Extracellular Matrix Components Regulate Cellular Polarity and Tissue Structure in the Developing and Mature Retina

A Mathematical Model of Interstitial Fluid Flow and Retinal Tissue Deformation in Macular Edema

Purpose

This study aims to develop a mathematical model to elucidate fluid circulation in the retina, focusing on the movement of interstitial fluid (comprising water and albumin) to understand the mechanisms underlying exudative macular edema (EME).

Methods

The model integrates physiological factors such as retinal pigment epithelium (RPE) pumping, osmotic pressure gradients, and tissue deformation. It accounts for spatial variability in hydraulic conductivity (HC) across the retina and incorporates the structural role of Müller cells (MCs) in maintaining retinal stability.

Results

The model predicts that tissue deformation is maximal at the center of the fovea despite fluid exudation from blood capillaries occurring elsewhere, aligning with clinical observations. Additionally, the model suggests that spatial variability in HC across the thickness of the retina plays a protective role against fluid accumulation in the fovea.

Conclusions

Despite inherent simplifications and uncertainties in parameter values, this study represents a step toward understanding the pathophysiology of EME. The findings provide insights into the mechanisms underlying fluid dynamics in the retina and fluid accumulation in the foveal region, showing that the specific conformation of Müller cells is likely to play a key role.

Defect of TIMP4 Is Associated with High Myopia and Participates in Rat Ocular Development in a Dose-Dependent Manner

Thinning of the sclera happens in myopia eyes owing to extracellular matrix (ECM) remodeling, but the initiators of the ECM remodeling in myopia are mainly unknown. The matrix metalloproteinase (MMPs) and tissue inhibitors of matrix metalloproteinase (TIMPs) regulate the homeostasis of the ECM. However, genetic studies of the MMPs and TIMPs in the occurrence of myopia are poor and limited. This study systematically investigated the association between twenty-nine genes of the TIMPs and MMPs families and early-onset high myopia (eoHM) based on whole exome sequencing data. Two TIMP4 heterozygous loss-of-function (LoF) variants, c.528C>A in six patients and c.234_235insAA in one patient, were statistically enriched in 928 eoHM probands compared to that in 5469 non-high myopia control (p = 3.7 × 10-5) and that in the general population (p = 2.78 × 10-9). Consequently, the Timp4 gene editing rat was further evaluated to explore the possible role of Timp4 on ocular and myopia development. A series of ocular morphology abnormalities in a dose-dependent manner (Timp4-/- < Timp4+/- < Timp4+/+) were observed in a rat model, including the decline in the retinal thickness, the elongation in the axial length, more vulnerable to the form deprivation model, morphology changes in sclera collagen bundles, and the decrease in collagen contents of the sclera and retina. Electroretinogram revealed that the b-wave amplitudes of Timp4 defect rats were significantly reduced, consistent with the shorter length of the bipolar axons detected by HE and IF staining. Heterozygous LoF variants in the TIMP4 are associated with early onset high myopia, and the Timp4 defect disturbs ocular development by influencing the morphology and function of the ocular tissue.

Extracellular-Matrix Mechanics Regulate the Ocular Physiological and Pathological Activities

The extracellular matrix (ECM) is a noncellular structure that plays an indispensable role in a series of cell life activities. Accumulating studies have demonstrated that ECM stiffness, a type of mechanical forces, exerts a pivotal influence on regulating organogenesis, tissue homeostasis, and the occurrence and development of miscellaneous diseases. Nevertheless, the role of ECM stiffness in ophthalmology is rarely discussed. In this review, we focus on describing the important role of ECM stiffness and its composition in multiple ocular structures (including cornea, retina, optic nerve, trabecular reticulum, and vitreous) from a new perspective. The abnormal changes in ECM can trigger physiological and pathological activities of the eye, suggesting that compared with different biochemical factors, the transmission and transduction of force signals triggered by mechanical cues such as ECM stiffness are also universal in different ocular cells. We expect that targeting ECM as a therapeutic approach or designing advanced ECM-based technologies will have a broader application prospect in ophthalmology.

Profiling of idiopathic macular hole vitreous proteome identifies the role of extracellular matrix remodelling, epithelial-mesenchymal transformation and unfolded protein-response pathways

Purpose

To analyze and describe the proteome of the vitreous humour in eyes with idiopathic macular holes.

Methods

We performed mass spectrometry (MS)-based label-free quantitative analysis of the vitreous proteome of idiopathic macular hole (IMH) and control donor vitreous. Comparative quantification was performed using SCAFFOLD software which calculated fold changes of differential expression. Bioinformatics analysis was performed using DAVID and STRING software.

Results

A total of 448 proteins were identified by LC-MS/MS in IMH and cadaveric eye vitreous samples, of which 199 proteins were common. IMH samples had 189 proteins that were unique and 60 proteins were present only in the control cadaveric vitreous. We found upregulation of several extracellular matrix (ECM) and cytoskeletal proteins, namely collagen alpha-1 (XVIII) chain, N-cadherin, EFEMP1/fibulin-3, basement membrane-specific heparan sulfate proteoglycan core protein, and target of Nesh-3. Several cytoskeleton proteins, namely tubulin, actin, and fibronectin levels, were significantly lower in IMH vitreous, probably reflecting increased ECM degradation. IMH vitreous also had a downregulation of unfolded protein response-mediated-mediated apoptosis proteins, possibly related to a state of increased cell survival and proliferation, along with a remodelling and aberrant production of ECM contents.

Conclusion

The pathogenesis of macular holes may involve ECM remodelling, epithelial-mesenchymal transformation, downregulation of apoptosis, protein folding defects, and complement pathway. The vitreo-retinal milieu in macular holes contain molecules related to both ECM degradation and inhibition of the same, thereby maintaining a homeostasis.

Photoreceptor laminin drives differentiation of human pluripotent stem cells to photoreceptor progenitors that partially restore retina function

Blindness caused by advanced stages of inherited retinal diseases and age-related macular degeneration are characterized by photoreceptor loss. Cell therapy involving replacement with functional photoreceptor-like cells generated from human pluripotent stem cells holds great promise. Here, we generated a human recombinant retina-specific laminin isoform, LN523, and demonstrated the role in promoting the differentiation of human embryonic stem cells into photoreceptor progenitors. This chemically defined and xenogen-free method enables reproducible production of photoreceptor progenitors within 32 days. We observed that the transplantation into rd10 mice were able to protect the host photoreceptor outer nuclear layer (ONL) up to 2 weeks post transplantation as measured by full-field electroretinogram. At 4 weeks post transplantation, the engrafted cells were found to survive, mature, and associate with the host's rod bipolar cells. Visual behavioral assessment using the water maze swimming test demonstrated visual improvement in the cell-transplanted rodents. At 20 weeks post transplantation, the maturing engrafted cells were able to replace the loss of host ONL by extensive association with host bipolar cells and synapses. Post-transplanted rabbit model also provided congruent evidence for synaptic connectivity with the degenerated host retina. The results may pave the way for the development of stem cell-based therapeutics for retina degeneration.

Beyond Genetics: The Role of Metabolism in Photoreceptor Survival, Development and Repair

Vision commences in the retina with rod and cone photoreceptors that detect and convert light to electrical signals. The irreversible loss of photoreceptors due to neurodegenerative disease leads to visual impairment and blindness. Interventions now in development include transplanting photoreceptors, committed photoreceptor precursors, or retinal pigment epithelial (RPE) cells, with the latter protecting photoreceptors from dying. However, introducing exogenous human cells in a clinical setting faces both regulatory and supply chain hurdles. Recent work has shown that abnormalities in central cell metabolism pathways are an underlying feature of most neurodegenerative disorders, including those in the retina. Reversal of key metabolic alterations to drive retinal repair thus represents a novel strategy to treat vision loss based on cell regeneration. Here, we review the connection between photoreceptor degeneration and alterations in cell metabolism, along with new insights into how metabolic reprogramming drives both retinal development and repair following damage. The potential impact of metabolic reprogramming on retinal regeneration is also discussed, specifically in the context of how metabolic switches drive both retinal development and the activation of retinal glial cells known as Müller glia. Müller glia display latent regenerative properties in teleost fish, however, their capacity to regenerate new photoreceptors has been lost in mammals. Thus, re-activating the regenerative properties of Müller glia in mammals represents an exciting new area that integrates research into developmental cues, central metabolism, disease mechanisms, and glial cell biology. In addition, we discuss this work in relation to the latest insights gleaned from other tissues (brain, muscle) and regenerative species (zebrafish).

Targeting matrix stiffness-induced activation of retinal pigment epithelial cells through the RhoA/YAP pathway ameliorates proliferative vitreoretinopathy

The purpose of this study was to investigate whether excessive extracellular matrix (ECM) deposition-induced mechanical matrix stiffness plays a key role in promoting retinal pigment epithelial (RPE) cell activation and the subsequent development of proliferative vitreoretinopathy (PVR). Human ARPE-19 cells were cultured on either 50 kappa (stiff) or 0.5 kappa (soft) gel-coated coverslips. Reverse and knockdown experiments were carried out to establish a model of matrix stiffness-induced activation in ARPE-19 cells in vitro. A PVR mouse model was established by the intravitreal injection of dispase. The effects of RhoA/YAP signalling blockade on matrix stiffness-induced ARPE-19 cell activation and PVR-induced retinal fibrosis were determined by using a combination of the Yes-associated protein (YAP) inhibitor verteporfin and the RhoA inhibitor C3 exoenzyme. Matrix stiffness stimulated YAP nuclear translocation and expression in ARPE-19 cells. The effect of YAP activation was dependent on F-actin cytoskeleton polymerization and RhoA activity, forming the RhoA/YAP signalling pathway. Upstream pharmacological blockade of RhoA by C3 exoenzyme or downstream blockade of YAP by verteporfin reduced the invasion, migration, and MMP expression of ARPE-19 cells and collagen gel contraction. Furthermore, blockade of RhoA/YAP signalling reduced PVR-induced retinal fibrogenesis and inhibited the TGF-β/Smad pathway in vivo. RhoA/YAP signalling modulates matrix stiffness-induced activation of ARPE-19 cells. Targeting this signalling pathway could alleviate PVR-induced retinal fibrosis and suggests attractive novel therapeutic strategies for intervening in the progression of PVR.

Neuronal and glial regulation of CNS angiogenesis and barriergenesis

Neurovascular pathologies of the central nervous system (CNS), which are associated with barrier dysfunction, are leading causes of death and disability. The roles that neuronal and glial progenitors and mature cells play in CNS angiogenesis and neurovascular barrier maturation have been elucidated in recent years. Yet how neuronal activity influences these processes remains largely unexplored. Here, we discuss our current understanding of how neuronal and glial development affects CNS angiogenesis and barriergenesis, and outline future directions to elucidate how neuronal activity might influence these processes. An understanding of these mechanisms is crucial for developing new interventions to treat neurovascular pathologies.

Invertebrate Retinal Progenitors as Regenerative Models in a Microfluidic System

Regenerative retinal therapies have introduced progenitor cells to replace dysfunctional or injured neurons and regain visual function. While contemporary cell replacement therapies have delivered retinal progenitor cells (RPCs) within customized biomaterials to promote viability and enable transplantation, outcomes have been severely limited by the misdirected and/or insufficient migration of transplanted cells. RPCs must achieve appropriate spatial and functional positioning in host retina, collectively, to restore vision, whereas movement of clustered cells differs substantially from the single cell migration studied in classical chemotaxis models. Defining how RPCs interact with each other, neighboring cell types and surrounding extracellular matrixes are critical to our understanding of retinogenesis and the development of effective, cell-based approaches to retinal replacement. The current article describes a new bio-engineering approach to investigate the migratory responses of innate collections of RPCs upon extracellular substrates by combining microfluidics with the well-established invertebrate model of Drosophila melanogaster. Experiments utilized microfluidics to investigate how the composition, size, and adhesion of RPC clusters on defined extracellular substrates affected migration to exogenous chemotactic signaling. Results demonstrated that retinal cluster size and composition influenced RPC clustering upon extracellular substrates of concanavalin (Con-A), Laminin (LM), and poly-L-lysine (PLL), and that RPC cluster size greatly altered collective migratory responses to signaling from Fibroblast Growth Factor (FGF), a primary chemotactic agent in Drosophila. These results highlight the significance of examining collective cell-biomaterial interactions on bio-substrates of emerging biomaterials to aid directional migration of transplanted cells. Our approach further introduces the benefits of pairing genetically controlled models with experimentally controlled microenvironments to advance cell replacement therapies.

Modeling Retinitis Pigmentosa: Retinal Organoids Generated From the iPSCs of a Patient With the USH2A Mutation Show Early Developmental Abnormalities

Retinitis pigmentosa (RP) represents a group of inherited retinopathies with early-onset nyctalopia followed by progressive photoreceptor degeneration causing irreversible vision loss. Mutations in USH2A are the most common cause of non-syndromic RP. Here, we reprogrammed induced pluripotent stem cells (iPSCs) from a RP patient with a mutation in USH2A (c.8559-2A > G/c.9127_9129delTCC). Then, multilayer retinal organoids including neural retina (NR) and retinal pigment epithelium (RPE) were generated by three-step “induction-reversal culture.” The early retinal organoids derived from the RP patient with the USH2A mutation exhibited significant defects in terms of morphology, immunofluorescence staining and transcriptional profiling. To the best of our knowledge, the pathogenic mutation (c.9127_9129delTCC) in USH2A has not been reported previously among RP patients. Notably, the expression of laminin in the USH2A mutation organoids was significantly lower than in the iPSCs derived from healthy, age- and sex-matched controls during the retinal organogenesis. We also observed that abnormal retinal neuroepithelium differentiation and polarization caused defective retinal progenitor cell development and retinal layer formation, disordered organization of NRs in the presence of the USH2A mutation. Furthermore, the USH2A mutation bearing RPE cells presented abnormal morphology, lacking pigmented foci and showing an apoptotic trend and reduced expression of specific makers, such as MITF, PEDF, and RPE65. In addition, the USH2A mutation organoids had lower expression of cilium-associated (especially CFAP43, PIFO) and dopaminergic synapse-related genes (including DLGAP1, GRIK1, SLC17A7, and SLC17A8), while there was higher expression of neuron apoptotic process-related genes (especially HIF1A, ADARB1, and CASP3). This study may provide essential assistance in the molecular diagnosis and screening of RP. This work recapitulates the pathogenesis of USH2A using patient-specific organoids and demonstrated that alterations in USH2A function due to mutations may lead to cellular and molecular abnormalities.

Early posterior vitreous detachment is associated with LAMA5 dominant mutation

BACKGROUND

Extracellular matrix molecular components, previously linked to multisystem syndromes include collagens, fibrillins and laminins. Recently, we described a novel multisystem syndrome caused by the c.9418G>A p.(V3140M) mutation in the laminin alpha-5 (LAMA5) gene, which affects connective tissues of all organs and apparatus in a three generation family. In the same family, we have also reported a myopic trait, which, however, was linked to the Prolyl 4-hydroxylase subunit alpha-2 (P4HA2) gene. Results of investigation on vitreous changes and their pathogenesis are reported in the present study.

MATERIALS AND METHODS

Nineteen family individuals underwent complete ophthalmic examination including best-corrected visual acuity (BCVA), fundus examination, fundus photography, intraocular pressure measurement, axial length measurement using ocular biometry, Goldmann visual field examination, standard electroretinogram, SD-OCT. Segregation analysis of LAMA5 and P4HA2 mutations was performed in enrolled members.

RESULTS

The vitreous alterations fully segregated with LAMA5 mutation in both young and adult family members. Slight reduction of retinal thickness and peripheral retinal degeneration in only two patients were reported.

CONCLUSIONS

In this work we showed that PVD is a common trait of LAMA5 multisystem syndrome, therefore occurring as an age-unrelated trait. We hypothesize that the p.(V3140M) mutation results in a reduction of retinal inner limiting membrane (ILM) stability, leading to a derangement in the macromolecular structure of the vitreous gel, and PVD. Further investigations will be necessary to elucidate the role of wild type and mutated LAMA5 in the pathogenesis of PVD.

Laminin β2 Chain Regulates Retinal Progenitor Cell Mitotic Spindle Orientation via Dystroglycan

Vertebrate retinal development follows a pattern during which retinal progenitor cells (RPCs) give rise to all retinal cell types in a highly conserved temporal sequence. RPC proliferation and cell cycle exit are tightly coordinated to ensure proper and timely production of each of the retinal cell types. Extracellular matrix (ECM) plays an important role in eye development, influencing RPC proliferation and differentiation. In this study, we demonstrate that laminins, key ECM components, in the inner limiting membrane, control mitotic spindle orientation by providing environmental cues to the RPCs. In vivo deletion of laminin β2 in mice of both sexes results in a loss RPC basal processes and contact with the ECM, leading to a shift of the mitotic spindle pole orientation toward asymmetric cell divisions. This leads to decreased proliferation and premature RPC pool depletion, resulting in overproduction of rod photoreceptors at the expense of bipolar cells and Müller glia. Moreover, we show that deletion of laminin β2 leads to disruption and mislocalization of its receptors: dystroglycan and β1-integrin. Addition of exogenous β2-containing laminins to laminin β2-deficient retinal explants stabilizes the RPC basal processes and directs their mitotic spindle orientation toward symmetric divisions, leading to increased RPC proliferation, as well as restores proper receptor localization at the retinal surface. Finally, functional blocking of dystroglycan in wild-type retinal explants phenocopies laminin β2 ablation. Our data suggest that dystroglycan-mediated signaling between RPCs and the ECM is of key importance in controlling critical developmental events during retinogenesis.SIGNIFICANCE STATEMENT The mechanisms governing retinogenesis are subject to both intrinsic and extrinsic signaling cues. Although the role of intrinsic signaling has been the subject of many studies, our understanding of the role of the microenvironment in retinal development remains unclear. Using a combination of in vivo and ex vivo approaches, we demonstrate that laminins, key extracellular matrix components, provide signaling cues that control retinal progenitor cell attachment to the basement membrane, mitotic axis, proliferation, and fate adoption. Moreover, we identify, for the first time, dystroglycan as the receptor responsible for directing retinal progenitor cell mitotic spindle orientation. Our data suggest a mechanism where dystroglycan-mediated signaling between the cell and the extracellular matrix controls the proliferative potential of progenitors in the developing CNS.

Role of Fibulins 2 and 5 in Retinal Development and Maintenance

Fibulins 2 and 5 are part of a seven-member family of proteins integral to the retinal extracellular matrix. Our study aimed to further explore the roles of both fibulins in retinal function. We obtained knockout mouse models of both fibulins and performed immunohistochemistry, electroretinography, and histology to investigate the outcome of eliminating these proteins. Immunohistochemical analysis showed that both fibulins are localized to the RPE, choroid, and Bruch's membrane. Functional testing showed a significantly reduced scotopic A response at 1 month of age, when compared to their wild-type counterpart. This functional reduction remained constant throughout the age of the animal and only declined as a result of normal aging. The functional decline was associated with reduced number of photoreceptor cells. The results presented clearly demonstrate that fibulins 2 and 5, as extracellular proteins, are necessary for normal retinal development.

Regenerative medicine in the retina: from stem cells to cell replacement therapy

Following the fast pace of the growing field of stem cell research, retinal cell replacement is finally emerging as a feasible mean to be explored for clinical application. Although neuroprotective treatments are able to slow the progression of retinal degeneration caused by diseases such as age-related macular degeneration and glaucoma, they are insufficient to fully halt disease progression and unable to recover previously lost vision. Comprehensive, technological and intellectual advances over the past years, including the in vitro differentiation of retinal cells at manufacturing scale from embryonic stem (ES) cell and induced pluripotent stem (iPS) cell cultures, progress within the area of retinal disease modeling, and the first clinical trials have started to shape the way towards addressing this treatment gap and translating retinal cell replacement to the clinic. Here, summarize the most recent advances within retinal cell replacement from both a scientific and clinical perspective, and discuss the remaining challenges towards the delivery of the first retinal cell products.

Epithelial disruptions, but not immune cell invasion, induced secretory dysfunction following innate immune activation in a novel model of acute salivary gland injury

BACKGROUND

Salivary gland (SG) injurious agents are all translated into loss of salivation (xerostomia). An association has been established between activation of innate immunity and SG injury and dysfunction. However, it remains unclear how the secretory epithelia respond by halting saliva production.

METHODS

C57BL/6 submandibular glands (SMGs) were acutely challenged using a single dose of the innate immune stimulant: polyinosinic-polycytidylic acid (poly (I:C)). Secretory capacity of the infected SMGs was substantiated by assessing the flow rate in response to pilocarpine stimulation. Depletion of the acute inflammatory cells was achieved by pre-treating mice with RB6-8C5 depletion antibody. Flow cytometry, histology and immunohistochemistry were conducted to verify the immune cell depletion. Epithelial expression of saliva-driving molecules: muscarinic 3 receptor (M3R), aquaporin 5 water channel (AQP5), Na-K-CL-Cotransporter 1 (NKCC1) and transmembrane member 16A (TMEM16A), was characterized using RT-qPCR and immunohistochemistry. Tight junction (TJ) protein; zonula occludens (ZO-1) and basement membrane (BM) protein; and laminin were assessed by immunohistochemistry.

RESULTS

Innate immune challenge prompted dysfunction in the exocrine SGs. Dysregulated gene and protein expression of molecules that drive saliva secretion was substantiated. Aberrant expression of TJ and BM proteins followed innate immune activation. Hyposalivation in the current model was independent of myeloperoxidase (MPO)-positive, acute inflammatory cells.

CONCLUSIONS

In this study, we developed a novel injury model of the SGs, featuring acute secretory dysfunction and immediate structural disruptions. Our results ruled out the injurious role of aggressively infiltrating inflammatory cells.

Retinal Proteoglycans Act as Cellular Receptors for Basement Membrane Assembly to Control Astrocyte Migration and Angiogenesis

The basement membrane is crucial for cell polarity, adhesion, and motility, but how it is assembled on the cell surface remains unclear. Here, we find that ablation of glycosaminoglycan (GAG) side chains of proteoglycans in the neuroretina disrupts the retinal basement membrane, leading to arrested astrocyte migration and reduced angiogenesis. Using genetic deletion and time-lapse imaging, we show that retinal astrocytes require neuronal-derived PDGF as a chemoattractive cue and the retinal basement membrane as a migratory substrate. Genetic ablation of heparan sulfates does not produce the same defects as GAG null mutants. In contrast, enzymatic removal of heparan sulfates and chondroitin sulfates together inhibits de novo laminin network assembly. These results indicate that both heparan and chondroitin sulfate proteoglycans participate in retinal basement membrane assembly, thus promoting astrocyte migration and angiogenesis.

Dystroglycan Maintains Inner Limiting Membrane Integrity to Coordinate Retinal Development

Proper neural circuit formation requires the precise regulation of neuronal migration, axon guidance, and dendritic arborization. Mutations affecting the function of the transmembrane glycoprotein dystroglycan cause a form of congenital muscular dystrophy that is frequently associated with neurodevelopmental abnormalities. Despite its importance in brain development, the role of dystroglycan in regulating retinal development remains poorly understood. Using a mouse model of dystroglycanopathy (ISPD^L79* ) and conditional dystroglycan mutants of both sexes, we show that dystroglycan is critical for the proper migration, axon guidance, and dendritic stratification of neurons in the inner retina. Using genetic approaches, we show that dystroglycan functions in neuroepithelial cells as an extracellular scaffold to maintain the integrity of the retinal inner limiting membrane. Surprisingly, despite the profound disruptions in inner retinal circuit formation, spontaneous retinal activity is preserved. These results highlight the importance of dystroglycan in coordinating multiple aspects of retinal development.SIGNIFICANCE STATEMENT The extracellular environment plays a critical role in coordinating neuronal migration and neurite outgrowth during neural circuit development. The transmembrane glycoprotein dystroglycan functions as a receptor for multiple extracellular matrix proteins and its dysfunction leads to a form of muscular dystrophy frequently associated with neurodevelopmental defects. Our results demonstrate that dystroglycan is required for maintaining the structural integrity of the inner limiting membrane (ILM) in the developing retina. In the absence of functional dystroglycan, ILM degeneration leads to defective migration, axon guidance, and mosaic spacing of neurons and a loss of multiple neuron types during retinal development. These results demonstrate that disorganization of retinal circuit development is a likely contributor to visual dysfunction in patients with dystroglycanopathy.

Architecture in 3D cell culture: An essential feature for in vitro toxicology

Three-dimensional cell culture has the potential to revolutionize toxicology studies by allowing human-based reproduction of essential elements of organs. Beyond the study of toxicants on the most susceptible organs such as liver, kidney, skin, lung, gastrointestinal tract, testis, heart and brain, carcinogenesis research will also greatly benefit from 3D cell culture models representing any normal tissue. No tissue function can be suitably reproduced without the appropriate tissue architecture whether mimicking acini, ducts or tubes, sheets of cells or more complex cellular organizations like hepatic cords. In this review, we illustrate the fundamental characteristics of polarity that is an essential architectural feature of organs for which different 3D cell culture models are available for toxicology studies in vitro. The value of tissue polarity for the development of more accurate carcinogenesis studies is also exemplified, and the concept of using extracellular gradients of gaseous or chemical substances produced with microfluidics in 3D cell culture is discussed. Indeed such gradients-on-a-chip might bring unprecedented information to better determine permissible exposure levels. Finally, the impact of tissue architecture, established via cell-matrix interactions, on the cell nucleus is emphasized in light of the importance in toxicology of morphological and epigenetic alterations of this organelle.