ABSTRACT
BACKGROUND: Atopic dermatitis (AD) is a chronic inflammatory skin disorder affecting up to 20% of children in developed countries. Although probiotics have shown promise as adjuvant treatments for AD, their mechanisms are not well understood. OBJECTIVE: Building upon our previous studies, we investigated whether Lactobacillus gasseri and its moonlighting glyceraldehyde 3-phosphate dehydrogenase (GAPDH), namely LGp40, could be beneficial in AD management. METHODS: In AD mouse models (SKH and C57BL/6J mice) with ovalbumin (OVA) and Dermatophagoides pteronyssinus (Der p) allergens, aligning with the "outside-in" and "inside-out" hypotheses, we administered L. gasseri orally and LGp40 intraperitoneally to investigate their protective effects. The evaluation involved measuring physiological, pathological, and immune function parameters. To delve deeper into the detailed mechanism of LGp40 protection in AD, additional assays were conducted using human skin keratinocytes (HaCaT) and monocytes (THP1) cell lines. RESULTS: L. gasseri and LGp40 enhanced skin barrier function and increased skin moisture retention. They also led to reduced infiltration of Langerhans cells in the dermis and mitigated skewed Th2 and Th17 immune responses. Moreover, LGp40 inhibited allergen-induced keratinocyte apoptosis through the blockade of the caspase-3 cascade and reduced the NLR family pyrin domain containing 3 (NLRP3) inflammasome in macrophages. These inhibitions were achieved through the activation of the peroxisome proliferator-activated receptor gamma (PPARγ) pathway. CONCLUSION: The results of this study provide a novel insight into the mechanism of action of probiotics in the prevention and treatment for allergic disorders through the moonlighting GAPDH protein.
ABSTRACT
Low-density lipoprotein receptor-related protein 4 (LRP4) is a multi-functional protein implicated in bone, kidney and neurological diseases including Cenani-Lenz syndactyly (CLS), sclerosteosis, osteoporosis, congenital myasthenic syndrome and myasthenia gravis. Why different LRP4 mutation alleles cause distinct and even contrasting disease phenotypes remain unclear. Herein, we utilized the zebrafish model to search for pathways affected by a deficiency of LRP4. The lrp4 knockdown in zebrafish embryos exhibits cyst formations at fin structures and the caudal vein plexus, malformed pectoral fins, defective bone formation and compromised kidney morphogenesis; which partially phenocopied the human LRP4 mutations and were reminiscent of phenotypes resulting form a perturbed Notch signaling pathway. We discovered that the Lrp4-deficient zebrafish manifested increased Notch outputs in addition to enhanced Wnt signaling, with the expression of Notch ligand jagged1b being significantly elevated at the fin structures. To examine conservatism of signaling mechanisms, the effect of LRP4 missense mutations and siRNA knockdowns, including a novel missense mutation c.1117C > T (p.R373W) of LRP4, were tested in mammalian kidney and osteoblast cells. The results showed that LRP4 suppressed both Wnt/ß-Catenin and Notch signaling pathways, and these activities were perturbed either by LRP4 missense mutations or by a knockdown of LRP4. Our finding underscore that LRP4 is required for limiting Jagged-Notch signaling throughout the fin/limb and kidney development, whose perturbation representing a novel mechanism for LRP4-related diseases. Moreover, our study reveals an evolutionarily conserved relationship between LRP4 and Jagged-Notch signaling, which may shed light on how the Notch signaling is fine-tuned during fin/limb development.