Differential regulation of progranulin derived granulin peptides

Abstract

Background Haploinsufficiency of progranulin (PGRN) is a leading cause of frontotemporal lobar degeneration (FTLD). PGRN is comprised of 7.5 granulin repeats and is processed into individual granulin peptides in the lysosome. However, very little is known about the levels and regulations of individual granulin peptides due to the lack of specific antibodies. Results 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 regulated differently compared to granulins A and B in various tissues. The levels of PGRN and granulin peptides vary in different brain regions and the ratio between granulins and PGRN is highest in the cortical region in the adult male mouse brain. Granulin-A is localized in the lysosome in both neurons and microglia and its levels in microglia increase under pathological conditions. Interestingly, the levels of granulin A in microglia change correspondingly with PGRN in response to stroke but not demyelination. Furthermore, deficiency of lysosomal proteases and the PGRN binding partner prosaposin leads to alterations in the ratios between individual granulin peptides. Granulins B, C and E are heavily glycosylated and the glycosylation patterns can be regulated under. Conclusion Our results support that the levels of individual granulin peptides are differentially regulated under physiological and pathological conditions and provide novel insights into how granulin peptides function in the lysosome.

Progranulin-derived granulin E and lysosome membrane protein CD68 interact to reciprocally regulate their protein homeostasis

“…PGRN is processed to individual granulin peptides in the lysosome and these granulin peptides are proposed to possess unique functions to regulate lysosomal activities (16,35). Although the granulin peptides are derived from the same precursor, our recent studies have shown that the levels of individual granulin peptides differ from each other (29). This is further supported by our observation that CD68 ablation specifically decreases the levels of granulin E but no other granulins tested (Fig.…”

“…Antibodies against granulin A, B, C, E, and F, but not D and G can detect endogenous granulin peptides specifically (Fig. 4A) (29). Notably, our results show that there is a significant reduction in the levels of granulin E, but no other granulins in Cd68 -/spleen lysates (Fig.…”

“…Rabbit anti-GFP antibodies were a gift from Professor Anthony Bretscher and rabbit anti-cathepsin D antibodies were a gift from Dr. William Brown at Cornell University. Antibodies against each granulin peptide have been previously characterized (29). Rabbit anti-mouse PSAP were generated by Pocono Rabbit Farm and Laboratory and previously characterized (15).…”

“…However, the function of each granulin peptide remains to be characterized. Interestingly, the levels of individual granulin peptides are differentially regulated despite being derived from the same precursor (29), but the mechanisms involved in modulating the stability of individual granulins in the lysosome remain unknown.…”

Progranulin in the Nucleus Accumbens Contributes to Neuroinflammation-Induced Depression-Like Behavior in Mice

“…In general, PGRN functions as a double-edged sword by playing proin ammatory and anti-in ammatory roles in immune-mediated conditions, and the roles played may rely on the pathology and physiology of the diseases. With regard to the central nervous system, it is well established that PGRN is expressed in neurons and microglia [31] and plays important roles in lysosomal function, neuronal survival and function and neuroin ammation and as a therapeutic target in frontotemporal dementia (FTD) [32,33]. Notably, FTD patients with a GRN variant and PGRN-de cient mice have been reported to display depression-like behaviors [34], indicating that PGRN may be involved in the development of depression.…”