Internalization and processing of basic fibroblast growth factor by neurons and astrocytes

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Basic fibroblast growth factor (FGF) is a signaling protein with potential roles in the central nervous system (CNS).
• Understanding the cellular fate and processing of FGF is crucial for elucidating its function as a neurotrophic factor.

Purpose of the Study:

• To investigate the intracellular trafficking and metabolic fate of iodinated basic FGF after binding to cultured astrocytes and hippocampal neurons.
• To identify the processed fragments of basic FGF and determine the conditions required for its metabolism.

Main Methods:

• Autoradiography coupled with light and electron microscopy to track internalized 125I-basic FGF.
• Biochemical analyses including polyacrylamide gel electrophoresis and immunoprecipitation to identify and characterize FGF metabolites.
• Treatment with trypsin, NaCl, and WGA to investigate the requirement of internalization and receptor binding for FGF processing.

Main Results:

• Internalized 125I-basic FGF localizes to cytoplasmic vesicles, perinuclear regions, and nuclear chromatin.
• Cells metabolize internalized basic FGF into three major heparin-binding peptides (15.5, 9, and 4 kDa).
• Metabolism is dependent on internalization and occurs after binding to the high-affinity receptor, with processing times varying between astrocytes and neurons.

Conclusions:

• Basic FGF undergoes significant intracellular processing after internalization by CNS cells.
• This metabolic pathway generates distinct peptides, suggesting a novel mechanism for FGF signaling or degradation.
• The findings support a potential neurotrophic role for basic FGF mediated through its internalization and processing in neurons and astrocytes.