Elsevier

Neurobiology of Aging

Volume 96, December 2020, Pages 255-266
Neurobiology of Aging

Regular article
Nucleus distribution of cathepsin B in senescent microglia promotes brain aging through degradation of sirtuins

https://doi.org/10.1016/j.neurobiolaging.2020.09.001Get rights and content

Highlights

  • Nuclear translocation of cathepsin B with aging relates to neuroinflammation.

  • Nuclear cathepsin B is responsible for the degradation of nuclear sirtuins during aging.

  • Microglial cathepsin B–mediated neuroinflammation contributes to neurodegeneration.

Abstract

Cathepsin B (CatB) leakage from the lysosome into the cytosol in senescent microglia is associated with cognitive impairment. However, whether cellular compartmental translocation of CatB is associated with brain aging remains unclear. In the present study, increased CatB was found in the nucleus of CatB-overexpressed microglia followed by L-leucyl-L-leucine methyl ester, a lysosome-destabilizing reagent, and in the nuclear fraction of the cortex and hippocampus from aged mice. Moreover, CatB enzymatic activity examination showed the nuclear CatB exhibited the proteolytic activity to cleave its specific substrates. The amount of sirtuin1 (Sirt1), Sirt6, Sirt7, and p-Sirt1 was decreased in the cortical lysates from aged mice, in parallel with increased expression of proinflammatory mediators, which were diminished by CatB deficiency. Furthermore, intralateral ventricle administration of microglia overexpressed CatB, and treatment with L-leucyl-L-leucine methyl ester induced cognitive impairment in middle-aged mice. These observations suggest that the increase and nucleus translocation of CatB in senescent microglia were involved in the degradation of nuclear Sirts, which induced proinflammatory responses, resulting in cognition impairment.

Introduction

Brain aging is determined by a complex interplay of regional and cell type–specific molecular events. Gene expression studies suggested glial-specific genes predict age with greater precision than neuron-specific genes (Soreq et al., 2017). Microglia are the primary immune cells of the central nervous system that are critically dependent on signaling through the colony-stimulating factor 1 receptor for their survival (Elmore et al., 2014), which provides an effective method to eliminate microglia by using colony-stimulating factor 1 receptor inhibitors. Elimination and repopulation of resident microglia in aged mice significantly improved spatial memory and increased both neurogenesis and dendritic spine densities (Elmore et al., 2018). On the other hand, sustained microglial elimination impaired parenchymal plaque development in Alzheimer's disease (AD) mouse model (Spangenberg et al., 2019). These observations indicate that microglia can be critical and causative in the development and progression of aging and AD.

Lysosomes are classically viewed as degradative organelles because of their contained hydrolytic proteases called cathepsin (Cat). Cats are believed to disintegrate larger structures and proteins through their irreversibly cleave peptide bonds. However, there has been renewed interest in the modulator action of Cats, by which substrates are activated after limited cleavage (Nakanishi, 2003). Our recent observations showed cathepsin B (CatB) could chronically activate nuclear factor-κB (NFκB) through degradation of the inhibitor of κBα, an NFκB endogenous inhibitor, in hypoxia-ischemic microglia. NFκB chronically upregulated the expression of proinflammatory mediators that induced brain damage (Ni et al., 2015). Besides, CatB was also proved to be critical to promoting chronic neuroinflammation through its lysosomal leakage and followed the degradation of mitochondrial transcription factor A in aged microglia (Ni et al., 2019b). CatB presented the enzymatic activity in the cytosol with neutral pH and indirectly activated NFκB, resulting in chronic neuroinflammation. Furthermore, CatB has been reported to play a critical role in neuroinflammation and impairment of learning and memory induced by chronic systemic exposure to lipopolysaccharide (LPS) derived from Porphyromonas gingivalis, the major periodontal bacteria, in middle-aged mice (Wu et al., 2017). However, the function of CatB in the neuron remains controversial. Embury et al., demonstrated overexpression of CatB in hippocampal neurons using adeno-associated virus serotype 2/1 ameliorated AD-like pathologies, including β-amyloidosis and impairment in learning and memory in the mouse brain (Embury et al., 2017). On the other hand, it was conversely reported that pharmacological or genetic inhibition of CatB decreases amyloid beta (Aβ) levels and improves the memory function in the mouse model of AD (Hook et al., 2009; Kindy et al., 2012).

It has been shown there is the presence of active Cats in cellular compartments and cytosol other than lysosomes. During aging, or on induction of apoptosis by intracellular stimuli, the lysosomal membrane becomes permeable, resulting in leakage of lysosomal Cats into the cytosol. Cytosolic Cats proteolytically activated the Bid protein and led to apoptosome formation (Stoka et al., 2016). Besides, CatB was also proved to be critical to promoting chronic neuroinflammation through its lysosomal leakage and followed the degradation of mitochondrial transcription factor A (Ni et al., 2019b) in aged microglia. Furthermore, several studies have highlighted the nucleus localization of CatL in breast, colon, and prostate cancers (Grotsky et al., 2013; Sullivan et al., 2009). Nuclear CatL was investigated to promote epithelial mesenchymal transition via proteolytically activating CCAAT displacement protein/cut homeobox transcription factor, associated with increased migration and invasion in cancer cells (Burton et al., 2017). This combination of observations provides more support for the conceptual premise that cellular compartments and cytosol translocated Cats may also have pathological functions.

Sirtuins (Sirts) have been the focus of intense scrutiny since the discovery of Sir2 as a yeast longevity factor. Sirts were reported to involve in central roles in age-associated metabolic disorders and in stress resistance (Nakagawa and Guarente, 2011). In mammals, 7 different Sirts have been described (Sir1 to 7). They localized in discrete subcellular compartments: Sirt1, 6, and 7 are mainly located in nuclear, whereas Sirt2 is cytoplasmic and Sirt3, 4, and 5 reside predominantly in mitochondria (Cencioni et al., 2015). Sirt1 has been reported to be cleaved by cysteine Cats in endothelial progenitor cells, which mediated stress-induced premature senescence (Chen et al., 2012). Therefore, it is interesting to know whether CatB promotes cell senescence through cleavage of Sirts during aging.

Owing to the importance of Sirts and CatB in aging, we hypothesized that during aging, or on stimuli, the lysosomal membrane becomes permeable, resulting in leakage of lysosomal CatB, which translocated to the nucleus in microglia. Nuclear CatB enzymatically digests Sirts in the nucleus with consequent microglial senescence on memory impairment.

Section snippets

Animals

Wild-type (WT) and CatB-/- mice of C57BL/6 background were kept in a specific pathogen-free condition at Kyushu University. The selection of homozygous offspring from their littermates was genotyped as previously reported (Sun et al., 2012). Male mice were used in the whole study. All experimental procedures of this study were approved by the Animal Care and Use Committee of Kyushu University and Sichuan University.

Cell culture

The c-myc–immortalized mouse microglial cell line, MG6 (Riken BioResource

Nuclear location of CatB in aged mouse brain and senescent microglia

Lysosomes are the main degradative organelles in the cells, ultimately connecting the endocytic, phagocytic, and autophagic pathways. Numerous endogenous and exogenous factors have been described to induce lysosomal membrane permeabilization in aging and neurodegenerative disease. The consequences of lysosomal damage and an acidic cocktail of diverse hydrolases constitute a potentially lethal threat to cellular integrity (Papadopoulos and Meyer, 2017). We have previously reported a cell cytosol

Discussion

The major finding of the present study was that the nuclear distribution of CatB in senescent microglia was responsible for the degradation of Sirts in the nucleus during aging. Subsequently, the reduced expression of Sirts in the nucleus was involved in the inflammatory phenotype of microglia through enhanced NF-κB activation. The consequence of chronic activation of NF-κB and neuroinflammation enhanced the impairment of learning and memory.

Research into the function of microglia has

Conclusion

In summary, we found that increased CatB was translocated into the nucleus of senescent microglia. The nuclear CatB was shown to be responsible for the reduction of Sirt1, Sirt6, Sirt7, and P-Sirt1 in the nucleus and subsequently elevated neuroinflammation in senescent microglia, which induced cognitive decline during aging. Therefore, the nuclear translocation of CatB may contribute to the acceleration of aging.

Disclosure statement

The authors have no conflicts of interest to disclose.

Acknowledgements

The authors would like to thank Christoph Peters (Albert-Ludwigs-Universität Freiburg) for providing CatB knock-out mice.

This work was supported by the Ministry of Science and Technology of China (2018YFC1312300 to PL and HQ), the National Natural Science Foundation of China (81870844, 81671268 to HQ; 81722016 to PL), Beijing Institute of Technology Research Fund Program for Young Scholars (2020CX04166 to JN), the National Clinical Research Center for Geriatrics, West China Hospital, Sichuan

References (40)

  • V. Stoka et al.

    Lysosomal cathepsins and their regulation in aging and neurodegeneration

    Ageing Res. Rev.

    (2016)
  • C. Wang et al.

    Cathepsin B degrades amyloid-beta in mice expressing wild-type human amyloid precursor protein

    J. Biol. Chem.

    (2012)
  • Z. Wu et al.

    Cathepsin B plays a critical role in inducing Alzheimer's disease-like phenotypes following chronic systemic exposure to lipopolysaccharide from Porphyromonas gingivalis in mice

    Brain Behav. Immun.

    (2017)
  • L.J. Burton et al.

    Targeting the nuclear cathepsin L CCAAT displacement protein/cut homeobox transcription factor-epithelial mesenchymal transition pathway in prostate and breast cancer cells with the Z-FY-CHO inhibitor

    Mol. Cell. Biol.

    (2017)
  • T.J. Bussian et al.

    Clearance of senescent glial cells prevents tau-dependent pathology and cognitive decline

    Nature

    (2018)
  • M. Dvir-Ginzberg et al.

    Tumor necrosis factor alpha-mediated cleavage and inactivation of SirT1 in human osteoarthritic chondrocytes

    Arthritis Rheum.

    (2011)
  • B. Elibol et al.

    High levels of SIRT1 expression as a protective mechanism against disease-related conditions

    Front. Endocrinol.

    (2018)
  • M.R.P. Elmore et al.

    Replacement of microglia in the aged brain reverses cognitive, synaptic, and neuronal deficits in mice

    Aging cell

    (2018)
  • C.M. Embury et al.

    Cathepsin B improves ss-amyloidosis and learning and memory in models of Alzheimer's disease

    J. NeuroImmune Pharmacol.

    (2017)
  • D.A. Grotsky et al.

    BRCA1 loss activates cathepsin L-mediated degradation of 53BP1 in breast cancer cells

    J. Cell. Biol.

    (2013)
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