USA: Stem Cell Research Helping the Body to Regenerate Joint Cartilage

A study released in Stem Cells moves scientists a step closer to finding how to help the body regenerate joint cartilage ravaged by disease. Their work reveals a new method to quickly and efficiently produce virtually unlimited numbers of chondrocytes, the cells that form cartilage, from human skin cells converted to induced pluripotent stem cells (iPSCs). This could be good news for patients suffering from arthritis.

Durham/USA — While a May 2018 report by Modern Healthcare says that currently over one million joint replacement surgeries occur every year in the United States alone — and that number is expected to exceed four million by 2030 — many medical researchers believe that the future of arthritis therapeutics lies in the application of stem cells to grow new joint cartilage (a process called “chondrogenesis”). Human iPSCs (hiPSCs) are a promising cell source for cartilage regenerative therapies and in vitro disease-modeling systems due to their pluripotency and unlimited proliferation capacity. Furthermore, iPSCs provide a means of developing patient-specific or genetically engineered cartilage to screen for osteoarthritis drugs.

That’s why finding methods to rapidly and efficiently differentiate hiPSCs into chondrocytes in a reproducible and robust manner is critical. Chondrocytes are the cells that produce and maintain the cartilage lining the surfaces of diarthrodial joints — the free-moving types of joints you find, for example, in the hip and knee.

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Farshid Guilak, Ph.D., from Washington University’s Center of Regenerative Medicine and Shriners Hospitals for Children (St. Louis, Missouri) is a co-senior author of the study in Stem Cells along with Charles A. Gersbach, Ph.D., from the Department of Biomedical Engineering at Duke University (Durham, North Carolina). Scientists from Cytex Therapeutics (Durham) and Stanford University (Stanford, Califorinia) also participated. Guilak explains that a disease like arthritis could destroy the cartilage in the joint and escalate inflammation. Ultimately, these changes would lead to pain and loss of function that currently necessitates total joint replacement with an artificial prosthesis.

In their study, the Guilak-Gersbach team demonstrated the development and application of a step-wise differentiation protocol validated in three unique and well-characterized hiPSC lines. They examined gene expression profiles and cartilaginous matrix production during the course of differentiation. To further purify committed chondroprogenitors, they used Crispr-Cas-9 genome engineering technology to knock-in a GFP reporter at the collagen type II alpha 1 chain (Col-2-A1) locus to test the hypothesis that purifying the chondroprogenitors could enhance articular cartilage-like matrix production.

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Most differentiation protocols to date have been based on trial-and-error delivery of growth factors without immediate consideration of the signaling pathways that direct and inhibit each stage of differentiation. Accordingly, chondrogenic differentiation is often dependent on the specific cell lines used, and broad application of iPSC chondrogenesis protocols has not been independently demonstrated with multiple cell lines and in multiple laboratories.

Recently, critical insights from developmental biology have elucidated the sequence of signaling pathways needed for PSC lineage specification to a number of cell fates.

By reproducing these reported signaling pathways in vitro, in combination with existing chondrogenic differentiation approaches, the scientists sought to establish a rapid and highly reproducible protocol for hiPSC chondrogenesis that is broadly applicable across various hiPSC lines. Chia-Lung Wu, Ph.D., the co-first author of the study, said that since hiPSC differentiation processes were inherently unpredictable and could often produce heterogeneous cell populations over the course of differentiation, an important goal of differentiation protocols was to minimize variability in hiPSC differentiation potential, which might arise from characteristics of the donor and/or reprogramming method. Therefore, they hypothesized that purifying the committed chondroprogenitors would improve hiPSC chondrogenesis. The method obtained the desired results.

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The purified chondroprogenitors demonstrated an improved chondrogenic capacity compared to unselected populations.The development of processes for rapid and repeatable induction of iPSCs into joint cell tissue will hopefully enable the identification of novel therapies for joint diseases such as osteoarthritis. According to Jan Nolta, Ph.D., Editor-in-Chief of Stem Cells, the elegant techniques used by the the Guilak-Gersbach team generated improved numbers of pure chondroprogenitors, a step that was crucially needed to propel the promising field of stem cell- mediated cartilage repair forward.

Access the full article, “Step-Wise Chondrogenesis of Human Induced Pluripotent Stem Cells and Purification Via a Reporter Allele Generated by CRISPR-Cas9 Genome Editing”

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