Identification of neurodevelopmental organization of the cell populations of juvenile Huntington’s disease using dorso-ventral HD organoids and HD mouse embryos

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    This manuscript describes the generation of a fused dorsal-ventral organoid system to model interactions between the cortex and striatum to study the onset and progression of Huntington's disease (HD) and other neurodegenerative disorders. While this approach is valuable, further methodological and analytical work is needed to fully support the interpretations and claims of the authors. Incomplete evidence suggests choroid plexus (ChP) abnormalities form a significant component of HD pathogenesis.

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Abstract

Huntington’s disease (HD) is a polyglutamine neurodegenerative disease involving pathogenesis within the striatum and cerebral cortex and a neurodevelopmental component, particularly in juvenile HD form (JOHD). We established a fused HD dorsal-ventral system, imitating the cortex and striatum interaction in a single organoid to discover neurodevelopmental impairments at the level of cell populations. We found a range of early pathogenic phenotypes indicating that brain development in HD is affected by impaired neurogenesis. The phenotypes occurred already in early-stage 60-day organoids and the brain of humanized mouse embryos, at time of the beginning of the neurogenesis and choroid plexus development. We demonstrated that HD organoids and HD mouse embryonic brains had gene expression profiles of impaired maturation of neurons and increased expression of genes responsible for proliferation compared to genes responsible for differentiation in control organoids. By using scRNA-seq, the choroid plexus population was highly abundant in HD organoids and embryonic brains. Cortical and choroid plexus cell populations in HD organoids and brains co-expressed genes responsible for HTT function (mitotic spindle and cilia). The impaired maturation and the increased occurrence of the choroid plexus populations were mitigated in our compensatory model, mosaic dorsal/ventral (D/V) or V/D HD/control organoids. Finally, we found that TTR protein, a choroid plexus marker, is elevated in the adult HD mouse serum, indicating that TTR may be a promising marker for detecting HD. In summary, the fused dorso-ventral HD organoids identify a spectrum of neurodevelopmental features, including increased proliferation and delayed cell maturation. We demonstrate that the choroid plexus population is characteristic of aberrant HD neurodevelopment, and contains TTR marker, which can be translated as a blood marker in HD.

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  1. eLife Assessment

    This manuscript describes the generation of a fused dorsal-ventral organoid system to model interactions between the cortex and striatum to study the onset and progression of Huntington's disease (HD) and other neurodegenerative disorders. While this approach is valuable, further methodological and analytical work is needed to fully support the interpretations and claims of the authors. Incomplete evidence suggests choroid plexus (ChP) abnormalities form a significant component of HD pathogenesis.

  2. Reviewer #1 (Public review):

    In the manuscript "Identification of neurodevelopmental organization of the cell populations of Juvenile Huntington's disease using dorso-ventral HD organoids and HD mouse embryos," the authors establish a fused dorso-ventral system that mimics cortex-striatum interactions within a single organoid and use this system to investigate neurodevelopmental impairments caused by HD. Specifically, they describe certain phenotypes in 60-day HD organoids and the brains of humanized mouse embryos, utilizing both wet-lab and single-cell sequencing techniques. The authors also develop dorsal/ventral and ventral/dorsal mosaic control/HD organoids, showing a capacity to rescue some HD phenotypes.

    The manuscript could be a valuable contribution to the field, however it has relevant drawbacks, the most significant being a lack of clarity regarding the replicates used for each genotype in the sequencing analyses. The lack of information on replicates raises the possibility that only a single replicate was analyzed for each organoid and brain sample. This approach may lead to concerns regarding the reproducibility of the findings, and it may be necessary for the authors to generate additional data to strengthen their conclusions. In addition, the analysis of the HD samples was conducted by pooling distinct cell populations from different brain regions (CTX, HIP, ChP for the dorsal brain, and STR, HYP, TH for the ventral brain). It is unclear why scRNA seq was used on pooled brain regions, which could obscure region-specific insights.

    Another issue pertains to their proposed outcome: "Finally, we found that TTR protein, a choroid plexus marker, is elevated in the adult HD mouse serum, indicating that TTR may be a promising marker for detecting HD". This statement appears to lack statistical support, which makes this set of data potentially misleading and inconclusive.

    The authors are encouraged to provide evidence of biological replicates, remove outcomes that lack statistical support, and address a series of points as detailed elsewhere.

  3. Reviewer #2 (Public review):

    The article titled "Identification of neurodevelopmental organization of the cell populations of juvenile Huntington's disease using dorso-ventral HD organoids and HD mouse embryos" analyses an in vitro human brain organoid model containig dorsal and ventral telencephalum structures derived from human iPSC from Huntington's disease patients or control subjects.

    The authors describe differences in the pattern of expression of genes related to proliferation and neuronal maturation, with a slower pattern of differentiation present in HD cells. Moreover, the authors described a higher differentiation capacity of HD cells to generate choroid plexus identity following dorsal telencephalon prime protocol differentiation when compared to control cells. Whereas the claims related to Choroid plexus identity are intriguing, most of the claims made through the manuscript are not sustained by quantitative data or consistent results in the different conditions analysed, or many experiments seem to be missing to reach final conclusions.

    In addition, the quality of the organoids used for experiments does not seem to have been assessed or satisfactorily presented in the figures of this paper. Many important details related to the experimental execution are missing in the current version of this manuscript.