Proteus mirabilis Urease: Unsuspected Non-Enzymatic Properties Relevant to Pathogenicity

Area of Science:

• Microbiology
• Pathogenesis
• Cell Biology

Background:

• Proteus mirabilis infection leads to urinary stones and catheter issues via urease-produced ammonia.
• Ureases, including from Helicobacter pylori, possess reported non-enzymatic pro-inflammatory and neurotoxic activities.
• The non-enzymatic functions of Proteus mirabilis urease (PMU) remain largely unexplored.

Purpose of the Study:

• To investigate the non-enzymatic properties of purified PMU on various human and murine cell types.
• To determine if PMU exhibits pro-inflammatory or cytotoxic effects independent of ammonia production.
• To explore the cellular localization and potential nuclear translocation of PMU.

Main Methods:

• Purified PMU was applied to human platelets, HEK293 cells, SH-SY5Y cells, and murine BV-2 microglia.
• Cellular viability, ammonia levels, reactive oxygen species (ROS), cytokine production (IL-1β, TNF-α), and intracellular calcium (Ca2+) were measured.
• Texas Red-labeled PMU was used to track its cellular and subcellular localization, with bioinformatic analysis for nuclear localization sequences.

Main Results:

• PMU induced platelet aggregation but did not affect overall cell viability or produce detectable ammonia.
• PMU-treated HEK293 cells showed increased ROS and cytokine production, indicating a pro-inflammatory response.
• SH-SY5Y cells exhibited elevated intracellular Ca2+ and ROS upon PMU stimulation, while BV-2 cells showed different cytokine responses. Labeled PMU localized to both cytoplasm and nucleus.

Conclusions:

• PMU possesses non-enzymatic, pro-inflammatory activities beyond its role in ammonia production and stone formation.
• PMU can influence cellular functions in various cell types, including those outside the renal system.
• These findings suggest PMU may contribute to pathogenesis in extra-urinary conditions.