Objective:

To explore the origins of metabolites and cellular states using advanced mass spectrometry techniques.

Approach:

• Microbiome Metabolites: Isotope tracing was used to determine the production of indole and phenol metabolites by mammalian cells, distinguishing between host and microbial contributions.
• Secretome Analysis: An in vivo proximity-labeling platform was developed to trace secreted proteins back to specific cell types and analyze changes across metabolic states.
• Cardiac Regeneration: Single-cell proteomic analysis linked Myc expression to metabolic reprogramming in cardiomyocytes, identifying a pro-regenerative cell population.
• Macrophage Phenotypes: Cell-resolved MALDI imaging differentiated macrophage phenotypes and highlighted phospholipid metabolism as a key factor.

Key Findings:

• Mammalian cells can produce several circulating indole and phenol metabolites independently of the gut microbiome, as shown by isotope tracing.
• The TurboID platform enabled the identification of low-abundance secreted proteins and their changes during metabolic states.
• Myc expression in cardiomyocytes shifted metabolic pathways from fatty acid oxidation to glycolysis, indicating a pro-regenerative state.
• M1 macrophages synthesized more phospholipids than M2 macrophages, suggesting a functional role in their antitumor activity.

Interpretation:

The studies highlight the need to distinguish between host and microbial contributions to metabolite production and the metabolic states of cells.

Limitations:

• The study on microbiome metabolites may not account for all variables influencing metabolite levels.
• The secretome analysis may not capture all secreted proteins due to detection limits.
• The findings on cardiac regeneration are based on mouse models and may not directly translate to human physiology.

Conclusion:

These findings provide insights into the metabolic origins of key metabolites and cellular states.