Porphyromonas gingivalis Sphingolipid Synthesis Limits the Host Inflammatory Response

Area of Science:

• Microbiology and Immunology
• Bacterial Pathogenesis
• Host-Microbe Interactions

Background:

• Porphyromonas gingivalis, a bacterium linked to periodontal disease, synthesizes sphingolipids (SLs), lipids also found in eukaryotes.
• The precise function of these bacterial SLs in P. gingivalis physiology and their role in host interactions remain largely unknown.
• A previous study identified a gene (PG1780) essential for SL synthesis in P. gingivalis.

Purpose of the Study:

• To characterize the serine palmitoyltransferase (SPT) enzyme encoded by PG1780.
• To investigate the impact of SL synthesis deficiency on P. gingivalis gene expression.
• To define the role of SL synthesis in P. gingivalis interactions with host immune cells.

Main Methods:

• Enzymatic assays to confirm SPT activity of the PG1780 protein.
• RNA-sequencing (RNA-Seq) to analyze gene expression changes in an SL-null mutant.
• Co-culture experiments with human THP1 macrophage-like cells to assess inflammatory responses.

Main Results:

• The protein encoded by PG1780 was confirmed to be an SPT, essential for SL synthesis.
• Deletion of the SPT gene led to differential expression of genes involved in secretion systems and stress response.
• The SL-null mutant induced a significantly heightened inflammatory response in macrophages compared to wild-type P. gingivalis.
• Sphingolipids produced by P. gingivalis can be transferred to host cells independently of direct cell contact.

Conclusions:

• Sphingolipid synthesis is crucial for P. gingivalis to modulate host inflammatory responses and establish homeostasis.
• The absence of SLs leads to increased bacterial virulence and heightened immune cell activation.
• Bacterial SLs represent a novel mechanism for host-pathogen interaction and immune evasion.