The parotid secretory protein BPIFA2 is a salivary surfactant that affects LPS action

Saliva plays important roles in the mastication, swallowing and digestion of food, speech and lubrication of oral mucosa, antimicrobial and anti-inflammatory activity and control of body temperature in grooming animals. The salivary protein BPIFA2 (BPI fold containing family A member 2; former names: Parotid Secretory Protein, PSP, SPLUNC2, C20orf70) is related to lipid-binding and LPS-binding proteins expressed in mucosa. Indeed, BPIFA2 binds LPS but the physiological role of BPIFA2 remains to be determined. To address this question, Bpifa2 knockout (Bpifa2tm1(KOMP)Vlcg) (KO) mice were phenotyped with a special emphasis on saliva and salivary glands. Saliva collected from KO mice was less able to spread on a hydrophobic surface than wild-type saliva and the surface tension of KO saliva was close to that of water. These data suggest that BPIFA2 is a salivary surfactant that is mainly responsible for the low surface tension of mouse saliva. The reduced surfactant activity of KO saliva did not affect consumption of dry food or grooming, but saliva from KO mice contained less LPS than wild-type saliva. Indeed, mice lacking BPIFA2 responded to ingested LPS with an increased stool frequency, suggesting that BPIFA2 plays a role in the solubilization and activity of ingested LPS. Consistent with these findings, BPIFA2-depleted mice also showed increased insulin secretion and metabolomic changes that were consistent with a mild endotoxemia. These results support the distal physiological function of a salivary protein and reinforce the connection between oral biology and systemic disease.

Evaluation of Autoantibodies in Patients with Primary and Secondary Sjogren’s Syndrome

Background: Antibodies to salivary gland protein 1 (SP1), carbonic anhydrase 6 (CA6) and parotid secretory protein (PSP) were discovered in an animal model of Sjogren’s syndrome (SS). Their expression was noted in patients with SS, especially those with lower focus scores on lip biopsies and those with early disease lacking antibodies to Ro and La. Objective: The current studies evaluated these autoantibodies in patients with long-standing SS expressing high levels of anti-Ro antibodies and in patients with Sjogren’s syndrome secondary to systemic lupus erythematosus (SLE), systemic sclerosis (SSc) and mixed connective tissue disease (MCTD). Method: Sera were obtained from patients and evaluated by ELISA for IgG, IgA and IgM antibodies to SP1, CA6 and PSP. Results: IgA anti-CA6 antibodies were noted in 38% of these patients, but anti-SP1, CA6 and PSP IgM or IgG antibodies were identified only in a minority of patients. In patients with secondary SS, antibodies to SP1/CA6/PSP were more sensitive and specific than anti-Ro . Conclusion: While more studies are needed, antibodies to SP1, CA6 and PSP provide valuable markers for the diagnosis of primary and secondary SS, especially early in the course of the disease.

Systematic nomenclature for the PLUNC/PSP/BSP30/SMGB proteins as a subfamily of the BPI fold-containing superfamily

We present the BPIFAn/BPIFBn systematic nomenclature for the PLUNC (palate lung and nasal epithelium clone)/PSP (parotid secretory protein)/BSP30 (bovine salivary protein 30)/SMGB (submandibular gland protein B) family of proteins, based on an adaptation of the SPLUNCn (short PLUNCn)/LPLUNCn (large PLUNCn) nomenclature. The nomenclature is applied to a set of 102 sequences which we believe represent the current reliable data for BPIFA/BPIFB proteins across all species, including marsupials and birds. The nomenclature will be implemented by the HGNC (HUGO Gene Nomenclature Committee).

The BPI-like/PLUNC family proteins in cattle

Members of the protein family having similarity to BPI (bactericidal/permeability increasing protein) (the BPI-like proteins), also known as the PLUNC (palate, lung and nasal epithelium clone) family, have been found in a range of mammals; however, those in species other than human or mouse have been relatively little characterized. Analysis of the BPI-like proteins in cattle presents unique opportunities to investigate the function of these proteins, as well as address their evolution and contribution to the distinct physiology of ruminants. The present review summarizes the current understanding of the nature of the BPI-like locus in cattle, including the duplications giving rise to the multiple BSP30 (bovine salivary protein 30 kDa) genes from an ancestral gene in common with the single PSP (parotid secretory protein) gene found in monogastric species. Current knowledge of the expression of the BPI-like proteins in cattle is also presented, including their pattern of expression among tissues, which illustrate their independent regulation at sites of high pathogen exposure, and the abundance of the BSP30 proteins in saliva and salivary tissues. Finally, investigations of the function of the BSP30 proteins are presented, including their antimicrobial, lipopolysaccharide-binding and bacterial aggregation activities. These results are discussed in relation to hypotheses regarding the physiological role of the BPI-like proteins in cattle, including the role they may play in host defence and the unique aspects of digestion in ruminants.

Dual host-defence functions of SPLUNC2/PSP and synthetic peptides derived from the protein

PSP (parotid secretory protein)/SPLUNC2 (short palate, lung and nasal epithelium clone 2) is expressed in human salivary glands and saliva. The protein exists as an N-glycosylated and non-glycosylated form and both appear to induce agglutination of bacteria, a major antibacterial function for salivary proteins. Both forms of PSP/SPLUNC2 bind LPS (lipopolysaccharide), suggesting that the protein may also play an anti-inflammatory role. Based on the predicted structure of PSP/SPLUNC2 and the location of known antibacterial and anti-inflammatory peptides in BPI (bactericidal/permeability-increasing protein) and LBP (LPS-binding protein), we designed GL13NH2 and GL13K, synthetic peptides that capture these proposed functions of PSP/SPLUNC2. GL13NH3 agglutinates bacteria, leading to increased clearance by macrophages and reduced spread of infection in a plant model. GL13K kills bacteria with a minimal inhibitory concentration of 5–10 μg/ml, kills bacteria in biofilm and retains activity in 150 mM NaCl and 50% saliva. Both peptides block endotoxin action, but only GL13K appears to bind endotoxin. The peptides do not cause haemolysis, haemagglutination in serum, inhibit mammalian cell proliferation or induce an inflammatory response in macrophages. These results suggest that the GL13NH2 and the modified peptide GL13K capture the biological activity of PSP/SPLUNC2 and can serve as lead compounds for the development of novel antimicrobial and anti-inflammatory peptides.