Regulation of musculoskeletal tissues in ageing and health: the human perspective – Celebrating the research of Professor Mike Rennie

Professor Michael Rennie died on 9 January 2017. He is best known for his research on skeletal muscle: the regulation of its mass and protein content by nutrition and exercise, in health and during disease and ageing, with experimental work dominated by the application of stable isotope tracers in human in vivo experimentation. Mike published a total of 435 scientific papers, of which 33 appeared in The Journal of Physiology and were compiled in a virtual commemorative issue of The Journal in February 2017. Of his 22 original, full papers, published by The Journal of Physiology 12 have received well over 100 citations. This Special Edition of The Journal of Physiology represents a contemporary forward looking undertaking that intentionally aims to capture new, innovative and impactful science to provide progressive insight into the regulation of musculoskeletal tissues in ageing and health. A focus towards the human condition is notable throughout given Mike’s overriding belief that to understand human metabolism human experimentation is vital. It is pleasing and appropriate that the Special Edition opens with an opinion piece from Mike’s close colleagues and long-time collaborators Joe Millward and Kenny Smith, titled ‘The application of stable-isotope tracers to study human musculoskeletal turnover: a tale of bag filling and bag enlargement’ (Millward & Smith, 2019). This review sets the scene for what is to follow by taking a historical look at the development and application of stable isotope tracers, right through to the application of new, impactful tracer techniques, such as heavy water, to study musculoskeletal tissues in humans. This Special Edition also contains six Topical Review articles focused on the musculoskeletal system, which are devoted to research areas in which Mike made major impact and were felt to be important in the context of human health and ageing. This naturally includes coverage of skeletal muscle metabolism, Mike’s principal research interest, represented here by ‘The impact of exercise and nutrition in the regulation of muscle mass’ from Chris McGlory, Stephan van Vilet, Tanner Stokes, Bettina Mittendorfer and Stuart Philipps (McGlory et al. 2019), and ‘The impact of immobilisation and inflammation on the regulation of muscle mass and insulin resistance: different routes to similar end points’ by Hannah Crossland, Sarah Skirrow, Zudin Puthucheary, Dumitru Constantin-Teodosiu and Paul Greenhaff (Crossland et al. 2019). The topic of physiological adaptation of musculoskeletal tissues to mechanoloading is extended to cartilage in the paper ‘Mechanoadaptation: articular cartilage through thick and thin’ by Tonia Vincent and Angus Wann (Vincent & Wann, 2019). Attention has also been directed towards musculoskeletal ageing research, not least because this is an area to which Mike made scientifically important and impactful research contributions over the final period of his career. This incorporates the articles ‘The impact of loading, unloading, ageing and injury on the human tendon’ from Peter Magnusson and Michael Kjaer (Magnusson & Kjaer, 2019) and ‘The relationships and interactions between age, exercise and physiological function’ from Norman Lazarus, Janet Lord and Stephen Harridge (Lazarus et al. 2019). Finally, focus is directed towards bone growth and development in the context of nutrition in the review article ‘Using stable isotope tracers to study bone metabolism in children’ from Kimberly O’Brien and Steven Abrams (O’Brien & Abrams, 2019). Bone research is an area Mike also contributed to believing that stable isotope tracers could be usefully applied to discover the impact of food, physical activity and drugs on bone collagen turnover, and how this could provide valuable insight into pathophysiology of ageing and bone disease. In closing, it is worthy of note that when approached all authors readily accepted the invitation to submit a Topical Review article, and fitting that several contributions have been received from Mike’s established collaborators. I am extremely grateful to friends and colleagues for taking the time and effort to mark the research contributions of Professor Mike Rennie in this fitting way. There is no doubt amongst those that knew Mike that he was a giant of a man, and in all possible ways. His important scientific legacy will live on through his publications, collaborators, students and friends for many decades to come.