Skeletal Muscle Mitochondrial Dysfunction Is Present in Patients with CKD before Initiation of Maintenance Hemodialysis

Abstract

Background and objectives: Patients with CKD suffer from frailty and sarcopenia, which is associated with higher morbidity and mortality. Skeletal muscle mitochondria are important for physical function and could be a target to prevent frailty and sarcopenia. In this study, we tested the hypothesis that mitochondrial dysfunction is associated with the severity of CKD. We also evaluated the interaction between mitochondrial function and coexisting comorbidities, such as impaired physical performance, intermuscular adipose tissue infiltration, inflammation, and oxidative stress.

Design, setting, participants, & measurements: Sixty-three participants were studied, including controls (n=21), patients with CKD not on maintenance hemodialysis (CKD 3-5; n=20), and patients on maintenance hemodialysis (n=22). We evaluated in vivo knee extensors mitochondrial function using ³¹P magnetic resonance spectroscopy to obtain the phosphocreatine recovery time constant, a measure of mitochondrial function. We measured physical performance using the 6-minute walk test, intermuscular adipose tissue infiltration with magnetic resonance imaging, and markers of inflammation and oxidative stress in plasma. In skeletal muscle biopsies from a select number of patients on maintenance hemodialysis, we also measured markers of mitochondrial dynamics (fusion and fission).

Results: We found a prolonged phosphocreatine recovery constant in patients on maintenance hemodialysis (53.3 [43.4-70.1] seconds, median [interquartile range]) and patients with CKD not on maintenance hemodialysis (41.5 [35.4-49.1] seconds) compared with controls (38.9 [32.5-46.0] seconds; P=0.001 among groups). Mitochondrial dysfunction was associated with poor physical performance (r=0.62; P=0.001), greater intermuscular adipose tissue (r=0.44; P=0.001), and increased markers of inflammation and oxidative stress (r=0.60; P=0.001). We found mitochondrial fragmentation and increased content of dynamin-related protein 1, a marker of mitochondrial fission, in skeletal muscles from patients on maintenance hemodialysis (0.86 [0.48-1.35] arbitrary units (A.U.), median [interquartile range]) compared with controls (0.60 [0.24-0.75] A.U.).

Conclusions: Mitochondrial dysfunction is due to multifactorial etiologies and presents prior to the initiation of maintenance hemodialysis, including in patients with CKD stages 3-5.

Keywords: Chronic; Chronic inflammation; DNM1L protein; Frailty; Inflammation; Magnetic Resonance Spectroscopy; Microtubule-Associated Proteins; Mitochondria; Mitochondrial Dynamics; Mitochondrial Proteins; Muscle; Phosphocreatine; Phosphorus; Renal Insufficiency; Sarcopenia; Skeletal; Skeletal muscle; Walk Test; chronic kidney disease; hemodialysis; human; mitochondria; oxidative stress.

Graphical abstract

Figure 1.

Mitochondrial function in patients with CKD. During exercise, phosphocreatine (PCr) is broken down to synthesize ATP for the working muscle. During recovery, PCr is resynthesized from ATP produced by oxidative phosphorylation, and the rate of recovery of PCr is a measure of mitochondrial oxidative capacity. The recovery of PCr after light- and moderate-intensity exercise follows a monoexponential pattern, and the time constant τ of PCr recovery is frequently used as an index of mitochondrial function. (A) Representative graph showing the PCr recovery kinetics after exercise in one healthy control and a patient on maintenance hemodialysis (MHD). (B) PCr recovery time constant τ was prolonged in patients on MHD (n=22) compared with controls (n=21) and patients with CKD stages 3–5 (n=20). (C) Patients with CKD 3–5 and control participants were divided into tertiles according to the eGFR. Patients within the lowest eGFR tertile (n=14) have a prolonged PCr recovery time compared with individuals within the highest eGFR tertile (n=14).

Figure 2.

Physical performance and mitochondrial function. (A) Physical performance, measured by the 6-minute walk test, was impaired in patients with CKD 3–5 (n=20) and patients on MHD (n=22) compared with control individuals (n=18). (B) Physical performance was significantly associated with mitochondrial function (n=57).

Figure 3.

Intermuscular adipose tissue and mitochondrial function. (A) Representative magnetic resonance imaging images showing increased intermuscular adipose tissue (IMAT) in a patient on MHD and a control individual. (B) IMAT infiltration (ratio of fat to muscle volume) in the quadriceps muscle was increased in patients with CKD 3–5 (n=20) and patients on MHD (n=15) compared with the control group (n=16). (C) Linear regression showing the association between mitochondrial function (time constant τ) and IMAT infiltration (n=49).

Figure 4.

Inflammation and mitochondrial function. TNFα (A) and IL-6 (B) levels in control individuals (n=21), patients with CKD 3–5 (n=20), and patients on MHD (n=21). Association of TNFα (C) and IL-6 (D) with mitochondrial function (n=59).

Figure 5.

Oxidative stress and mitochondrial function. (A) Coenzyme Q₁₀ (CoQ₁₀) redox ratio (ratio of reduced to oxidized CoQ₁₀) in control individuals (n=21), patients with CKD 3–5 (n=20), and patients on MHD (n=21). (B) Association between CoQ₁₀ redox ratio and mitochondrial function (n=59).

Figure 6.

Mitochondrial fragmentation in patients on MHD in skeletal muscle biopsies from the vastus lateralis. (A) Electron microscopies showing that mitochondria (white arrows) are smaller in patients on MHD. (B) Quantification of mitochondrial areas in control individuals (n=15) and patients on MHD (n=9). Each dot represents the median area of hundreds of mitochondria in each subject. (C) Frequency distribution of individual mitochondria areas showing a greater proportion of smaller mitochondria in patients on MHD.

Figure 7.

Western blot analysis of dynamin-related protein 1 (DRP1). (A) Representative western blot of DRP1, a marker of mitochondrial fission. (B) DRP1 is increased in patients on MHD when compared with control subjects with no history of CKD. Skeletal muscle biopsies were obtained from the vastus lateralis (n=9 in each group). A.U., arbitrary units.

Figure 8.

The possible association among factors that could be implicated in the pathogenesis of frailty in patients with CKD.