Differential regulation of progranulin derived granulin peptides

Abstract

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. 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 differentially regulated compared to granulins A and B. 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. Deficiency of lysosomal proteases leads to alterations in the levels of a specific subset of granulins. These data 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.

Cytoplasmic Colocalization of Granulins and TDP-43 Prion-like Domain Involves Electrostatically Driven Coacervation Tuned by the Redox State of Cysteines

“…Unfortunately, we do not have experimental evidence for this extreme case (high positive charges and no negative charges), as such a mutant posed difficulties in recombinant expression (data not shown). However, the results obtained from , which has a high number of positive charge (+8) serves as a good proxy and strengthen the validity of the idea that GRNs have modulatory capabilities especially when it is known that not all GRNs level are the same in cells (T. Zhang et al, 2021).…”

“…Perhaps the most interesting aspect when observing the sequence of the seven GRNs is that they seem to have a perfect combination and spectrum of positive and negative charges to eloquently modulate TDP-43 phase transitions. It also seems to be that the extracellular cleavage of PGRN may be asymmetric leading to a greater abundance of one GRN over another 95 , which could play in the modulation of TDP-43. Nevertheless, precisely what cellular consequences do these inclusions and coacervates possess remain unclear at this time.…”

Microglia regulate brain progranulin levels through the endocytosis/lysosomal pathway

“…Finally, because Pgrn is processed into stable granulin peptides in the lysosome, which have been recently reported to have several detrimental ( 72 ) or beneficial ( 68 ) putative cellular functions, what effect does Nlk reduction have on the levels of individual granulins, and how might this affect overall lysosomal function? Although we were not able to reliably detect granulins in protein extracts used in this study (data not shown), follow-up studies using more sensitive immunoassays involving antibodies against specific granulin peptides ( 73 – 75 ) are warranted. Collectively, the findings of our study open the door for a more detailed mechanistic examination of the precise Nlk-mediated microglia-modulating effects, including characterization of the effects of varying Nlk levels on synaptic pruning and neuronal numbers in a brain circuit–specific manner, which may be involved in the behavioral changes we report here.…”

Regulation of lysosomal trafficking of progranulin by sortilin and prosaposin

“…Next, we examined the levels of granulin peptides and PGRN in the cortical lysates from 3-month-old WT and Sort −/− mice by western blot analyses, using polyclonal antibodies that recognize both full-length PGRN and granulin peptides. 46 Concomitant with an increase in the levels of full-length PGRN in Sort −/− mice, 30 a significant reduction in the levels of granulin peptides were observed in the cortical lysates from Sort −/− mice, which results in a significant decrease in the ratio between granulin peptides and full-length PGRN ( Fig. 2 ).…”