Increased lysosomal biogenesis in activated microglia and exacerbated neuronal damage after traumatic brain injury in progranulin-deficient mice

Abstract

Progranulin (PGRN) is known to play a role in the pathogenesis of neurodegenerative diseases. Recently, it has been demonstrated that patients with the homozygous mutation in the GRN gene present with neuronal ceroid lipofuscinosis, and there is growing evidence that PGRN is related to lysosomal function. In the present study, we investigated the possible role of PGRN in the lysosomes of activated microglia in the cerebral cortex after traumatic brain injury (TBI). We showed that the mouse GRN gene has two possible coordinated lysosomal expression and regulation (CLEAR) sequences that bind to transcription factor EB (TFEB), a master regulator of lysosomal genes. PGRN was colocalized with Lamp1, a lysosomal marker, and Lamp1-positive areas in GRN-deficient (KO) mice were significantly expanded compared with wild-type (WT) mice after TBI. Expression of all the lysosome-related genes examined in KO mice was significantly higher than that in WT mice. The number of activated microglia with TFEB localized to the nucleus was also significantly increased in KO as compared with WT mice. Since the TFEB translocation is regulated by the mammalian target of rapamycin complex 1 (mTORC1) activity in the lysosome, we compared ribosomal S6 kinase 1 (S6K1) phosphorylation that reflects mTORC1 activity. S6K1 phosphorylation in KO mice was significantly lower than that in WT mice. In addition, the number of nissl-positive and fluoro-jade B-positive cells around the injury was significantly decreased and increased, respectively, in KO as compared with WT mice. These results suggest that PGRN localized in the lysosome is involved in the activation of mTORC1, and its deficiency leads to increased TFEB nuclear translocation with a resultant increase in lysosomal biogenesis in activated microglia and exacerbated neuronal damage in the cerebral cortex after TBI.

Keywords: AD; ALS; ANOVA; Alzheimer’s disease; Analysis of variance; Aβ; C4; CLEAR; Cyba; DW; EDTA; FTLD; FjB; GRN; GRN-deficient; Gba; HPRT; IR; Iba1; KO; LSD; Lamp1; Mpeg1; NCL; PBS containing Triton X-100; PBST; PGRN; PMSF; PNPP; PVDF; RT; S6K1; SEM; TAR DNA-binding protein-43; TBI; TBS containing Tween 20; TBST; TDP-43; TFEB; WT; amyloid β; amyotrophic lateral sclerosis; bHLH; basic Helix-Loop-Helix; beta-glucocerebrosidase; complement C4; coordinated lysosomal expression and regulation; cytochrome b-245 light chain; distilled water; ethylenediaminetetraacetic acid; fluoro-jade B; frontotemporal lobar degeneration; granulin; hypoxanthine phosphoribosyltransferase; immunoreactive; ionized calcium-binding adaptor molecule 1; lysosomal storage disease; lysosome; lysosome-associated membrane protein 1; mTORC1; macrophage expressed gene 1; mammalian target of rapamycin complex 1; microglia; neuronal ceroid lipofuscinosis; p-nitrophenyl phosphate; phenylmethylsulfonyl fluoride; polyvinylidene fluoride; progranulin; ribosomal S6 kinase 1; room temperature; standard error of the mean; transcription factor EB; traumatic brain injury; v-ATPase; vacuolar H(+)-ATPase; wild-type.