Histoplasma capsulatum Relies on Tryptophan Biosynthesis To Proliferate within the Macrophage Phagosome

Area of Science:

• Medical Mycology
• Infectious Diseases
• Host-Pathogen Interactions

Background:

• Histoplasma capsulatum yeasts survive within macrophage phagosomes, a nutrient-limited environment.
• Acquiring essential nutrients, including amino acids, is crucial for fungal survival and virulence.
• Aromatic amino acids (phenylalanine, tyrosine, tryptophan) are vital for Histoplasma, but their acquisition during infection is unclear.

Purpose of the Study:

• To investigate the acquisition mechanisms of aromatic amino acids by Histoplasma yeasts within macrophages.
• To determine the role of de novo aromatic amino acid biosynthesis in Histoplasma virulence.
• To evaluate the potential of targeting the aromatic amino acid pathway as an antifungal drug strategy.

Main Methods:

• Gene deletion studies to assess the necessity of phenylalanine, tyrosine, and tryptophan biosynthesis.
• Macrophage infection models to evaluate yeast proliferation.
• In vivo murine infection models to assess fungal virulence.
• Treatment with glyphosate, an inhibitor of the aromatic amino acid pathway, and subsequent rescue experiments.

Main Results:

• Histoplasma yeasts could proliferate in macrophages even when phenylalanine or tyrosine biosynthesis was impaired.
• Tryptophan biosynthesis was essential for optimal growth within macrophages and for full virulence in vivo.
• Glyphosate inhibited yeast growth, with partial rescue by supplementing aromatic amino acids or overexpressing ARO1.
• These findings indicate phenylalanine and tyrosine are acquired from the host, while tryptophan is synthesized.

Conclusions:

• Histoplasma capsulatum scavenges phenylalanine and tyrosine from the macrophage phagosome.
• Tryptophan biosynthesis is critical for Histoplasma virulence, making it a potential drug target.
• The aromatic amino acid biosynthetic pathway represents a promising target for developing novel antifungal therapies against histoplasmosis.