Awakening the dark side: retrotransposon activation in neurodegenerative disorders.
Elizabeth Ochoa Thomas, Gabbe Zuniga, Wenyan Sun, Bess Frost.
Current Opinion in Neurobiology. 2020 Apr;61:65-72. doi: 10.1016/j.conb.2020.01.012. Epub 2020 Feb 21.
Nearly half (45%) of the human genome is composed of transposable elements, or ‘jumping genes’. Since Barbara McClintock’s original discovery of transposable elements in 1950, we have come to appreciate that transposable element mobilization is a major driver of evolution that transposons are active in the germline and the soma, and that transposable element dysregulation is causally associated with many human disorders. In the present review, we highlight recent studies investigating transposable element activation in the adult brain and in the context of neurodegeneration. Collectively, these studies contribute to a greater understanding of the frequency of complete retrotransposition in the adult brain as well as the presence of transposable element-derived RNA and protein in brain and fluids of patients with neurodegenerative disorders. We discuss therapeutic opportunities and speculate on the larger implications of transposable element activation in regard to current hot topics in the field of neurodegeneration.
mTOR drives cerebrovascular, synaptic, and cognitive dysfunction in normative aging.
Van Skike CE, Lin AL, Roberts Burbank R, Halloran JJ, Hernandez SF, Cuvillier J, Soto VY, Hussong SA, Jahrling JB, Javors MA, Hart MJ, Fischer KE, Austad SN, Galvan V.
Aging Cell. 2020 Jan;19(1):e13057. doi: 10.1111/acel.13057. Epub 2019 Nov 6.
Cerebrovascular dysfunction and cognitive decline are highly prevalent in aging, but the mechanisms underlying these impairments are unclear. Cerebral blood flow decreases with aging and is one of the earliest events in the pathogenesis of Alzheimer’s disease (AD). We have previously shown that the mechanistic/mammalian target of rapamycin (mTOR) drives disease progression in mouse models of AD and in models of cognitive impairment associated with atherosclerosis, closely recapitulating vascular cognitive impairment. In the present studies, we sought to determine whether mTOR plays a role in cerebrovascular dysfunction and cognitive decline during normative aging in rats. Using behavioral tools and MRI-based functional imaging, together with biochemical and immunohistochemical approaches, we demonstrate that chronic mTOR attenuation with rapamycin ameliorates deficits in learning and memory, prevents neurovascular uncoupling, and restores cerebral perfusion in aged rats. Additionally, morphometric and biochemical analyses of hippocampus and cortex revealed that mTOR drives age-related declines in synaptic and vascular density during aging. These data indicate that in addition to mediating AD-like cognitive and cerebrovascular deficits in models of AD and atherosclerosis, mTOR drives cerebrovascular, neuronal, and cognitive deficits associated with normative aging. Thus, inhibitors of mTOR may have potential to treat age-related cerebrovascular dysfunction and cognitive decline. Since treatment of age-related cerebrovascular dysfunction in older adults is expected to prevent further deterioration of cerebral perfusion, recently identified as a biomarker for the very early (preclinical) stages of AD, mTOR attenuation may potentially block the initiation and progression of AD.
Age-dependent autophagy induction after injury promotes axon regeneration by limiting NOTCH.
Ko SH, Apple EC, Liu Z, Chen L
Autophagy. 2020 Jan 13:1-17. doi: 10.1080/15548627.2020.1713645. [Epub ahead of print]
Macroautophagy/autophagy is essential for maintaining cellular homeostasis through the degradation of organelles and proteins. It also has a prominent role in modulating aging. However, the role of autophagy in the neuronal response to axon injury and axon regeneration, particularly in the context of aging, remains largely unknown. Our candidate genetic screen for axon regeneration regulators has identified genes in the autophagy pathway. Using a reporter that monitors autophagosomes and autolysosomes, we were able to monitor the dynamics of autophagy during axon regeneration. In response to axon injury, there was a significant increase in the number of autophagic vesicles. Injury-triggered autophagy activation and axon regeneration capacity undergo an age-dependent decline, and autophagy-activating agents partially rescued these declines. We found that DLK-1 was both required and sufficient for injury-induced autophagy activation. Autophagic vesicles co-localized with the NOTCH4 ortholog, LIN-12 receptor, a previously identified inhibitor of axon regeneration. Epistasis analyses indicate that LIN-12 might be a target of autophagy in axon regeneration. Together, our data suggest that DLK-mediated injury signaling can activate autophagy, which might limit the level of LIN-12 and NOTCH proteins to promote axon regeneration. Our findings reveal that autophagy activation can promote axon regeneration in neurons that lack maximal regrowth capacity, providing a promising therapeutic strategy for axon injury.
Abbreviations: 3-MA: 3-methyladenine; ALs: autolysosomes; APs: autophagosomes; ARF-6: ADP-Ribosylation Factor related 6; ATG-9: AuTophaGy (yeast Atg homolog) 9; ATG9A: autophagy related 9A; BA1: bafilomycin A1; BEC-1: BEClin (human autophagy) homolog; BECN1: beclin 1; C. elegans: Caenorhabditis elegans; CEBP-1: C/EBP (CCAAT/enhancer-binding protein) homolog; CNS: central nervous system; DLK-1: Dual-Leucine zipper Kinase; DMSO: dimethyl sulfoxide; DRG: dorsal root ganglion; FOS: Fos proto-oncogene, AP-1 transcription factor subunit; GABA: gamma-aminobutyric acid; GFP: green fluorescent protein; HDA-3: Histone DeAcetylase; IP3: inositol trisphosphate; ITR-1: Inositol Triphosphate Receptor; KLF-2: Kruppel-Like Factor (zinc finger protein) 2; LGG-1: LC3, GABARAP and GATE-16 family; MAK-2: MAP kinase Activated protein Kinase; MAP kinase: mitogen-activated protein kinase; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MKK-4: mitogen activated protein kinase kinase 4; MTOR: mechanistic target of rapamycin kinase; NGM: nematode growth medium; NICD: Notch intracellular domain; NOTCH: notch receptor; PLM: posterior lateral microtubule; PMK-3: P38 Map kinase family; PNS: peripheral nervous system; SCG10: superior cervical ganglion protein 10; SCI: spinal cord injury; UNC-51: UNCoordinated 51; ULK1: unc-51 like autophagy activating kinase 1; wnd: wallenda.
Acarbose blocks the digestion of complex carbohydrates, and the NIA Intervention Testing Program (ITP) found that it improved survival when fed to mice. Yet, we do not know if lifespan extension was caused by its effect on metabolism with regard to the soma or cancer suppression. Cancer caused death for ~80% of ITP mice. The ITP found rapamycin, an inhibitor to the pro-growth mTORC1 (mechanistic target of rapamycin complex 1) pathway, improved survival and it suppressed tumors in Apc+/Min mice providing a plausible rationale to ask if acarbose had a similar effect. Apc+/Min is a mouse model prone to intestinal polyposis and a mimic of familial adenomatous polyposis in people. Polyp-associated anemia contributed to their death. To address this knowledge gap, we fed two doses of acarbose to Apc+/Min mice. Acarbose improved median survival at both doses. A cross-sectional analysis was performed next. At both doses, ACA fed mice exhibited reduced intestinal crypt depth, weight loss despite increased food consumption and reduced postprandial blood glucose and plasma insulin, indicative of improved insulin sensitivity. Dose-independent and dose-dependent compensatory liver responses were observed for AMPK and mTORC1 activities, respectively. Only mice fed the high dose diet exhibited reductions in tumor number with higher hematocrits. Because low-dose acarbose improved lifespan but failed to reduced tumors, its effects seem to be independent of cancer. These data implicate the importance of improved carbohydrate metabolism on survival.
APOE2 orchestrated differences in transcriptomic and lipidomic profiles of postmortem AD brain.
Lefterov I, Wolfe CM, Fitz NF, Nam KN, Letronne F, Biedrzycki RJ, Kofler J, Han X, Wang J, Schug J, Koldamova R
Alzheimers Res Ther. 2019 Dec 30;11(1):113. doi: 10.1186/s13195-019-0558-0.
BACKGROUND: The application of advanced sequencing technologies and improved mass-spectrometry platforms revealed significant changes in gene expression and lipids in Alzheimer’s disease (AD) brain. The results so far have prompted further research using “multi-omics” approaches. These approaches become particularly relevant, considering the inheritance of APOEε4 allele as a major genetic risk factor of AD, disease protective effect of APOEε2 allele, and a major role of APOE in brain lipid metabolism.
METHODS: Postmortem brain samples from inferior parietal lobule genotyped as APOEε2/c (APOEε2/carriers), APOEε3/3, and APOEε4/c (APOEε4/carriers), age- and gender-matched, were used to reveal APOE allele-associated changes in transcriptomes and lipidomes. Differential gene expression and co-expression network analyses were applied to identify up- and downregulated Gene Ontology (GO) terms and pathways for correlation to lipidomics data.
RESULTS: Significantly affected GO terms and pathways were determined based on the comparisons of APOEε2/c datasets to those of APOEε3/3 and APOEε4/c brain samples. The analysis of lists of genes in highly correlated network modules and of those differentially expressed demonstrated significant enrichment in GO terms associated with genes involved in intracellular proteasomal and lysosomal degradation of proteins, protein aggregates and organelles, ER stress, and response to unfolded protein, as well as mitochondrial function, electron transport, and ATP synthesis. Small nucleolar RNA coding units important for posttranscriptional modification of mRNA and therefore translation and protein synthesis were upregulated in APOEε2/c brain samples compared to both APOEε3/3 and APOEε4/c. The analysis of lipidomics datasets revealed significant changes in ten major lipid classes (exclusively a decrease in APOEε4/c samples), most notably non-bilayer-forming phosphatidylethanolamine and phosphatidic acid, as well as mitochondrial membrane-forming lipids.
CONCLUSIONS: The results of this study, despite the advanced stage of AD, point to the significant differences in postmortem brain transcriptomes and lipidomes, suggesting APOE allele associated differences in pathogenic mechanisms. Correlations within and between lipidomes and transcriptomes indicate coordinated effects of changes in the proteasomal system and autophagy-canonical and selective, facilitating intracellular degradation, protein entry into ER, response to ER stress, nucleolar modifications of mRNA, and likely myelination in APOEε2/c brains. Additional research and a better knowledge of the molecular mechanisms of proteostasis in the early stages of AD are required to develop more effective diagnostic approaches and eventually efficient therapeutic strategies.
Nexrutine and exercise similarly prevent high grade prostate tumors in transgenic mouse model.
Patel DI, Abuchowski K, Bedolla R, Rivas P, Musi N, Reddick R, Kumar AP
PLoS One. 2019 Dec 19;14(12):e0226187. doi: 10.1371/journal.pone.0226187. eCollection 2019.
The purpose of this investigation was to compare the antitumorigenic effects of the natural product Nexrutine to voluntary wheel running (VWR) in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Forty-five, 10-week old TRAMP mice were randomized to either receive free access to the running wheel, Nexrutine pelleted into chow at 600 mg/kg or no treatment control. Mice were serially sacrificed at weeks 4, 8,12 and 20 weeks. Palpable tumors, body weight, food consumption and running wheel activity were monitored weekly. At necropsy, tumors and serum were harvested and stored for analysis. Serum was used to quantify circulating cytokines in 4 and 20 week time points. Nexrutine supplementation led to a 66% protection against high grade tumors. Exercise resulted in a 60% protection against high grade tumors. Both interventions reduced concentrations of IL-1α. Exercise also significantly lowered concentrations of eotaxin, IL-5, IL-12(p40) and VEGF. While there were no significant differences at baseline, exercise mice had significantly lower IL-5 and VEGF compared to control at the 20 week time point. Nexrutine also significantly reduced circulating IL-9 concentrations. No significant differences were observed when compared to the control group. Immunohistochemistry of tumor sections showed significantly lower expression of pAkt in Nexrutine fed mice with no visible differences for NFκB. In conclusion, both Nexrutine and exercise suppressed tumor growth. Though similar outcomes were seen in this comparative effectiveness study, the mechanisms by which exercise and Nexrutine exert this benefit may focus on different pathways.
Aging Induces an Nlrp3 Inflammasome-Dependent Expansion of Adipose B Cells That Impairs Metabolic Homeostasis.
Camell CD, Günther P, Lee A, Goldberg EL, Spadaro O, Youm YH, Bartke A, Hubbard GB, Ikeno Y, Ruddle NH, Schultze J, Dixit VD
Cell Metab. 2019 Dec 3;30(6):1024-1039.e6. doi: 10.1016/j.cmet.2019.10.006. Epub 2019 Nov 14.
During aging, visceral adiposity is often associated with alterations in adipose tissue (AT) leukocytes, inflammation, and metabolic dysfunction. However, the contribution of AT B cells in immunometabolism during aging is unexplored. Here, we show that aging is associated with an expansion of a unique population of resident non-senescent aged adipose B cells (AABs) found in fat-associated lymphoid clusters (FALCs). AABs are transcriptionally distinct from splenic age-associated B cells (ABCs) and show greater expansion in female mice. Functionally, whole-body B cell depletion restores proper lipolysis and core body temperature maintenance during cold stress. Mechanistically, the age-induced FALC formation, AAB, and splenic ABC expansion is dependent on the Nlrp3 inflammasome. Furthermore, AABs express IL-1R, and inhibition of IL-1 signaling reduces their proliferation and increases lipolysis in aging. These data reveal that inhibiting Nlrp3-dependent B cell accumulation can be targeted to reverse metabolic impairment in aging AT.
Body image in older women: a mediator of BMI and wellness behaviors.
Kilpela LS, Verzijl CL, Becker CB
J Women Aging. 2019 Nov 21:1-14. doi: 10.1080/08952841.2019.1692629. [Epub ahead of print]
Negative body image is prevalent among mid- and late-life women. In younger women, negative body image is associated with reduced quality of life (QOL) when controlling for body mass index (BMI), and mediates the relationship between obesity and emotional wellbeing. Yet, much remains unknown about body image in older populations. In our sample of women aged 50-86 (N = 181), negative body image mediated the relationship between BMI and sleep, all four domains of QOL, negative affect, nutritious food consumption, and psychosocial impairment, but not enjoyment of physical activity. Findings suggest negative body image impacts the wellbeing of older women.
Deficiency in the DNA repair protein ERCC1 triggers a link between senescence and apoptosis in human fibroblasts and mouse skin.
Kim DE, Dollé MET, Vermeij WP, Gyenis A, Vogel K, Hoeijmakers JHJ, Wiley CD, Davalos AR, Hasty P, Desprez PY, Campisi J
Aging Cell. 2019 Nov 18:e13072. doi: 10.1111/acel.13072. [Epub ahead of print]
ERCC1 (excision repair cross complementing-group 1) is a mammalian endonuclease that incises the damaged strand of DNA during nucleotide excision repair and interstrand cross-link repair. Ercc1-/Δ mice, carrying one null and one hypomorphic Ercc1 allele, have been widely used to study aging due to accelerated aging phenotypes in numerous organs and their shortened lifespan. Ercc1-/Δ mice display combined features of human progeroid and cancer-prone syndromes. Although several studies report cellular senescence and apoptosis associated with the premature aging of Ercc1-/Δ mice, the link between these two processes and their physiological relevance in the phenotypes of Ercc1-/Δ mice are incompletely understood. Here, we show that ERCC1 depletion, both in cultured human fibroblasts and the skin of Ercc1-/Δ mice, initially induces cellular senescence and, importantly, increased expression of several SASP (senescence-associated secretory phenotype) factors. Cellular senescence induced by ERCC1 deficiency was dependent on activity of the p53 tumor-suppressor protein. In turn, TNFα secreted by senescent cells induced apoptosis, not only in neighboring ERCC1-deficient nonsenescent cells, but also cell autonomously in the senescent cells themselves. In addition, expression of the stem cell markers p63 and Lgr6 was significantly decreased in Ercc1-/Δ mouse skin, where the apoptotic cells are localized, compared to age-matched wild-type skin, possibly due to the apoptosis of stem cells. These data suggest that ERCC1-depleted cells become susceptible to apoptosis via TNFα secreted from neighboring senescent cells. We speculate that parts of the premature aging phenotypes and shortened health- or lifespan may be due to stem cell depletion through apoptosis promoted by senescent cells.