Genetically modified non-human primate models for research on neurodegenerative diseases

Neurodegenerative diseases(NDs)are a group of debilitating neurological disorders that primarily affect elderly populations and include Alzheimer's disease(AD),Parkinson's disease(PD),Huntington's disease(HD),and amyotrophic lateral sclerosis(ALS).Currently,there are no therapies available that can delay,stop,or reverse the pathological progression of NDs in clinical settings.As the population ages,NDs are imposing a huge burden on public health systems and affected families.Animal models are important tools for preclinical investigations to understand disease pathogenesis and test potential treatments.While numerous rodent models of NDs have been developed to enhance our understanding of disease mechanisms,the limited success of translating findings from animal models to clinical practice suggests that there is still a need to bridge this translation gap.Old World nonhuman primates(NHPs),such as rhesus,cynomolgus,and vervet monkeys,are phylogenetically,physiologically,biochemically,and behaviorally most relevant to humans.This is particularly evident in the similarity of the structure and function of their central nervous systems,rendering such species uniquely valuable for neuroscience research.Recently,the development of several genetically modified NHP models of NDs has successfully recapitulated key pathologies and revealed novel mechanisms.This review focuses on the efficacy of NHPs in modeling NDs and the novel pathological insights gained,as well as the challenges associated with the generation of such models and the complexities involved in their subsequent analysis.

Differential distribution of PINK1 and Parkin in the primate brain implies distinct roles

The vast majority of in vitro studies have demonstrated that PINK1 phosphorylates Parkin to work together in mitophagy to protect against neuronal degeneration.However,it remains largely unclear how PINK1 and Parkin are expressed in mammalian brains.This has been difficult to address because of the intrinsically low levels of PINK1 and undetectable levels of phosphorylated Parkin in small animals.Understanding this issue is critical for elucidating the in vivo roles of PINK1 and Parkin.Recently,we showed that the PINK1 kinase is selectively expressed as a truncated form(PINK1–55)in the primate brain.In the present study,we used multiple antibodies,including our recently developed monoclonal anti-PINK1,to validate the selective expression of PINK1 in the primate brain.We found that PINK1 was stably expressed in the monkey brain at postnatal and adulthood stages,which is consistent with the findings that depleting PINK1 can cause neuronal loss in developing and adult monkey brains.PINK1 was enriched in the membrane-bound fractionations,whereas Parkin was soluble with a distinguishable distribution.Immunofluorescent double staining experiments showed that PINK1 and Parkin did not colocalize under physiological conditions in cultured monkey astrocytes,though they did colocalize on mitochondria when the cells were exposed to mitochondrial stress.These findings suggest that PINK1 and Parkin may have distinct roles beyond their well-known function in mitophagy during mitochondrial damage.

Comparative analysis of primate and pig cells reveals primate-specific PINK1 expression and phosphorylation

PTEN-induced putative kinase 1(PINK1),a mitochondrial kinase that phosphorylates Parkin and other proteins,plays a crucial role in mitophagy and protection against neurodegeneration.Mutations in PINK1 and Parkin can lead to loss of function and early onset Parkinson's disease.However,there is a lack of strong in vivo evidence in rodent models to support the theory that loss of PINK1 affects mitophagy and induces neurodegeneration.Additionally,PINK1 knockout pigs(Sus scrofa)do not appear to exhibit neurodegeneration.In our recent work involving non-human primates,we found that PINK1 is selectively expressed in primate brains,while absent in rodent brains.To extend this to other species,we used multiple antibodies to examine the expression of PINK1 in pig tissues.In contrast to tissues from cynomolgus monkeys(Macaca fascicularis),our data did not convincingly demonstrate detectable PINK1expression in pig tissues.Knockdown of PINK1 in cultured pig cells did not result in altered Parkin and BAD phosphorylation,as observed in cultured monkey cells.A comparison of monkey and pig striatum revealed more PINK1-phosphorylated substrates in the monkey brain.Consistently,PINK1 knockout in pigs did not lead to obvious changes in the phosphorylation of Parkin and BAD.These findings provide new evidence that PINK1expression is specific to primates,underscoring the importance of non-human primates in investigating PINK1function and pathology related to PINK1 deficiency.

Large animal models for Huntington's disease research

Huntington'sdisease(HD)isahereditary neurodegenerative disorder for which there is currently no effectivetreatmentavailable.Consequently,the development of appropriate disease models is critical to thoroughly investigate disease progression.The genetic basis of HD involves the abnormal expansion of CAG repeats in the huntingtin(HTT)gene,leading to the expansion of a polyglutamine repeat in the HTT protein.Mutant HTT carrying the expanded polyglutamine repeat undergoes misfolding and forms aggregates in the brain,which precipitate selective neuronal loss in specific brain regions.Animal models play an important role in elucidating the pathogenesis of neurodegenerative disorders such as HD and in identifying potential therapeutic targets.Due to the marked species differences between rodents and larger animals,substantial efforts have been directed toward establishing large animal models for HD research.These models are pivotal for advancing the discovery of novel therapeutic targets,enhancing effective drug delivery methods,and improving treatment outcomes.We have explored the advantages of utilizing large animal models,particularly pigs,in previous reviews.Since then,however,significant progress has been made in developing more sophisticated animal models that faithfully replicate the typical pathology of HD.In the current review,we provide a comprehensive overview of large animal models of HD,incorporating recent findings regarding the establishment of HD knock-in(KI)pigs and their genetic therapy.We also explore the utilization of large animal models in HD research,with a focus on sheep,non-human primates(NHPs),and pigs.Our objective is to provide valuable insights into the application of these large animal models for the investigation and treatment of neurodegenerative disorders.

A booming field of large animal model research

Animal models are integral to the study of fundamental biological processes and the etiology of human diseases.Small animal models,especially those involving mice,have yielded abundant and significant insights,greatly enhancing our understanding of biological phenomena and disease mechanisms.

Reduced mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor contributes to neurodegeneration in a model of spinal and bulbar muscular atrophy pathology

Spinal and bulbar muscular atrophy is a neurodegenerative disease caused by extended CAG trinucleotide repeats in the androgen receptor gene,which encodes a ligand-dependent transcription facto r.The mutant androgen receptor protein,characterized by polyglutamine expansion,is prone to misfolding and forms aggregates in both the nucleus and cytoplasm in the brain in spinal and bulbar muscular atrophy patients.These aggregates alter protein-protein interactions and compromise transcriptional activity.In this study,we reported that in both cultured N2a cells and mouse brain,mutant androgen receptor with polyglutamine expansion causes reduced expression of mesencephalic astrocyte-de rived neurotrophic factor.Overexpressio n of mesencephalic astrocyte-derived neurotrophic factor amelio rated the neurotoxicity of mutant androgen receptor through the inhibition of mutant androgen receptor aggregation.Conversely.knocking down endogenous mesencephalic astrocyte-derived neurotrophic factor in the mouse brain exacerbated neuronal damage and mutant androgen receptor aggregation.Our findings suggest that inhibition of mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor is a potential mechanism underlying neurodegeneration in spinal and bulbar muscular atrophy.

PINK1 kinase dysfunction triggers neurodegeneration in the primate brain without impacting mitochondrial homeostasis

In vitro studies have established the prevalent theory that the mitochondrial kinase PINK1 protects neurodegeneration by removing damaged mitochondria in Parkinson's disease(PD).However,difficulty in detecting endogenous PINK1 protein in rodent brains and cell lines has prevented the rigorous investigation of the in vivo role of PINK1.Here we report that PINK1 kinase form is selectively expressed in the human and monkey brains.CRISPR/Cas9-mediated deficiency of PINK1 causes similar neurodegeneration in the brains of fetal and adult monkeys as well as cultured monkey neurons without affecting mitochondrial protein expression and morphology.Importantly,PINK1 mutations in the primate brain and human cells reduce protein phosphorylation that is important for neuronal function and survival.Our findings suggest that PINK1 kinase activity rather than its mitochondrial function is essential for the neuronal survival in the primate brains and that its kinase dysfunction could be involved in the pathogenesis of PD.

CRISPR-Based Genome-Editing Tools for Huntington’s Disease Research and Therapy

Huntington’s disease(HD)is an autosomal dominantly-inherited neurodegenerative disease,which is caused by CAG trinucleotide expansion in exon 1 of the Huntingtin(HTT)gene.Although HD is a rare disease,its monogenic nature makes it an ideal model in which to understand pathogenic mechanisms and to develop therapeutic strategies for neurodegenerative diseases.Clustered regularly-interspaced short palindromic repeats(CRISPR)is the latest technology for genome editing.Being simple to use and highly efficient,CRISPR-based genome-editing tools are rapidly gaining popularity in biomedical research and opening up new avenues for disease treatment.Here,we review the development of CRISPR-based genome-editing tools and their applications in HD research to offer a translational perspective on advancing the genome-editing technology to HD treatment.

Tauopathy promotes spinal cord-dependent production of toxic amyloid-beta in transgenic monkeys

Tauopathy,characterized by the hyperphosphorylation and accumulation of the microtubule-associated protein tau,and the accumulation of Aβ oligomers,constitute the major pathological hallmarks of Alzheimer's disease.However,the relationship and causal roles of these two pathological changes in neurodegeneration remain to be defined,even though they occur together or independently in several neurodegenerative diseases associated with cognitive and movement impairment.

Generation of inactivated IL2RG and RAG1 monkeys with severe combined immunodeficiency using base editing

Severe combined immunodeficiency(SCiD)encompasses a range of inherited disorders that lead to a profound deterioration of the immune system.Among the pivotal genes associated with SCID,RAG1 and IL2RG play crucial roles.IL2RG is essential for the development,differentiation,and functioning of T,B,and NK cells,while RAG1 critically contributes to adaptive immunity by facilitating V(D)J recombination during the maturation of lymphocytes.Animal models carrying mutations in these genes exhibit notable deficiencies in their immune systems.

TBtools-II: A “one for all, all for one” bioinformatics platform for biological big-data mining

Since the official release of the stand-alone bioinformatics toolkit TBtools in 2020,its superior functionality in data analysis has been demonstrated by its widespread adoption by many thousands of users and references in more than 5000 academic articles.Now,TBtools is a commonly used tool in biological laboratories.Over the past 3 years,thanks to invaluable feedback and suggestions from numerous users,we have optimized and expanded the functionality of the toolkit,leading to the development of an upgraded version—TBtools-II.In this upgrade,we have incorporated over 100 new features,such as those for comparative genomics analysis,phylogenetic analysis,and data visualization.Meanwhile,to better meet the increasing needs of personalized data analysis,we have launched the plugin mode,which enables users to develop their own plugins and manage their selection,installation,and removal according to individual needs.To date,the plugin store has amassed over 50 plugins,with more than half of them being independently developed and contributed by TBtools users.These plugins offer a range of data analysis options including co-expression network analysis,single-cell data analysis,and bulked segregant analysis sequencing data analysis.Overall,TBtools is now transforming from a stand-alone software to a comprehensive bioinformatics platform of a vibrant and cooperative community in which users are also developers and contributors.By promoting the theme“one for all,all for one”,we believe that TBtools-II will greatly benefit more biological researchers in this big-data era.

New pathogenic insights from large animal models of neurodegenerative diseases

Animal models are essential for investigating the pathogenesis and developing the treatment of human diseases.Identification of genetic mutations responsible for neurodegenerative diseases has enabled the creation of a large number of small animal models that mimic genetic defects found in the affected individuals.Of the current animal models,rodents with genetic modifications are the most commonly used animal models and provided important insights into pathogenesis.However,most of genetically modified rodent models lack overt neurodegeneration,imposing challenges and obstacles in utilizing them to rigorously test the therapeutic effects on neurodegeneration.Recent studies that used CRISPR/Cas9-targeted large animal(pigs and monkeys)have uncovered important pathological events that resemble neurodegeneration in the patient’s brain but could not be produced in small animal models.Here we highlight the unique nature of large animals to model neurodegenerative diseases as well as the limitations and challenges in establishing large animal models of neurodegenerative diseases,with focus on Huntington disease,Amyotrophic lateral sclerosis,and Parkinson diseases.We also discuss how to use the important pathogenic insights from large animal models to make rodent models more capable of recapitulating important pathological features of neurodegenerative diseases.

Targeting PFKL with penfluridol inhibits glycolysis and suppresses esophageal cancer tumorigenesis in an AMPK/FOXO3a/BIM-dependent manner

As one of the hallmarks of cancer,metabolic reprogramming leads to cancer progression,and targeting glycolytic enzymes could be useful strategies for cancer therapy.By screening a small molecule library consisting of 1320 FDA-approved drugs,we found that penfluridol,an antipsychotic drug used to treat schizophrenia,could inhibit glycolysis and induce apoptosis in esophageal squamous cell carcinoma(ESCC).Gene profiling and Ingenuity Pathway Analysis suggested the important role of AMPK in action mechanism of penfluridol.By using drug affinity responsive target stability(DARTS)technology and proteomics,we identified phosphofructokinase,liver type(PFKL),a key enzyme in glycolysis,as a direct target of penfluridol.Penfluridol could not exhibit its anticancer property in PFKL-deficient cancer cells,illustrating that PFKL is essential for the bioactivity of penfluridol.High PFKL expression is correlated with advanced stages and poor survival of ESCC patients,and silencing of PFKL significantly suppressed tumor growth.Mechanistically,direct binding of penfluridol and PFKL inhibits glucose consumption,lactate and ATP production,leads to nuclear translocation of FOXO3a and subsequent transcriptional activation of BIM in an AMPK-dependent manner.Taken together,PFKL is a potential prognostic biomarker and therapeutic target in ESCC,and penfluridol may be a new therapeutic option for management of this lethal disease.

Pathological insights from amyotrophic lateral sclerosis animal models:comparisons,limitations,and challenges

In order to dissect amyotrophic lateral sclerosis(ALS),a multigenic,multifactorial,and progressive neurodegenerative disease with heterogeneous clinical presentations,researchers have generated numerous animal models to mimic the genetic defects.Concurrent and comparative analysis of these various models allows identification of the causes and mechanisms of ALS in order to finally obtain effective therapeutics.However,most genetically modified rodent models lack overt pathological features,imposing challenges and limitations in utilizing them to rigorously test the potential mechanisms.Recent studies using large animals,including pigs and non-human primates,have uncovered important events that resemble neurodegeneration in patients’brains but could not be produced in small animals.Here we describe common features as well as discrepancies among these models,highlighting new insights from these models.Furthermore,we will discuss how to make rodent models more capable of recapitulating important pathological features based on the important pathogenic insights from large animal models.