Human and Nonhuman Primate Lineage-Specific Footprints in the Salivary Proteome.

Proteins in saliva are needed for preprocessing food in the mouth, maintenance of tooth mineralization, and protection from microbial pathogens. Novel insights into human lineage-specific functions of salivary proteins and clues to their involvement in human disease can be gained through evolutionary studies, as recently shown for salivary amylase AMY1 and salivary agglutinin DMBT1/gp340. However, the entirety of proteins in saliva, the salivary proteome, has not yet been investigated from an evolutionary perspective. Here, we compared the proteomes of human saliva and the saliva of our closest extant evolutionary relatives, chimpanzees and gorillas, using macaques as an outgroup, with the aim to uncover features in saliva protein composition that are unique to each species. We found that humans produce a waterier saliva, containing less than half total protein than great apes and Old World monkeys. For all major salivary proteins in humans, we could identify counterparts in chimpanzee and gorilla saliva. However, we discovered unique protein profiles in saliva of humans that were distinct from those of nonhuman primates. These findings open up the possibility that dietary differences and pathogenic pressures may have shaped a distinct salivary proteome in the human lineage.

Oral streptococci utilize a Siglec-like domain of serine-rich repeat adhesins to preferentially target platelet sialoglycans in human blood.

Damaged cardiac valves attract blood-borne bacteria, and infective endocarditis is often caused by viridans group streptococci. While such bacteria use multiple adhesins to maintain their normal oral commensal state, recognition of platelet sialoglycans provides an intermediary for binding to damaged valvular endocardium. We use a customized sialoglycan microarray to explore the varied binding properties of phylogenetically related serine-rich repeat adhesins, the GspB, Hsa, and SrpA homologs from Streptococcus gordonii and Streptococcus sanguinis species, which belong to a highly conserved family of glycoproteins that contribute to virulence for a broad range of Gram-positive pathogens. Binding profiles of recombinant soluble homologs containing novel sialic acid-recognizing Siglec-like domains correlate well with binding of corresponding whole bacteria to arrays. These bacteria show multiple modes of glycan, protein, or divalent cation-dependent binding to synthetic glycoconjugates and isolated glycoproteins in vitro. However, endogenous asialoglycan-recognizing clearance receptors are known to ensure that only fully sialylated glycans dominate in the endovascular system, wherein we find these particular streptococci become primarily dependent on their Siglec-like adhesins for glycan-mediated recognition events. Remarkably, despite an excess of alternate sialoglycan ligands in cellular and soluble blood components, these adhesins selectively target intact bacteria to sialylated ligands on platelets, within human whole blood. These preferred interactions are inhibited by corresponding recombinant soluble adhesins, which also preferentially recognize platelets. Our data indicate that circulating platelets may act as inadvertent Trojan horse carriers of oral streptococci to the site of damaged endocardium, and provide an explanation why it is that among innumerable microbes that gain occasional access to the bloodstream, certain viridans group streptococci have a selective advantage in colonizing damaged cardiac valves and cause infective endocarditis.

Recent evolution of the salivary mucin MUC7.

Genomic structural variants constitute the majority of variable base pairs in primate genomes and affect gene function in multiple ways. While whole gene duplications and deletions are relatively well-studied, the biology of subexonic (i.e., within coding exon sequences), copy number variation remains elusive. The salivary MUC7 gene provides an opportunity for studying such variation, as it harbors copy number variable subexonic repeat sequences that encode for densely O-glycosylated domains (PTS-repeats) with microbe-binding properties. To understand the evolution of this gene, we analyzed mammalian and primate genomes within a comparative framework. Our analyses revealed that (i) MUC7 has emerged in the placental mammal ancestor and rapidly gained multiple sites for O-glycosylation; (ii) MUC7 has retained its extracellular activity in saliva in placental mammals; (iii) the anti-fungal domain of the protein was remodified under positive selection in the primate lineage; and (iv) MUC7 PTS-repeats have evolved recurrently and under adaptive constraints. Our results establish MUC7 as a major player in salivary adaptation, likely as a response to diverse pathogenic exposure in primates. On a broader scale, our study highlights variable subexonic repeats as a primary source for modular evolutionary innovation that lead to rapid functional adaptation.

Hypothalamic alterations in fetuses of high fat diet-fed obese female rats.

The offspring of high fat (HF) diet-fed rats display increased body weight during adulthood. However, it is not known whether the changes in appetite regulation in these animals occur in utero or postnatally. We investigated the effects of maternal obesity induced by a HF diet prior to and during pregnancy on leptin and insulin signaling and the expression of orexigenic and anorexigenic peptides in term fetal hypothalami. The consumption of a HF diet prior to and during pregnancy resulted in obesity in HF female rats; additionally, HF female rats exhibited hyperinsulinemia and hyperleptinemia which were exaggerated in late gestation compared with control female rats that were fed a standard rodent laboratory chow (LC). Term fetuses of HF female rats (FHF) also had significantly higher serum leptin and insulin levels compared with control fetuses (FLC) while there was no difference in average fetal weight between the two groups. FHF hypothalami showed elevated levels of mRNA and proteins for leptin long receptor and insulin receptor beta-subunit. However, the protein levels of signal transducers and activators of transcription-3 and insulin receptor substrate-2, the downstream signaling components of leptin and insulin signaling respectively were decreased. Also, FHF hypothalami had increased mRNA levels of neuropeptide Y and agouti-related polypeptide indicating that orexigenic neuropeptides in HF progeny are already upregulated by term fetal stage. Additionally, the mRNA levels of pro-opiatemelanocortin and melanocortin receptor-4 were also increased in the HF fetal hypothalami. These findings indicate potential programming effects of an altered intrauterine environment induced by HF diet consumption on appetite-regulating neuropeptides and leptin and insulin signaling in the late fetal period.