A drug-screening platform for autism spectrum disorders using human astrocytes
Autism spectrum disorders (ASD) are complex neurodevelopmental diseases that affect about 1% of children in the United States. Such diseases are mainly characterized by deficits in verbal communication, impaired social interaction, and limited and repetitive interests and behavior. The causes and best treatments remain uncertain. One of the major impediments to ASD research is the lack of relevant human disease models. Reprogramming of somatic cells to a pluripotent state (induced pluripotent stem cells, iPSCs) has been accomplished using human cells. Isogenic pluripotent cells are attractive from the prospective to understanding complex diseases, such as ASD. The main goal of this project is to accelerate drug discovery to treat ASD using astrocytes generated from human iPSC. The model recapitulates early stages of ASD and represents a promising cellular tool for drug screening, diagnosis and personalized treatment. By testing whether drugs have differential effects in iPSC-derived astrocytes, we can begin to unravel how genetic variation in ASD dictates responses to different drugs. Insights that emerge from our studies may drive the development of new therapeutic interventions for ASD. They may also illuminate possible differences in drug responsiveness in different patients and potentially define a molecular signature resulting from ASD variants, which could predict the onset of disease before symptoms are seen.
Autism spectrum disorders, including Rett syndrome, Angelman syndrome, Timothy syndrome, Fragile X syndrome, Tuberous sclerosis, Asperger syndrome or childhood disintegrative disorder, affect many Californian children. In the absence of a functionally effective cure or early diagnostic tool, the cost of caring for patients with such pediatric diseases is high, in addition to a major personal and family impact since childhood. The strikingly high prevalence of ASD, dramatically increasing over the past years, has led to the emotional view that ASD can be traced to a single source, such as vaccine, preservatives or other environmental factors. Such perspective has a negative impact on science and society in general. Our major goal is to develop a drug-screening platform to rescue deficiencies showed from brain cells derived from induced pluripotent stem cells generated from patients with ASD. If successful, our model will bring novel insights on the dentification of potential diagnostics for early detection of ASD risk, or ability to predict severity of particular symptoms. In addition, the development of this type of pharmacological therapeutic approach in California will serve as an important proof of principle and stimulate the formation of businesses that seek to develop these types of therapies (providing banks of inducible pluripotent stem cells) in California with consequent economic benefit.
The progress in our research regarding the role of human astrocytes in Rett syndrome (RTT) showed us that RTT-derived astrocyte display several phenotypes that illustrate its differences compared to healthy control astrocytes (WT). RTT astrocytes are unable to propagate calcium wave when mechanically stimulated . In addition to that, when placed in medium that contains glutamate, the natural uptake and buffering of this compound is impaired in RTT-derived astrocytes. Furthermore, when WT neurons are placed on top of RTT astrocytes, there is a clear the negative effect of these cells in neuronal homeostasis. Remarkably, WT astrocytes are able to rescue RTT neuronal phenotypes when in direct contact, illustrating the important role that astrocytes have in maintaining neuronal viability and maturation. Several mis-regulation in gene expression pathways indicated those phenotypes, both in calcium and glutamate dependent genes. Strikingly, further genetic analysis led us to identify several mis-regulations in pro-inflammatory cytokines. Multiplex ELISA platforms also pointed towards a difference in cytokine secretion between WT and RTT syndrome astrocytes, being the RTT cells illustrative of a pro-inflammatory scenario. We have define one of these secreted cytokines as our primary read out for the HT-screening. We are now facing a transportation issue with very sensitive cells, but have an innovative plan to make it to work and also get some quick results that may have clinical relevance.
During the project period we characterized several phenotypes related to Rett syndrome-derived astrocytes, including the release of pro-inflammatory cytokines. We also validated some of these phenotypes in cells derived from patients with idiopathic autism. Thus, our data will likely be relevant to a larger fraction of the autism spectrum. During the period, we optimize the transport of human astrocytes to our screening facility at NIH. The logistic was problematic as these cells would become reactivated, affecting our cellular readouts. We propose alternatives for the primary read out and made progress on the 384-well format plating required for the drug screening automated platform. We expect to conclude the screening in the next report period and start secondly assays for validation of prioritized leads.
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