Cellular And Small Animal Models Of Neurodegenerative Diseases

Editorial

Neurodegenerative diseases including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and frontotemporal dementia are devastating disorders with no known cure, mainly due to the lack of understanding of the underlying disease mechanisms. Numerous mutant strains of mice have been generated as models to investigate these diseases^1,2,3,4,5. While fundamental insights into disease pathology and mechanisms have been obtained, investigations at a subcellular resolution and high-throughput analyses such as drug screens are not feasible in animal models. Cellular and small animal model systems fill this niche.

Human induced pluripotent stem cell (hIPSC) cultures and neuronal differentiation are a powerful system to study the effects of genetic alterations in a human background. Yet, different culturing conditions, differentiation protocols, and user-based biases many times lead to reproducibility issues. Dhingra et al. present the automation of hiPSC cultures and neuronal differentiations compatible with automated imaging and analysis⁶. This system does not only lead to more reproducible culturing and differentiation of human IPS cells into neuronal lineages but also enables the automated live tracking of cellular phenotypes, including the quantification of neurite lengths, aggregate formation, or the uptake of pathogenic protein species, and neurodegeneration over a 2 month period.

Changes in calcium homeostasis have been linked to various neurodegenerative diseases, in particular Parkinson’s disease⁷. Bancroft and Srinivasan present a protocol to quantify calcium flux in cultured dopaminergic neurons⁸. The presented system can lead to a better understanding of how abnormal calcium signaling triggers the loss of dopaminergic neurons and can be utilized as a high-throughput drug screening platform for the identification of neuroprotective compounds.

Synapse loss is a common feature among neurodegenerative diseases⁹. Yet, the underlying reasons remain unclear. Sidiski and Babcock present a method to quantify synaptic integrity in an age-dependent manner in the neuromuscular junctions of the dorsal longitudinal muscle (DLM) tissue in Drosophila melanogaster¹⁰. Importantly, their dissection protocol, which involves the flash freezing of tissue, preserves both the neuronal and muscle tissue and, due to the ease of genetic manipulation of the fly, enables the study of changes in synaptic integrity and its degeneration in models of neurodegenerative diseases.

Neurodegenerative diseases and aging are linked to proteostasis failures¹¹, and both protein degradation and synthesis have been implicated. Papandreou et al. present a protocol to quantify de novo protein synthesis¹², utilizing fluorescence recovery after photobleaching (FRAP) in C. elegans models expressing GFP. This system can be extended to GFP fusions of any disease-linked protein, either widely expressed in the worm nervous system or targeted to specific cells or tissues, and enables the in vivo study of protein synthesis in the absence of nonradioactive and noninvasive methods, in addition to having the ability to perform genetic or small molecule screens to identify novel modulators to overcome proteostatic dysfunction.

Protection against protein aggregation and neuron death are sought-after strategies to slow down neurodegenerative diseases. Palikaras et al. describe how heat shock preconditioning in C. elegans promotes neuroprotection against alpha-synuclein-triggered cell death and a decrease in PolyQ-induced aggregates¹³.

Neurodegenerative diseases affect more than 50 million people across the globe, with no known cure. With the recent advances in genetic editing and IPSC technology, cellular and small animal models have the advantage of addressing the underlying molecular and cellular disease mechanisms acutely, enable fast and cost-effective genetic manipulations, and are ideal as a high-throughput screening platform for libraries of new therapeutic compounds. This collection of disease methods facilitates researchers to use some of these models.