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The chondroprotective effect of urocortin involves modulation of the mechanosensitive ion channel Piezo1
[Thesis]. Manchester, UK: The University of Manchester; 2019.
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Abstract
Osteoarthritis (OA) is one of the leading causes of morbidity worldwide. Single injurious mechanical impact to joints as seen in sports injury is known to be associated with a high risk of later development of OA, known as post-traumatic OA (PTOA). PTOA affects a younger population of patients and significantly increases the socio-economic burden of the disease on society. Breakdown of articular cartilage in the joint is one of the characterising features of OA. Cartilage is populated with chondrocytes responsible for production and turnover of the matrix. Chondrocyte death is known to occur following impact, suggesting a chondroprotective agent might provide a promising candidate as a disease modifying drug. Urocortin (Ucn), a small peptide member of the Corticotrophin- Releasing Factor (CRF) family, has previously been seen to be essential for chondrocyte survival, where depletion of Ucn led to chondrocyte cell death. This thesis sought to elucidate the mechanism of this chondroprotection by Ucn. Initial chondrocyte cell line and monolayer primary cell studies showed a significant increase in calcium influx when cells were deprived of Ucn. A siRNA screen of candidate ion channels highlighted Piezo1 as being involved in this excessive influx. An ex-vivo model of single impact then was developed to study the effect of overloading on cartilage explants over a short timeframe. Both pre-impact and crucially post-impact addition of Ucn to porcine explants significantly increased chondrocyte survival 72 hrs after challenge. This corresponded to a reduction in excessive calcium influx. Further study with specific mechanosensitive ion channel blockers and activators confirmed Piezo1 as the ion channel modulated by Ucn in order to prevent this calcium overload. Observation of these cells on a subcellular level highlighted a distinct programmed cell death response to impact, although molecular biology techniques indicated this was in the absence of caspase-3 activation. This work has detailed a previously unseen chondroprotective role of Ucn in response to single impact. In particular, the protection observed even when Ucn was added postimpact suggests Ucn as an interesting candidate for further study in a post-impact injury context, thereby limiting chondrocyte cell death early after damage and potentially leading to a reduced incidence of PTOA.
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