Research topic: Investigating whether a synthetic gene circuit engineered to alter the pathway that forms bone from cartilage can enhance cartilage regeneration.
Research results: Determination of whether regulating the transcription factor responsible for giving instructions for building bones (RUNX2) using a closed-loop synthetic gene circuit will improve cartilage tissue formed by isolated patient-derived cells.
Patient care application of results: Making autologous chondrocyte implantations more effective in repairing traumatic cartilage damage of the knee, reducing the chance of premature osteoarthritis
Simplified patient care application: Better options for repairing cartilage to replace damaged tissue and prevent osteoarthritis
Oh, My Aching Knees
OREF-AOSSM grant recipient working to advance articular cartilage regeneration
Targeted drug therapies that enlist an individual’s metabolism to combat cancer cells are bringing new hope to patients while fueling advances in synthetic biology. Can orthopaedic researchers build on that success to create customized therapies that will regenerate cartilage tissue?
University of Michigan Assistant Professor Rhima M. Coleman, PhD, believes the answer is, “yes.”
Dr. Coleman’s interest in orthopaedic research was inspired by her mother, who was diagnosed with osteoporosis at age 28. “I went to grad school with a grand ambition that I would cure osteoporosis through tissue engineering,” said Dr. Coleman, describing her dream as “ridiculous.” And yet, she has gone on to participate in and lead studies in multiple tissue engineering topic areas. In addition, imaging techniques that Dr. Coleman developed are being used to research defects in the growth plate due to injury and genetic diseases. Now, Dr. Coleman has her sights on cartilage repair.
Problem acute, patience required
The potential for effective therapies to heal cartilage is vast,” Dr. Coleman said. Her research is focused on these therapies because, “everyone has bad knees.” In fact, asymptomatic knee osteoarthritis (OA) is on the rise. OA is the 11th highest contributor to global disability, up from 15th place in 1990. This trend is expected to continue as the population continues to age.1
Dr. Coleman successfully applied for a 2018 Orthopaedic Research and Education Foundation (OREF) Soft Tissue Repair and Regeneration Sports Medicine Grant in Honor of Dr. Russell Warren. Awarded by OREF in partnership with American Orthopaedic Society for Sports Medicine (AOSSM), the grant provides $225,000 to support the development of new cell and tissue-based strategies to prevent, repair, regenerate, or replace injured musculoskeletal tissues.
Broadly, Dr. Coleman hopes to extend the life and optimize performance of articular joints through customized therapies based on patient-specific metrics. More specifically, she is looking for ways to improve outcomes for autologous chondrocyte implantation (ACI) procedures used to repair damaged cartilage and prevent premature OA of the knee.
“Stem cells can do many things, but they can’t make cartilage very well, and that is because the endochondral ossification pathway that makes bone from cartilage occurs whether you want it to or not.”
Dr. Coleman wanted to find a way to prevent cartilage from mineralizing into bone and wondered if chondrocytes could be reprogrammed so that they resisted the urge to transition from the cartilage to the bone phenotype. If they could, she might have a solution for engineering cartilage.
The personalized tissue engineering therapies that Dr. Coleman hypothesizes won’t come quickly. Significant advances in understanding cartilage repair are required, which depend on exploring new ways of genetically reprogramming aged cartilage cells with the help of synthetic gene circuits.
Synthetic gene circuits are key building blocks for personalized medicine, which enlists human cells as therapeutic agents. When successful, these circuits are able to override or control human cell functions with high precision, on a per-patient basis, toward treating a range of diseases and conditions.
Modulation is key
The central hypothesis of Dr. Coleman’s OREF-AOSSM-supported study is that ACI outcomes can be improved for patients over age 50 by reducing the impact of a specific transcription factor: RUNX2, the gene responsible for giving instructions for building bone and cartilage.2
“RUNX2 is a vital transcription factor, so we can’t just silence it completely,” Dr. Coleman explained. “We have to understand how varying different parts of the gene circuit will affect its activity, and how affecting that activity affects the important outcomes, which are matrix production.”
To modulate the effects of RUNX2, Dr. Coleman is testing a closed-loop gene circuit that her team developed. The study calls for the circuit to be introduced into human chondrocytes and then implanted in a rodent model, where its functionality will be measured over time.
With the help of cell donors and knee replacement patients at Michigan Medicine and the University of Michigan Department of Orthopaedics, the research team is collecting osteoarthritic cartilage cell samples from patients aged 50–75 and comparing them to cells from patients aged 30–40.
Dr. Coleman and her team want to know how modification of the circuit itself affects chondrocyte behavior and whether it can be used to improve procedures such as ACI.
In the lab, team members reprogram half the collected cell samples, introducing the gene circuit with a modified lentivirus. The other half of the collected cell samples are reserved as controls.
The modified cell samples are examined for the levels of RUNX2 expression over time, that is, whether the gene circuit has been successful in reprogramming the damaged cells. Then the functionality of the reprogrammed cell samples is compared with that of the control samples by measuring matrix production.
Dr. Coleman expects to find the reprogramed cell samples will show clinically relevant improved cartilage repair, including increased levels of aggrecan and collage II content, improved graft integration, and restoration of the healthy subchondral bone. She also expects the reprogramed cells will generate a higher volume of cartilage tissue and will maintain lower RUNX2 expression levels.
In the near future, with the data this study yields, Dr. Coleman expects to secure R01 grant funding from the National Institutes of Health that will support an investigation of how patient metrics, including age, sex, health history and co-morbidities, contribute to synthetic gene circuit modulation of the RUNX2 pathway in chondrocytes. The results of this research will represent an important step toward patient-specific therapies designed to optimize cartilage performance.
Provided the gene circuit is successful in producing functional cartilage tissue, it can also help other research teams. The circuit could be used as a test bed for other genetic targets and to farm engineered cartilage tissue for use in studies designed to develop drugs capable of improving ACI outcomes.
Research teams often comprise both clinicians and PhD researchers. Bringing together the ideas of both can aid in solving problems, such as finding new ways to repair cartilage. OREF grants encourage these collaborations.
“As a researcher, I encourage clinicians to solve problems creatively. Research is part of that process, and I think supporting the OREF is important because it is focused on educating the next generation of surgeons and showing them how research can be tied directly into their clinical practices” Dr. Coleman said.
Sharon Johnson is a contributing writer for OREF. She can be reached at firstname.lastname@example.org.
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Guillemin F, Hill CL, Laslett LL, Jones G, Cicuttini F, Osborne R, Vos T, Buchbinder R,
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global burden of disease 2010 study. Ann Rheum Dis. 2014;73(7):1323-30. doi:
10.1136/annrheumdis-2013-204763. PubMed PMID: 24553908.
2. RUNX2 gene. Genetics Home Reference. https://ghr.nlm.nih.gov/gene/RUNX2#synonyms. Published 2020. Accessed February 3, 2020.