Dr. Tom Appleton was the recipient of a 2017 ORADE grant. Below is a summary of his learnings.
Cartilage Biology & Pathology Gordon Research Conference 2017, Tuscany, Italy
My sincere thanks to the ORA for the opportunity to attend this conference via the ORADE grant. The Gordon Research Conferences are an invite-only bleeding-edge conference that restricts attendance to <200 participants including the top experts in specific fields of research in the world. The format permits extended time for interaction, networking, and discussions in an intense, 4-day program.
There were several sessions and workshops of note and it would be impossible to cover them all, so I have focused on the highlights from sessions related to OA pathophysiology.
Too much NF-kB signaling accelerates onset of age-associated OA
Not all OA is the same. Some OA comes after joint injury, some is associated with metabolic syndrome, and a lot is associated with advanced ageing. One of the features of ageing includes increased basal inflammation, including cells with the senescence-associated secretory phenotype. Some refer to this phenomenon as “inflammaging”. Several have shown that age-associated OA has several inflammatory features. If so, increased basal inflammation should result in premature onset of OA.
Dr. Sarah Catheline from the University of Rochester made a transgenic mouse to that allowed them to choose when to turn off an endogenous inhibitor of the NF-kB (nuclear factor-kappa B) pathway. This is the common final pathway of so many inflammatory mechanisms in nearly all cell types. To keep inflammation under control, cells have natural inhibitors of NF-kB. This group showed that turning off these inhibitors (resulting in persistently higher levels of background inflammatory signaling in cartilage cells) within a few months of birth caused earlier onset of knee OA associated with ageing. Normally, mice start developing OA around 18 months of age (fairly old for a mouse that would normally not be expected to live longer than 2 years). This points to cartilage-specific age-related changes being causative of OA, but interestingly these mice also had much worse synovitis and meniscal damage compared with mice the same age.
If we see the same thing in people, it might point to an important role for targeting inflammaging in age-associated OA.
Tick-Tock… Did you know cartilage has a clock?
Most cell types generate circadian rhythms – daily fluctuations in gene expression, calcium signaling, and other homeostatic processes. Loss of the regular circadian rhythm, controlled by the sensation light in suprachiasmatic nuclei, results in a myriad of diseases. Qing-Jun Meng, University of Manchester, showed that circadian rhythm also has important implications for joint disease. For example, morning stiffness coincides with diurnal fluctuations in IL-6, which normally peaks at 5 AM.
At present, our understanding of circadian rhythm is that the “clock” is controlled by 10 genes. Bmal1 is the only one that doesn’t have a redundant counterpart, so genetic knockouts can’t compensate for loss of Bmal1. It was fascinating about 2 years ago when this group showed that persistent disruption of day-night cycles in mice causes premature onset of OA, but now they demonstrated that cartilage-specific gene knockout of Bmal1 causes premature onset of spontaneous knee OA at 2-3 months of age! Further experiments showed intricate control of extracellular matrix genes critical for cartilage formation including type II collagen, probably explaining the effect. I’m not sure of the clinical relevance of this finding but, as mentioned before, ageing causes impairment of the circadian cycle (“the clock”), so perhaps this gives us a clue. One final (bizarre) twist – glucocorticoid treatment of the chondrocytes in culture (lacking Bmal1) restored their gene expression levels to normal.
Connecting the DOTs between genomic, epigenomic, and transcriptomic data in OA cartilage
Disrupter of telomeric silencing 1 (DOTL1) may be a key safeguard protecting cartilage against various insults. Rik Lories, Belgium, presented a really impressive set of studies linking a lot of different observations. Big genomic (genome-wide association/GWAS) studies have linked DOTL1 to cartilage thickness in patients with knee OA. His lab demonstrated that the methylation of chondrocytes from OA cartilage is altered in a pattern consistent with the histone methyltransferase activity fingerprints of DOTL1 activity.
Taking these genomic/epigenomic links to the next level, a DOTL1 inhibitor in chondrocytes caused changes in mice consistent with OA and chondrocyte gene expression (transcriptomic data) linked DOTL1 inhibition with Wnt signaling. This isn’t the first time, since microarray (transcriptomic data) in human OA cartilage has previously linked expression changes in large gene sets to Wnt signaling as well. But Dr. Lories experiments demonstrated that DOTL1 inhibitor caused increased Wnt activity that could be reversed with a Wnt inhibitor, protecting against the induced OA phenotype.
Together, these are among the first complete set of data linking genome-wide association data with changes in epigenetic regulation, downstream gene expression, and the disease phenotype in OA. It’s a compelling argument. And taken together with the decades-old Wnt signaling story in OA, this is yet another piece of evidence that Wnt signaling inhibitors may be a viable treatment for various types of OA. It’s worth noting that Samumed has had a phase 2 RCT ongoing for over a year now looking at a Wnt inhibitor for knee OA. Stay tuned…
More importantly, thanks again to the ORA. This conference was a tremendous experience, not just for key learnings but also for the opportunity to present some of my own data, network with key leaders in the OA field in the world, and enjoy some outstanding Tuscan Chianti!