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.

Outlook of PINK1/Parkin signaling in molecular etiology of Parkinson's disease,with insights into Pink1 knockout models

Parkinson’s disease(PD)relates to defective mitochondrial quality control in the dopaminergic motor network.Genetic studies have revealed that PINK1 and Parkin mutations are indicative of a heightened propensity to PD onset,pinpointing mitophagy and inflammation as the culprit pathways involved in neuronal loss in the substantia nigra(SNpc).In a reciprocal manner,LRRK2 functions in the regulation of basal flux and inflammatory responses responsible for PINK1/Parkin-dependent mitophagy activation.Pharmacological intervention in these diseasemodifying pathways may facilitate the development of novel PD therapeutics,despite the current lack of an established drug evaluation model.As such,we reviewed the feasibility of employing the versatile global Pink1knockout(KO)rat model as a self-sufficient,spontaneous PD model for investigating both disease etiology and drug pharmacology.These rats retain clinical features encompassing basal mitophagic flux changes with PD progression.We demonstrate the versatility of this PD rat model based on the incorporation of additional experimental insults to recapitulate the proinflammatory responses observed in PD patients.

Melatonin ameliorates microvessel abnormalities in the cerebral cortex and hippocampus in a rat model of Alzheimer’s disease

Melatonin can attenuate cardiac microvascular ischemia/reperfusion injury,but it remains unclear whether melatonin can also ameliorate cerebral microvascular abnormalities.Rat models of Alzheimer’s disease were established by six intracerebroventricular injections of amyloidbeta 1–42,administered once every other day.Melatonin(30 mg/kg)was intraperitoneally administered for 13 successive days,with the first dose given 24 hours prior to the first administration of amyloid-beta 1–42.Melatonin ameliorated learning and memory impairments in the Morris water maze test,improved the morphology of microvessels in the cerebral cortex and hippocampus,increased microvessel density,alleviated pathological injuries of cerebral neurons,and decreased the expression of vascular endothelial growth factor and vascular endothelial growth factor receptors 1 and 2.These findings suggest that melatonin can improve microvessel abnormalities in the cerebral cortex and hippocampus by lowering the expression of vascular endothelial growth factor and its receptors,thereby improving the cognitive function of patients with Alzheimer’s disease.This study was approved by the Animal Care and Use Committee of Jinzhou Medical University,China(approval No.2019015)on December 6,2018.

Therapeutic potential of dental pulp stem cell transplantation in a rat model of Alzheimer’s disease

Dental pulp stem cells are dental pulp-derived mesenchymal stem cells that originate from the neural crest.They exhibit greater potential for the treatment of nervous system diseases than other types of stem cells because of their neurogenic differentiation capability and their ability to secrete multiple neurotrophic factors.Few studies have reported Alzheimer’s disease treatment using dental pulp stem cells.Rat models of Alzheimer’s disease were established by injecting amyloid-β1–42 into the hippocampus.Fourteen days later,5×106 dental pulp stem cells were injected into the hippocampus.Immunohistochemistry and western blot assays showed that dental pulp stem cell transplantation increased the expression of neuron-related doublecortin,NeuN,and neurofilament 200 in the hippocampus,while the expression of amyloid-βwas decreased.Moreover,cognitive and behavioral abilities were improved.These findings indicate that dental pulp stem cell transplantation in rats can improve cognitive function by regulating the secretion of neuron-related proteins,which indicates a potential therapeutic effect for Alzheimer’s disease.This study was approved by the Animal Ethics Committee of Harbin Medical University,China(approval No.KY2017-132)on February 21,2017.

Bacterial melanin in rat models of Parkinson's disease: a potential neuroprotective strategy

Melanins are widely used in medicine, pharmacology and cosmetics. Different technologies have been used to obtain melanin including： chemical synthesis based on oxidation of tyrosine and its derivatives; extraction from animal materials; alkaline extraction from plant material; and microbiological synthesis. A few number of works have been published that were focused on purification of water insoluble 3,4-dihy- droxy-phenylalanine-melanins （Kukulianskaia et al., 2002）. The majority of synthetic and natural melanins are insoluble in wa- ter that significantly complicates preparation of pharmacolog- ical and cosmetic preparations. Obtaining of low-cost soluble biotechnological melanin can speed up application of melanin in medicine and other fields. For the first time, melanin-syn-thesizing strain with high level of pigment synthesis - Bacillus thuringiensis was obtained. The ecologically safe technology of biosynthesis, isolation and purification of the bacterial melanin has been elaborated.

Zhichan decoction induces differentiation of dopaminergic neurons in Parkinson's disease rats after neural stem cell transplantation

The goal of this study was to increase the dopamine content and reduce dopaminergic metabolites in the brain of Parkinson’s disease rats. Using high-performance liquid chromatography, we found that dopamine and dopaminergic metabolite（dihydroxyphenylacetic acid and homovanillic acid） content in the midbrain of Parkinson’s disease rats was increased after neural stem cell transplantation ＋ Zhichan decoction, compared with neural stem cell transplantation alone. Our genetic algorithm results show that dihydroxyphenylacetic acid and homovanillic acid levels achieve global optimization. Neural stem cell transplantation ＋ Zhichan decoction increased dihydroxyphenylacetic acid levels up to 10-fold, while transplantation alone resulted in a 3-fold increment. Homovanillic acid levels showed no apparent change. Our experimental findings show that after neural stem cell transplantation in Parkinson’s disease rats, Zhichan decoction can promote differentiation of neural stem cells into dopaminergic neurons.

Structural and molecular features of intestinal strictures in rats with Crohn's-like disease

AIM: To develop a new rat model we wanted to gain a better understanding of stricture formation in Crohn’s disease (CD).METHODS: Chronic colitis was induced locally by the administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS). The relapsing inflammation characteristic to CD was mimicked by repeated TNBS treatments. Animals were randomly divided into control, once, twice and three times TNBS-treated groups. Control animals received an enema of saline. Tissue samples were taken from the strictured colonic segments and also adjacent proximally and distally to its 60, 90 or 120 d after the last TNBS or saline administrations. The frequency and macroscopic extent of the strictures were measured on digital photographs. The structural features of strictured gut wall were studied by light- and electron microscopy. Inflammation related alterations in TGF-beta 2 and 3, matrix metalloproteinases 9 (MMP9) and TIMP1 mRNA and protein expression were determined by quantitative real-time PCR and western blot analysis. The quantitative distribution of caspase 9 was determined by post-embedding immunohistochemistry.RESULTS: Intestinal strictures first appeared 60 d after TNBS treatments and the frequency of them increased up to day 120. From day 90 an intact lamina epithelialis, reversible thickening of lamina muscularis mucosae and irreversible thickening of the muscularis externa were demonstrated in the strictured colonic segments. Nevertheless the morphological signs of apoptosis were frequently seen and excess extracellular matrix deposition was recorded between smooth muscle cells (SMCs). Enhanced caspase 9 expression on day 90 in the SMCs and on day 120 also in myenteric neurons indicated the induction of apoptosis. The mRNA expression profile of TGF-betas after repeated TNBS doses was characteristic to CD, TGF-beta 2, but not TGF-beta 3 was up-regulated. Overexpression of MMP9 and down-regulation of TIMP1 were demonstrated. The progressive increase in the amount of MMP9 protein in the strictures was also obvious between days 90 and 120 but TIMP1 protein was practically undetectable at this time.CONCLUSION: These findings indicate that aligned structural and molecular changes in the gut wall rather than neuronal cell death play the primary role in stricture formation.

Visceral hypersensitivity and altered colonic motility after subsidence of inflammation in a rat model of colitis

AIM:Irritable bowel syndrome(IBS)is a functional bowel disorder characterized by visceral hypersensitivity and altered bowel motility.There is increasing evidence suggesting the role of inflammation in the pathogenesis of IBS,which addresses the possibility that formerly established rat model of colitis could be used as an IBS model after the inflammation subsided. METHODS:Colitis was induced by intracolonic instillation of 4% acetic acid in male Sprague-Dawley rats.The extent of inflammation was assessed by histological examination and myeloperoxidase(MPO)activity assay.After subsidence of colitis,the rats were subjected to rectal distension and restraint stress,then the abdominal withdrawal reflex and the number of stress-induced fecal output were measured, respectively. RESULTS:At 2 days post-induction of colitis,the colon showed characteristic inflammatory changes in histology and 8-fold increase in MPO activity.At 7 days post-induction of colitis,the histological features and MPO activity returned to normal.The rats at 7 days post-induction of colitis showed hypersensitive response to rectal distension without an accompaning change in rectal compliance,and defecated more stools than control animals when under stress.CONCLUSION: These results concur largely with the characteristic features of IBS, visceral hypersensitivity and altered defecation pattern in the absence of detectable disease, suggesting that this animal model is a methodologically convenient and useful model for studying a subset of IBS.

Changes of CD8+CD28-T regulatory cells in rat model of colitis induced by 2,4-dinitrofluorobenzene

AIM:To determine the changes of CD8+ T subsets especially CD8+CD28-T regulatory cells in rat model of experimental colitis induced by 2,4-dinitrofluorobenzene (DNFB). METHODS:The rat model of experimental colitis was induced by enema with DNFB.Ten days later,colonic intraepithelial and splenic lymphooltes were isolated from colitis animals (n=16) and controls (n=8).The proportion of CD8+ T cells,CD8+CD28+ T cells and CD8+CD28-T regulatory cells were determined by flow cytometry. RESULTS:The model of experimental colitis was successfully established by DNFB that was demonstrated by bloody diarrhea,weight loss and colonic histopathology.The proportion of CD8+ T cells in either splenic or colonic intraepithelial lymphocytes was not significantly different between colitis animals and controls (spleen:34.6±7.24 % vs 33.5±9.41%, colon:14.0±8.93 % vs 18.0±4.06 %,P>0.05).But CD8+CD28- T regulatory cells from colitis animals were significantly more than those from controls (spleen:11.3±2.26 % vs 5.64±1.01%, colon:6.50±5.37 % vs 1.07±0.65 %,P<0.05).In contrast, CD8+CD28+ T cells from colitis animals were less than those from controls (spleen:23.3±6.14 % vs 27.8±9.70 %,P=0.06; colon:7.52±4.18 % vs 16.9±4.07 %,P<0.05).The proportion of CD8+CD28-T regulatory cells in splenic and colon intraepithelial CD8+ T cells from colitis animals was higher than that from controls (spleen:33.3±5.49 % vs 18.4±7.26 %, colon:46.0±14.3 % vs6.10±3.72 %,P<0.005). CONCLUSION:Experimental colitis of rats can be induced by DNFB with simplicity and good reproducibility.The proportion of CD8+CD28-T regulatory cells in rats with experimental colitis is increased,which may be associated with the pathogenesis of colitis.

Short-term versus long-term water maze training effects on hippocampal neuronal synaptic plasticity in a rat model of senile dementia

BACKGROUND： Changes in synaptic plasticity might underlie senile dementia, and might be the neurobiological basis for learning and memory dysfunctions in patients with Alzheimer＇s Disease. OBJECTIVE： To investigate the effects of water maze training on hippocampal neuronal synaptic plasticity in rats with senile dementia, and to compare changes in synaptic plasticity between short- and long-term water maze training sessions. DESIGN, TIME AND SETTING： A randomized, controlled, neuromorphological observation with animal models of senile dementia was performed at the laboratory of College of Pharmacy, Chongqing Medical University between November 2006 and April 2007. MATERIALS： Fifty male, Sprague Dawley rats were randomized into five groups, with 10 rats per group： model, control, sham-operated, short-term water maze training, and long-term water maze training. METHODS： In the model group, senile dementia was induced by fimbria-fornix lesion method. The control rats remained untreated. In the sham-operated group, water maze training was performed without fimbria-fomix lesion induction. Rats from the short-term water maze training group underwent 20-day water maze training from day 26 after fimbria-fornix lesion induction. The long-term water maze training group underwent 40-day water maze training beginning at day 6 following fimbria-fornix lesion induction. Beginning at day 41, each group underwent 5-day spatial learning and memory training. MAIN OUTCOME MEASURES： Following experimentation, the morphological parameters of synapses, including synaptic numerical density, synaptic surface density, and the average synapse size were stereologically measured. Through the use of an electron microscope, synaptic morphological changes in the hippocampal CA3 region were observed. RESULTS： Compared with the control group, synaptic numerical and surface densities were significantly decreased in the model group （P 〈 0.01）. Synaptic numerical and surface densities significantly increased in the short- and long-term water maze training groups, compared with the model group （P 〈 0.01 ）, and these values were also significantly greater in the long-term water maze training group than in the short-term water maze training group. The model group exhibited larger average sizes of synaptic conjunctions, compared with the control group （P 〈 0.01）. Synaptic conjunction size was significantly less in the short- and long-term water maze training groups than in the model group （P 〈 0.01 ）, and the long-term water maze training group exhibited smaller synaptic conjunction sizes compared with the short-term water maze training group （P 〈 0.05）. Synaptic morphological changes in the hippocampal neurons were in accordance with stereological measurements. CONCLUSION： Water maze training increased synaptic numerical and surface densities in the hippocampal CA3 region, resulting in numerical and functional changes in synaptic plasticity in rats with senile dementia. Long-term water maze training resulted in better therapeutic effects than short-term water mate training.

Involvement of CRH Receptors in the Neuroprotective Action of R-Apomorphine in the Striatal 6-OHDA Rat Model

The dopamine D1-D2 receptor agonist, R-apomorphine, has been shown to be neuroprotective in different models of Parkinson’s disease. Different mechanisms of action for this effect have been proposed, but not verified in the striatal 6-hydroxydopamine rat model. In this study, the expression of a set of genes involved in 1) signaling, 2) growth and differentiation, 3) neuronal regeneration and survival, 4) apoptosis and 5) inflammation in the striatum was measured after a subchronic R-apomorphine treatment (10 mg/kg/day, subcutaneously, during 11 days) in the striatal 6-hydroxydopamine rat model. The expression of 84 genes was analysed by using the rat neurotrophins and receptors RT2 ProfilerTM PCR array. The neuroprotective effects of R-apomorphine in the striatal 6-hydroxydopamine model were confirmed by neurochemical and behavioural analysis. The expression data suggest the observed neuroprotection involved the alteration of the gene and the protein expression levels of the anti-inflammatory corticotropin releasing hormone receptor (CRHR) 1 and the pro-inflammatory CRHR2 receptor confirming its potential anti-inflammatory action.

海人酸、使君子酸致Huntington病鼠纹状体NOS阳性细胞的变化

为了研究海人酸和使君子酸对大鼠纹状体 NOS阳性细胞的影响 ,用神经毒海人酸、使君子酸破坏大鼠左侧尾壳核 ,将夜间活动超过 6 0 0次、主动回避试验阳性率在 35 %以下的大鼠作为成功的 Huntington舞蹈病模型。注射后 2个月 ,将动物脑切片进行 Nissl、NADPH-d组化和 GF AP免疫组化反应。结果表明 ,海人酸和使君子酸均可使纹状体 n NOS阳性神经元丢失、出现i NOS阳性胶质细胞和侧脑室扩大 ,两者无显著差异。在损伤中心区 n NOS阳性神经元减少甚至消失 ,但这种变化自中心向周围呈渐变趋势 ;i NOS阳性胶质细胞呈两种不同形态 :一类胞体略大而突起粗短 ,一类胞体小而突起相对较长。对侧纹状体及伤侧纹状体非损毁部均未见 NOS阳性胶质细胞 ;NADPH-d组化和 GFAP免疫组化双重反应表明一些 i NOS胶质细胞为 GFAP阳性胶质细胞。本研究提示 ,海人酸和使君子酸均可使纹状体 n NOS神经元减少消失 ,损毁区出现的 NOS阳性胶质细胞为诱导型神经胶质细胞 (i NOS)。海人酸和使君子酸所引起的

Inhibiting effect of antisense oligonucleotides phosphorthioate on gene expression of TIMP-1 in rat liver fibrosis

AIM: To observe the inhibition of antisense oligonucleotides (asON) phosphorthioate to the tissue inhibitors metalloproteinase-1 (TIMP-1) gene and protein expression in the liver tissue of immunologically induced hepatic fibrosis rats. The possibility of reversing hepatic fibrosis through gene therapy was observed. METHODS: Human serum albumin (HSA) was used to attack rats, as hepatic fibrosis model, in which asONs were used to block the gene and protein expressing TIMP-1. According to the analysis of modulator, structure protein, coding series of TIMP-1 genome, we designed four different asONs. These asONs were injected into the hepatic fibrosis models through coccygeal vein. The results was observed by RT-PCR for measuring TIMP-1 mRNA expression, immunohistochemistry and in situ hybridization for collagen I, II, special staining of collagen fiber, and electron microscopic examination. RESULTS: Hepatic fibrosis could last within 363 days in our modified model. The expressing level of TIMP-1 was high during hepatic fibrosis process. It has been proved by the immunohistochemical and the electron microscopic examination that the asON phosphorthioate of TIMP-1 could exactly express in vivo. The effect of colchicine was demonstrated to inhibit the expressing level of mRNA and the content of collagen I, III in the liver of experimental hepatic fibrosis rats. However, the electron microscopy research and the pathologic grading of hepatic fibrosis showed that there was no significant difference between the treatment group and the model group (P】 0.05). CONCLUSION: The experimental rat model of hepatic fibrosis is one of the preferable models to estimate the curative effect of anti-hepatic fibrosis drugs. The asON phosphorthioate of TIMP-1 could block the gene and protein expression of TIMP-1 in the liver of experimental hepatic fibrosis rats at the mRNA level. It is possible to reverse hepatic fibrosis, and it is expected to study a new drug of antihepatic fibrosis on the genetic level. Colchicine has very limited therapeutic effect on hepatic fibrosis, furthermore, its toxicity and side effects are obvious.

Gastrin,somatostatin,G and D cells of gastric ulcer in rats

AIM: To investigate the relationship among gastrin, somatostatin, G and D cells in gastric ulcer and in its healing process in rats. METHODS: Fourty-nine Wistar rats were divided into 7 groups. The gastric ulcer model was induced by acetic acid successfully. The gastrin and the somatostatin in rat plasma, gastric fluid and antral tissue were measured by radioimmunoassay(RIA). G and D cells in antral mucosa were analyzed with polyclonal antibody of gastrin and somatostatin by immunohistochemical method and Quantimet 500 image analysis system. RESULTS: In gastric ulcer, the level of gastrin in plasma, gastric fluid, and antral tissue increased, that of somatostatin declined, and the disorder gradually recovered to the normal level in the healing process. Immunohistochemical technique of G and D cells in antral mucosa demonstrated that the number of G cells increased and that of D cells decreased, both areas of G and D cells declined, the ratio of number and area of G/D increased in gastric ulcer, and the disorder gradually recovered in the healing process. CONCLUSION: In gastric ulcer, the increased gastrin secreted by G cells, the declined somatostatin secreted by D cells, and the disordered G/D cell ratio can lead to gastrointestinal dysfunction.

Effects of glycyrrhetinic acid on collagen metabolism of hepatic stellate cells at different stages of liver fibrosis in rats

INTRODUCTIONLiver fibrosis is a dynamic course leading tocirrhosis from a various chronic liver diseases. Thepathological basis of fibrosis is the disturbance ofproduction and degradation of the extracellularmatrix (ECM), which causes accumulation of ECMin the liver[1,2].

Transplantation of human hepatocytes into tolerized genetically immunocompetent rats

AIM: To determine whether normal genetically immunocompetent rodent hosts could be manipulated to accept human hepatocyte transplants with long term survival without immunosuppression. METHODS: Tolerance towards human hepatocytes was established by injection of primary human hepatocytes or Huh7 human hepatoma cells into the peritoneal cavities of fetal rats. Corresponding cells were subsequently transplanted into newborn rats via intrasplenic injection within 24h after birth. RESULTS: Mixed lymphocyte assays showed that spleen cells from non-tolerized rats were stimulated to proliferate when exposed to human hepatocytes, while cells from tolerized rats were not. Injections made between 15 d and 17 d of gestation produced optimal tolerization. Transplanted human hepatocytes in rat livers were visualized by immunohistochemical staining of human albumin. By dot blotting of genomic DNA in livers of tolerized rats 16 weeks after hepatocyte transplantation, it was found that approximately 2.5 X 10(5) human hepatocytes survived per rat liver. Human albumin mRNA was detected in rat livers by RT-PCR for 15 wk, and human albumin protein was also detectable in rat serum. CONCLUSION: Tolerization of an immuno-competent rat can permit transplantation, and survival of functional human hepatocytes.

Safe upper limit of intermittent hepatic inflow occlusion for liver resection in cirrhotic rats

AIM: To evaluate the effects of varying ischemic durations on cirrhotic liver and to determine the safe upper limit of repeated intermittent hepatic inflow occlusion. METHODS: Hepatic ischemia in cirrhotic rats was induced by clamping the common pedicle of left and median lobes after non-ischemic lobes resection. The cirrhotic rats were divided into six groups according to the duration and form of vascular clamping: sham occlusion (SO), intermittent occlusion for 10 (IO-10), 15(IO-15), 20(IO-20) and 30(IO-30) minutes with 5 minutes of reflow and continuous occlusion for 60 minutes (CO-60). All animals received a total duration of 60 minutes of hepatic inflow occlusion. Liver viability was investigated in relation of hepatic adenylate energy charge (EC). Triphenyltetrazollum chloride (TTC) reduction activities were assayed to qualitatively evaluate the degree of irreversible hepatocellular injury. The biochemical and morphological changes were also assessed and a 7-day mortality was observed. RESULTS: At 60 minutes after reperfusion following a total of 60 minutes of hepatic inflow occlusion, EC values in IO-10 (0.749 +/- 0.012) and IO-15 (0.699 +/- 0.002) groups were rapidly restored to that in SO group (0.748 +/- 0.016), TTC reduction activities remained in high levels (0.144 +/- 0.002 mg/mg protein, 0.139 +/- 0.003 mg/mg protein and 0.121 +/- 0.003 mg/mg protein in SO, IO-10 and IO-15 groups, respectively). But in IO-20 and IO-30 groups, EC levels were partly restored (0.457 +/- 0.023 and 0.534 +/- 0.027) accompanying with a significantly decreased TTC reduction activities (0.070 +/- 0.005 mg/mg protein and 0.061 +/- 0.003 mg/mg protein). No recovery in EC values (0.228 +/- 0.004) and a progressive decrease in TTC reduction activities (0.033 +/- 0.002 mg/mg protein) were shown in CO-60 group. Although not significantly different, the activities of the serum aspartate aminotransferase (AST) on the third postoperative day (POD(3)) and POD(7) and of the serum alanine aminotransferase (ALT) on POD(3) in CO-60 group remained higher than that in intermittent occlusion groups. Moreover, a 60% animal mortality rate and more severe morphological alterations were also shown in CO-60 group. CONCLUSION: Hepatic inflow occlusion during 60 minutes for liver resection in cirrhotic rats resulted in less hepatocellular injury when occlusion was intermittent rather than continuous. Each period of 15 minutes was the safe upper limit of repeated intermittent vascular occlusion that the cirrhotic liver could tolerate without undergoing irreversible hepatocellular injury.

Pluripotent Stem Cells Models for Huntington's Disease:Prospects and Challenges

Pluripotent cellular models have shown great promise in the study of a number of neurological disorders. Several advantages of using a stem cell model include the potential for cells to derive disease relevant neuronal cell types, providing a system for researchers to monitor disease progression during neurogenesis, along with serving as a platform for drug discovery. A number of stem cell derived models have been employed to establish in ~,itro research models of Huntington＇s disease that can be used to investigate cellular pathology and screen lk^r drug and cell-based therapies. Although some progress has been made, there are a number of challenges and limitations that must be overcome before the true potential of this research strategy is achieved. In this article we review current stem cell models that have been reported, as well as discuss the issues that impair these studies. We also highlight the prospective application of Huntington＇s disease stem cell models in the development of novel therapeutic strategies and advancement of personalized medicine.

Cellular and molecular mechanisms implicated in pathogenesis of selective neurodegeneration in Huntington＇s disease

Huntington＇s disease （HD） is one of the most common dominantly-inherited neurodegenerative disorders and is caused by a CAG repeat expansion in the huntingtin gene. HD is characterized by selective degeneration of subpopulations of neurons in the brain, however the precise underlying mechanisms how a ubiquitously expressed disease protein could target specific types of neurons for degeneration remains a critical, yet unanswered question for HD and other major neurodegenerative disorders. In this review, we describe the expanding view of selective neuronal vulnerability in HD, based on recent neuropathological and neuroimaging studies. We will also summarize the systematic effort to define the cell types in which mutant Huntingtin expression is critical for pathogenesis of vulnerable neurons in the striatum and cortex. Finally, we will describe selected, emerging molecular mechanisms that are implicated in selective disease processes in HD. Together, the field has begun to appreciate the distinct molecular pathogenic roles of mutant huntingtin in different cell types that may contribute to the selective neuronal vulnerability, with dissection of such mechanisms likely to yield novel molecular targets for HD therapy.

Using Huntingtin Knock-In Minipigs to Fill the Gap Between Mouse Models and Patients with Huntington's Disease

Huntington＇s disease （HD） is an inherited autosomal dominant neurodegenerative disease characterized by pro- gressive motor deficits, cognitive decline, and psychiatric symptoms. It is caused by a pathological expansion of CAG trinucleotide repeats in exon 1 of the HD gene, resulting in the translation of a mutant form of huntingtin protein （mutant Htt） with an expanded polyglutamine domain in the N-terminal region [1 ]. Despite great progress in understanding the pathogenesis of HD using multiple mouse models, the exact mechanisms by which mutant Htt induces neuronal dysfunction and death are still not completely clear, and there is no curative treatment for this disease. An important reason is that the mouse, which is the most widely used animal model in HD research, differs from the human in many aspects, including the physiology, drug metabolism, blood-brain barrier, life span, brain volume, and neuroanatomical organization [2]. Thus, it is necessary to establish HD models with higher species than rodents, such as the dog, pig, and non- human primate, so as to bridge the gap between preclinical mouse models and clinical studies.