Mfsd7b facilitates choline transport and missense mutations affect choline transport function

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• MFSD7b, part of the Major Facilitator Superfamily, was previously identified as a heme exporter involved in heme homeostasis.
• Mutations in MFSD7b (FLVCR1) are associated with neurological disorders like retinitis pigmentosa.
• Despite its known role in heme export, MFSD7b is widely expressed, suggesting additional functions.

Purpose of the Study:

• To investigate the non-heme transport functions of MFSD7b.
• To determine if MFSD7b transports other small molecules, specifically choline.
• To characterize the mechanism and conservation of MFSD7b's transport activity.

Main Methods:

• Mammalian cell culture and expression systems.
• Choline uptake assays to measure transport rates.
• Gene knockdown and site-directed mutagenesis to assess MFSD7b function.
• Cross-species conservation studies.

Main Results:

• MFSD7b expression significantly increased choline import into mammalian cells.
• Knockdown of MFSD7b reduced cellular choline influx.
• Choline transport by MFSD7b is dependent on intracellular choline levels and metabolizing enzymes (e.g., CHKA) but not cation gradients.
• MFSD7b's choline transport function is conserved across species from flies to humans.
• Identified missense mutations in MFSD7b that impair its choline transport activity.

Conclusions:

• MFSD7b functions as a facilitative choline transporter in mammalian cells.
• This finding expands the known physiological roles of MFSD7b beyond heme transport.
• MFSD7b represents a novel target for understanding choline homeostasis and related pathologies.