Guided tissue organization and disease modeling in a kidney tubule array

Minimal Kidney Disease Phenotype in Shroom3 Heterozygous Null Mice

Background

Shroom family member 3 (SHROOM3) encodes an actin-associated protein that regulates epithelial morphology during development. Several genome-wide association studies (GWAS) have identified genetic variances primarily in the 5' region of SHROOM3, associated with chronic kidney disease (CKD) and poor transplant outcomes. These genetic variants are associated with alterations in Shroom3 expression.

Objective

Characterize the phenotypic abnormalities associated with reduced Shroom3 expression in postnatal day 3-, 1-month and 3-month-old mice.

Methods

The Shroom3 protein expression pattern was determined by immunofluorescence. We generated Shroom3 heterozygous null mice (Shroom3Gt/+) and performed comparative analyses with wild type littermates based on somatic and kidney growth, gross renal anatomy, renal histology, renal function at postnatal day 3, 1 month, and 3 months.

Results

The Shroom3 protein expression localized to the apical regions of medullary and cortical tubular epithelium in postnatal wild type kidneys. Co-immunofluorescence studies confirmed protein expression localized to the apical side of the tubular epithelium in proximal convoluted tubules, distal convoluted tubules, and collecting ducts. While Shroom3 heterozygous null mice exhibited reduced Shroom3 protein expression, no differences in somatic and kidney growth were observed when compared to wild type mice. Although, rare cases of unilateral hypoplasia of the right kidney were observed at postnatal 1 month in Shroom3 heterozygotes. Yet renal histological analysis did not reveal any overt abnormalities in overall kidney structure or in glomerular and tubular organization in Shroom3 heterozygous null mice when compared to wild type mice. Analysis of the apical-basolateral orientation of the tubule epithelium demonstrated alterations in the proximal convoluted tubules and modest disorganization in the distal convoluted tubules at 3 months in Shroom3 heterozygotes. Additionally, these modest abnormalities were not accompanied by tubular injury or physiological defects in renal and cardiovascular function.

Conclusion

Taken together, our results describe a mild kidney disease phenotype in adult Shroom3 heterozygous null mice, suggesting that Shroom3 expression and function may be required for proper structure and maintenance of the various tubular epithelial parenchyma of the kidney.

MiR-29a-deficiency causes thickening of the basilar membrane and age-related hearing loss by upregulating collagen IV and laminin

Age-related hearing loss (ARHL) is the most common sensory degenerative disease and can significantly impact the quality of life in elderly people. A previous study using GeneChip miRNA microarray assays showed that the expression of miR-29a changes with age, however, its role in hearing loss is still unclear. In this study, we characterized the cochlear phenotype of miR-29a knockout (miR-29a^-/-) mice and found that miR-29a-deficient mice had a rapid progressive elevation of the hearing threshold from 2 to 5 months of age compared with littermate controls as measured by the auditory brainstem response. Stereocilia degeneration, hair cell loss and abnormal stria vascularis (SV) were observed in miR-29a^-/- mice at 4 months of age. Transcriptome sequencing results showed elevated extracellular matrix (ECM) gene expression in miR-29a^-/- mice. Both Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that the key differences were closely related to ECM. Further examination with a transmission electron microscope showed thickening of the basilar membrane in the cochlea of miR-29a^-/- mice. Five Col4a genes (Col4a1-a5) and two laminin genes (Lamb2 and Lamc1) were validated as miR-29a direct targets by dual luciferase assays and miR-29a inhibition assays with a miR-29a inhibitor. Consistent with the target gene validation results, the expression of these genes was significantly increased in the cochlea of miR-29a^-/- mice, as shown by RT-PCR and Western blot. These findings suggest that miR-29a plays an important role in maintaining cochlear structure and function by regulating the expression of collagen and laminin and that the disturbance of its expression could be a cause of progressive hearing loss.

Bioengineering Strategies To Develop Podocyte Culture Systems

Unraveling the complex behavior of healthy and disease podocytes by analyzing the changes in their unique arrangement of foot processes, slit diaphragm and the 3D morphology is a long-standing goal in kidney-glomerular research. The complexities surrounding the podocytes' accessibility in animal models and growing evidence of differences between humans and animal systems have compelled researchers to look for alternate approaches to study podocyte behaviors. With the advent of bioengineered models, an increasingly powerful and diverse set of tools is available to develop novel podocyte culture systems. This review discusses the pertinence of various culture models of podocytes to study podocyte mechanisms in both normal physiology and disease conditions. While no one in vitro system comprehensively recapitulates podocytes' in vivo architecture, we emphasize how the existing systems can be exploited to answer targeted questions on podocyte structure and function. We highlight the distinct advantages and limitations of using these models to study podocyte behaviors and screen therapeutics. Finally, we discuss various considerations and potential engineering strategies for developing next-generation complex 3D culture models for studying podocyte behaviors in vitro.

Fabrication approaches for high-throughput and biomimetic disease modeling

There is often a tradeoff between in vitro disease modeling platforms that capture pathophysiologic complexity and those that are amenable to high-throughput fabrication and analysis. However, this divide is closing through the application of a handful of fabrication approaches-parallel fabrication, automation, and flow-driven assembly-to design sophisticated cellular and biomaterial systems. The purpose of this review is to highlight methods for the fabrication of high-throughput biomaterial-based platforms and showcase examples that demonstrate their utility over a range of throughput and complexity. We conclude with a discussion of future considerations for the continued development of higher-throughput in vitro platforms that capture the appropriate level of biological complexity for the desired application. STATEMENT OF SIGNIFICANCE: There is a pressing need for new biomedical tools to study and understand disease. These platforms should mimic the complex properties of the body while also permitting investigation of many combinations of cells, extracellular cues, and/or therapeutics in high-throughput. This review summarizes emerging strategies to fabricate biomimetic disease models that bridge the gap between complex tissue-mimicking microenvironments and high-throughput screens for personalized medicine.

A Multitubular Kidney-on-Chip to Decipher Pathophysiological Mechanisms in Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a major renal pathology provoked by the deletion of PKD1 or PKD2 genes leading to local renal tubule dilation followed by the formation of numerous cysts, ending up with renal failure in adulthood. In vivo, renal tubules are tightly packed, so that dilating tubules and expanding cysts may have mechanical influence on adjacent tubules. To decipher the role of this coupling between adjacent tubules, we developed a kidney-on-chip reproducing parallel networks of tightly packed tubes. This original microdevice is composed of cylindrical hollow tubes of physiological dimensions, parallel and closely packed with 100-200 μm spacing, embedded in a collagen I matrix. These multitubular systems were properly colonized by different types of renal cells with long-term survival, up to 2 months. While no significant tube dilation over time was observed with Madin-Darby Canine Kidney (MDCK) cells, wild-type mouse proximal tubule (PCT) cells, or with PCT Pkd1 +/- cells (with only one functional Pkd1 allele), we observed a typical 1.5-fold increase in tube diameter with isogenic PCT Pkd1 -/- cells, an ADPKD cellular model. This tube dilation was associated with an increased cell proliferation, as well as a decrease in F-actin stress fibers density along the tube axis. With this kidney-on-chip model, we also observed that for larger tube spacing, PCT Pkd1 -/- tube deformations were not spatially correlated with adjacent tubes whereas for shorter spacing, tube deformations were increased between adjacent tubes. Our device reveals the interplay between tightly packed renal tubes, constituting a pioneering tool well-adapted to further study kidney pathophysiology.

Aligned Silk Sponge Fabrication and Perfusion Culture for Scalable Proximal Tubule Tissue Engineering

Chronic kidney disease and kidney failure are on the rise globally, yet there has not been a corresponding improvement in available therapies. A key challenge in a biological approach to developing kidney tissue is to identify scaffolding materials that support cell growth both in vitro and in vivo to facilitate translational goals. Scaffolds composed of silk fibroin protein possess the biocompatibility, mechanical robustness, and stability required for tissue engineering. Here, we use a silk sponge system to support kidney cells in a perfused bioreactor system. Silk fibroin protein underwent directional freezing to form parallel porous structures that mimic the native kidney structure of aligned tubules and are able to support more cells than nonaligned silk sponges. Adult immortalized renal proximal tubule epithelial cells were seeded into the sponges and cultured under static conditions for 1 week, then grown statically or with perfusion with culture media flowing through the sponge to enhance cell alignment and maturation. The sponges were imaged with confocal and scanning electron microscopies to analyze and quantify cell attachment, alignment, and expression of proteins important to proximal tubule differentiation and function. The perfused tissue constructs showed higher number of cells that are more evenly distributed through the construct and increased gene expression of several key markers of proximal tubule epithelial cell function compared to sponges grown under static conditions. These perfused tissue constructs represent a step toward a scalable approach to engineering proximal tubule structures with the potential to be used as in vitro models or as in vivo implantable tissues to supplement or replace impaired kidney function.

Organ-on-a-Chip Systems for Modeling Pathological Tissue Morphogenesis Associated with Fibrosis and Cancer

Tissue building does not occur exclusively during development. Even after a whole body is built from a single cell, tissue building can occur to repair and regenerate tissues of the adult body. This confers resilience and enhanced survival to multicellular organisms. However, this resiliency comes at a cost, as the potential for misdirected tissue building creates vulnerability to organ deformation and dysfunction-the hallmarks of disease. Pathological tissue morphogenesis is associated with fibrosis and cancer, which are the leading causes of morbidity and mortality worldwide. Despite being the priority of research for decades, scientific understanding of these diseases is limited and existing therapies underdeliver the desired benefits to patient outcomes. This can largely be attributed to the use of two-dimensional cell culture and animal models that insufficiently recapitulate human disease. Through the synergistic union of biological principles and engineering technology, organ-on-a-chip systems represent a powerful new approach to modeling pathological tissue morphogenesis, one with the potential to yield better insights into disease mechanisms and improved therapies that offer better patient outcomes. This Review will discuss organ-on-a-chip systems that model pathological tissue morphogenesis associated with (1) fibrosis in the context of injury-induced tissue repair and aging and (2) cancer.