An assembloid is an in vitro model that combines two or more organoids, spheroids, or cultured cell types to recapitulate structural and functional properties of an organ.[1] They are typically derived from induced pluripotent stem cells. Assembloids have been used to study cell migration, neural circuit assembly, neuro-immune interactions, metastasis, and other complex tissue processes.[2][3][4] The term "assembloid" was coined by Sergiu P. Pașca's lab in 2017.[5]

Example image of an assembloid modeling human forebrain circuits (Pasca Lab, Stanford University)

Generation of assembloids

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Assembloids were described in 2017 in a study from a laboratory at Stanford to model forebrain development.[5][6] Assembloids joining ventral and dorsal forebrain neural organoids demonstrated that cortical interneurons migrate and integrate into synaptically connected cortical microcircuits.[5] This was confirmed by multiple research groups applying similar approaches to model regionalized organoid interactions and study interneuron migration.[7][8] Assembloids have subsequently been generated to model projections between brain regions, such as cortico-striatal,[9] cortico-spinal,[10] or retino-thalamic.[11] Methods such as Cre recombination combined with G-deleted rabies tracing can be used to identify cells projecting within assembloids; additionally, optogenetic stimulation can demonstrate the assembly of functional neural circuits in vitro.[12]

Assembloid formation starts with the generation of organoids. Initially, human induced pluripotent stem (hiPS) cells are aggregated to generate regionalized organoids through directed differentiation.[2] There are multiple ways in which organoids can be assembled. Regionalized organoids can be put in close proximity resulting in their fusion to generate multi-region assembloids.[13] Alternatively, organoids can be assembled by co-culture with other cell lineages, such as microglia or endothelial cells, or with tissue samples from animal dissection, leading to multi-lineage assembloids.[14] Lastly, organoids can be assembled with morphogenic or organizer-like cells, thus generating polarized assembloids.[15]

The assembloid type depends on the scientific question and the accessibility of cell types required. Major biological fields utilizing the assembloid technique include cancer, gastroenterology, cardiology, and neuroscience. For instance, there are liver assembloids,[16] kidney assembloids,[17] pericytes assembloids to study SARS-COVID2,[18] endometrium assembloids,[19] stomach and colon assembloids,[20] and bladder assembloids.[21]

Types

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Assembloids are composed of at least two organoids and/or cells derived from stem cells or primary tissue. They can be assembled to form multi-region or multi-lineage assembloids, as described above.[22]

A. Multi-region assembloids of the nervous system There are techniques to guide organoid differentiation into specific regions of the nervous system. For example, fusion of thalamic and cortical neural organoids models thalamo-cortical projections of ascending sensory input while cortico-striatal assembloids generate the initial projections of motor planning circuits.[8][9] Forebrain assembloids model interneuron migration into the cerebral cortex.[5] Cortico-motor assembloids can reconstitute aspects of the cortico-spinal-muscle circuit in vitro.[10] Finally, retinal organoids can be combined with thalamic and cortical organoids to model aspects of the ascending visual pathway.[11]

B. Multi-lineage assembloids of the nervous system Some cell types of interest are challenging to differentiate within organoids but can be isolated from tissue explants or derived in monolayer culture. These tissue samples or enriched cell populations can then be integrated with organoid(s) of interest to study their interaction. For example, one current limitation of organoids and assembloids is their lack of functional vasculature, which hinders the supply of nutrients and trophic factors. In a technical advancement, researchers have been able to achieve vascularization by combining neural organoids with endothelial organoids and mesenchymal cells or human embryonic stem cell-derived vascular organoids.[23][24][25] Next, microglia-like cells derived from hiPS cells can be introduced into midbrain neural organoids to model neuro-immune interactions.[26] Similarly, oligodendrocytes can be generated in neural organoids and then migrate from the ventral forebrain to the dorsal forebrain.[27][28][29] Lastly, combining hiPS cell-derived intestinal organoids with neural crest cells can derive assembloids of the enteric nervous system.[30]

Additionally, assembloids can be categorized as inter-individual or inter-species, depending on whether the organoids are combined from different stem cell lines (e.g., control with disease-associated lines) or different species, respectively.[31] These combinations help determine what aspects of development are cell-autonomous.

Disease models and applications

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Assembloids help determine the complex pathophysiology of developmental disorders. For example, Timothy syndrome, which affects L-type calcium channels, was modeled in neural assembloid experiments. When dorsal and ventral forebrain organoids were integrated into an assembloid, interneurons migrated into the dorsal cortical neurons. Timothy syndrome-derived interneurons showed impaired migration.[5] The resulting assembloids developed hypersynchronous neuronal activity, hypothesized to be due to abnormal interneuron integration into circuits.[22] Next, Phelan-McDermid syndrome, also known as 22q13.3 deletion syndrome, is a neurodevelopmental disorder with a high risk of autism spectrum disorder that was modeled in assembloids containing cortical and striatal organoids. This research demonstrated increased striatal medium spiny neuron activity in Phelan-McDermid-derived assembloids after fusion of striatal and cortical organoids but not in isolated striatal organoids.[9] Rett syndrome-derived assembloids displayed hypersynchronous activity perhaps due to an increase in calretinin interneurons.[32] Alzheimer's disease risk allele APOE4, which increases the risk of dementia, has been modeled in assembloids.[14] APOE4-derived assembloids of neural organoids combined with microglia demonstrated increased amyloid-beta-42 secretion, a known Alzheimer biomarker. APOE4 microglia in assembloids had a more complex morphology than in two-dimensional culture and had limited amyloid-beta-42 clearance.

Limitations

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Despite the research benefits of assembloids, as for any model system, they have limitations. First, assembloids, like organoids, lack vascularisation, which impairs nutrient diffusion to the surface and eventually leads to necrosis in the core, thus limiting their growth.[33] One way to address this limitation is through transplantation. Grafting cortical organoids into the brains of laboratory rats leads to improved growth and neural development.[34]Another critique of both assembloids and organoids is the lack of sensory input, which is important for the maturation and shaping of circuits during embryonic development.[35] Assembloids and organoids do not currently have a blood brain barrier or immune cells, limiting the biological validity for drug screening or disease modeling.[36]There is a temporal limitation on the investigation of clinically relevant pathophysiology; organoids most closely model initial developmental stages corresponding to fetal and infant neurodevelopment and thus may not accurately model later-onset psychiatric disorders or degenerative conditions. Future directions to address this limitation include studies to understand and accelerate developmental clocks.[37]Next, organoids and assembloids have batch-to-batch variability. Guided differentiation methods reduce variability significantly, yet reproducibility still requires optimization.[35] Finally, the derivation and maintenance of organoids and assembloids require expertise and can be time-intensive and expensive.

See also

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References

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  1. ^ Pașca SP, Arlotta P, Bateup HS, Camp JG, Cappello S, Gage FH (2022). "A nomenclature consensus for nervous system organoids and assembloids". Nature. 609 (7929): 907–910. Bibcode:2022Natur.609..907P. doi:10.1038/s41586-022-05219-6. PMC 10571504. PMID 36171373.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ a b Pașca SP (2018). "The rise of three-dimensional human brain cultures". Nature. 553 (7689): 437–445. Bibcode:2018Natur.553..437P. doi:10.1038/nature25032. PMID 29364288. S2CID 205262820.
  3. ^ Paşca SP (2019). "Assembling human brain organoids". Science. 363 (6423): 126–127. Bibcode:2019Sci...363..126P. doi:10.1126/science.aau5729. PMID 30630918. S2CID 57825925.
  4. ^ Schmidt C (2021). "The rise of the assembloid". Nature. 597 (7878): S22–S23. Bibcode:2021Natur.597S..22S. doi:10.1038/d41586-021-02628-x. S2CID 238229376.
  5. ^ a b c d e Birey F, Andersen J, Makinson CD, Islam S, Wei W, Huber N (2017). "Assembly of functionally integrated human forebrain spheroids". Nature. 545 (7652): 54–59. Bibcode:2017Natur.545...54B. doi:10.1038/nature22330. PMC 5805137. PMID 28445465.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Pașca, Sergiu (August 24, 2022). How we're reverse engineering the human brain in the lab. Vancouver, Canada: TED. Retrieved 2023-12-10.
  7. ^ Bagley JA, Reumann D, Bian S, Lévi-Strauss J, Knoblich JA (2017). "Fused cerebral organoids model interactions between brain regions". Nat Methods. 14 (7): 743–751. doi:10.1038/nmeth.4304. PMC 5540177. PMID 28504681.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ a b Xiang Y, Tanaka Y, Patterson B, Kang YJ, Govindaiah G, Roselaar N; et al. (2017). "Fusion of regionally specified hPSC-derived organoids models human brain development and interneuron migration". Cell Stem Cell. 21 (3): 383–398.e7. doi:10.1016/j.stem.2017.07.007. PMC 5720381. PMID 28757360.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ a b c Miura Y, Li MY, Birey F, Ikeda K, Revah O, Thete MV; et al. (2020). "Generation of human striatal organoids and cortico-striatal assembloids from human pluripotent stem cells". Nat Biotechnol. 38 (12): 1421–1430. doi:10.1038/s41587-020-00763-w. PMC 9042317. PMID 33273741.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ a b Andersen J, Revah O, Miura Y, Thom N, Amin ND, Kelley KW; et al. (2020). "Generation of functional human 3d cortico-motor assembloids". Cell. 183 (7): 1913–1929.e26. doi:10.1016/j.cell.2020.11.017. PMC 8711252. PMID 33333020.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  11. ^ a b Fligor CM, Lavekar SS, Harkin J, Shields PK, VanderWall KB, Huang KC, Gomes C, Meyer JS (2021). "Extension of retinofugal projections in an assembled model of human pluripotent stem cell-derived organoids". Stem Cell Rep. 16 (9): 2228–2241. doi:10.1016/j.stemcr.2021.05.009. PMC 8452489. PMID 34115986.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Miura Y, Li MY, Revah O, Yoon SJ, Narazaki G, Pașca SP (2022). "Engineering brain assembloids to interrogate human neural circuits". Nat Protoc. 17 (1): 15–35. doi:10.1038/s41596-021-00632-z. PMID 34992269. S2CID 245773595.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  13. ^ Sloan SA, Andersen J, Pașca AM, Birey F, Pașca SP (2018). "Generation and assembly of human brain region–specific three-dimensional cultures". Nat Protoc. 13 (9): 2062–2085. doi:10.1038/s41596-018-0032-7. PMC 6597009. PMID 30202107.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ a b Lin YT, Seo J, Gao F, Feldman HM, Wen HL, Penney J; et al. (2018). "APOE4 causes widespread molecular and cellular alterations associated with Alzheimer's disease phenotypes in human ipsc-derived brain cell types". Neuron. 98 (6): 1141–1154.e7. doi:10.1016/j.neuron.2018.05.008. PMC 6023751. PMID 29861287.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ Cederquist GY, Asciolla JJ, Tchieu J, Walsh RM, Cornacchia D, Resh MD, Studer L (2019). "Specification of positional identity in forebrain organoids". Nat Biotechnol. 37 (4): 436–444. doi:10.1038/s41587-019-0085-3. PMC 6447454. PMID 30936566.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Takeishi K, Collin de l'Hortet A, Wang Y, Handa K, Guzman-Lepe J, Matsubara K; et al. (2020). "Assembly and function of a bioengineered human liver for transplantation generated solely from induced pluripotent stem cells". Cell Rep. 31 (9): 107711. doi:10.1016/j.celrep.2020.107711. PMC 7734598. PMID 32492423.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Tsujimoto H, Kasahara T, Sueta SI, Araoka T, Sakamoto S, Okada C; et al. (2020). "A modular differentiation system maps multiple human kidney lineages from pluripotent stem cells". Cell Rep. 31 (1): 107476. doi:10.1016/j.celrep.2020.03.040. hdl:2433/250216. PMID 32268094. S2CID 215610752.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Wang L, Sievert D, Clark AE, Lee S, Federman H, Gastfriend BD; et al. (2021). "A human three-dimensional neural-perivascular "assembloid" promotes astrocytic development and enables modeling of SARS-CoV-2 neuropathology". Nat Med. 27 (9): 1600–1606. doi:10.1038/s41591-021-01443-1. PMC 8601037. PMID 34244682.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  19. ^ Rawlings TM, Makwana K, Taylor DM, Molè MA, Fishwick KJ, Tryfonos M; et al. (2021). "Modelling the impact of decidual senescence on embryo implantation in human endometrial assembloids". eLife. 10. doi:10.7554/eLife.69603. PMC 8523170. PMID 34487490.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  20. ^ Establishment of gastrointestinal assembloids to study the interplay between epithelial crypts and their mesenchymal niche. Lin, M., Hartl, K., Heuberger, J., Beccaceci, G., Berger, H., Li, H., Liu, L., Müllerke, S., Conrad, T., Heymann, F., Woehler, A., Tacke, F., Rajewsky, N., & Sigal, M. (2023). Nature communications, 14(1), 3025. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10212920/
  21. ^ Kim E, Choi S, Kang B, Kong J, Kim Y, Yoon WH; et al. (2020). "Creation of bladder assembloids mimicking tissue regeneration and cancer". Nature. 588 (7839): 664–669. Bibcode:2020Natur.588..664K. doi:10.1038/s41586-020-3034-x. PMID 33328632. S2CID 229293144.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  22. ^ a b Birey F, Li MY, Gordon A, Thete MV, Valencia AM, Revah O; et al. (2022). "Dissecting the molecular basis of human interneuron migration in forebrain assembloids from Timothy syndrome". Cell Stem Cell. 29 (2): 248–264.e7. doi:10.1016/j.stem.2021.11.011. PMID 34990580.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Song L, Yuan X, Jones Z, Griffin K, Zhou Y, Ma T, Li Y (2019). "Assembly of human stem cell-derived cortical spheroids and vascular spheroids to model 3-D brain-like tissues". Sci Rep. 9 (1): 5977. Bibcode:2019NatSR...9.5977S. doi:10.1038/s41598-019-42439-9. PMC 6461701. PMID 30979929.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  24. ^ Cakir B, Xiang Y, Tanaka Y, Kural MH, Parent M, Kang YJ; et al. (2019). "Engineering of human brain organoids with a functional vascular-like system". Nat Methods. 16 (11): 1169–1175. doi:10.1038/s41592-019-0586-5. PMC 6918722. PMID 31591580.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  25. ^ Sun XY, Ju XC, Li Y, Zeng PM, Wu J, Zhou YY; et al. (2022). "Generation of vascularized brain organoids to study neurovascular interactions". eLife. 11. doi:10.7554/eLife.76707. PMC 9246368. PMID 35506651.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  26. ^ Sabate-Soler S, Nickels SL, Saraiva C, Berger E, Dubonyte U, Barmpa K; et al. (2022). "Microglia integration into human midbrain organoids leads to increased neuronal maturation and functionality". Glia. 70 (7): 1267–1288. doi:10.1002/glia.24167. PMC 9314680. PMID 35262217.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. ^ Madhavan M, Nevin ZS, Shick HE, Garrison E, Clarkson-Paredes C, Karl M; et al. (2018). "Induction of myelinating oligodendrocytes in human cortical spheroids". Nat Methods. 15 (9): 700–706. doi:10.1038/s41592-018-0081-4. PMC 6508550. PMID 30046099.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  28. ^ Marton RM, Miura Y, Sloan SA, Li Q, Revah O, Levy RJ; et al. (2019). "Differentiation and maturation of oligodendrocytes in human three-dimensional neural cultures". Nat Neurosci. 22 (3): 484–491. doi:10.1038/s41593-018-0316-9. PMC 6788758. PMID 30692691.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  29. ^ Shaker MR, Pietrogrande G, Martin S, Lee JH, Sun W, Wolvetang EJ (2021). "Rapid and efficient generation of myelinating human oligodendrocytes in organoids". Front Cell Neurosci. 15. doi:10.3389/fncel.2021.631548. PMC 8010307. PMID 33815061.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  30. ^ Workman MJ, Mahe MM, Trisno S, Poling HM, Watson CL, Sundaram N; et al. (2017). "Engineered human pluripotent-stem-cell-derived intestinal tissues with a functional enteric nervous system". Nat Med. 23 (1): 49–59. doi:10.1038/nm.4233. PMC 5562951. PMID 27869805.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  31. ^ Kanton S, Paşca SP (2022). "Human assembloids". Development. 149 (20). doi:10.1242/dev.201120. PMID 36317797. S2CID 253246025.
  32. ^ Samarasinghe RA, Miranda OA, Buth JE, Mitchell S, Ferando I, Watanabe M; et al. (2021). "Identification of neural oscillations and epileptiform changes in human brain organoids". Nat Neurosci. 24 (10): 1488–1500. doi:10.1038/s41593-021-00906-5. PMC 9070733. PMID 34426698.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  33. ^ Qian X, Song H, Ming GL (2019). "Brain organoids: advances, applications and challenges". Development. 146 (8)). doi:10.1242/dev.166074. PMC 6503989. PMID 30992274.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  34. ^ Revah O, Gore F, Kelley KW, Andersen J, Sakai N, Chen X; et al. (2022). "Maturation and circuit integration of transplanted human cortical organoids". Nature. 610 (7931): 319–326. Bibcode:2022Natur.610..319R. doi:10.1038/s41586-022-05277-w. PMC 9556304. PMID 36224417.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  35. ^ a b Makrygianni EA, Chrousos GP (2021). "From brain organoids to networking assembloids: implications for neuroendocrinology and stress medicine". Frontiers in Physiology. 12. doi:10.3389/fphys.2021.621970. PMC 8222922. PMID 34177605.
  36. ^ Andrews MG, Kriegstein AR (2022). "Challenges of organoid research". Annu Rev Neurosci. 45: 23–39. doi:10.1146/annurev-neuro-111020-090812. PMC 10559943. PMID 34985918.
  37. ^ Levy RJ, Paşca SP (2023). "What have organoids and assembloids taught us about the pathophysiology of neuropsychiatric disorders?". Biol Psychiatry. 93 (7): 632–641. doi:10.1016/j.biopsych.2022.11.017. PMID 36739210. S2CID 254167227.