Epigenetic mechanism controls PDK4 gene activation before and after exercise therapy following artificial knee arthroplasty

Abstract

Purpose: DNA methylation is thought to play a role in exercise-induced gene expression. We aimed to examine changes in muscular strength and body composition in elderly patients with end-stage knee osteoarthritis before and after artificial knee arthroplasty and exercise therapy. We aimed to confirm the relationship between DNA methylation and body composition, using the methylation rate of the pyruvate dehydrogenase kinase 4 (PDK4) gene that regulates skeletal muscle and fat metabolism.

Patients and methods: Patients underwent artificial knee arthroplasty between April 2017 and June 2017 at Kansai Medical University Hospital. Six patients (seven knees) were included in the analysis (four males/two females; average age, 75.7 years; body mass index, 25.1 kg/m²). Body composition and knee extension muscle strength were measured before surgery and 5 months after surgery. Rehabilitation was performed for 3 months after surgery. In the remaining 2 months, patients performed resistance training and aerobic exercise using an ergometer for 20 mins, twice a week. A biopsy of the vastus medialis was taken during surgery and 5 months post-surgery. Biopsy samples were treated with bisulfite after DNA extraction, and DNA methylation rate was calculated.

Results: Body weight (P=0.046), total weight (P=0.027), and total fat mass (P=0.028) were significantly lower 5 months postoperatively than preoperatively. Five months post-surgery, the PDK4 gene was significantly more hypomethylated at eight sites in the CpG island, compared to pre-surgery. There was a significant correlation (r=0.88, P=0.02) between promoter region hypomethylation and weight loss. Total methylation rate and weight loss were significantly correlated (r=0.829, P=0.042). Total methylation rate and decrease in total fat mass showed a positive trending relationship (r=0.812, P=0.05).

Conclusion: Rehabilitative exercise resulted in significant decreases in weight and body fat. Hypomethylation of the PDK4 gene promoter region signified the effect of postoperative management focus on exercise therapy on weight and fat loss.

Keywords: elderly person; methylation; muscle biopsy; rehabilitation.

Figure 1

Designed primer. Note: The PDK4 gene is designed with 13 fragments. Abbreviations: PDK4, pyruvate dehydrogenase kinase 4; BSP, bisulfite sequencing polymerase chain reaction.

Figure 2

Total base sequence of PDK4 gene CpG island. Notes: is cytosine that is significantly hypomethylated in the reaction by bisulfite treatment. is cytosine that was CpG site after PCR amplification. A is the transcription initiation codon. ATG is the translation initiation codon. 3ʹ-GAGAGTGCGGGGAGACAAAACCTCGGGCGGCGGCGGCTGGGAAGACTTGAACT-5ʹ is the promoter region of the PDK4 gene. Abbreviation: PDK4, pyruvate dehydrogenase kinase 4.

Figure 3

Correlation chart between promoter change in the PDK4 gene and body weight change. A positive correlation is found between hypomethylation change at the promoter region in the PDK4 gene and body weight change. Abbreviation: PDK4, pyruvate dehydrogenase kinase 4.

Figure 4

Correlation between total methylation change in the PDK4 gene and body weight change. A positive correlation is found between total methylation change in the PDK4 gene and body weight change. Abbreviation: PDK4, pyruvate dehydrogenase kinase 4.

Figure 5

Correlation between total methylation change in the PDK4 gene and body fat mass change. There is a positive correlative tendency between total methylation change in the PDK4 gene and body fat mass change. Abbreviation: PDK4, pyruvate dehydrogenase kinase 4.