Lactiplantibacillus plantarum LM1001 Improves Digestibility of Branched-Chain Amino Acids in Whey Proteins and Promotes Myogenesis in C2C12 Myotubes.

Lactiplantibacillus plantarum is a valuable potential probiotic species with various proven health-beneficial effects. L. plantarum LM1001 strain was selected among ten strains of L. plantarum based on proteolytic activity on whey proteins. L. plantarum LM1001 produced higher concentrations of total free amino acids and branched-chain amino acids (Ile, Leu, and Val) than other L. plantarum strains. Treatment of C2C12 myotubes with whey protein culture supernatant (1%, 2% and 3%, v/v) using L. plantarum LM1001 significantly increased the expression of myogenic regulatory factors, such as Myf-5, MyoD, and myogenin, reflecting the promotion of myotubes formation (p<0.05). L. plantarum LM1001 displayed ß-galactosidase activity but did not produce harmful ß-glucuronidase. Thus, the intake of whey protein together with L. plantarum LM1001 has the potential to aid protein digestion and utilization.

Bacillus subtilis Induces Human Beta Defensin-2 Through its Lipoproteins in Human Intestinal Epithelial Cells.

Human intestinal epithelial cells (IECs) play an important role in maintaining gut homeostasis by producing antimicrobial peptides (AMPs). Bacillus subtilis, a commensal bacterium, is considered a probiotic. Although its protective effects on intestinal health are widely reported, the key component of B. subtilis responsible for its beneficial effects remains elusive. In this study, we tried to identify the key molecules responsible for B. subtilis-induced AMPs and their molecular mechanisms in a human IEC line, Caco-2. B. subtilis increased human beta defensin (HBD)-2 mRNA expression in a dose- and time-dependent manner. Among the B. subtilis microbe-associated molecular patterns, lipoprotein (LPP) substantially increased the mRNA expression and protein production of HBD-2, whereas lipoteichoic acid and peptidoglycan did not show such effects. Those results were confirmed in primary human IECs. In addition, both LPP recognition and HBD-2 secretion mainly took place on the apical side of fully differentiated and polarized Caco-2 cells through Toll-like receptor 2-mediated JNK/p38 MAP kinase/AP-1 and NF-κB pathways. HBD-2 efficiently inhibited the growth of the intestinal pathogens Staphylococcus aureus and Bacillus cereus. Furthermore, LPPs pre-incubated with lipase or proteinase K decreased LPP-induced HBD-2 expression, suggesting that the lipid and protein moieties of LPP are crucial for HBD-2 expression. Q Exactive Plus mass spectrometry identified 35 B. subtilis LPP candidates within the LPP preparation, and most of them were ABC transporters. Taken together, these results suggest that B. subtilis promotes HBD-2 secretion in human IECs mainly with its LPPs, which might enhance the protection from intestinal pathogens.

Induction of Apoptotic Cell Death by Oral Streptococci in Human Periodontal Ligament Cells.

Initiation and progression of oral infectious diseases are associated with streptococcal species. Bacterial infection induces inflammatory responses together with reactive oxygen species (ROS), often causing cell death and tissue damage in the host. In the present study, we investigated the effects of oral streptococci on cytotoxicity and ROS production in human periodontal ligament (PDL) cells. Streptococcus gordonii showed cell cytotoxicity in a dose- and time-dependent manner. The cytotoxicity might be due to apoptosis since S. gordonii increased annexin V-positive cells, and the cytotoxicity was reduced by an apoptosis inhibitor, Z-VAD-FMK. Other oral streptococci such as Streptococcus mitis, Streptococcus sanguinis, and Streptococcus sobrinus also induced apoptosis, whereas Streptococcus mutans did not. All streptococci tested except S. mutans triggered ROS production in human PDL cells. Interestingly, however, streptococci-induced apoptosis appears to be ROS-independent, as the cell death induced by S. gordonii was not recovered by the ROS inhibitor, resveratrol or n-acetylcysteine. Instead, hydrogen peroxide (H2O2) appears to be important for the cytotoxic effects of streptococci since most oral streptococci except S. mutans generated H2O2, and the cytotoxicity was dramatically reduced by catalase. Furthermore, streptococcal lipoproteins are involved in cytotoxicity, as we observed that cytotoxicity induced by the lipoprotein-deficient S. gordonii mutant was less potent than that by the wild-type and was attenuated by anti-TLR2-neutralizing antibody. Indeed, lipoproteins purified from S. gordonii alone were sufficient to induce cytotoxicity. Notably, S. gordonii lipoproteins did not induce H2O2 or ROS but cooperatively induced cell death when co-treated with H2O2. Taken together, these results suggest that most oral streptococci except S. mutans efficiently induce damage to human PDL cells by inducing apoptotic cell death with bacterial H2O2 and lipoproteins, which might contribute to the progression of oral infectious diseases such as apical periodontitis.

Streptococcus gordonii: Pathogenesis and Host Response to Its Cell Wall Components.

Streptococcus gordonii, a Gram-positive bacterium, is a commensal bacterium that is commonly found in the skin, oral cavity, and intestine. It is also known as an opportunistic pathogen that can cause local or systemic diseases, such as apical periodontitis and infective endocarditis. S. gordonii, an early colonizer, easily attaches to host tissues, including tooth surfaces and heart valves, forming biofilms. S. gordonii penetrates into root canals and blood streams, subsequently interacting with various host immune and non-immune cells. The cell wall components of S. gordonii, which include lipoteichoic acids, lipoproteins, serine-rich repeat adhesins, peptidoglycans, and cell wall proteins, are recognizable by individual host receptors. They are involved in virulence and immunoregulatory processes causing host inflammatory responses. Therefore, S.gordonii cell wall components act as virulence factors that often progressively develop diseases through overwhelming host responses. This review provides an overview of S. gordonii, and how its cell wall components could contribute to the pathogenesis and development of therapeutic strategies.