The role of exosomes in adult neurogenesis:implications for neurodegenerative diseases

Exosomes are cup-shaped extracellular vesicles with a lipid bilayer that is approximately 30 to 200 nm in thickness.Exosomes are widely distributed in a range of body fluids,including urine,blood,milk,and saliva.Exosomes exert biological function by transporting factors between different cells and by regulating biological pathways in recipient cells.As an important form of intercellular communication,exosomes are increasingly being investigated due to their ability to transfer bioactive molecules such as lipids,proteins,mRNAs,and microRNAs between cells,and because they can regulate physiological and pathological processes in the central nervous system.Adult neurogenesis is a multistage process by which new neurons are generated and migrate to be integrated into existing neuronal circuits.In the adult brain,neurogenesis is mainly localized in two specialized niches:the subventricular zone adjacent to the lateral ventricles and the subgranular zone of the dentate gyrus.An increasing body of evidence indicates that adult neurogenesis is tightly controlled by environmental conditions with the niches.In recent studies,exosomes released from different sources of cells were shown to play an active role in regulating neurogenesis both in vitro and in vivo,thereby participating in the progression of neurodegenerative disorders in patients and in various disease models.Here,we provide a state-of-the-art synopsis of existing research that aimed to identify the diverse components of exosome cargoes and elucidate the therapeutic potential of exosomal contents in the regulation of neurogenesis in several neurodegenerative diseases.We emphasize that exosomal cargoes could serve as a potential biomarker to monitor functional neurogenesis in adults.In addition,exosomes can also be considered as a novel therapeutic approach to treat various neurodegenerative disorders by improving endogenous neurogenesis to mitigate neuronal loss in the central nervous system.

Therapeutic advances in neural regeneration for Huntington’s disease

Huntington’s disease is a neurodegenerative disease caused by the expansion mutation of a cytosine-adenine-guanine triplet in the exon 1 of the HTT gene which is responsible for the production of the huntingtin (Htt) protein. In physiological conditions, Htt is involved in many cellular processes such as cell signaling, transcriptional regulation, energy metabolism regulation, DNA maintenance, axonal trafficking, and antiapoptotic activity. When the genetic alteration is present, the production of a mutant version of Htt (mHtt) occurs, which is characterized by a plethora of pathogenic activities that, finally, lead to cell death. Among all the cells in which mHtt exerts its dangerous activity, the GABAergic Medium Spiny Neurons seem to be the most affected by the mHtt-induced excitotoxicity both in the cortex and in the striatum. However, as the neurodegeneration proceeds ahead the neuronal loss grows also in other brain areas such as the cerebellum, hypothalamus, thalamus, subthalamic nucleus, globus pallidus, and substantia nigra, determining the variety of symptoms that characterize Huntington’s disease. From a clinical point of view, Huntington’s disease is characterized by a wide spectrum of symptoms spanning from motor impairment to cognitive disorders and dementia. Huntington’s disease shows a prevalence of around 3.92 cases every 100,000 worldwide and an incidence of 0.48 new cases every 100,000/year. To date, there is no available cure for Huntington’s disease. Several treatments have been developed so far, aiming to reduce the severity of one or more symptoms to slow down the inexorable decline caused by the disease. In this context, the search for reliable strategies to target the different aspects of Huntington’s disease become of the utmost interest. In recent years, a variety of studies demonstrated the detrimental role of neuronal loss in Huntington’s disease condition highlighting how the replacement of lost cells would be a reasonable strategy to overcome the neurodegeneration. In this view, numerous have been the attempts in several preclinical models of Huntington’s disease to evaluate the feasibility of invasive and non-invasive approaches. Thus, the aim of this review is to offer an overview of the most appealing approaches spanning from stem cell-based cell therapy to extracellular vesicles such as exosomes in light of promoting neurogenesis, discussing the results obtained so far, their limits and the future perspectives regarding the neural regeneration in the context of Huntington’s disease.

Antisense therapy:a potential breakthrough in the treatment of neurodegenerative diseases

Neurodegenerative diseases are a group of disorders characterized by the progressive degeneration of neurons in the central or peripheral nervous system.Currently,there is no cure for neurodegenerative diseases and this means a heavy burden for patients and the health system worldwide.Therefore,it is necessary to find new therapeutic approaches,and antisense therapies offer this possibility,having the great advantage of not modifying cellular genome and potentially being safer.Many preclinical and clinical studies aim to test the safety and effectiveness of antisense therapies in the treatment of neurodegenerative diseases.The objective of this review is to summarize the recent advances in the development of these new technologies to treat the most common neurodegenerative diseases,with a focus on those antisense therapies that have already received the approval of the U.S.Food and Drug Administration.

Long-noncoding RNAs as epigenetic regulators in neurodegenerative diseases

The growing and rapid development of high-throughput sequencing technologies have allowed a greater understanding of the mechanisms underlying gene expression regulation.Editing the epigenome and epitranscriptome directs the fate of the transcript influencing the functional outcome of each mRNA.In this context,non-coding RNAs play a decisive role in addressing the expression regulation at the gene and chromosomal levels.Long-noncoding RNAs,consisting of more than 200 nucleotides,have been shown to act as epigenetic regulators in several key molecular processes involving neurodegenerative disorders,such as Alzheimer’s disease,Parkinson’s disease,amyotrophic lateral sclerosis and Huntington’s disease.Long-noncoding RNAs are abundantly expressed in the central nervous system,suggesting that their deregulation could trigger neuronal degeneration through RNA modifications.The evaluation of their diagnostic significance and therapeutic potential could lead to new treatments for these diseases for which there is no cure.

Mitochondria in Huntington’s disease:implications in pathogenesis and mitochondrial-targeted therapeutic strategies

Huntington’s disease is a genetic disease caused by expanded CAG repeats on exon 1 of the huntingtin gene located on chromosome 4.Compelling evidence implicates impaired mitochondrial energetics,altered mitochondrial biogenesis and quality control,disturbed mitochondrial trafficking,oxidative stress and mitochondrial calcium dyshomeostasis in the pathogenesis of the disorder.Unfortunately,conventional mitochondrial-targeted molecules,such as cysteamine,creatine,coenzyme Q10,or triheptanoin,yielded negative or inconclusive results.However,future therapeutic strategies,aiming to restore mitochondrial biogenesis,improving the fission/fusion balance,and improving mitochondrial trafficking,could prove useful tools in improving the phenotype of Huntington’s disease and,used in combination with genome-editing methods,could lead to a cure for the disease.

Intergeneration CAG expansion in a Wuhan juvenile-onset Huntington disease family

Objective To make early diagnosis of IT15 gene mutation in a Wuhan juvenile-onset Huntington disease （HD） family, for providing them with genetic counseling, and making preparation for the further research on pathogenesis and experimental therapy of HD. Methods According to the principle of informed consent, we extracted genomic DNA from peripheral blood samples and carried genetic diagnosis of pathogenic exon 1 of IT15 gene by modified touchdown PCR and DNA sequencing methods. Results Eight of twenty-five family members carried abnormal allele： Ⅲ10 Ⅲ12, IIIt4, Ⅳ3, and Ⅴ2 carded （CAG） 48, Ⅳ11 and Ⅳ12 carried （CAG） 67, and Ⅳ14 carried （CAG） 63, in contrast with the 8-25 CAG trinucleotides in the members of control group. Ⅳ14 carried 15 more CAG trinucleotides than her father Ⅲ10. Conclusion The results definitely confirm the diagnosis of HD and indicate the CAG trinucleotide repeat expansion of IT15 gene in this HD family. In addition, CAG expansion results in juvenile-onset and anticipation （characterized by earlier age of onset and increasing severity） of the patientⅣ12.

Promising use of metformin in treating neurological disorders:biomarker-guided therapies

Neurological disorders are a diverse group of conditions that affect the nervous system and include neurodegenerative diseases(Alzheimer’s disease,multiple sclerosis,Parkinson’s disease,Huntington’s disease),cerebrovascular conditions(stroke),and neurodevelopmental disorders(autism spectrum disorder).Although they affect millions of individuals around the world,only a limited number of effective treatment options are available today.Since most neurological disorders express mitochondria-related metabolic perturbations,metformin,a biguanide type II antidiabetic drug,has attracted a lot of attention to be repurposed to treat neurological disorders by correcting their perturbed energy metabolism.However,controversial research emerges regarding the beneficial/detrimental effects of metformin on these neurological disorders.Given that most neurological disorders have complex etiology in their pathophysiology and are influenced by various risk factors such as aging,lifestyle,genetics,and environment,it is important to identify perturbed molecular functions that can be targeted by metformin in these neurological disorders.These molecules can then be used as biomarkers to stratify subpopulations of patients who show distinct molecular/pathological properties and can respond to metformin treatment,ultimately developing targeted therapy.In this review,we will discuss mitochondria-related metabolic perturbations and impaired molecular pathways in these neurological disorders and how these can be used as biomarkers to guide metformin-responsive treatment for the targeted therapy to treat neurological disorders.

Clinical trial perspective for adult and juvenile Huntington's disease using genetically-engineered mesenchymal stem cells

Progress to date from our group and others indicate that using genetically-engineered mesenchymal stem cells（MSC） to secrete brain-derived neurotrophic factor（BDNF） supports our plan to submit an Investigational New Drug application to the Food and Drug Administration for the future planned Phase 1 safety and tolerability trial of MSC/BDNF in patients with Huntington＇s disease（HD）. There are also potential applications of this approach beyond HD. Our biological delivery system for BDNF sets the precedent for adult stem cell therapy in the brain and could potentially be modified for other neurodegenerative disorders such as amyotrophic lateral sclerosis（ALS）, spinocerebellar ataxia（SCA）, Alzheimer＇s disease, and some forms of Parkinson＇s disease. The MSC/BDNF product could also be considered for studies of regeneration in traumatic brain injury, spinal cord and peripheral nerve injury. This work also provides a platform for our future gene editing studies, since we will again use MSCs to deliver the needed molecules into the central nervous system.

Therapeutic potential of α7 nicotinic receptor agonists to regulate neuroinflammation in neurodegenerative diseases

Neurodegenerative diseases, such as Alzheimer＇s, Parkinson＇s and Huntington＇s diseases, are all character- ized by a component of innate immunity called neuroinflammation. Neuronal loss and neuroinflammation are two phenomena closely linked. Hence, the neuroinflammation is a relevant target for the management of the neurodegenerative diseases given that, to date, there is no treatment to stop neuronal loss. Several studies have investigated the potential effects of activators of alpha 7 nicotinic acetylcholine receptors in animal models of neurodegenerative diseases. These receptors are widely distributed in the central nervous system. After activation, they seem to mediate the cholinergic anti-inflammatory pathway in the brain. This anti-inflammatory pathway, first described in periphery, regulates activation of microglial cells considered as the resident macrophage population of the central nervous system. In this article, we shortly review the agonists of the alpha 7 nicotinic acetylcholine receptors that have been evaluated in vivo and we focused on the selective positive allosteric modulators of these receptors. These compounds represent a key element to enhance receptor activity only in the presence of the endogenous agonist.

Mitochondrial dysfunction and Huntington disease

Huntington disease （HD） is a chronic autosomal-dominant neurodegenerative disease. The gene coding Huntingtin has been identified, but the pathogenic mechanisms of the disease are still not fully understood. This paper reviews the involvement of mitochondrial dysfunction in pathogenesis of HD.

Altered microRNA expression in animal models of Huntington’s disease and potential therapeutic strategies

A review of recent animal models of Huntington’s disease showed many microRNAs had altered expression levels in the striatum and cerebral cortex,and which were mostly downregulated.Among the altered microRNAs were miR-9/9*,miR-29b,miR-124a,miR-132,miR-128,miR-139,miR-122,miR-138,miR-23b,miR-135b,miR-181(all downregulated)and miR-448(upregulated),and similar changes had been previously found in Huntington’s disease patients.In the animal cell studies,the altered microRNAs included miR-9,miR-9*,miR-135b,miR-222(all downregulated)and miR-214(upregulated).In the animal models,overexpression of miR-155 and miR-196a caused a decrease in mutant huntingtin mRNA and protein level,lowered the mutant huntingtin aggregates in striatum and cortex,and improved performance in behavioral tests.Improved performance in behavioral tests also occurred with overexpression of miR-132 and miR-124.In the animal cell models,overexpression of miR-22 increased the viability of rat primary cortical and striatal neurons infected with mutant huntingtin and decreased huntingtin-enriched foci of≥2μm.Also,overexpression of miR-22 enhanced the survival of rat primary striatal neurons treated with 3-nitropropionic acid.Exogenous expression of miR-214,miR-146a,miR-150,and miR-125b decreased endogenous expression of huntingtin mRNA and protein in HdhQ111/HdhQ111 cells.Further studies with animal models of Huntington’s disease are warranted to validate these findings and identify specific microRNAs whose overexpression inhibits the production of mutant huntingtin protein and other harmful processes and may provide a more effective means of treating Huntington’s disease in patients and slowing its progression.

Promises and pitfalls of immune-based strategies for Huntington's disease

Huntington＇s disease （HD） is an autosomal-dominant neurodegenerative disease characterized by the selec- tive loss of neurons in the striatum and cortex, leading to progressive motor dysfunction, cognitive decline and behavioral symptoms. HD is caused by a trinucleotide （CAG） repeat expansion in the gene encoding for huntingtin. Several studies have suggested that inflammation is an important feature of HD and it is already observed in the early stages of the disease. Recently, new molecules presenting anti-inflammatory and/or immunomodulatory have been investigated for HD. The objective of this review is to discuss the data obtained so far on the immune-based therapeutic strategies for HD.

Factors contributing to clinical picture and progression of Huntington's disease

Huntington’s disease（HD）is an autosomal dominant,monogenic,progressive,neurodegenerative and rare disease with a frequency of10 per 100,000 in the Caucasian population and occurring more rarely in other races（Squitieri et al.,1994）.HD is,nevertheless,one of the most frequently and extensively studied diseases of those caused by a dynamic mutation.The HD mutation is located on the short arm of the 4th chromosome within the HTT gene.

Stem cell therapy in neurodegenerative diseases From principles to practice

The lack of curative therapies for neurodegenerative diseases has high economic impact and places huge burden on the society.The contribution of stem cells to cure neurodegenerative diseases has been unraveled and explored extensively over the past few years.Beyond substitution of the lost neurons,stem cells act as immunomodulators and neuroprotectors.A large number of preclinical and a small number of clinical studies have shown beneficial outcomes in this context.In this review,we have summarized the current concepts of stem cell therapy in neurodegenerative diseases and the recent advances in this field,particularly between 2010 and 2012.Further studies should be encouraged to resolve the clinical issues and vague translational findings for maximum optimization of the efficacy of stem cell therapy in neurodegenerative diseases.

Proteolysis targeting chimera technology:a novel strategy for treating diseases of the central nervous system

Neurological diseases such as stroke,Alzheimer’s disease,Parkinson’s disease,and Huntington’s disease are among the intractable diseases for which appropriate drugs and treatments are lacking.Proteolysis targeting chimera(PROTAC)technology is a novel strategy to solve this problem.PROTAC technology uses the ubiquitin-protease system to eliminate mutated,denatured,and harmful proteins in cells.It can be reused,and utilizes the protein destruction mechanism of the cells,thus making up for the deficiencies of traditional protein degradation methods.It can effectively target and degrade proteins,including proteins that are difficult to identify and bind.Therefore,it has extremely important implications for drug development and the treatment of neurological diseases.At present,the targeted degradation of mutant BTK,mHTT,Tau,EGFR,and other proteins using PROTAC technology is gaining attention.It is expected that corresponding treatment of nervous system diseases can be achieved.This review first focuses on the recent developments in PROTAC technology in terms of protein degradation,drug production,and treatment of central nervous system diseases,and then discusses its limitations.This review will provide a brief overview of the recent application of PROTAC technology in the treatment of central nervous system diseases.

Adenyl cyclase activator forskolin protects against Huntington's disease-like neurodegenerative disorders

Long term suppression of succinate dehydrogenase by selective inhibitor 3-nitropropionic acid has been used in rodents to model Huntington＇s disease where mitochondrial dysfunction and oxidative damages are primary pathological hallmarks for neuronal damage. Improvements in learning and memory abilities, recovery of energy levels, and reduction of excitotoxicity damage can be achieved through activation of Adenyl cyclase enzyme by a specific phytochemical forskolin. In this study, intraperitoneal administration of 10 mg/kg 3-nitropropionic acid for 15 days in rats notably reduced body weight, worsened motor cocordination（grip strength, beam crossing task, locomotor activity）, resulted in learning and memory deficits, greatly increased acetylcholinesterase, lactate dehydrogenase, nitrite, and malondialdehyde levels, obviously decreased adenosine triphosphate, succinate dehydrogenase, superoxide dismutase, catalase, and reduced glutathione levels in the striatum, cortex and hippocampus. Intragastric administration of forskolin at 10, 20, 30 mg/kg dose-dependently reversed these behavioral, biochemical and pathological changes caused by 3-nitropropionic acid. These results suggest that forskolin exhibits neuroprotective effects on 3-nitropropionic acid-induced Huntington＇s disease-like neurodegeneration.

Clinical features of Huntington disease in 243 Chinese patients

OBJECTIVE： To thoroughly explore the clinical characteristics of Huntington disease in China. METHODS： A computer-based online search of China National Knowledge Infrastructure was performed to review case reports concerning Huntington disease published between 1980 and 2008; the clinical characteristics were analyzed. RESULTS： A total of 80 studies involving 243 patients （142 males and 101 females） were collected, 82.0% of which were from provinces of North China. In addition, 97.1% of the cases had a family history of Huntington disease, and paternal inheritance （64.6%） was greater than maternal inheritance （35.4%）. Moreover, onset age was significantly less than from maternal inheritance. The mean onset age of Huntington disease was （35.2 ± 11.5） years, mean age of death was （45.6 ± 13.5） years, and the mean course of disease from onset to death was （11.6 ± 5.6） years. Onset characterized by involuntary movement accounted for 47.7%, including 66.4% in the entire body, 16.4% in the upper limbs, and 14.7% in the head and face. Psychiatric symptoms accounted for 18.1%, and disturbed intelligence accounted for 2.1%. With disease progression, 99.5% of patients exhibited involuntary movement, 69.8% displayed cognitive impairment, and 39.2% suffered from psychiatric symptoms. In addition, 38.7% of patients were complicated by dysarthria, dysphagia, and cough after drinking. A total of 70.8% of patients exhibited an abnormal electroencephalogram, 18.8% had mild abnormalities in the cerebrospinal fluid, and 70.1% displayed brain atrophy and lateral ventriculomegaly on CT or MRI. A total of 88.9% of patients scored ≤ 23 in the Mini-Mental State Examination （MMSE）. Of the reported patients, only 22 underwent/T15 gene testing with positive results. CONCLUSION： Huntington disease is more frequently detected in males than females, and the majority has a family history. The disease has high incidence in Northern China, in particular with paternal inheritance. In addition, the disease often struck middle-aged people, and the time of onset in paternal inheritance was earlier than maternal inheritance. There were no significant differences in age of onset between males and females, and the course of disease was not related to paternal or maternal inheritance. The symptoms of onset included involuntary movement, complicated by psychiatric symptoms, and rarely cognitive impairment. In addition, involuntary movement of the pharynx was commonly observed in patients. Genetic detection has been the gold standard for clinical diagnosis of Huntington disease, and more attention should be paid to this detection method.

High resolution impedance manometric findings in dysphagia of Huntington's disease

Conventional manometry presents significant challenges,especially in assessment of pharyngeal swallowing,because of the asymmetry and deglutitive movements of oropharyngeal structures.It only provides information about intraluminal pressure and thus it is difficult to study functional details of esophageal motility disorders.New technology of solid high resolution impedance manometry(HRIM),with 32 pressure sensors and 6 impedance sensors,is likely to provide better assessment of pharyngeal swallowing as well as more information about esophageal motility disorders.However,the clinical usefulness of application of HRIM in patients with oropharyngeal dysphagia or esophageal dysphagia is not known.We experienced a case of Huntington's disease presenting with both oropharyngeal and esophageal dysphagia,in which HRIM revealed the mechanism of oropharyngeal dysphagia and provided comprehensive information about esophageal dysphagia.

Hope in Huntington's disease A survey in counseling patients with Huntington's disease,as well as the caregivers

BACKGROUND： It is difficult to attract interest in non-compulsory, preventive, medical care, and persons diagnosed with certain diseases often ignore the existence of these diseases. However, Huntington＇s disease （HD） is an exception. OBJECTIVE： To qualitatively analyze factors motivating HD patients to participate in a study, namely the European Huntington＇s Disease Network （EHDN） REGISTRY. DESIGN, TIME AND SETTING： An observational survey was conducted in the EHDN Study Site in Poznan, Poland between 2007 and 2008. PARTICIPANTS： The study involved 22 persons affected with HD and 3 pre-symptomatic individuals totaling 9 males and 16 females. The 24 participants in this study had 24 different caregivers. A total of 25 symptomatic or pre-symptomatic subjects participated in the initial REGISTRY visit, as well as 6 in the second, and 1 in the third. All subjects did not know each other prior to the visit. METHODS： A mutation in the IT15 gene was confirmed in each patient or pre-symptomatic mutation carrier. An in-depth interview produced detailed information on the HD patients, as well as the caregivers, for the REGISTRY study. MAIN OUTCOME MEASURES： A qualitative analysis of the factors motivating HD patients and the pre-symptomatic mutation carriers to participate in the REGISTRY longitudinal, observational, research project was performed. RESULTS： The primary motivating factor for involvement of HD patients and the caregivers in the REGISTRY study was the hope that an effective HD therapy would soon be discovered. In HD patients and the pre-symptomatic group, the response to participate in the REGISTRY project reached 100%, despite the fact that they knew the project was only an observational study. CONCLUSION： Patient hope is thought to be a factor for engaging in preventive, therapeutic activities. However, this is rarely mentioned in medical papers and clinical textbooks, and is usually overlooked in medical teaching. Clearly, efforts should be made to include this in clinical practice.

Neuroimaging in Huntington's disease

Huntington's disease(HD) is a progressive and fatal neurodegenerative disorder caused by an expanded tri-nucleotide CAG sequence in huntingtin gene(HTT) on chromosome 4. HD manifests with chorea, cognitive and psychiatric symptoms. Although advances in genetics allow identification of individuals carrying the HD gene, much is still unknown about the mechanisms underly-ing the development of overt clinical symptoms and the transitional period between premanifestation and mani-festation of the disease. HD has no cure and patients rely only in symptomatic treatment. There is an urgent need to identify biomarkers that are able to monitor disease progression and assess the development and efficacy of novel disease modifying drugs. Over the past years, neuroimaging techniques such as magnetic resonance imaging(MRI) and positron emission tomog-raphy(PET) have provided important advances in our understanding of HD. MRI provides information about structural and functional organization of the brain, while PET can detect molecular changes in the brain. MRI and PET are able to detect changes in the brains of HD gene carriers years ahead of the manifestation of the dis-ease and have also proved to be powerful in assessingdisease progression. However, no single technique hasbeen validated as an optimal biomarker. An integrativemultimodal imaging approach, which combines differ-ent MRI and PET techniques, could be recommendedfor monitoring potential neuroprotective and preventivetherapies in HD. In this article we review the currentneuroimaging literature in HD.