Poster Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

Targeted postnatal deletion of vitamin D receptor demonstrates its importance in muscle (#329)

Julian Chu 1 2 3 , Alexandra O'Donohue 1 3 4 , Josephine Yu 3 , Samantha Ginn 2 5 , Jenny Gunton 2 3 6 , Aaron Schindeler 1 3 4
  1. Bioengineering and Molecular Medicine Laboratory, The Children's Hospital at Westmead, Westmead, NSW, Australia
  2. School of Medical Science & Sydney Medical School, Faculty of Health and Medicine, The University of Sydney, Camperdown, NSW, Australia
  3. Centre of Diabetes, Obesity and Endocrinology, Westmead Institute of Medical Research, Westmead, NSW, Australia
  4. School of Chemical and Biomolecular Engineering, Faculty of Engineering, The University of Sydney, Camperdown, NSW, Australia
  5. Gene Therapy Unit, the Children's Medical Research Institute, Westmead, NSW, Australia
  6. Department of Diabetes and Endocrinology, Westmead Hospital, Westmead, NSW, Australia

Background: Vitamin D maintains calcium homeostasis and is modulated by the vitamin D receptor (VDR). While VDR is well-known for its integral role in healthy bone development, evidence from a muscle-specific VDR-knockout (mVDR) mouse line demonstrated it to be essential for muscle development [1]. We hypothesized that targeted postnatal deletion of VDR in muscle would be a more relevant method to model and assess its importance in age-related loss of muscle tone.

Methods: Postnatal targeting of the VDRflox allele was performed using a custom adeno-associated viral vector (AAV) expressing Cre recombinase restricted to muscle. 8-week-old mice received a single IP injection of either AAVMYO-tMCK63-Cre at 5x1011 vg/mouse or saline. Throughout the 6-week study, mice underwent a series of functional muscle tests (grip-strength, endurance running and voluntary running in Promethion metabolic cages). At the study endpoint, muscle specimens were collected for measurement of gene recombination, RNA expression and histology.

Results: Analysis of VDRflox recombination by PCR from gDNA confirmed gene deletion in AAV-injected mice. Evidence for loss of VDR protein was observed by immunofluorescence staining in muscle from AAV-treated mice compared to control mice. Muscle fibre size and morphology appeared altered (larger and less round) in AAV-treated mice by H&E staining in quadriceps muscle. Functional outcomes (i.e. grip strength, running) showed a trend towards impaired performance with VDR deletion (P=0.06-0.08) but did not reach significance.

Conclusion: The AAVMYO-tMCK63-Cre proved an efficient and selective vector for targeting muscle and has broad utility targeted gene deletion in floxed lines. This is particularly relevant to dissect developmental vs postnatal gene functions. Data from the VDRflox/flox mouse reinforce the importance of VDR in muscle, supporting Vitamin D signalling as critical in maintaining musculoskeletal health in aging.

  1. C. M. Girgis et al., "Mice with myocyte deletion of vitamin D receptor have sarcopenia and impaired muscle function," Journal of Cachexia, Sarcopenia and Muscle, vol. 10, no. 6, pp. 1228-1240, 2019, doi: 10.1002/jcsm.12460.