Mature primary human osteocytes in mini organotypic cultures secrete FGF23 and PTH1-34-regulated sclerostin.

Introduction: For decades, functional primary human osteocyte cultures have been crucially needed for understanding their role in bone anabolic processes and in endocrine phosphate regulation via the bone-kidney axis. Mature osteocyte proteins (sclerostin, DMP1, Phex and FGF23) play a key role in various systemic diseases and are targeted by successful bone anabolic drugs (anti-sclerostin antibody and teriparatide (PTH1-34)). However, cell lines available to study osteocytes produce very little sclerostin and low levels of mature osteocyte markers. We have developed a primary human 3D organotypic culture system that replicates the formation of mature osteocytes in bone. Methods: Primary human osteoblasts were seeded in a fibrinogen / thrombin gel around 3D-printed hanging posts. Following contraction of the gel around the posts, cells were cultured in osteogenic media and conditioned media was collected for analysis of secreted markers of osteocyte formation. Results: The organoids were viable for at least 6 months, allowing co-culture with different cell types and testing of bone anabolic drugs. Bulk RNAseq data displayed the developing marker trajectory of ossification and human primary osteocyte formation in vitro over an initial 8- week period. Vitamin D3 supplementation increased mineralization and sclerostin secretion, while hypoxia and PTH1-34 modulated sclerostin. Our culture system also secreted FGF23, enabling the future development of a bone-kidney-parathyroid-vascular multi-organoid or organ-on-a-chip system to study disease processes and drug effects using purely human cells. Discussion: This 3D organotypic culture system provides a stable, long-lived, and regulated population of mature human primary osteocytes for a variety of research applications.

Platelet rich Plasma in Achilles Tendon Healing 2 (PATH-2) trial: protocol for a multicentre, participant and assessor-blinded, parallel-group randomised clinical trial comparing platelet-rich plasma (PRP) injection versus placebo injection for Achilles tendon rupture.

BACKGROUND: Achilles tendon injuries give rise to substantial long-lasting morbidity and pose considerable challenges for clinicians and patients during the lengthy healing period. Current treatment strategies struggle to curb the burden of this injury on health systems and society due to lengthy rehabilitation, work absence and reinjury risk. Platelet-rich plasma (PRP) is an autologous preparation that has been shown to improve the mechanobiological properties of tendons in laboratory and animal studies. The use of PRP in musculoskeletal injuries is on the increase despite the lack of adequately powered clinical studies. METHODS AND DESIGN: This is a multicentre randomised controlled trial to evaluate the efficacy and mechanism of PRP in patients with acute Achilles tendon rupture (ATR). All adults with acute ATR presenting within 12 days of the injury who are to be treated non-operatively are eligible. A total of 230 consenting patients will be randomly allocated via a remote web-based service to receive PRP injection or placebo injection to the site of the injury. All participants will be blinded to the intervention and will receive standardised rehabilitation to reduce efficacy interference.Participants will be followed up with blinded assessments of muscle-tendon function, quality of life, pain and overall patient's functional goals at 4, 7, 13, 24 weeks and 24 months post-treatment. The primary outcome is the heel-rise endurance test (HRET), which will be supervised by a blinded assessor at 24 weeks. A subgroup of 16 participants in one centre will have needle biopsy under ultrasound guidance at 6 weeks. Blood and PRP will be analysed for cell count, platelet activation and growth factor concentrations. ETHICS AND DISSEMINATION: The protocol has been approved by the Oxfordshire Research Ethics Committee (Oxfordshire Research Ethics Committee A, reference no 14/SC/1333). The trial will be reported in accordance with the CONSORT statement and published in peer-reviewed scientific journals. TRIAL REGISTRATION NUMBER: ISRCTN: 54992179, assigned 12 January 2015. ClinicalTrials.gov: NCT02302664, received 18 November 2014. UK Clinical Research Network Study Portfolio Database: ID 17850.