Interfacial Tissue Regeneration with Bone

PURPOSE OF REVIEW

Interfacial tissue exists throughout the body at cartilage-to-bone (osteochondral interface) and tendon-to-bone (enthesis) interfaces. Healing of interfacial tissues is a current challenge in regenerative approaches because the interface plays a critical role in stabilizing and distributing the mechanical stress between soft tissues (e.g., cartilage and tendon) and bone. The purpose of this review is to identify new directions in the field of interfacial tissue development and physiology that can guide future regenerative strategies for improving post-injury healing.

RECENT FINDINGS

Cues from interfacial tissue development may guide regeneration including biological cues such as cell phenotype and growth factor signaling; structural cues such as extracellular matrix (ECM) deposition, ECM, and cell alignment; and mechanical cues such as compression, tension, shear, and the stiffness of the cellular microenvironment. In this review, we explore new discoveries in the field of interfacial biology related to ECM remodeling, cellular metabolism, and fate. Based on emergent findings across multiple disciplines, we lay out a framework for future innovations in the design of engineered strategies for interface regeneration. Many of the key mechanisms essential for interfacial tissue development and adaptation have high potential for improving outcomes in the clinic.

Abstract P2121: Modeling Genetic Dilated Cardiomyopathies With Engineered Heart Tissues From Patient-derived And Isogenic Mutant Induced Pluripotent Stem Cells

The availability of human induced pluripotent stem cells (hiPSCs) has offered the possibility to study human-derived models of different genetic strata of cardiomyopathy for mechanistic discovery and therapeutic development. However, the phenotypes derived from cardiomyocytes differentiated from hiPSCs in conventional 2-dimensional culture systems often fail to reproducibly model clinical presentations, thereby reducing the translatability of readouts from these assays. Here we report 3-dimensional engineered heart tissues (EHTs) produced with a variety of cell lines harboring patient-derived mutations (TTN, RBM20, BAG3) known to cause dilated cardiomyopathy (DCM) which recapitulate contractile deficits associated with DCM. Internal development of EHTs also recapitulate contractile defects with small interfering RNA (siRNA) knockdown models of haploinsufficiency across multiple disease states. These observed findings with EHTs suggests improved maturity in cardiomyocytes through the presentation of microenvironmental cues akin to those seen in vivo . With continued advances in EHT technologies and capabilities, this platform may serve to significantly reduce drug candidate attrition, as well as provide new insights into pathology, prototyping of therapeutic approaches, and mechanism of action that were previously difficult to obtain.

Abstract P436: Modeling Genetic Dilated Cardiomyopathy Using Induced Pluripotent Stem Cell-derived Engineered Heart Tissues For Precision Medicine

Recent advancement of human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) technologies has opened the door to next-generation modeling of human cardiac biology and disease. Not only does this alleviate the need for human primary tissue and compensate for the well documented deficiencies of rodent models for cardiovascular disease, but these technologies may lead to the identification of better candidates for clinical development. Unfortunately, most current 2D hiPSC-CM models lack the biochemical, mechanical, and electrical feedback that cardiomyocytes endure in a multi-cellular aligned tissue, which limits their translatability into clinical settings. To address this, we incorporated hiPSC-CMs modeling various genetic dilated cardiomyopathies (DCM) into 3D engineered heart tissues (EHTs). Here, we show these models develop distinguishable contractile defects recapitulating hallmarks of DCM when compared to biologically relevant controls. Moreover, this distinct phenotype is quantitative, reproducible, and demonstrates utility for drug discovery. As this innovative technology continues to develop, EHTs are on the forefront of emerging biomimetic assays that can be used to prevent drug attrition in the late stages of drug development.

Human iPSC Modeling Reveals Mutation-Specific Responses to Gene Therapy in a Genotypically Diverse Dominant Maculopathy

Dominantly inherited disorders are not typically considered to be therapeutic candidates for gene augmentation. Here, we utilized induced pluripotent stem cell-derived retinal pigment epithelium (iPSC-RPE) to test the potential of gene augmentation to treat Best disease, a dominant macular dystrophy caused by over 200 missense mutations in BEST1. Gene augmentation in iPSC-RPE fully restored BEST1 calcium-activated chloride channel activity and improved rhodopsin degradation in an iPSC-RPE model of recessive bestrophinopathy as well as in two models of dominant Best disease caused by different mutations in regions encoding ion-binding domains. A third dominant Best disease iPSC-RPE model did not respond to gene augmentation, but showed normalization of BEST1 channel activity following CRISPR-Cas9 editing of the mutant allele. We then subjected all three dominant Best disease iPSC-RPE models to gene editing, which produced premature stop codons specifically within the mutant BEST1 alleles. Single-cell profiling demonstrated no adverse perturbation of retinal pigment epithelium (RPE) transcriptional programs in any model, although off-target analysis detected a silent genomic alteration in one model. These results suggest that gene augmentation is a viable first-line approach for some individuals with dominant Best disease and that non-responders are candidates for alternate approaches such as gene editing. However, testing gene editing strategies for on-target efficiency and off-target events using personalized iPSC-RPE model systems is warranted. In summary, personalized iPSC-RPE models can be used to select among a growing list of gene therapy options to maximize safety and efficacy while minimizing time and cost. Similar scenarios likely exist for other genotypically diverse channelopathies, expanding the therapeutic landscape for affected individuals.