Intervertebral disc degeneration is a feature of aging, and injury can produce further challenges. A range of approaches have been assessed to enhance the regenerative capacity of disc tissue, useful not just after injury, but also to reverse some of the declines in disc structure and function produced by aging. Stem cell therapies have been attempted, and are widely available via medical tourism, but unfortunately that diverse population of patients contributes next to no publicly available data to help researchers understand whether or not this is a viable approach, and how to improve on it. First generation stem cell therapies are gradually being replaced by exosome therapies, as these are logistically easier to manage. Exosomes can be harvested and stored, it is easier to produce consistent batches from one central location for manufacture, and the benefits of stem cell therapies are in any case mediated by the signaling produced by these cells, largely carried in extracellular vesicles such as exosomes.

Thus in today’s open access paper, we see an example of researchers building on the exosome therapy approach rather than the cell therapy approach. Beyond the logistics, another advantage of exosomes is that they can be readily engineered to carry additional cargo into cells. In this case, researchers are delivery a DNA plasmid to express FOXF1. The usual challenge with DNA plasmids is that they express poorly, as passage into the cell nucleus and access to transcriptional machinery that can read the plasmid only efficiently occurs during cell division. The researchers used an injury model in mice, so there will tend to be more cellular replication in this circumstance as regeneration takes place. In any case, the researchers observed improvements in the treated mice versus controls. We are likely to see a range of similar approaches based on the use of extracellular vesicles as a gene therapy vector emerge in the years ahead.

Engineered extracellular vesicle-based gene therapy for the treatment of discogenic back pain

Painful musculoskeletal disorders such as chronic low back pain (LBP) are leading causes of disability worldwide and their prevalence and societal impact continues to rise with expansion of the aging population and growing opioid crisis. Intervertebral disc (IVD) degeneration is a major cause of LBP, often referred to as discogenic back pain (DBP), with epidemiological studies estimating that approximately 40% of cases are attributed to IVD degeneration. The IVD functions as an avascular and aneural joint, sandwiched between adjacent vertebral bodies of the spinal column. It is comprised of a gelatinous proteoglycan-rich nucleus pulposus (NP) core encapsulated by rings of collagen that form the annulus fibrosus (AF). In degeneration, mechanical imbalances, loss of critical extracellular matrix (ECM) components such as proteoglycans, increased catabolism, inflammation, and neurovascular invasion contribute to a detrimental shift in homeostasis that leads to the loss of tissue function and increased pain.

n previous studies, we have demonstrated the potential of developmental transfection factors such as Brachyury (T) and Forkhead Box F1 (FOXF1), both of which are healthy immature NP markers involved in growth during development, to drive cellular reprogramming of diseased human NP cells to a pro-anabolic phenotype in vitro. These studies also highlight the feasibility of using engineered extracellular vesicles (eEVs) to mediate the delivery of FOXF1 to diseased cells, and their potential to be used as a minimally invasive gene delivery mechanism.

Here we have developed a novel non-viral gene therapy, using eEVs to deliver FOXF1 to the degenerated IVD in an in vivo model. Injured IVDs treated with eEVs loaded with FOXF1 demonstrated robust sex-specific reductions in pain behaviors compared to control groups. Furthermore, significant restoration of IVD structure and function in animals treated with FOXF1 eEVs were observed, with significant increases in disc height, tissue hydration, proteoglycan content, and mechanical properties. This is the first study to successfully restore tissue function while modulating pain behaviors in an animal model of DBP using eEV-based non-viral delivery of transcription factor genes. Such a strategy can be readily translated to other painful musculoskeletal disorders.

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