Single-cell Tsc1 knockout during corticogenesis generates tuber-like lesions and reduces seizure threshold in mice

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Abstract

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder characterized by mutations in Tsc1 or Tsc2 that lead to mammalian target of rapamycin (mTOR) hyperactivity. Patients with TSC suffer from intractable seizures resulting from cortical malformations known as tubers, but research into how these tubers form has been limited because of the lack of an animal model. To address this limitation, we used in utero electroporation to knock out Tsc1 in selected neuronal populations in mice heterozygous for a mutant Tsc1 allele that eliminates the Tsc1 gene product at a precise developmental time point. Knockout of Tsc1 in single cells led to increased mTOR activity and soma size in the affected neurons. The mice exhibited white matter heterotopic nodules and discrete cortical tuber-like lesions containing cytomegalic and multinucleated neurons with abnormal dendritic trees resembling giant cells. Cortical tubers in the mutant mice did not exhibit signs of gliosis. Furthermore, phospho-S6 immunoreactivity was not upregulated in Tsc1-null astrocytes despite a lower seizure threshold. Collectively, these data suggest that a double-hit strategy to eliminate Tsc1 in discrete neuronal populations generates TSC-associated cortical lesions, providing a model to uncover the mechanisms of lesion formation and cortical hyperexcitability. In addition, the absence of glial reactivity argues against a contribution of astrocytes to lesion-associated hyperexcitability.

Authors

David M. Feliciano, Tiffany Su, Jean Lopez, Jean-Claude Platel, Angélique Bordey

Dysregulated brain creatine kinase is associated with hearing impairment in mouse models of Huntington disease

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Abstract

Huntington disease (HD) is a degenerative disorder caused by expanded CAG repeats in exon 1 of the huntingtin gene (HTT). Patients with late-stage HD are known to have abnormal auditory processing, but the peripheral auditory functions of HD patients have yet to be thoroughly assessed. In this study, 19 HD patients (aged 40–59 years) were assessed for hearing impairment using pure-tone audiometry and assessment of auditory brainstem responses (ABRs). PTA thresholds were markedly elevated in HD patients. Consistent with this, elevated ABR thresholds were also detected in two mouse models of HD. Hearing loss thus appears to be an authentic symptom of HD. Immunohistochemical analyses demonstrated the presence of mutant huntingtin that formed intranuclear inclusions in the organ of Corti of HD mice, which might interfere with normal auditory function. Quantitative RT-PCR and Western blot analyses further revealed reduced expression of brain creatine kinase (CKB), a major enzyme responsible for ATP regeneration via the phosphocreatine–creatine kinase (PCr-CK) system, in the cochlea of HD mice. Treatment with creatine supplements ameliorated the hearing impairment of HD mice, suggesting that the impaired PCr-CK system in the cochlea of HD mice may contribute to their hearing impairment. These data also suggest that creatine may be useful for treating the hearing abnormalities of patients with HD.

Authors

Yow-Sien Lin, Chiung-Mei Chen, Bing-wen Soong, Yih-Ru Wu, Hui-Mei Chen, Wen-Ying Yeh, Dai-Rong Wu, Yi-Jun Lin, Paul Wai-Fung Poon, Mei-Ling Cheng, Chih-Hung Wang, Yijuang Chern

Peripheral calcium-permeable AMPA receptors regulate chronic inflammatory pain in mice

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Abstract

α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid–type (AMPA-type) glutamate receptors (AMPARs) play an important role in plasticity at central synapses. Although there is anatomical evidence for AMPAR expression in the peripheral nervous system, the functional role of such receptors in vivo is not clear. To address this issue, we generated mice specifically lacking either of the key AMPAR subunits, GluA1 or GluA2, in peripheral, pain-sensing neurons (nociceptors), while preserving expression of these subunits in the central nervous system. Nociceptor-specific deletion of GluA1 led to disruption of calcium permeability and reduced capsaicin-evoked activation of nociceptors. Deletion of GluA1, but not GluA2, led to reduced mechanical hypersensitivity and sensitization in models of chronic inflammatory pain and arthritis. Further analysis revealed that GluA1-containing AMPARs regulated the responses of nociceptors to painful stimuli in inflamed tissues and controlled the excitatory drive from the periphery into the spinal cord. Consequently, peripherally applied AMPAR antagonists alleviated inflammatory pain by specifically blocking calcium-permeable AMPARs, without affecting physiological pain or eliciting central side effects. These findings indicate an important pathophysiological role for calcium-permeable AMPARs in nociceptors and may have therapeutic implications for the treatment chronic inflammatory pain states.

Authors

Vijayan Gangadharan, Rui Wang, Bettina Ulzhöfer, Ceng Luo, Rita Bardoni, Kiran Kumar Bali, Nitin Agarwal, Irmgard Tegeder, Ullrich Hildebrandt, Gergely G. Nagy, Andrew J. Todd, Alessia Ghirri, Annette Häussler, Rolf Sprengel, Peter H. Seeburg, Amy B. MacDermott, Gary R. Lewin, Rohini Kuner

Rapid, reversible activation of AgRP neurons drives feeding behavior in mice

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Abstract

Several different neuronal populations are involved in regulating energy homeostasis. Among these, agouti-related protein (AgRP) neurons are thought to promote feeding and weight gain; however, the evidence supporting this view is incomplete. Using designer receptors exclusively activated by designer drugs (DREADD) technology to provide specific and reversible regulation of neuronal activity in mice, we have demonstrated that acute activation of AgRP neurons rapidly and dramatically induces feeding, reduces energy expenditure, and ultimately increases fat stores. All these effects returned to baseline after stimulation was withdrawn. In contrast, inhibiting AgRP neuronal activity in hungry mice reduced food intake. Together, these findings demonstrate that AgRP neuron activity is both necessary and sufficient for feeding. Of interest, activating AgRP neurons potently increased motivation for feeding and also drove intense food-seeking behavior, demonstrating that AgRP neurons engage brain sites controlling multiple levels of feeding behavior. Due to its ease of use and suitability for both acute and chronic regulation, DREADD technology is ideally suited for investigating the neural circuits hypothesized to regulate energy balance.

Authors

Michael J. Krashes, Shuichi Koda, ChianPing Ye, Sarah C. Rogan, Andrew C. Adams, Daniel S. Cusher, Eleftheria Maratos-Flier, Bryan L. Roth, Bradford B. Lowell

Direct regulation of complex I by mitochondrial MEF2D is disrupted in a mouse model of Parkinson disease and in human patients

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Abstract

The transcription factors in the myocyte enhancer factor 2 (MEF2) family play important roles in cell survival by regulating nuclear gene expression. Here, we report that MEF2D is present in rodent neuronal mitochondria, where it can regulate the expression of a gene encoded within mitochondrial DNA (mtDNA). Immunocytochemical, immunoelectron microscopic, and biochemical analyses of rodent neuronal cells showed that a portion of MEF2D was targeted to mitochondria via an N-terminal motif and the chaperone protein mitochondrial heat shock protein 70 (mtHsp70). MEF2D bound to a MEF2 consensus site in the region of the mtDNA that contained the gene NADH dehydrogenase 6 (ND6), which encodes an essential component of the complex I enzyme of the oxidative phosphorylation system; MEF2D binding induced ND6 transcription. Blocking MEF2D function specifically in mitochondria decreased complex I activity, increased cellular H2O2 level, reduced ATP production, and sensitized neurons to stress-induced death. Toxins known to affect complex I preferentially disrupted MEF2D function in a mouse model of Parkinson disease (PD). In addition, mitochondrial MEF2D and ND6 levels were decreased in postmortem brain samples of patients with PD compared with age-matched controls. Thus, direct regulation of complex I by mitochondrial MEF2D underlies its neuroprotective effects, and dysregulation of this pathway may contribute to PD.

Authors

Hua She, Qian Yang, Kennie Shepherd, Yoland Smith, Gary Miller, Claudia Testa, Zixu Mao

α-Synuclein propagates from mouse brain to grafted dopaminergic neurons and seeds aggregation in cultured human cells

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Abstract

Post-mortem analyses of brains from patients with Parkinson disease who received fetal mesencephalic transplants show that α-synuclein–containing (α-syn–containing) Lewy bodies gradually appear in grafted neurons. Here, we explored whether intercellular transfer of α-syn from host to graft, followed by seeding of α-syn aggregation in recipient neurons, can contribute to this phenomenon. We assessed α-syn cell-to-cell transfer using microscopy, flow cytometry, and high-content screening in several coculture model systems. Coculturing cells engineered to express either GFP– or DsRed-tagged α-syn resulted in a gradual increase in double-labeled cells. Importantly, α-syn–GFP derived from 1 neuroblastoma cell line localized to red fluorescent aggregates in other cells expressing DsRed–α-syn, suggesting a seeding effect of transmitted α-syn. Extracellular α-syn was taken up by cells through endocytosis and interacted with intracellular α-syn. Next, following intracortical injection of recombinant α-syn in rats, we found neuronal uptake was attenuated by coinjection of an endocytosis inhibitor. Finally, we demonstrated in vivo transfer of α-syn between host cells and grafted dopaminergic neurons in mice overexpressing human α-syn. In summary, intercellularly transferred α-syn interacts with cytoplasmic α-syn and can propagate α-syn pathology. These results suggest that α-syn propagation is a key element in the progression of Parkinson disease pathology.

Authors

Christian Hansen, Elodie Angot, Ann-Louise Bergström, Jennifer A. Steiner, Laura Pieri, Gesine Paul, Tiago F. Outeiro, Ronald Melki, Pekka Kallunki, Karina Fog, Jia-Yi Li, Patrik Brundin

Genetic rescue of nonclassical ERα signaling normalizes energy balance in obese Erα-null mutant mice

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Abstract

In addition to its role in reproduction, estradiol-17β is critical to the regulation of energy balance and body weight. Estrogen receptor α–null (Erα–/–) mutant mice develop an obese state characterized by decreased energy expenditure, decreased locomotion, increased adiposity, altered glucose homeostasis, and hyperleptinemia. Such features are reminiscent of the propensity of postmenopausal women to develop obesity and type 2 diabetes. The mechanisms by which ERα signaling maintains normal energy balance, however, have remained unclear. Here we used knockin mice that express mutant ERα that can only signal through the noncanonical pathway to assess the role of nonclassical ERα signaling in energy homeostasis. In these mice, we found that nonclassical ERα signaling restored metabolic parameters dysregulated in Erα–/– mutant mice to normal or near-normal values. The rescue of body weight and metabolic function by nonclassical ERα signaling was mediated by normalization of energy expenditure, including voluntary locomotor activity. These findings indicate that nonclassical ERα signaling mediates major effects of estradiol-17β on energy balance, raising the possibility that selective ERα agonists may be developed to reduce the risks of obesity and metabolic disturbances in postmenopausal women.

Authors

Cheryl J. Park, Zhen Zhao, Christine Glidewell-Kenney, Milos Lazic, Pierre Chambon, Andrée Krust, Jeffrey Weiss, Deborah J. Clegg, Andrea Dunaif, J. Larry Jameson, Jon E. Levine

Dysregulation of the ALS-associated gene TDP-43 leads to neuronal death and degeneration in mice

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Abstract

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are characterized by cytoplasmic protein aggregates in the brain and spinal cord that include TAR-DNA binding protein 43 (TDP-43). TDP-43 is normally localized in the nucleus with roles in the regulation of gene expression, and pathological cytoplasmic aggregates are associated with depletion of nuclear protein. Here, we generated transgenic mice expressing human TDP-43 with a defective nuclear localization signal in the forebrain (hTDP-43-ΔNLS), and compared them with mice expressing WT hTDP-43 (hTDP-43-WT) to determine the effects of mislocalized cytoplasmic TDP-43 on neuronal viability. Expression of either hTDP-43-ΔNLS or hTDP-43-WT led to neuron loss in selectively vulnerable forebrain regions, corticospinal tract degeneration, and motor spasticity recapitulating key aspects of FTLD and primary lateral sclerosis. Only rare cytoplasmic phosphorylated and ubiquitinated TDP-43 inclusions were seen in hTDP-43-ΔNLS mice, suggesting that cytoplasmic inclusions were not required to induce neuronal death. Instead, neurodegeneration in hTDP-43 and hTDP-43-ΔNLS–expressing neurons was accompanied by a dramatic downregulation of the endogenous mouse TDP-43. Moreover, mice expressing hTDP-43-ΔNLS exhibited profound changes in gene expression in cortical neurons. Our data suggest that perturbation of endogenous nuclear TDP-43 results in loss of normal TDP-43 function(s) and gene regulatory pathways, culminating in degeneration of selectively vulnerable affected neurons.

Authors

Lionel M. Igaz, Linda K. Kwong, Edward B. Lee, Alice Chen-Plotkin, Eric Swanson, Travis Unger, Joe Malunda, Yan Xu, Matthew J. Winton, John Q. Trojanowski, Virginia M.-Y. Lee

Blocking the mitochondrial apoptotic pathway preserves motor neuron viability and function in a mouse model of amyotrophic lateral sclerosis

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Abstract

Apoptosis of motor neurons is a well-documented feature in amyotrophic lateral sclerosis (ALS) and related motor neuron diseases (MNDs). However, the role of apoptosis in the pathogenesis of these diseases remains unresolved. One possibility is that the affected motor neurons only succumb to apoptosis once they have exhausted functional capacity. If true, blocking apoptosis should confer no therapeutic benefit. To directly investigate this idea, we tested whether tissue-specific deletion in the mouse CNS of BCL2-associated X protein (BAX) and BCL2-homologous antagonist/killer (BAK), 2 proapoptotic BCL-2 family proteins that together represent an essential gateway to the mitochondrial apoptotic pathway, would protect against motor neuron degeneration. We found that neuronal deletion of Bax and Bak in a mouse model of familial ALS not only halted neuronal loss, but prevented axonal degeneration, symptom onset, weight loss, and paralysis and extended survival. These results show that motor neurons damaged in ALS activate the mitochondrial apoptotic pathway early in the disease process and that apoptotic signaling directly contributes to neuromuscular degeneration and neuronal dysfunction. Hence, inhibiting apoptosis upstream of mitochondrial permeabilization represents a possible therapeutic strategy for preserving functional motor neurons in ALS and other MNDs.

Authors

Nichole A. Reyes, Jill K. Fisher, Kathryn Austgen, Scott VandenBerg, Eric J. Huang, Scott A. Oakes

Inhibition of TRPC6 degradation suppresses ischemic brain damage in rats

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Abstract

Brain injury after focal cerebral ischemia, the most common cause of stroke, develops from a series of pathological processes, including excitotoxicity, inflammation, and apoptosis. While NMDA receptors have been implicated in excitotoxicity, attempts to prevent ischemic brain damage by blocking NMDA receptors have been disappointing. Disruption of neuroprotective pathways may be another avenue responsible for ischemic damage, and thus preservation of neuronal survival may be important for prevention of ischemic brain injury. Here, we report that suppression of proteolytic degradation of transient receptor potential canonical 6 (TRPC6) prevented ischemic neuronal cell death in a rat model of stroke. The TRPC6 protein level in neurons was greatly reduced in ischemia via NMDA receptor–dependent calpain proteolysis of the N-terminal domain of TRPC6 at Lys16. This downregulation was specific for TRPC6 and preceded neuronal death. In a rat model of ischemia, activating TRPC6 prevented neuronal death, while blocking TRPC6 increased sensitivity to ischemia. A fusion peptide derived from the calpain cleavage site in TRPC6 inhibited degradation of TRPC6, reduced infarct size, and improved behavioral performance measures via the cAMP response element–binding protein (CREB) signaling pathway. Thus, TRPC6 proteolysis contributed to ischemic neuronal cell death, and suppression of its degradation preserved neuronal survival and prevented ischemic brain damage.

Authors

Wanlu Du, Junbo Huang, Hailan Yao, Kechun Zhou, Bo Duan, Yizheng Wang