Publications

Translational and HIF-1α-Dependent Metabolic Reprogramming Underpin Metabolic Plasticity and Responses to Kinase Inhibitors and Biguanides.
Hulea L, Gravel SP, Morita M, Cargnello M, Uchenunu O, Im YK, Lehuédé C, Ma EH, Leibovitch M, McLaughlan S, Blouin MJ, Parisotto M, Papavasiliou V, Lavoie C, Larsson O, Ohh M, Ferreira T, Greenwood C, Bridon G, Avizonis D, Ferbeyre G, Siegel P, Jones RG, Muller W, Ursini-Siegel J, St-Pierre J, Pollak M, Topisirovic I
Cell Metabolism. 2018 Dec 4;28(6):817-832.e8. doi: 10.1016/j.cmet.2018.09.001.. Epub 2018 Sep 20.

Abstract:

There is increasing interest in therapeutically exploiting metabolic differences between normal and cancer cells. We show that kinase inhibitors (KIs) and biguanides synergistically and selectively target a variety of cancer cells. Synthesis of non-essential amino acids (NEAAs) aspartate, asparagine, and serine, as well as glutamine metabolism, are major determinants of the efficacy of KI/biguanide combinations. The mTORC1/4E-BP axis regulates aspartate, asparagine, and serine synthesis by modulating mRNA translation, while ablation of 4E-BP1/2 substantially decreases sensitivity of breast cancer and melanoma cells to KI/biguanide combinations. Efficacy of the KI/biguanide combinations is also determined by HIF-1α-dependent perturbations in glutamine metabolism, which were observed in VHL-deficient renal cancer cells. This suggests that cancer cells display metabolic plasticity by engaging non-redundant adaptive mechanisms, which allows them to survive therapeutic insults that target cancer metabolism.


NFκB Regulates Muscle Development and Mitochondrial Function.
Valentine JM, Li ME, Shoelson SE, Zhang N, Reddick RL, Musi N
J Gerontol A Biol Sci Med Sci. 2018 Nov 13. doi: 10.1093/gerona/gly262. [Epub ahead of print]

Abstract:

NFκB is a transcription factor that controls immune and inflammatory signaling pathways. In skeletal muscle, NFκB has been implicated in the regulation of metabolic processes and tissue mass; yet, its affects on mitochondrial function in this tissue are unclear. To investigate the role of NFκB on mitochondrial function and its relationship with muscle mass across the lifespan, we study a mouse model with muscle-specific NFκB suppression (MISR mice). In wild type mice there was a natural decline in muscle mass with aging that was accompanied by decreased mitochondrial function and mRNA expression of electron transport chain subunits. NFκB inactivation downregulated expression of PPARGC1A, while upregulating TFEB and PPARGC1B, as well as decreased gastrocnemius (but not soleus) muscle mass in early life (1-6 months old). Lower oxygen consumption rates occurred in gastrocnemius and soleus muscles from young MISR mice, whereas soleus (but not gastrocnemius) muscles from old MISR mice displayed increased oxygen consumption compared to age-matched controls. We conclude that the NFκB pathway plays an important role in muscle development and growth. The extent to which NFκB suppression alters mitochondrial function is age-dependent and muscle-specific. Lastly, mitochondrial function and muscle mass are tightly associated in both genotypes and across the lifespan.


Tau‐induced nuclear envelope invagination causes a toxic accumulation of mRNA in Drosophila
Cornelison GL, Levy SA, Jenson T, Frost B
Aging Cell. 2018 Nov 9:e12847. doi: 10.1111/acel.12847. [Epub ahead of print]

Abstract:

The nucleus is a spherical dual-membrane bound organelle that encapsulates genomic DNA. In eukaryotes, messenger RNAs (mRNA) are transcribed in the nucleus and transported through nuclear pores into the cytoplasm for translation into protein. In certain cell types and pathological conditions, nuclei harbor tubular invaginations of the nuclear envelope known as the “nucleoplasmic reticulum.” Nucleoplasmic reticulum expansion has recently been established as a mediator of neurodegeneration in tauopathies, including Alzheimer’s disease. While the presence of pore-lined, cytoplasm-filled, nuclear envelope invaginations has been proposed to facilitate the rapid export of RNAs from the nucleus to the cytoplasm, the functional significance of nuclear envelope invaginations in regard to RNA export in any disorder is currently unknown. Here, we report that polyadenylated RNAs accumulate within and adjacent to tau-induced nuclear envelope invaginations in a Drosophila model of tauopathy. Genetic or pharmacologic inhibition of RNA export machinery reduces accumulation of polyadenylated RNA within and adjacent to nuclear envelope invaginations and reduces tau-induced neuronal death. These data are the first to point toward a possible role for RNA export through nuclear envelope invaginations in the pathogenesis of a neurodegenerative disorder and suggest that nucleocytoplasmic transport machinery may serve as a possible novel class of therapeutic targets for the treatment of tauopathies.


Marmoset as a model to study kidney changes associated with aging.
Lee HJ, Gonzalez O, Dick EJ Jr, Donati A, Feliers D, Goutam Ghosh C, Ross C, Venkatachalam M, Tardif SD, Kasinath BS
J Gerontol A Biol Sci Med Sci. 2018 Oct 13. doi: 10.1093/gerona/gly237. [Epub ahead of print]
DOI: 10.1093/gerona/gly237

Abstract:

We evaluated whether the marmoset, a nonhuman primate, can serve as a good model to study aging related changes in the kidney by employing healthy young and aged marmosets of both sexes. Aging was associated with glomerulosclerosis, interstitial fibrosis and arteriolosclerosis in both sexes; correspondingly, the content of matrix proteins was increased. Functionally, aging resulted in an increase in urinary albumin and protein excretion. There was a robust correlation between markers of fibrosis and functional changes. We explored signaling pathways as potential mechanistic events. Aging in males, but not in females, was associated with reduced renal cortical activity of AMP-activated protein kinase (AMPK) and a trend toward activation of mechanistic target of rapamycin complex 1 (mTORC1); upstream of AMPK and mTORC1, Akt and IGF-1 receptor were activated. In both sexes, aging promoted kidney activation of transforming growth factor β-1 signaling pathway. While the expression of cystathionine β-synthase (CBS), an enzyme involved hydrogen sulfide (H2S) synthesis, was reduced in both aged males and females, decreased H2S generation was seen in only males. Our studies show that the marmoset is a valid model to study kidney aging; some of the signaling pathways involved in renal senescence differ between male and female marmosets.


Long-term treatment with the mTOR inhibitor rapamycin has minor effect on clinical laboratory markers in middle-aged marmosets.
Sills AM, Artavia JM, DeRosa BD, Ross CN, Salmon AB
American Journal of Primatology. 2018 Oct 12:e22927. doi: 10.1002/ajp.22927. [Epub ahead of print].

Abstract:

Interventions to extend lifespan and improve health with increasing age would have significant impact on a growing aged population. There are now several pharmaceutical interventions that extend lifespan in laboratory rodent models with rapamycin, an inhibitor of mechanistic target of rapamycin (mTOR) being the most well studied. In this study, we report on the hematological effects in a cohort of middle-aged common marmosets (Callithrix jacchus) that were enrolled in a study to test the effects of daily rapamycin treatment on aging in this species. In addition, we assessed whether sex was a significant factor in either baseline assessment or as an interaction with rapamycin treatment. Among our cohort at baseline, we found few differences in either basic morphology or hematological markers of blood cell counts, metabolism or inflammation between male and female marmosets. After dosing with rapamycin, surprisingly we found trough blood concentrations of rapamycin were significantly lower in female compared to male marmosets. Despite this pharmacological difference, both sexes had only minor changes in cellular blood counts after 9 months of rapamycin. These data then suggest that the potential clinical hematological side effects of rapamycin are not likely outcomes of long-term rapamycin in relatively healthy, middle-aged marmosets.


Microtubules and axon regeneration in C. elegans.
Chen L
Molecular and Cellular Neurosciences. 2018 Sep;91:160-166. doi: 10.1016/j.mcn.2018.03.007. Epub 2018 Mar 16.

Abstract:

Axon regeneration is a fundamental and conserved process that allows the nervous system to repair circuits after trauma. Due to its conserved genome, transparent body, and relatively simple neuroanatomy, C. elegans has become a powerful model organism for studying the cellular and molecular mechanisms underlying axon regeneration. Various studies from different model organisms have found microtubule dynamics to be pivotal to axon regrowth. In this review, we will discuss the latest findings on how microtubule dynamics are regulated during axon regeneration in C. elegans. Understanding the mechanisms of axon regeneration will aid in the development of more effective therapeutic strategies for treatments of diseases involving disconnection of axons, such as spinal cord injury and stroke.


Tau protein aggregation is associated with cellular senescence in the brain.
Musi N, Valentine JM, Sickora KR, Baeuerle E, Thompson CS, Shen Q, Orr ME
Aging Cell. 2018 Aug 20:e12840. doi: 10.1111/acel.12840. [Epub ahead of print]

Abstract:

Tau protein accumulation is the most common pathology among degenerative brain diseases, including Alzheimer’s disease (AD), progressive supranuclear palsy (PSP), traumatic brain injury (TBI) and over twenty others. Tau‐containing neurofibrillary tangle (NFT) accumulation is the closest correlate with cognitive decline and cell loss (Arriagada et al., 1992), yet mechanisms mediating tau toxicity are poorly understood. NFT formation does not induce apoptosis (de Calignon et al., 2009), which suggests secondary mechanisms are driving toxicity. Transcriptomic analyses of NFT‐containing neurons microdissected from postmortem AD brain revealed an expression profile consistent with cellular senescence. This complex stress response induces aberrant cell cycle activity, adaptations to maintain survival, cellular remodeling, and metabolic dysfunction. Using four AD transgenic mouse models, we found that NFTs, but not Aβ plaques, display a senescence‐like phenotype. Cdkn2a transcript level, a hallmark measure of senescence, directly correlated with brain atrophy and NFT burden in mice. This relationship extended to postmortem brain tissue from humans with PSP to indicate a phenomenon common to tau toxicity. Tau transgenic mice with late stage pathology were treated with senolytics to remove senescent cells. Despite the advanced age and disease progression, MRI brain imaging and histopathological analyses indicated a reduction in total NFT density, neuron loss and ventricular enlargement. Collectively, these findings indicate a strong association between the presence of NFTs and cellular senescence in the brain, which contributes to neurodegeneration. Given the prevalence of tau protein deposition among neurodegenerative diseases, these findings have broad implications for understanding, and potentially treating, dozens of brain diseases.


Thioredoxin overexpression in both the cytosol and mitochondria accelerates age-related disease and shortens lifespan in male C57BL/6 mice.
Cunningham GM, Flores LC, Roman MG, Cheng C, Dube S, Allen C, Valentine JM, Hubbard GB, Bai Y, Saunders TL, Ikeno Y
Geroscience. 2018 Aug 18. doi: 10.1007/s11357-018-0039-6. [Epub ahead of print]

Abstract:

To investigate the role of increased levels of thioredoxin (Trx) in both the cytosol (Trx1) and mitochondria (Trx2) on aging, we have conducted a study to examine survival and age-related diseases using male mice overexpressing Trx1 and Trx2 (TXNTg × TXN2Tg). Our study demonstrated that the upregulation of Trx in both the cytosol and mitochondria in male TXNTg × TXN2Tg C57BL/6 mice resulted in a significantly shorter lifespan compared to wild-type (WT) mice. Cross-sectional pathology data showed a slightly higher incidence of neoplastic diseases in TXNTg × TXN2Tg mice than WT mice. The incidence of lymphoma, a major neoplastic disease in C57BL/6 mice, was slightly higher in TXNTg × TXN2Tg mice than in WT mice, and more importantly, the severity of lymphoma was significantly higher in TXNTg × TXN2Tg mice compared to WT mice. Furthermore, the total number of histopathological changes in the whole body (disease burden) was significantly higher in TXNTg × TXN2Tg mice compared to WT mice. Therefore, our study suggests that overexpression of Trx in both the cytosol and mitochondria resulted in deleterious effects on aging and accelerated the development of age-related diseases, especially cancer, in male C57BL/6 mice.


DEP domain-containing mTOR-interacting protein suppresses lipogenesis and ameliorates hepatic steatosis and acute-on-chronic liver injury in alcoholic liver disease
Chen H, Shen F, Sherban A, Nocon A, Li Y, Wang H, Xu MJ, Rui X, Han J, Jiang B, Lee D, Li N, Keyhani-Nejad F, Fan JG, Liu F, Kamat A, Musi N, Guarente L, Pacher P, Gao B, Zang M
Hepatology. 2018 Aug;68(2):496-514. doi: 10.1002/hep.29849. Epub 2018 May 21.
PMCID: PMC6097912

Abstract:

Alcoholic liver disease (ALD) is characterized by lipid accumulation and liver injury. However, how chronic alcohol consumption causes hepatic lipid accumulation remains elusive. The present study demonstrates that activation of the mechanistic target of rapamycin complex 1 (mTORC1) plays a causal role in alcoholic steatosis, inflammation, and liver injury. Chronic-plus-binge ethanol feeding led to hyperactivation of mTORC1, as evidenced by increased phosphorylation of mTOR and its downstream kinase S6 kinase 1 (S6K1) in hepatocytes. Aberrant activation of mTORC1 was likely attributed to the defects of the DEP domain-containing mTOR-interacting protein (DEPTOR) and the nicotinamide adenine dinucleotide-dependent deacetylase sirtuin 1 (SIRT1) in the liver of chronic-plus-binge ethanol-fed mice and in the liver of patients with ALD. Conversely, adenoviral overexpression of hepatic DEPTOR suppressed mTORC1 signaling and ameliorated alcoholic hepatosteatosis, inflammation, and acute-on-chronic liver injury. Mechanistically, the lipid-lowering effect of hepatic DEPTOR was attributable to decreased proteolytic processing, nuclear translocation, and transcriptional activity of the lipogenic transcription factor sterol regulatory element-binding protein-1 (SREBP-1). DEPTOR-dependent inhibition of mTORC1 also attenuated alcohol-induced cytoplasmic accumulation of the lipogenic regulator lipin 1 and prevented alcohol-mediated inhibition of fatty acid oxidation. Pharmacological intervention with rapamycin alleviated the ability of alcohol to up-regulate lipogenesis, to down-regulate fatty acid oxidation, and to induce steatogenic phenotypes. Chronic-plus-binge ethanol feeding led to activation of SREBP-1 and lipin 1 through S6K1-dependent and independent mechanisms. Furthermore, hepatocyte-specific deletion of SIRT1 disrupted DEPTOR function, enhanced mTORC1 activity, and exacerbated alcoholic fatty liver, inflammation, and liver injury in mice.

Conclusion:

The dysregulation of SIRT1-DEPTOR-mTORC1 signaling is a critical determinant of ALD pathology; targeting SIRT1 and DEPTOR and selectively inhibiting mTORC1-S6K1 signaling may have therapeutic potential for treating ALD in humans. (Hepatology 2018).


Pathogenic tau-induced piRNA depletion promotes neuronal death through transposable element dysregulation in neurodegenerative tauopathies.
Sun W, Samimi H, Gamez M, Zare H, Frost B
Nature Neuroscience. 2018 Aug;21(8):1038-1048. doi: 10.1038/s41593-018-0194-1. Epub 2018 Jul 23.
PMCID: PMC6095477

Abstract

Transposable elements, known colloquially as ‘jumping genes’, constitute approximately 45% of the human genome. Cells utilize epigenetic defenses to limit transposable element jumping, including formation of silencing heterochromatin and generation of piwi-interacting RNAs (piRNAs), small RNAs that facilitate clearance of transposable element transcripts. Here we utilize Drosophila melanogaster and postmortem human brain samples to identify transposable element dysregulation as a key mediator of neuronal death in tauopathies, a group of neurodegenerative disorders that are pathologically characterized by deposits of tau protein in the brain. Mechanistically, we find that heterochromatin decondensation and reduction of piwi and piRNAs drive transposable element dysregulation in tauopathy. We further report a significant increase in transcripts of the endogenous retrovirus class of transposable elements in human Alzheimer’s disease and progressive supranuclear palsy, suggesting that transposable element dysregulation is conserved in human tauopathy. Taken together, our data identify heterochromatin decondensation, piwi and piRNA depletion and consequent transposable element dysregulation as a pharmacologically targetable, mechanistic driver of neurodegeneration in tauopathy.


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