23 Oct 2019

A multi-institutional group, including members of the Tau Consortium, unveiled a stem cell tool kit for scientists studying primary tauopathies. In the November 12 issue of Stem Cell Reports, researchers co-led by Celeste Karch ofWashington University, St. Louis, and Alison Goate and Sally Temple of Icahn School of Medicine in New York, describe a collection of fibroblasts, induced pluripotent stem cells, and neural precursor cells. The cells come from 140 skin samples, some given by donors with richly documented clinical histories who carry pathogenic MAPT mutations or risk variants. Others come from noncarrier family members, patients with a sporadic tauopathy, and cognitively normal controls. The set includes induced pluripotent stem cell lines from 31 donors and 21 CRISPR-engineered isogenic lines. The cells are available to other researchers for study.

These types of high-quality repositories are becoming increasingly important for the scientific community, Clive Svendsen of the Cedars-Sinai Medical Center in Los Angeles wrote to Alzforum.

This is the way the field is going, agreed Lawrence Golbe of CurePSP, New York. Golbes organization funds research into progressive nuclear palsy (PSP) and related disorders, and collaborates with the Tau Consortium on other projects. Enthusiastic about the resources potential, Golbe hopes CurePSP grantees will get an automatic pass to use the cells.

Choice Mutations. Cells in the new iPSC collection carry some of the most common MAPT mutations, covering a wide range of clinical and neuropathological phenotypes of frontotemporal lobe dementia (FTLD)-Tau. [Courtesy of Karch et al., 2019.]

Tauopathies have proven difficult to study in animal models, in part because unlike other neuropathologies, they seem to afflict only humans (Heuer et al., 2012). Moreover, while adult human brains express approximately equal amounts of the tau spliced isoforms 3R and 4R, rodents produce almost exclusively 4R (Trabzuni et al., 2012). This is problematic. For example, leading proposals to explain how tau mutations cause disease point to abnormalities in splicing and microtubule binding, which differ between isoforms. The models we had been focusing on were not capturing the complexity of MAPT in human cells, said first author Karch. As a result, human induced pluripotent stem cells (iPSCs) have been gaining popularity in the field. The NINDS Human Cell and Data Repository is helping meet the demand by offering iPSC lines derived from 10 patients harboring MAPT mutations.

However, Karch and her collaborators think the field could benefit from a larger and more diverse collection of human cells, including isogenic iPSC lines. To accomplish this, they collected skin samples from 140 people carrying MAPT pathogenic mutations or risk variants, non-mutation carriers, and patients with sporadic PSP or corticobasal syndrome (CBS), most with comprehensive clinical histories. Although a few cells came from the NINDS repository, most came from patients participating in longitudinal studies at the Memory and Aging Center at the University of California, San Francisco, and the Knight Alzheimer Disease Research Center at WashU. The clinical records of most of these patients include detailed neurological and neuropathological workups, as well as fluid biomarkers and neuroimaging data collected from MRI, A-PET, and tau-PET studies.

To capture a broad range of phenotypes associated with some of the most common MAPT mutations, the authors created 36 fibroblast lines and 29 iPSC lines from individuals carrying the P301L, S305I,IVS10+16, V337M, G389R, and R406W mutations, as well as from carriers of the A152T variant, which increases the risk for both PSP and CBS (image above). The latter could be particularly useful for dissecting the mechanisms that underlie the phenotypic differences between the two diseases. The researchers also obtained iPSC lines from two noncarrier family members, and two people who suffered from autopsy-confirmed sporadic PSP. In addition, they stored fibroblast lines from 12 patients with sporadic PSP, five with CBS, 10 with a mixed PSP/CBS presentation, and 69 cognitively normal controls.

Biopsies are available for 27 of the 31 patients whose cells were used to generate iPSCs, and autopsy data for seven, including the two cases of sporadic PSP.

Importantly, the researchers edited 21 iPSC lines using CRISPR/Cas 9. They corrected cells with these mutations: MAPT IVS10+16,P301L, S305I, R406W, and V337M. Conversely, they inserted into control iPSCs these mutations: R5H, P301L,G389R, S305I, or S305S.

The authors also created a stem cell line carrying MAPT P301S,a mutation commonly overexpressed in tauopathy mouse models but not present in the available donors, by editing the P301L line. Isogenic lines are so powerful, particularly in these diseases which are so variable in their onset and progression, even within the same family, said Karch. Gnter Hglinger and Tabea Strauss at the German Center for Neurodegenerative Disease (DZNE) in Munich agreed. Having a pool of cell lines with different disease-linked mutations and risk variants from several individuals and their isogenic control cells is an excellent resource for the research community to enlighten disease mechanisms, they wrote (full comment below).

Several of the reported lines have already starred in recent studies of tauopathy mechanisms and candidate therapies (e.g., Sep 2019 conference news; Nakamura et al., 2019; Hernandez et al., 2019; Silva et al., 2019).

Karch and colleagues have partially differentiated some of the iPSCs and stored them as neural progenitor cells (NPCs), so that researchers can relatively easily thaw, expand, and differentiate them into neurons. These NPCs have proved useful for large-scale functional-genomics studies, proteomics, and genetic modifier screens (e.g., Cheng et al., 2017; Boselli et al., 2017;Tian et al., 2019).

In addition, the authors inserted a neurogenin-2 transgene into two healthy controls and two MAPT mutant stem cells, P301L and R406W. Neurogenin-2 enables low-cost, large-scale differentiation of stem cells into homogenous excitatory neurons. These transgenic cells are particularly useful for high-throughput drug screens (Wang et al., 2017; Sohn et al., 2019).

Researchers can request all the reported cells online at http://neuralsci.org/tau. They must provide a summary of experimental plans, an institutional material transfer agreement, and a nominal fee to cover maintenance and distribution costs. Karch said the process resembles that of the Coriell Institute and the NINDS repository. Our goal is to share with as few hurdles as possible, she said.

While the authors are still reprogramming fibroblasts they have already collected, they also plan to add more causative mutations, generate more isogenic lines, and obtain more cells from members of the same families to help shed light on phenotypic variability. In addition, Karch said, she hopes repository users will resubmit lines with new modifications they generate.

Jeffrey Rothstein, Johns Hopkins University, Baltimore, welcomed the new resource. I think it is great they have assembled this collection, he said. Rothstein founded and co-directs the Answer ALS research project, which has amassed 600 iPSC lines from controls and patients with amyotrophic lateral sclerosis (ALS).

Rothstein suggested the tauopathy collection may want to prioritize adding cells from donors with the most common form of disease, that is, sporadic. His group aims to generate 1,000 iPSC lines, with a large fraction representing sporadic diseasealso the most common form of ALSto identify the most prevalent disease subtypes. One strategy that has helped his group build their collection, he said, is using peripheral blood mononuclear cells instead of fibroblasts to create iPSCs. More donors are willing to donate blood than have a piece of skin punched out. In addition, iPSCs derived from blood cells are genetically more stable, he noted.

Rothstein emphasized the importance of assembling a large collection of healthy controls. Although isogenic controls are of great value, he cautioned they can be subject to artifacts. One problem is that the cell population can change due to selective pressures during CRISPR editing (Budde et al., 2017). To address this, Karch and colleagues are collecting not only modified iPSC clones, but also control clones that have gone through the editing pipeline but remain unmodified.

Stem-cell users studying tauopathies face another challenge: iPSC-derived neurons express primarily the fetal isoform of tau, 3R0N. However, citing a study that shows three-dimensional neuronal cultures switch to the adult profile relatively quickly (Miguel et al., 2019), Hglinger and Strauss wrote, [It] allows us to be optimistic that current challenges of this model system can be overcome in the future.Marina Chicurel

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Introducing: iPSC Collection from Tauopathy Patients - Alzforum