ProSAAS-derived peptides are differentially processed and sorted in mouse brain and AtT-20 cells

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• ProSAAS is a precursor protein for abundant peptides in the brain, including SAAS, PEN, and LEN.
• Differential processing generates various forms (big and little) of SAAS and LEN peptides.
• Initial proSAAS processing involves furin and carboxypeptidase D, with further processing by granule convertases and carboxypeptidase E.

Purpose of the Study:

• To investigate the processing and localization of proSAAS-derived peptides.
• To determine the role of initial cleavage enzymes in peptide sorting and maturation.
• To understand the differential distribution of SAAS, PEN, and LEN peptides in neurons.

Main Methods:

• Immunohistochemistry in mouse hypothalamus to examine peptide colocalization.
• Transfection of AtT-20 cells with rat proSAAS to study peptide distribution.
• Site-directed mutagenesis of proSAAS cleavage sites to alter enzyme specificity.

Main Results:

• Little LEN and SAAS were found in the mouse hypothalamus but not in neuropeptide Y neurons.
• PEN and big LEN showed colocalization in the hypothalamus, but big and little LEN did not.
• Mutating furin cleavage sites in proSAAS increased colocalization of PEN and SAAS peptides in AtT-20 cells.

Conclusions:

• ProSAAS is initially cleaved by furin in the Golgi/trans-Golgi network.
• Cleavage fragments are sorted into distinct vesicles for further processing.
• Enzyme specificity in initial cleavage influences the sorting and maturation pathways of proSAAS peptides.