Porphyromonas gingivalis-Derived Phosphoglycerol-isoC17:0-Dihydroceramide Reprograms Sphingolipid Metabolism in Human...

Intracellular sphingolipids play a complex role in the survival and migration of oral squamous cell carcinoma (OSCC). For instance, dihydroceramide and ceramide sphingolipids suppress proliferation, whereas sphingosine-1-phosphate (S-1-P) promotes it. The balance between ceramide/S-1-P is critically regulated by the ceramide-hydrolyzing enzyme, acid ceramidase (aCDase), in OSCC. Indeed, aCDase mRNA expression is significantly upregulated compared with that in healthy epithelial cells. Our group identified that Porphyromonas gingivalis synthesizes a structurally unique phosphoglycerol-isoC17:0-dihydroceramide (PGDHC) sphingolipid. Our understanding of whether PGDHC modulates the critical ceramide/S-1-P balance and aCDase levels in OSCC remains limited. The effects of PGDHC on human OSCC cell lines and healthy oral epithelial cells were evaluated in vitro using conventional assays combined with untargeted and ceramide-targeted lipidomic screenings. Human tongue oral malignancy and the adjacent normal tissue from the same patient were also evaluated for the prevalence of anti-P. gingivalis IgG. Additionally, aCDase levels were evaluated in OSCC cell lines, clinical oral malignancy samples, and mouse models of 4-nitroquinoline-1-oxide (4-NQO)-induced OSCC. We identified the accelerated prevalence of aCDase in clinical and experimental malignant lesions. In contrast, we observed a lower prevalence of PGDHC-producing P. gingivalis in malignant lesions than in adjacent normal tissue. Indeed, our in vitro observations further demonstrated that PGDHC accelerates the accumulation of C16:0 dihydroceramide in OSCC by inhibiting acid ceramidase/ASAH1 mRNA expression. Altogether, PGDHC alters sphingolipid metabolism in human OSCC cells through the acid ceramidase/dihydroceramide axis. This finding lays the foundation for developing novel therapeutic strategies for oral cancer using PGDHC as a novel class of OSCC-suppressing compounds.