Innovative Applications of Organoid and Assembloid In vitro Model Systems in Human Diseases or Disorders

Modeling Primary Microcephaly with Human Brain Organoids Reveals Fundamental Roles of CIT Kinase Activity This study by Pallavicini et al.[1] delineates the roles of hypomorphic citron kinase (CIT-K) signaling and CIT loss-of-function (LoF) defects in the development of the human and mouse brain. The mouse and human biallelic CIT missense models showed a high frequency of binucleated neurons, indicating a conserved role of CIT-K in cytokinesis completion in humans and mice. Whereas the hypomorphic cytokinesis defects in CITKI/KI mice do not significantly alter brain size or structure, the CITFS/FS mice exhibit characteristics that more closely resemble the human microcephaly phenotype. The differences between hypomorphic and LoF CIT-K mouse models highlight a human-specific role for CIT-K catalytic activity in cytokinesis, impacting neural rosette structure and neural progenitor cell mitotic symmetry. The increased apoptosis in LoF neural tissues in both species underlines DNA damage-dependent apoptosis as a conserved factor affecting brain size. The three-dimensional brain organoids reveal a new role of CIT-K in polarized cytoarchitecture dynamics. Mouse models mirror severe microcephaly seen in humans with CITFS/FS variants, with failed cytokinesis, DNA damage, apoptosis, and reduced brain size. CITKI/KI and CITFS/FS organoids exhibit mitotic defects and delays, with genotype-dependent severity. Live-cell imaging reveals profound mitotic defects in CITKI/KI and CITFS/FS organoids. The study conclusively demonstrates that human brain organoid models exhibit altered mitotic dynamics and apoptosis, indicating the vulnerability of the developing brain to cytokinesis defects. Ultimately, their research underscores the exceptional potential of human forebrain organoids derived from affected individuals, positioning them as an indispensable resource for investigating the effects of primary microcephaly (MCPH)-associated pathogenic genetic variants on neurodevelopment which cannot be recapitulated by using animal models. Transplantation of Derivative Retinal Organoids from Chemically Induced Pluripotent Stem Cells Restored Visual Function In this study, Zhao et al. have generated chemically induced pluripotent stem cells (CiPSCs) from mouse embryonic fibroblasts using a small set of small molecules, a breakthrough in stem cell research. CiPSCs offer a safer alternative by minimizing the risks of genomic instability that are typically associated with exogenous DNAs derived from viruses or plasmids.[2] This new method holds much potential for use in regenerative medicine. The generated CiPSCs were differentiated into three-dimensional retinal organoids (ROs) and characterized for all the major retinal cell types and the retinal gene expression as observed during the in vivo development. They transplanted these retinal photoreceptors derived from CiPSCs ROs into the subretinal space of eyes in the mouse models with retinal degeneration. The transplanted retinal photoreceptors led to successful integration, and synaptic connection establishment, resulting in the partial improvement of visual functions in the retinal degenerative mouse model. This study has developed a new method to convert somatic cells into CiPSCs and further into ROs using only small molecules, thereby offering new cell sources for clinical replacement therapy. Rapid and Scalable Personalized ASO Screening in Patient-derived Organoids The overall research introduces a scalable platform for generating patient-derived organoid models for the preclinical evaluation of personalized antisense oligonucleotides (ASOs) designed to treat rare genetic diseases, particularly Duchenne muscular dystrophy (DMD).[3] The study elucidates that patient-specific ASOs can effectively restore dystrophin expression and reverse disease-related phenotypes in cardiac organoids from DMD patients. The methodology confirmed that ASOs could effectively transfect cardiac organoids, restoring rhythmic calcium fluctuations and demonstrating no adverse effects on cell viability. The authors have presented an accessible methodology for creating these organoids, highlighting their potential for rapid preclinical assessment of tailored ASO therapeutics in disease in a dish model. By emphasizing the importance of patient-specific cellular models, the research aims to enhance treatment strategies for various rare diseases, representing a significant advancement in therapeutic options and patient outcomes within a limited time frame. Construction of a rodent neural network-skeletal muscle Assembloid that simulates the postnatal development of spinal cord motor neuronal network The researchers have developed in vitro rodent bioengineered spinal cord neural network-skeletal muscle (NN-SkM) Assembloids to overcome the limitation of conventional in vitro models that required longer time and even lack important neurological cells as observed in neuromuscular disorders during the postnatal period.[4] Their innovative approach employs advanced tissue engineering techniques to create structures that respond to motor regulation signals, mimicking the control of SkM by spinal cord neurons (NNs). The findings of this research study not only enhance our understanding of postnatal development but also offer valuable insights into potential therapeutic strategies for neuromuscular diseases. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.