Volume 33, Issue 3

The human retina is a highly structured and complex neurosensory tissue central to perceiving and processing visual signals. In a healthy individual, the close interplay between the neuronal retina, the adjacent retinal pigment epithelium and the underlying blood supply, the choriocapillaris, is critical for maintaining eyesight over a lifetime. An impairment of this delicate and metabolically highly active system, caused by genetic alteration, environmental impact or both, results in a multitude of pathological phenotypes of the retina. Understanding and treating these disease processes are motivated by a marked medical need in young as well as in older patients. While naturally occurring or gene-manipulated animal models have been used successfully in ophthalmological research for many years, recent advances in induced pluripotent stem cell technology have opened up new avenues to generate patient-derived retinal model systems. Here, we explore to what extent these cellular models can be useful to mirror human pathologies in vitro ultimately allowing to analyze disease mechanisms and testing treatment options in the cell type of interest on an individual patient-specific genetic background.

The generation of three-dimensional (3D) cancer models is a novel and fascinating development in the study of personalized medicine and tumor-specific drug delivery. In addition to the classical two-dimensional (2D) adherent cell culture models, 3D spheroid and organoid cancer models that mimic the microenvironment of cancer tissue are emerging as an important preclinical model system. 3D cancer models form, similar to cancer, multiple cell–cell and cell–extracellular matrix interactions and activate different cellular cascades/pathways, like proliferation, quiescence, senescence, and necrotic or apoptotic cell death. Further, it is possible to analyze genetic variations and mutations, the microenvironment of cell–cell interactions, and the uptake of therapeutics and nanoparticles in nanomedicine. Important is also the analysis of cancer stem cells (CSCs), which could play key roles in resistance to therapy and cancer recurrence. Tumor spheroids can be generated from one tumor-derived cell line or from co-culture of two or more cell lines. Tumor organoids can be derived from tumors or may be generated from CSCs that differentiate into multiple facets of cancerous tissue. Similarly, tumorspheres can be generated from a single CSC. By transplanting spheroids and organoids into immune-deficient mice, patient-derived xenografts can serve as a preclinical model to test therapeutics in vivo . Although the handling and analysis of 3D tumor spheroids and organoids is more complex, it will provide insights into various cancer processes that cannot be provided by 2D culture. Here a short overview of 3D tumor systems as preclinical models is provided.

Hypertrophic cardiomyopathy (HCM) is a clinically heterogeneous cardiac disease that is mainly characterized by left ventricular hypertrophy in the absence of any additional cardiac or systemic disease. HCM is genetically heterogeneous, inherited mainly in an autosomal dominant pattern, and so far pathogenic variants have been identified in more than 20 genes, mostly encoding proteins of the cardiac sarcomere. Based on its variable penetrance and expressivity, pathogenicity of newly identified variants often remains unsolved, underlining the importance of cellular and tissue-based models that help to uncover causative genetic alterations and, additionally, provide appropriate systems for the analysis of disease hallmarks as well as for the design and application of new therapeutic strategies like drug screenings and genome/base editing approaches. Here, we review the current state of cellular and tissue-engineered models and provide future perspectives for personalized therapeutic strategies of HCM.

Neurogenetic diseases represent a broad group of diseases with variable genetic causes and clinical manifestations. Among these, polymerase-gamma (POLG)-spectrum disorders are relatively frequent with an estimated disease frequency of ∼1:10.000. Also, mutations in the POLG gene are by far the most important cause for mitochondriopathy. POLG-spectrum disorders usually result in progressive loss of brain function and may involve severe and deadly encephalopathy, seizures, and neuromuscular disease, as well as cardiac and hepatic failure in some cases. Onset of disease may range from birth to late adulthood, and disease duration ranges from weeks in severe cases to decades. There is no curative treatment; current animal models do not faithfully recapitulate human disease, complicating preclinical therapeutic studies. Human-based preclinical model systems must be developed to understand the human disease mechanisms and develop therapeutic approaches. In this review, we provide an overview of the current approaches to model neurogenetic disorders in a human cellular and neuronal environment with a focus on POLG-spectrum disorders. We discuss the necessity of using neuronal cells and the advantages and pitfalls of currently available cell model approaches, namely (i) CRISPR-based (i. e., genetically engineered) and induced pluripotent stem cell (iPSC) (i. e., stem cell like)-derived neuronal models and (ii) the reprogramming of patient-derived cells into iPSCs and derived neurons. Despite the fact that cell models are by definition in vitro systems incapable of recapitulating all aspects of human disease, they are still the reasonable point of start to discover disease mechanisms and develop therapeutic approaches to treat neurogenetic diseases.

Cerebral cavernous malformations (CCMs) are vascular lesions that can cause severe neurological complications due to intracranial hemorrhage. Although the CCM disease genes, CCM1 , CCM2 , and CCM3 , have been known for more than 15 years now, our understanding of CCM pathogenesis is still incomplete. CCM research currently focuses on three main disease mechanisms: (1) clonal expansion of endothelial cells with biallelic inactivation of CCM1 , CCM2 , or CCM3 , (2) recruitment of cells with preserved CCM protein expression into the growing lesion, and (3) disruption of endothelial cell–cell junctions in CCMs. We here describe novel CRISPR/Cas9-based in vitro models of CCM and discuss their strengths and limitations in the context of high-throughput drug screening and repurposing approaches.

Neuromuscular disorders are a heterogeneous group of diseases ranging from mild to devastating phenotypes depending on the disorder’s origin. Pathophysiologies for many of these disorders are not fully understood and efficient therapies are urgently needed. Recent advances in the field of induced pluripotent stem cells and organ-on-a-chip technologies have brought enormous improvement in modeling neuromuscular diseases. Even complex units, like the neuromuscular junction, can now be built, enabling researchers to study each component of the motor unit by itself or interacting with others, allowing the identification of disease mechanisms. This article aims to introduce these new modeling systems to study neuromuscular disorders and the possibilities of organ-on-a-chip platforms to shed light on disease pathologies and their use for therapy development.