Innovations in Joint Biomimetics and Stem Cells

Human pluripotent stem cells (hPSCs) have been identified by researchers and the pharmaceutical industry as valuable tools for generating models of both rare and more common diseases, particularly monogenic disorders that originate during fetal development. These cells can be expanded almost indefinitely and have the potential to differentiate into any cell type in the body.

The advent of complex differentiation protocols to generate organoids and other 3D assemblies of cells has further increased interest in hPSC models and improved their validity. In our lab, we have generated models for kidney, skeletal, and neural tissues, enabling us to investigate how development is altered in rare conditions caused by monogenic mutations.

Our aim is to identify early cellular and molecular changes in human fetal tissue development and to pinpoint target genes that could serve as the basis for drug repositioning or discovery. We hypothesize that timely use of such drugs could prevent or reverse developmental abnormalities during childhood. To date, we have identified such pathways in several distinct diseases.

As an example, I will highlight our use of an hPSC-based growth plate cartilage development model, which we validated through comparison to human limb development using single-nucleus RNA sequencing (snRNA-seq). We used this model to investigate the mechanisms underlying growth plate abnormalities resulting from heterozygous mutations in Matrilin 3, which cause Multiple Epiphyseal Dysplasia (MED)—a form of chondrodysplasia characterized by early joint pain and moderate short stature.

We generated CRISPR-Cas9-edited heterozygous mutant hPSCs and compared them to patient-derived iPSC lines and unaffected control lines. RNA-seq analysis revealed that similar pathways were disrupted in both the CRISPR-edited and patient-derived iPSCs compared to controls after differentiation into cartilage organoids.

While homozygous mouse models of the disease exhibit endoplasmic reticulum (ER) stress, we observed only mild signs of this in our hPSC-derived chondrocytes (correlating with high MTN expression). However, we identified disrupted cellular lipid synthesis and abnormal extracellular matrix assembly in the human mutant models.

We are now using our models to further investigate cellular mechanisms in other monogenic skeletal disorders, including Pseudoachondroplasia (PSACH) and Acrodysostosis, as well as the effects of inflammation on skeletal development.

Joint diseases such as osteoarthritis (OA) are highly prevalent and represent the leading cause of physical disability worldwide. While restorative surgeries have seen significant success, functional biological reconstruction of diseased or traumatized articular tissues remains an unmet medical need. This is largely due to our limited understanding of disease mechanisms and the inherent challenges in engineering functionally mature articular tissues.

Recent advances in tissue engineering have enabled functional regeneration at both macro- and micro-scales. Macro-scale efforts have primarily focused on the development of regenerative implants, while micro-scale approaches have centered on disease modeling and drug testing.

This lecture will explore the promises and challenges of stem cell- and smart biomaterial-based strategies in articular tissue engineering. Key topics include:

1. Biological optimization of stem cell differentiation and maturation
2. Design and fabrication of biomimetic 3D biomaterial scaffolds
3. Development of a human stem cell-derived joint-on-a-chip system—miniJoint—for modeling OA pathogenesis and screening candidate therapeutics.

These studies underscore the potential of stem cell-based tissue engineering to generate both functional biological implants and physiologically relevant OA models. Ultimately, successful tissue engineering requires multidisciplinary, convergent collaboration with a strong focus on both physiological function and structural integrity—working toward the goal to repair, restore, and re-create articular tissues.