Longevity Briefs: Rewinding The Ageing Clock To Cure Back Pain

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

The problem:

Back pain is a common problem in old age, and part of this problem can be traced to cells in the spine called nucleus pulposus cells. These cells maintain the discs that sit between the vertebrae, allowing the spine to flex and absorb shocks. Nucleus pulposus cells lose their function with age, undergoing age-related changes like senescence (losing the ability to multiply), leading to disk shrinkage and problems like posture change, nerve compression and increased pressure on the spine.

One exciting strategy for rejuvenating aged cells is partial epigenetic reprogramming. During ageing, cells accumulate epigenetic modifications – alterations to and around the DNA molecule that change how it is read, without changing the genetic code itself. Research has shown that by exposing cells to molecules called reprogramming factors, these epigenetic modifications can be erased, which also erases all signs of ageing. It is important not to erase all epigenetic modifications, since some of them are tied to the cell’s identity (all cells have the same DNA, but the epigenetic modifications are what makes a heart cell a heart cell, for example). Fortunately, by carefully controlling the exposure to reprogramming factors, it is possible to partially reprogram a cell, reversing age-related epigenetic changes without erasing the cell’s identity. That is the strategy that researchers employ here in a an attempt rejuvenate intervertebral discs in rats.

The discovery:

In order to partially reprogram nucleus pulposus cells, researchers engineered a plasmid (a circular piece of DNA) to contain genes coding for three reprogramming factors (Oct4, Klf4, and Sox2) abbreviated to OKS. One of the main challenges of partial reprogramming is delivering reprogramming factors to the intended cells, so to achieve this, the researchers also engineered exosomes. These are tiny membrane packages naturally released by cells to deliver genetic material and signalling molecules to other cells via the blood. The researchers isolated exosomes released from bone marrow stem cells and modified them with Cavin2, a protein that enhances exosome uptake.

As a first test, the researchers took rat nucleus pulposus cells that had become senescent and treated them with their exosomes loaded with OKS plasmids. They found that this treatment effectively reduced molecular markers of senescence, decreased DNA damage, and restored the cells’ ability to proliferate. Encouraged by these results, they performed an animal experiment with four groups of 5 rats whose intervertebral discs had been surgically damaged, and one intact (sham) group as a control. Each experimental group received injections into the nucleus pulposus: one group received saline solution as a control treatment, one received empty exosomes, one received OKS plasmids on their own, and one received exosomes loaded with OKS plasmids.

The results showed that rats treated with OKS plasmid-containing exosomes had improved intervertebral disc height, nucleus pulposus hydration, tissue structure and behaviours related to pain reduction when compared to other treatments. By several metrics, these rats were indistinguishable from rats that had never been injured in the first place. Plasmids or exosomes alone, on the other hand, were in most cases not statistically significantly better than saline solution. Analysis of gene expression also suggested a reduction in senescence as found in the previous cell culture experiments. Similar results were also found in human nucleus pulposus tissue samples that were collected from human patients with disc degeneration.

The implications:

This research offers hope for a promising new approach to treating disc degeneration, but there is still a very long way to go. While partial reprogramming is an exciting technology that could potentially be applied to all age-related diseases, its use in humans has to be approached with caution due to the risk of accidentally reprogramming cells too far, erasing their identity and causing them to become stem cells. Furthermore, the rats in this study had their discs artificially damaged by puncturing, which is obviously not the same as age-related damage sustained by humans over decades. While the results from human tissue samples are encouraging, this research is still in its early stages.