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Subramaniam S, Boregowda S. Curbing Rhes Actions: Mechanism-based Molecular Target for Huntington's Disease and Tauopathies. CNS & NEUROLOGICAL DISORDERS DRUG TARGETS 2024; 23:21-29. [PMID: 36959146 DOI: 10.2174/1871527322666230320103518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 02/10/2023] [Accepted: 02/13/2023] [Indexed: 03/25/2023]
Abstract
A highly interconnected network of diverse brain regions is necessary for the precise execution of human behaviors, including cognitive, psychiatric, and motor functions. Unfortunately, degeneration of specific brain regions causes several neurodegenerative disorders, but the mechanisms that elicit selective neuronal vulnerability remain unclear. This knowledge gap greatly hinders the development of effective mechanism-based therapies, despite the desperate need for new treatments. Here, we emphasize the importance of the Rhes (Ras homolog-enriched in the striatum) protein as an emerging therapeutic target. Rhes, an atypical small GTPase with a SUMO (small ubiquitin-like modifier) E3-ligase activity, modulates biological processes such as dopaminergic transmission, alters gene expression, and acts as an inhibitor of motor stimuli in the brain striatum. Mutations in the Rhes gene have also been identified in selected patients with autism and schizophrenia. Moreover, Rhes SUMOylates pathogenic form of mutant huntingtin (mHTT) and tau, enhancing their solubility and cell toxicity in Huntington's disease and tauopathy models. Notably, Rhes uses membrane projections resembling tunneling nanotubes to transport mHTT between cells and Rhes deletion diminishes mHTT spread in the brain. Thus, we predict that effective strategies aimed at diminishing brain Rhes levels will prevent or minimize the abnormalities that occur in HD and tauopathies and potentially in other brain disorders. We review the emerging technologies that enable specific targeting of Rhes in the brain to develop effective disease-modifying therapeutics.
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Affiliation(s)
- Srinivasa Subramaniam
- Department of Neuroscience, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, 130 Scripps Way, C323, Florida, Jupiter, 33458, USA
| | - Siddaraju Boregowda
- Department of Molecular Therapeutics, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, 130 Scripps Way, C323, Florida, Jupiter, 33458, USA
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Pan Y, Tang B, Li XJ, Li S, Liu Q. Rhes depletion promotes striatal accumulation and aggregation of mutant huntingtin in a presymptomatic HD mouse model. Front Aging Neurosci 2023; 15:1237018. [PMID: 37637962 PMCID: PMC10449645 DOI: 10.3389/fnagi.2023.1237018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Accepted: 07/31/2023] [Indexed: 08/29/2023] Open
Abstract
Introduction Huntington's disease (HD) is caused by CAG trinucleotide repeats in the HTT gene. Selective neurodegeneration in the striatum is prominent in HD, despite widespread expression of mutant HTT (mHTT). Ras homolog enriched in the striatum (Rhes) is a GTP-binding protein enriched in the striatum, involved in dopamine-related behaviors and autophagy regulation. Growing evidence suggests Rhes plays a critical role in the selective striatal degeneration in HD, but its specific function in this context remains complex and controversial. Methods In this study, we utilized CRISPR/Cas9 to knockdown Rhes at different disease stages through adeno-associated virus (AAV) transduction in HD knock-in (KI) mice. Immunoblotting and immunofluorescence were employed to assess the impact of Rhes depletion on mHTT levels, neuronal loss, astrogliosis and autophagy activity. Results Rhes depletion in 22-week-old HD KI mice (representing the presymptomatic stage) led to mHTT accumulation, reduced neuronal cell staining, and increased astrogliosis. However, no such effects were observed in 36-week-old HD KI mice (representing the symptomatic stage). Additionally, Rhes deletion in 22-week-old HD KI mice resulted in increased P62 levels, reduced LC3-II levels, and unchanged phosphorylation of mTOR and beclin-1, unchanged mTOR protein level, except for a decrease in beclin-1. Discussion Our findings suggest that knockdown Rhes promotes striatal aggregation of mutant huntingtin by reducing autophagy activity in a mTOR-independent manner. Rhes plays a protective role during the presymptomatic stage of HD KI mice.
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Affiliation(s)
- Yongcheng Pan
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan, China
- Key Laboratory of Hunan Province in Neurodegenerative Disorders, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Beisha Tang
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan, China
- Key Laboratory of Hunan Province in Neurodegenerative Disorders, Xiangya Hospital, Central South University, Changsha, Hunan, China
- National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xiao-Jiang Li
- Guangdong Key Laboratory of Non-human Primate Research, Key Laboratory of CNS Regeneration (Ministry of Education), GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China
| | - Shihua Li
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan, China
- Guangdong Key Laboratory of Non-human Primate Research, Key Laboratory of CNS Regeneration (Ministry of Education), GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China
| | - Qiong Liu
- Department of Neurology, Xiangya Hospital, Central South University, Changsha, Hunan, China
- Key Laboratory of Hunan Province in Neurodegenerative Disorders, Xiangya Hospital, Central South University, Changsha, Hunan, China
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Yang YT, Jin S, Bai YB, Liu Y, Hogervorst E. Association of Subclinical Thyroid Dysfunction with Cognitive Impairment in Rats: The Role of Autophagy. J NIPPON MED SCH 2023; 90:372-380. [PMID: 37940558 DOI: 10.1272/jnms.jnms.2023_90-506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2023]
Abstract
BACKGROUND We investigated the effect of subclinical hyperthyroidism and subclinical hypothyroidism on cognitive function in rats and the role of autophagy in this process. METHODS Forty Wistar rats were randomized into normal control (NC), hyperthyroidism (Hyper), hypothyroidism (Hypo), subclinical hyperthyroidism (sHyper), and subclinical hypothyroidism (sHypo) groups. Cognitive function (spatial learning and memory) was tested by the Morris water maze test. Hippocampal histopathology was analyzed by H&E staining, and expression levels of caspase-3 in hippocampal CA1 neurons were measured. In addition, immunoblot analysis was performed to detect hippocampal autophagy-related proteins. RESULTS Escape latency from day 1 to day 4 was significantly longer in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). In addition, the number of rats crossing the virtual platform was significantly lower in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). Compared with the NC group, all four groups had significantly lower residence time in the target quadrant (P < 0.05). Beclin-1 and LC3-II protein expression in hippocampal tissues was significantly higher in the Hyper and sHyper groups than in the NC group (P < 0.01). Beclin-1 and LC3-II protein expression in hippocampal tissues did not significantly differ between the sHypo group and NC group (P > 0.05). CONCLUSIONS Subclinical thyroid dysfunction in rats might lead to cognitive impairment. Subclinical hyperthyroidism might be associated with excessive activation of autophagy and hippocampal neuron damage and necrosis.
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Affiliation(s)
- Yun-Tian Yang
- School of Sport, Exercise and Health Sciences, Loughborough University
- Departments of Neurology, Affiliated Hospital of Inner Mongolia Medical University
| | - Shan Jin
- School of Sport, Exercise and Health Sciences, Loughborough University
- Department of General Surgery, Affiliated Hospital of Inner Mongolia Medical University
| | - Yin-Bao Bai
- Departments of Thyroid Surgery, People's Hospital of Inner Mongolia Autonomous Region
| | - Yousheng Liu
- Department of General Surgery, Datong Third People's Hospital
| | - Eef Hogervorst
- School of Sport, Exercise and Health Sciences, Loughborough University
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Subramaniam S. Striatal Induction and Spread of the Huntington’s Disease Protein: A Novel Rhes Route. J Huntingtons Dis 2022; 11:281-290. [PMID: 35871361 PMCID: PMC9484121 DOI: 10.3233/jhd-220548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The CAG/CAA expansion encoding polyQ huntingtin (mutant huntingtin [mHTT]) causes Huntington’s disease (HD), which is characterized by atrophy and loss of striatal medium spiny neurons (MSNs), which are preceded by neuropathological alterations in the cortex. Previous studies have shown that mHTT can spread in the brain, but the mechanisms involved in the stereotyped degeneration and dysfunction of the neurons from the striatum to the cortex remain unclear. In this study, we found that the mHTT expression initially restricted in the striatum later spread to the cortical regions in mouse brains. Such transmission was diminished in mice that lacked the striatal-enriched protein Ras-homolog enriched in the striatum (Rhes). Rhes restricted to MSNs was also found in the cortical layers of the brain, indicating a new transmission route for the Rhes protein to the brain. Mechanistically, Rhes promotes such transmission via a direct cell-to-cell contact mediated by tunneling nanotubes (TNTs), the membranous protrusions that enable the transfer of mHTT, Rhes, and other vesicular cargoes. These transmission patterns suggest that Rhes and mHTT are likely co-transported in the brain using TNT-like cell-to-cell contacts. On the basis of these new results, a perspective is presented in this review: Rhes may ignite the mHTT transmission from the striatum that may coincide with HD onset and disease progression through an anatomically connected striato-cortical retrograde route.
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Soares ES, Prediger RD, Brocardo PS, Cimarosti HI. SUMO-modifying Huntington's disease. IBRO Neurosci Rep 2022; 12:203-209. [PMID: 35746980 PMCID: PMC9210482 DOI: 10.1016/j.ibneur.2022.03.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 03/06/2022] [Indexed: 12/25/2022] Open
Abstract
Small ubiquitin-like modifiers, SUMOs, are proteins that are conjugated to target substrates and regulate their functions in a post-translational modification called SUMOylation. In addition to its physiological roles, SUMOylation has been implicated in several neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's diseases (HD). HD is a neurodegenerative monogenetic autosomal dominant disorder caused by a mutation in the CAG repeat of the huntingtin (htt) gene, which expresses a mutant Htt protein more susceptible to aggregation and toxicity. Besides Htt, other SUMO ligases, enzymes, mitochondrial and autophagic components are also important for the progression of the disease. Here we review the main aspects of Htt SUMOylation and its role in cellular processes involved in the pathogenesis of HD.
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Affiliation(s)
- Ericks S. Soares
- Post-graduate Program in Pharmacology, Federal University of Santa Catarina (UFSC), Florianópolis, Santa Catarina, Brazil
| | - Rui D. Prediger
- Post-graduate Program in Pharmacology, Federal University of Santa Catarina (UFSC), Florianópolis, Santa Catarina, Brazil
- Post-graduate Program in Neuroscience, UFSC, Florianópolis, Santa Catarina, Brazil
| | - Patricia S. Brocardo
- Post-graduate Program in Neuroscience, UFSC, Florianópolis, Santa Catarina, Brazil
| | - Helena I. Cimarosti
- Post-graduate Program in Pharmacology, Federal University of Santa Catarina (UFSC), Florianópolis, Santa Catarina, Brazil
- Post-graduate Program in Neuroscience, UFSC, Florianópolis, Santa Catarina, Brazil
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Ramírez-Jarquín UN, Sharma M, Shahani N, Li Y, Boregowda S, Subramaniam S. Rhes protein transits from neuron to neuron and facilitates mutant huntingtin spreading in the brain. SCIENCE ADVANCES 2022; 8:eabm3877. [PMID: 35319973 PMCID: PMC8942366 DOI: 10.1126/sciadv.abm3877] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 02/02/2022] [Indexed: 05/12/2023]
Abstract
Rhes (RASD2) is a thyroid hormone-induced gene that regulates striatal motor activity and promotes neurodegeneration in Huntington disease (HD) and tauopathy. Rhes moves and transports the HD protein, polyglutamine-expanded huntingtin (mHTT), via tunneling nanotube (TNT)-like membranous protrusions between cultured neurons. However, similar intercellular Rhes transportation in the intact brain was unknown. Here, we report that Rhes induces TNT-like protrusions in the striatal medium spiny neurons (MSNs) and transported between dopamine-1 receptor (D1R)-MSNs and D2R-MSNs of intact striatum and organotypic brain slices. Notably, mHTT is robustly transported within the striatum and from the striatum to the cortical areas in the brain, and Rhes deletion diminishes such transport. Moreover, Rhes moves to the cortical regions following restricted expression in the MSNs of the striatum. Thus, Rhes is a first striatum-enriched protein demonstrated to move and transport mHTT between neurons and brain regions, providing new insights into interneuronal protein transport in the brain.
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Affiliation(s)
| | - Manish Sharma
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
| | - Neelam Shahani
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
| | - Yuqing Li
- Department of Neurology, University of Florida, Gainesville, FL 32610, USA
| | - Siddaraju Boregowda
- Department of Molecular Medicine, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
| | - Srinivasa Subramaniam
- Department of Neuroscience, The Scripps Research Institute, 130 Scripps Way, Jupiter, FL 33458, USA
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Johnson CW, Seo HS, Terrell EM, Yang MH, KleinJan F, Gebregiworgis T, Gasmi-Seabrook GMC, Geffken EA, Lakhani J, Song K, Bashyal P, Popow O, Paulo JA, Liu A, Mattos C, Marshall CB, Ikura M, Morrison DK, Dhe-Paganon S, Haigis KM. Regulation of GTPase function by autophosphorylation. Mol Cell 2022; 82:950-968.e14. [PMID: 35202574 PMCID: PMC8986090 DOI: 10.1016/j.molcel.2022.02.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 11/29/2021] [Accepted: 02/04/2022] [Indexed: 10/19/2022]
Abstract
A unifying feature of the RAS superfamily is a conserved GTPase cycle by which these proteins transition between active and inactive states. We demonstrate that autophosphorylation of some GTPases is an intrinsic regulatory mechanism that reduces nucleotide hydrolysis and enhances nucleotide exchange, altering the on/off switch that forms the basis for their signaling functions. Using X-ray crystallography, nuclear magnetic resonance spectroscopy, binding assays, and molecular dynamics on autophosphorylated mutants of H-RAS and K-RAS, we show that phosphoryl transfer from GTP requires dynamic movement of the switch II region and that autophosphorylation promotes nucleotide exchange by opening the active site and extracting the stabilizing Mg2+. Finally, we demonstrate that autophosphorylated K-RAS exhibits altered effector interactions, including a reduced affinity for RAF proteins in mammalian cells. Thus, autophosphorylation leads to altered active site dynamics and effector interaction properties, creating a pool of GTPases that are functionally distinct from their non-phosphorylated counterparts.
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Affiliation(s)
- Christian W Johnson
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Hyuk-Soo Seo
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Elizabeth M Terrell
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, MD 21702, USA
| | - Moon-Hee Yang
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA 02115, USA
| | - Fenneke KleinJan
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Teklab Gebregiworgis
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada
| | | | - Ezekiel A Geffken
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Jimit Lakhani
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Kijun Song
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Puspalata Bashyal
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Olesja Popow
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA 02115, USA; Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Joao A Paulo
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Andrea Liu
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA
| | - Carla Mattos
- Department of Chemistry and Chemical Biology, Northeastern University, Boston, MA 02115, USA
| | | | - Mitsuhiko Ikura
- Princess Margaret Cancer Centre, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Deborah K Morrison
- Laboratory of Cell and Developmental Signaling, NCI-Frederick, Frederick, MD 21702, USA
| | - Sirano Dhe-Paganon
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Biological Chemistry & Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Kevin M Haigis
- Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA 02215, USA; Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
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Abnormal RasGRP1 Expression in the Post-Mortem Brain and Blood Serum of Schizophrenia Patients. Biomolecules 2022; 12:biom12020328. [PMID: 35204828 PMCID: PMC8869509 DOI: 10.3390/biom12020328] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/15/2022] [Accepted: 02/15/2022] [Indexed: 11/16/2022] Open
Abstract
Schizophrenia (SCZ) is a polygenic severe mental illness. Genome-wide association studies (GWAS) have detected genomic variants associated with this psychiatric disorder and pathway analyses have indicated immune system and dopamine signaling as core components of risk in dorsolateral-prefrontal cortex (DLPFC) and hippocampus, but the mechanistic links remain unknown. The RasGRP1 gene, encoding for a guanine nucleotide exchange factor, is implicated in dopamine signaling and immune response. RasGRP1 has been identified as a candidate risk gene for SCZ and autoimmune disease, therefore representing a possible point of convergence between mechanisms involving the nervous and the immune system. Here, we investigated RasGRP1 mRNA and protein expression in post-mortem DLPFC and hippocampus of SCZ patients and healthy controls, along with RasGRP1 protein content in the serum of an independent cohort of SCZ patients and control subjects. Differences in RasGRP1 expression between SCZ patients and controls were detected both in DLPFC and peripheral blood of samples analyzed. Our results indicate RasGRP1 may mediate risk for SCZ by involving DLPFC and peripheral blood, thus encouraging further studies to explore its possible role as a biomarker of the disease and/or a target for new medication.
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Cho YY, Kim B, Shin DW, Youn J, Mok JO, Kim CH, Kim SW, Chung JH, Han K, Kim TH. OUP accepted manuscript. Brain Commun 2022; 4:fcac014. [PMID: 35187486 PMCID: PMC8853722 DOI: 10.1093/braincomms/fcac014] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 10/26/2021] [Accepted: 02/03/2022] [Indexed: 11/13/2022] Open
Affiliation(s)
- Yoon Young Cho
- Division of Endocrinology and Metabolism, Department of Medicine, Soonchunhyang University Bucheon Hospital, Bucheon, Korea
| | - Bongseong Kim
- Department of Statistics and Actuarial Science, Soongsil University, Seoul, Korea
| | - Dong Wook Shin
- Supportive Care Center/Department of Family Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
- Department of Clinical Research Design & Evaluation, Samsung Advanced Institute for Health Science & Technology, Sungkyunkwan University, Seoul, Korea
| | - Jinyoung Youn
- Department of Neurology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
- Neuroscience Center, Samsung Medical Center, Seoul, Korea
| | - Ji Oh Mok
- Division of Endocrinology and Metabolism, Department of Medicine, Soonchunhyang University Bucheon Hospital, Bucheon, Korea
| | - Chul-Hee Kim
- Division of Endocrinology and Metabolism, Department of Medicine, Soonchunhyang University Bucheon Hospital, Bucheon, Korea
| | - Sun Wook Kim
- Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Jae Hoon Chung
- Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea
| | - Kyungdo Han
- Correspondence may also be addressed to: Kyungdo Han, PhD Department of Statistics and Actuarial Science Soongsil University 369 Sangdo-ro Dongjak-gu, 06978 Seoul, Korea E-mail:
| | - Tae Hyuk Kim
- Correspondence to: Tae Hyuk Kim, MD, PhD Division of Endocrinology and Metabolism Department of Medicine, Thyroid Center Samsung Medical Center Sungkyunkwan University School of Medicine 81 Irwon-ro, Gangnam-gu 06351 Seoul, Korea E-mail:
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Foradori CD, Mackay L, Huang CCJ, Kemppainen RJ. Expression of Rasd1 in mouse endocrine pituitary cells and its response to dexamethasone. Stress 2021; 24:659-666. [PMID: 33840368 PMCID: PMC8405551 DOI: 10.1080/10253890.2021.1907340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
Dexamethasone-induced Ras-related protein 1 (Rasd1) is a member of the Ras superfamily of monomeric G proteins that have a regulatory function in signal transduction. Rasd1, also known as Dexras1 or AGS1, is rapidly induced by dexamethasone (Dex). While prior data indicates that Rasd1 is highly expressed in the pituitary and that the gene may function in regulation of corticotroph activity, its exact cellular localization in this tissue has not been delineated. Nor has it been determined which endocrine pituitary cell type(s) are responsive to Dex-induced expression of Rasd1. We hypothesized that Rasd1 is primarily localized in corticotrophs and furthermore, that its expression in these cells would be upregulated in response to exogenous Dex administration. Rasd1 expression in each pituitary cell type both under basal conditions and 1-hour post Dex treatment were examined in adult male mice. While a proportion of all endocrine pituitary cell types expressed Rasd1, a majority of corticotrophs and thyrotrophs expressed Rasd1 under basal condition. In vehicle treated animals, approximately 50-60% of corticotrophs and thyrotrophs cells expressed Rasd1 while the gene was detected in only 15-30% of lactotrophs, somatotrophs, and gonadotrophs. In Dex treated animals, Rasd1 expression was significantly increased in corticotrophs, somatotrophs, lactotrophs, and gonadotrophs but not thyrotrophs. In Dex treated animals, Rasd1 was detected in 80-95% of gonadotrophs and corticotrophs. In contrast, Dex treatment increased Rasd1 expression to a lesser extent (55-60%) in somatotrophs and lactotrophs. Corticotrophs of the pars intermedia, which lack glucocorticoid receptors, failed to display increased Rasd1 expression in Dex treated animals. Rasd1 is highly expressed in corticotrophs under basal conditions and is further increased after Dex treatment, further supporting its role in glucocorticoid negative feedback. In addition, the presence and Dex-induced expression of Rasd1 in endocrine pituitary cell types, other than corticotrophs, may implicate Rasd1 in novel pituitary functions.
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Affiliation(s)
- Chad D Foradori
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA
| | - Laci Mackay
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA
| | - Chen-Che J Huang
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA
| | - Robert J Kemppainen
- Department of Anatomy, Physiology and Pharmacology, College of Veterinary Medicine, Auburn University, Auburn, AL, USA
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Serra M, Pinna A, Costa G, Usiello A, Pasqualetti M, Avallone L, Morelli M, Napolitano F. Involvement of the Protein Ras Homolog Enriched in the Striatum, Rhes, in Dopaminergic Neurons' Degeneration: Link to Parkinson's Disease. Int J Mol Sci 2021; 22:ijms22105326. [PMID: 34070217 PMCID: PMC8158741 DOI: 10.3390/ijms22105326] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 05/14/2021] [Accepted: 05/17/2021] [Indexed: 12/17/2022] Open
Abstract
Rhes is one of the most interesting genes regulated by thyroid hormones that, through the inhibition of the striatal cAMP/PKA pathway, acts as a modulator of dopamine neurotransmission. Rhes mRNA is expressed at high levels in the dorsal striatum, with a medial-to-lateral expression gradient reflecting that of both dopamine D2 and adenosine A2A receptors. Rhes transcript is also present in the hippocampus, cerebral cortex, olfactory tubercle and bulb, substantia nigra pars compacta (SNc) and ventral tegmental area of the rodent brain. In line with Rhes-dependent regulation of dopaminergic transmission, data showed that lack of Rhes enhanced cocaine- and amphetamine-induced motor stimulation in mice. Previous studies showed that pharmacological depletion of dopamine significantly reduces Rhes mRNA levels in rodents, non-human primates and Parkinson's disease (PD) patients, suggesting a link between dopaminergic innervation and physiological Rhes mRNA expression. Rhes protein binds to and activates striatal mTORC1, and modulates L-DOPA-induced dyskinesia in PD rodent models. Finally, Rhes is involved in the survival of mouse midbrain dopaminergic neurons of SNc, thus pointing towards a Rhes-dependent modulation of autophagy and mitophagy processes, and encouraging further investigations about mechanisms underlying dysfunctions of the nigrostriatal system.
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Affiliation(s)
- Marcello Serra
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, 09042 Cagliari, Italy; (M.S.); (G.C.); (M.M.)
| | - Annalisa Pinna
- National Research Council of Italy (CNR), Neuroscience Institute—Cagliari, Cittadella Universitaria, 09042 Cagliari, Italy;
| | - Giulia Costa
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, 09042 Cagliari, Italy; (M.S.); (G.C.); (M.M.)
| | - Alessandro Usiello
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania Luigi Vanvitelli, 81100 Caserta, Italy;
- Laboratory of Behavioral Neuroscience, Ceinge Biotecnologie Avanzate, 80145 Naples, Italy
| | - Massimo Pasqualetti
- Unit of Cell and Developmental Biology, Department of Biology, University of Pisa, 56127 Pisa, Italy;
| | - Luigi Avallone
- Department of Veterinary Medicine and Animal Productions, University of Naples “Federico II”, 80137 Naples, Italy;
| | - Micaela Morelli
- Department of Biomedical Sciences, Section of Neuroscience, University of Cagliari, 09042 Cagliari, Italy; (M.S.); (G.C.); (M.M.)
- National Research Council of Italy (CNR), Neuroscience Institute—Cagliari, Cittadella Universitaria, 09042 Cagliari, Italy;
| | - Francesco Napolitano
- Laboratory of Behavioral Neuroscience, Ceinge Biotecnologie Avanzate, 80145 Naples, Italy
- Department of Veterinary Medicine and Animal Productions, University of Naples “Federico II”, 80137 Naples, Italy;
- Correspondence:
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Chen X, Zhang Y, Wang Q, Qin Y, Yang X, Xing Z, Shen Y, Wu H, Qi Y. The function of SUMOylation and its crucial roles in the development of neurological diseases. FASEB J 2021; 35:e21510. [PMID: 33710677 DOI: 10.1096/fj.202002702r] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Revised: 02/02/2021] [Accepted: 02/22/2021] [Indexed: 11/11/2022]
Abstract
Neurological diseases are relatively complex diseases of a large system; however, the detailed mechanism of their pathogenesis has not been completely elucidated, and effective treatment methods are still lacking for some of the diseases. The SUMO (small ubiquitin-like modifier) modification is a dynamic and reversible process that is catalyzed by SUMO-specific E1, E2, and E3 ligases and reversed by a family of SENPs (SUMO/Sentrin-specific proteases). SUMOylation covalently conjugates numerous cellular proteins, and affects their cellular localization and biological activity in numerous cellular processes. A wide range of neuronal proteins have been identified as SUMO substrates, and the disruption of SUMOylation results in defects in synaptic plasticity, neuronal excitability, and neuronal stress responses. SUMOylation disorders cause many neurodegenerative diseases, such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. By modulating the ion channel subunit, SUMOylation imbalance is responsible for the development of various channelopathies. The regulation of protein SUMOylation in neurons may provide a new strategy for the development of targeted therapeutic drugs for neurodegenerative diseases and channelopathies.
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Affiliation(s)
- Xu Chen
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Yuhong Zhang
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Qiqi Wang
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Yuanyuan Qin
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Xinyi Yang
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Zhengcao Xing
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Yajie Shen
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Hongmei Wu
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
| | - Yitao Qi
- Key Laboratory of the Ministry of Education for Medicinal Resources and Natural Pharmaceutical Chemistry, National Engineering Laboratory for Resource Developing of Endangered Chinese Crude Drugs in Northwest of China, College of Life Sciences, Shaanxi Normal University, Xi'an, China
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Mishra J, Vishwakarma J, Malik R, Gupta K, Pandey R, Maurya SK, Garg A, Shukla M, Chattopadhyay N, Bandyopadhyay S. Hypothyroidism Induces Interleukin-1-Dependent Autophagy Mechanism as a Key Mediator of Hippocampal Neuronal Apoptosis and Cognitive Decline in Postnatal Rats. Mol Neurobiol 2021; 58:1196-1211. [PMID: 33106949 DOI: 10.1007/s12035-020-02178-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2020] [Accepted: 10/14/2020] [Indexed: 02/07/2023]
Abstract
Thyroid hormone (TH) is essential for brain development, and hypothyroidism induces cognitive deficits in children and young adults. However, the participating mechanisms remain less explored. Here, we examined the molecular mechanism, hypothesizing the involvement of a deregulated autophagy and apoptosis pathway in hippocampal neurons that regulate cognitive functions. Therefore, we used a rat model of developmental hypothyroidism, generated through methimazole treatment from gestation until young adulthood. We detected that methimazole stimulated the autophagy mechanism, characterized by increased LC3B-II, Beclin-1, ATG7, and ATG5-12 conjugate and decreased p-mTOR/mTOR and p-ULK1/ULK1 autophagy regulators in the hippocampus of developing and young adult rats. This methimazole-induced hippocampal autophagy could be inhibited by thyroxine treatment. Subsequently, probing the upstream mediators of autophagy revealed an increased hippocampal neuroinflammation, marked by upregulated interleukin (IL)-1alpha and beta and activated microglial marker, Iba1, promoting neuronal IL-1 receptor-1 expression. Hence, IL-1R-antagonist (IL-1Ra), which reduced hippocampal neuronal IL-1R1, also inhibited the enhanced autophagy in hypothyroid rats. We then linked these events with hypothyroidism-induced apoptosis and loss of hippocampal neurons, where we observed that like thyroxine, IL-1Ra and autophagy inhibitor, 3-methyladenine, reduced the cleaved caspase-3 and TUNEL-stained apoptotic neurons and enhanced Nissl-stained neuronal count in methimazole-treated rats. We further related these molecular results with cognition through Y-maze and passive avoidance tests, demonstrating an IL-1Ra and 3-methyladenine-mediated improvement in learning-memory performances of the hypothyroid rats. Taken together, our study enlightens the critical role of neuroinflammation-dependent autophagy mechanism in TH-regulated hippocampal functions, disrupted in developmental hypothyroidism.
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Affiliation(s)
- Juhi Mishra
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
- Department of Biochemistry, Babu Banarasi Das University, Faizabad Road, Lucknow, Uttar Pradesh, India
| | - Jitendra Vishwakarma
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India
| | - Rafat Malik
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
| | - Keerti Gupta
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India
| | - Rukmani Pandey
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India
- Department of Psychiatry, Center for Molecular Biology and Genetics of Neurodegeneration, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Shailendra Kumar Maurya
- Division of Endocrinology, CSIR-Central Drug Research Institute (CSIR-CDRI), Lucknow, Uttar Pradesh, India
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA
| | - Asmita Garg
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India
| | - Manoj Shukla
- Department of Endocrinology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
| | - Naibedya Chattopadhyay
- Division of Endocrinology, CSIR-Central Drug Research Institute (CSIR-CDRI), Lucknow, Uttar Pradesh, India
| | - Sanghamitra Bandyopadhyay
- Developmental Toxicology Laboratory, Systems Toxicology & Health Risk Assessment Group, CSIR-Indian Institute of Toxicology Research (CSIR-IITR), Vishvigyan Bhavan, Lucknow, Uttar Pradesh, 226001, India.
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh, India.
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Mohammadi S, Dolatshahi M, Rahmani F. Shedding light on thyroid hormone disorders and Parkinson disease pathology: mechanisms and risk factors. J Endocrinol Invest 2021; 44:1-13. [PMID: 32500445 DOI: 10.1007/s40618-020-01314-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Accepted: 05/27/2020] [Indexed: 02/07/2023]
Abstract
Parkinson's disease (PD) is a neurodegenerative disorder characterized by loss of dopaminergic neurons. Dopaminergic system is interconnected with the hypothalamic-pituitary-thyroid axis. Dopamine (DA) upregulates thyrotropin releasing hormone (TRH) while downregulating thyroid stimulating hormone (TSH) and thyroid hormones. Moreover, TRH stimulates DA release. PD is associated with impaired regulation of TSH and thyroid hormones (TH) levels, which in turn associate with severity and different subtypes of PD, while levodopa and bromocriptine treatment can interfere with hypothalamic-pituitary-thyroid axis. Thyroid disturbances, including hypothyroidism, Hashimoto's thyroiditis (HT), hyperthyroidism and Graves' disease (GD) not only increase the risk of PD but also share some clinical signs with PD. Also, several genes including RASD2, WSB1, MAPT, GIRK2, LRRK2 and gene products like neurotensin and NOX/DUOX affect the risk for both PD and thyroid disease. Hypothyroidism is associated with obesity, hypercholesterolemia, anemia and altered cerebral blood flow which are associated with PD pathology. Herein we provide a comprehensive view on the association between PD and thyroid hormones regulation and dysregulations, hoping to provide new avenues towards targeted treatment of PD. We performed a comprehensive search in literature using Pubmed and Scopus, yielding to a total number of 36 original articles that had addressed the association between thyroid hormone disorders and PD.
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Affiliation(s)
- S Mohammadi
- Student's Scientific Research Center (SSRC), Tehran University of Medical Sciences, Tehran, Iran
- NeuroImaging Network (NIN), Universal Scientific Education and Research Network (USERN), Tehran, Iran
| | - M Dolatshahi
- Student's Scientific Research Center (SSRC), Tehran University of Medical Sciences, Tehran, Iran
- NeuroImaging Network (NIN), Universal Scientific Education and Research Network (USERN), Tehran, Iran
| | - F Rahmani
- Department of Radiology, Washington University School of Medicine, St. Louis, MO, USA.
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The striatal-enriched protein Rhes is a critical modulator of cocaine-induced molecular and behavioral responses. Sci Rep 2019; 9:15294. [PMID: 31653935 PMCID: PMC6814836 DOI: 10.1038/s41598-019-51839-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 10/09/2019] [Indexed: 12/31/2022] Open
Abstract
Previous evidence pointed out a role for the striatal-enriched protein Rhes in modulating dopaminergic transmission. Based on the knowledge that cocaine induces both addiction and motor stimulation, through its ability to enhance dopaminergic signaling in the corpus striatum, we have now explored the involvement of Rhes in the effects associated with this psychostimulant. Our behavioral data showed that a lack of Rhes in knockout animals caused profound alterations in motor stimulation following cocaine exposure, eliciting a significant leftward shift in the dose-response curve and triggering a dramatic hyperactivity. We also found that Rhes modulated either short- or long-term motor sensitization induced by cocaine, since lack of this protein prevents both of them in mutants. Consistent with this in vivo observation, we found that lack of Rhes in mice caused a greater increase in striatal cocaine-dependent D1R/cAMP/PKA signaling, along with considerable enhancement of Arc, zif268, and Homer1 mRNA expression. We also documented that lack of Rhes in mice produced cocaine-related striatal alterations in proteomic profiling, with a differential expression of proteins clustering in calcium homeostasis and cytoskeletal protein binding categories. Despite dramatic striatal alterations associated to cocaine exposure, our data did not reveal any significant changes in midbrain dopaminergic neurons as a lack of Rhes did not affect: (i) DAT activity; (ii) D2R-dependent regulation of GIRK; and (iii) D2R-dependent regulation of dopamine release. Collectively, our results strengthen the view that Rhes acts as a pivotal physiological “molecular brake” for striatal dopaminergic system overactivation induced by psychostimulants, thus making this protein of interest in regulating the molecular mechanism underpinning cocaine-dependent motor stimulatory effects.
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Lack of Rhes Increases MDMA-Induced Neuroinflammation and Dopamine Neuron Degeneration: Role of Gender and Age. Int J Mol Sci 2019; 20:ijms20071556. [PMID: 30925704 PMCID: PMC6480667 DOI: 10.3390/ijms20071556] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 03/21/2019] [Accepted: 03/24/2019] [Indexed: 02/06/2023] Open
Abstract
Ras homolog enriched in striatum (Rhes) is a protein that exerts important physiological functions and modulates psychostimulant drug effects. On this basis, the object of this study was to assess 3,4-methylenedioxymethamphetamine (MDMA) effects on microglial (CD11b) and astroglial (GFAP) activation and on dopamine neuron degeneration (TH) in wild-type (WT) and Rhes knockout (KO) male and female mice of different ages. Motor activity was also evaluated. Adult (3 months) MDMA-treated mice displayed an increase in GFAP-positive cells in striatum (STR), whereas the substantia nigra pars compacta (SNc) was affected only in male mice. In these mice, the increase of CD11b was more extensive including STR, SNc, motor cortex (CTX), ventral tegmental area (VTA), and nucleus accumbens (NAc). MDMA administration also affected TH immunoreactivity in both STR and SNc of male but not female WT and Rhes KO mice. In middle-aged mice (12 months), MDMA administration further increased GFAP and CD11b and decreased TH immunoreactivity in STR and SNc of all mice. Finally, MDMA induced a higher increase of motor activity in adult Rhes KO male, but not female mice. The results show that Rhes protein plays an important role on MDMA-mediated neuroinflammation and neurodegeneration dependent on gender and age, and confirm the important role of Rhes protein in neuroinflammatory and neurodegenerative processes.
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Stepien BK, Huttner WB. Transport, Metabolism, and Function of Thyroid Hormones in the Developing Mammalian Brain. Front Endocrinol (Lausanne) 2019; 10:209. [PMID: 31001205 PMCID: PMC6456649 DOI: 10.3389/fendo.2019.00209] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 03/14/2019] [Indexed: 12/22/2022] Open
Abstract
Ever since the discovery of thyroid hormone deficiency as the primary cause of cretinism in the second half of the 19th century, the crucial role of thyroid hormone (TH) signaling in embryonic brain development has been established. However, the biological understanding of TH function in brain formation is far from complete, despite advances in treating thyroid function deficiency disorders. The pleiotropic nature of TH action makes it difficult to identify and study discrete roles of TH in various aspect of embryogenesis, including neurogenesis and brain maturation. These challenges notwithstanding, enormous progress has been achieved in understanding TH production and its regulation, their conversions and routes of entry into the developing mammalian brain. The endocrine environment has to adjust when an embryo ceases to rely solely on maternal source of hormones as its own thyroid gland develops and starts to produce endogenous TH. A number of mechanisms are in place to secure the proper delivery and action of TH with placenta, blood-brain interface, and choroid plexus as barriers of entry that need to selectively transport and modify these hormones thus controlling their active levels. Additionally, target cells also possess mechanisms to import, modify and bind TH to further fine-tune their action. A complex picture of a tightly regulated network of transport proteins, modifying enzymes, and receptors has emerged from the past studies. TH have been implicated in multiple processes related to brain formation in mammals-neuronal progenitor proliferation, neuronal migration, functional maturation, and survival-with their exact roles changing over developmental time. Given the plethora of effects thyroid hormones exert on various cell types at different developmental periods, the precise spatiotemporal regulation of their action is of crucial importance. In this review we summarize the current knowledge about TH delivery, conversions, and function in the developing mammalian brain. We also discuss their potential role in vertebrate brain evolution and offer future directions for research aimed at elucidating TH signaling in nervous system development.
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