Haploinsufficiency of progranulin (PGRN) is a leading cause of frontotemporal lobar degeneration (FTLD). PGRN is comprised of 7.5 granulin repeats and the precursor is processed into individual granulin peptides by lysosome proteases. The granulin peptides are also haplo-insufficient in FTLD and proposed to possess unique functions. However, very little is known about the levels and regulations of each granulin peptide in the lysosome due to the lack of reagents to specifically detect each individual granulin peptide. Here we report the generation and characterization of antibodies specific to each granulin peptide. We found that the levels of granulins C, E and F are lower than granulins A and B under certain conditions, indicating differences in the stability of individual granulin peptides within the lysosome once liberated from PGRN. Furthermore, we demonstrated that granulin B, C and E are heavily glycosylated and the glycosylation pattern of granulin C varies in different physiological and pathological conditions. The ratio between granulins and PGRN is highest in the cortex region in the male mouse brain. Loss of lysosomal protease cathepsin B leads to an increase in the levels of granulins A and B without affecting the levels of granulins C and F in the cortex. Deletion of cathepsin D results in a decrease in the ratio between granulin A, B and C, but not granulin F and full length PGRN. These data support that the levels of individual granulin peptides are differentially regulated under physiological and pathological conditions and provide novel insights into how PGRN functions in the lysosome.
bioRxiv Subject Collection: Neuroscience