prominently expressed in fetal stromal and macrophage populations, including Hofbauer cells, and PAQR9 showed prominent enrichment in syncytiotrophoblasts. Selected cell-type-specific patterns were further supported by spatial transcriptomic analysis. These findings provide a cell-type-resolved framework for investigating how distinct progesterone receptor systems mediate progesterone signaling across maternal and fetal cellular compartments during early human placentation.

Preen gland secretions are known to vary depending on sex, season and species and are thought to play essential roles in avian life history. However, their chemical composition and functions remain largely unclear in Procellariiform seabirds with well‐developed olfactory senses. Storm petrels, known for their distinctive body odour, may use preen gland secretions as cues for social communication. This study aimed to provide foundational insight into the function of the preen gland in storm petrels by examining the chemical composition and seasonal variation of secretions in male and female Tristram's Storm Petrels Hydrobates tristrami during the breeding season. Qualitative analysis using gas chromatography–mass spectrometry revealed that the major components were lipid esters, particularly octadecyl octanoate, along with hydrocarbons and aliphatic alcohols. The composition showed sex‐specific seasonal variation across breeding stages. While few compounds in females showed significant seasonal variation, a greater number of compounds in males changed significantly from the early breeding period to incubation. Notably, 1‐hexadecanol significantly increased from incubation to chick‐rearing in both sexes. The drivers of these changes remain unclear, whether related to diet, endocrine dynamics or breeding behaviour. Future integrative research, including the monitoring of prey composition and parent–offspring interactions, is needed to clarify these relationships. This study presents the first description of the chemical composition and seasonal variation of preen gland secretions in storm petrels, forming a basis for further investigation into the functional role of the preen gland during the breeding season.

Mastitis remains one of the most prevalent and economically significant diseases in dairy cattle worldwide. Although somatic cell count (SCC) is widely used as an indicator for mastitis diagnosis, its physiological variability limits its utility for predicting individual susceptibility. In this study, we aimed to identify genomic markers associated with recurrent clinical mastitis by defining mastitis-susceptible cows as those experiencing three or more episodes within a single lactation. Whole-genome resequencing was conducted on 50 Holstein cows (25 mastitis-susceptible and 25 healthy controls), yielding 536,184 high-quality SNPs after stringent quality control. A genome-wide association analysis identified 86 SNPs surpassing the significance threshold (–log₁₀P > 5.0), and seven candidate SNPs were evaluated in an independent cohort of 100 cows. Notably, the majority of candidate SNPs were localized on the X chromosome, suggesting a potential role for X-linked variation in mastitis immune response and disease resistance. While the candidate marker panel combining SNP1, SNP2, and SNP7 demonstrated moderate sensitivity (47%), its high specificity (98%) highlights its potential utility as a preliminary screening tool for identifying individuals at increased risk of recurrent mastitis. These findings provide a foundation for further functional validation and large-scale replication studies, which are essential for implementing effective genomic selection strategies to mitigate mastitis incidence in dairy herds.

Maternal separation (MS) is a widely used model of early-life stress, yet the biological pathways transmitting maternal stress signals to offspring remain incompletely understood. Breast milk represents a primary biological interface between mother and infant, and stress-induced changes in milk composition may influence offspring development through the gut microbiota–brain axis. Here, we investigated whether MS alters the breast milk metabolome and whether such changes are associated with offspring gut microbiota composition, serum metabolite profiles, and serotonin-related gene expression in the prefrontal cortex. Using an integrated multi-omics approach in mice, we found that MS dams had elevated myristic acid and ethanolamine levels in breast milk. MS offspring exhibited reduced A. muciniphila abundance in the cecal microbiota, elevated myristic acid and decreased inosine in cecal contents, decreased inosine in serum, and reduced Tph2 and Htr1b expression in the prefrontal cortex. Oral myristic acid supplementation in neonatal pups reduced A. muciniphila abundance, and inosine supplementation selectively increased Htr1a expression. Spearman correlation analyses using paired individual data revealed a negative association between cecal myristic acid and cecal inosine levels, and a positive correlation between cecal inosine and prefrontal Tph2 expression, supporting quantitative links among these components. Collectively, these findings identify coordinated associations among maternal stress-induced milk fatty acid changes, offspring gut microbiota, microbial metabolites, and serotonin-related gene expression, providing an exploratory framework for understanding milk-mediated effects on the developing gut–brain axis.

Macropod progressive periodontal disease (MPPD) is a severe oral condition frequently observed in captive macropods, particularly red kangaroos ( Osphranter rufus ), yet its underlying biological features remain poorly understood. In this exploratory descriptive study, we investigated oral and fecal microbiomes and metabolomic profiles in captive red kangaroos to characterise microbial and metabolic patterns associated with MPPD. Oral swabs, fecal samples and serum were collected from clinically healthy individuals and animals diagnosed with MPPD. Microbiome profiling was performed using 16S rRNA gene sequencing, and untargeted metabolomic analyses were conducted using GC–MS. All analyses were conducted in a descriptive manner to summarise observed patterns and trends rather than to support formal statistical inference. Descriptive comparisons suggested differences in the oral microbiome composition of animals with MPPD, including increased representation of several taxa previously associated with periodontal disease in other species. Oral metabolomic profiling indicated variation in multiple metabolites, including lower relative levels of guanosine higher relative levels of suberic acid and lower relative levels of L‐octanoylcarnitine and adipic acid in affected animals. In contrast, fecal microbiome and serum metabolome profiles showed comparatively limited variation across groups. Although limited by small sample size, this study provides preliminary, descriptive observations on microbiome and metabolome features associated with MPPD in captive red kangaroos. These findings offer an initial framework to inform future hypothesis‐driven investigations using larger cohorts.