Targeting circadian clock mechanisms in the intervertebral disc towards therapies for low back pain

Low back pain (LBP), caused by degeneration of the fibro-cartilaginous intervertebral disc in the spine, is amongst the most prevalent spinal diseases. It affects millions of individuals worldwide, causing severe pain and loss of mobility, with currently no long-term cure. Ageing is a major risk factor. However, we do not fully understand why age increases susceptibility to disc degeneration and LBP. Body clocks are responsible for generating 24 hour rhythms in behaviour and physiology. Rhythm disruptions by ageing or shift work can significantly increase disease risks. Crucially, our group, for the first time, has discovered a functional body clock in the intervertebral disc. This peripheral body clock weakens with age and its disruption leads to tissue damage characteristic of disc degeneration. This project will establish the disease relevance and explore the therapeutic potential of the body clocks in this tissue. Specifically, we will use our novel disc "clockless" mouse model, intervertebral disc explant culture and patient samples to test the following hypotheses: 1). Daily loading cycle associated with rest/activity can reset the IVD circadian rhythm; 2). Disruption to the IVD circadian rhythm compromises tissue homeostasis/integrity, and leads to increased susceptibility to degeneration; 3). Targeting IVD clock mechanisms provide a novel therapeutic approach for disc degeneration. Our research holds strong potential to identify novel therapeutic strategies for low back pain and therefore has an enormous potential for improving health and quality of life. Moreover, our findings emphasize the importance of maintaining robust body clocks through healthy life styles, which will have a long lasting impact on the health and well-being of the ageing population. This is particularly important because the greying of the population and the ever-increasing demands of our modern 24/7 society frequently disrupt our body clocks which can significantly increase risk of many diseases.

Circadian clocks drive ~24 hour rhythms in nearly all aspects of physiology and behavior. Changes of circadian rhythms during ageing underpin many of the age-associated pathologies. Low back pain (LBP) is amongst the most prevalent spinal diseases associated with old age. It causes severe pain and loss of mobility, with currently no long-term cure. Progressive degeneration of the intervertebral disc (IVD) tissue is a major contributing factor. However, how susceptibility to IVD degeneration and LBP increases with age is poorly understood. Our preliminary data demonstrates cell autonomous circadian clocks in mouse intervertebral disc tissue and human disc cells. Significantly, our circadian transcriptome profiling data strongly implicate the circadian clock as a key regulatory mechanism for genes involved in disc tissue homeostasis. Therefore, it is timely to explicitly demonstrate the mechanistic links between the IVD clock and disc tissue homeostasis. Specifically, this research will combine our unique transgenic mouse, ex vivo disc explant and experiments utilising human IVDs to test the following hypotheses: 1) Daily osmotic changes associated with diurnal loading cycle can entrain the IVD circadian rhythm; 2) Disruption to the disc circadian rhythm compromises IVD homeostasis and leads to increased susceptibility to degeneration; 3) Targeting IVD clock mechanisms provides a novel approach to modulate the expression/activity of processes linked to disc degeneration. Key methodologies will include histology, RNAseq, qPCR and Western Blotting analysis to measure rhythmic patterns of gene expression, lentiviral gene delivery, real time bioluminescence monitoring of the dynamics of clock gene reporters, ChIP and functional luciferase assays. Importantly, this new avenue of research holds strong potential to identify new drugs (e.g. clock acting compounds) or improve current treatments (such as timing the delivery of drugs) for IVD degeneration and LBP.

Low back pain (LBP), caused by degeneration of the intervertebral disc (IVD), is amongst the most prevalent spinal diseases. It affects millions of individuals, causing severe pain and loss of mobility, with currently no long-term cure. Ageing is a major risk factor. However, we do not fully understand why age increases susceptibility to disc degeneration and LBP. Our modern 24/7 society and ageing frequently disrupt circadian rhythms generated by our body clocks. We have discovered a functional clock in the IVD which weakens with age and its disruption leads to tissue damage. This project will establish the disease relevance and explore the therapeutic potential of the body clocks in this tissue. Our research may identify novel therapeutic strategies for spine diseases (including LBP), or improve the efficacy of current treatments and thus has enormous potential for improving health and quality of life.

Scientific Impact
This project will initially benefit a wide range of researchers (see Academic Beneficiaries). We will reveal for the first time the genome-wide rhythmic target genes in the IVD, and establish mechanistic links between IVD clock dysregulation and tissue damage. This knowledge will significantly advance our understanding of disc physiology and disease. Second, our research will reveal a completely new mechanism of clock entrainment by dynamic osmotic changes associated with the daily loading cycle. This new mechanism may also apply to other musculoskeletal tissues, and therefore will impact on researchers in other fields of skeletal biology or chronobiology. Finally, we will link circadian rhythms to human IVD degeneration for the first time, and explore the clock-targeting potential to modify disc pathways.

Novel Technology
To address the functional significance of the IVD peripheral clock, we have generated a unique conditional IVD-"clockless" mouse model. This novel mouse line is essential because current available models of circadian rhythm disruptions (e.g. whole body clock mutant mice, or mice kept under weekly reversal of light/dark cycle) lead to global disruptions to circadian rhythms, which will severely confound the interpretation of results. In addition, the use of the clock gene reporter mouse (PER2::Luciferase) and human IVD clock reporter cell line models will greatly facilitate the accurate evaluation of the molecular circadian clocks.


Translational impact
The pathways identified by this project that link circadian clocks to intervertebral disc biology (such as REV-ERBa and RORa the possibilities of targeting NHRs (PPARs and LXR) for skeletal diseases. Over the last few years, QJM has established collaborative links with GSK and Pfizer, which will ensure rapid translation of the research findings.

Societal and health impact
Our studies will have profound impacts on public understanding of rhythm disruptions and disease risks. We expect that the outcomes will be media worthy and be of great interest to the sufferers of LBP, healthcare professionals, the general public and the elderly population. The rhythmic nature of the clock targets identified in this study calls for novel treatment strategies for spine diseases, which take into accounts the time-of-day effect, i.e., chronopharmacology. Furthermore, the quest for prognostic biomarkers also has to consider their potential daily variations. Our research will also reveal detrimental effects of rotating shift work to spine health and LBP, and therefore could influence the policy-makers regarding how to best set up schedules for shift workers. Finally, understanding the time-of-day exacerbation of their symptoms may help LBP sufferers better manage their pain and mobility.