Audrey E Brown, Beth Dibnah, Emily Fisher, Julia L Newton and Mark Walker
Institute of Cellular Medicine, Newcastle University; Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK
Skeletal muscle fatigue and post-exertional malaise are key symptoms of Myalgic Encephalomyelitis (ME/CFS). We have previously shown that AMPK activation and glucose uptake are impaired in primary human skeletal muscle cell cultures derived from patients with ME/CFS in response to electrical pulse stimulation, a method which induces contraction of muscle cells in vitro. The aim of this study was to assess if AMPK could be activated pharmacologically in ME/CFS.
Primary skeletal muscle cell cultures from patients with ME/CFS and healthy controls were treated with either metformin or 991. AMPK activation was assessed by Western blot and glucose uptake measured.
Both metformin and 991 treatment significantly increased AMPK activation and glucose uptake in muscle cell cultures from both controls and ME/CFS. Cellular ATP content was unaffected by treatment although ATP content was significantly decreased in ME/CFS compared to controls.
Pharmacological activation of AMPK can improve glucose uptake in muscle cell cultures from patients with ME/CFS. This suggests that the failure of electrical pulse stimulation to activate AMPK in these muscle cultures is due to a defect proximal to AMPK. Further work is required to delineate the defect and determine whether pharmacological activation of AMPK improves muscle function in patients with ME/CFS.
The work was funded by ME Research UK and supported by the NIHR Newcastle Clinical Research Facility.
Comment by ME Research UK
Abnormal muscle fatigue is one of the most common symptoms reported by people with ME/CFS, and can occur even after periods of only mild exercise.
Since 2006, ME Research UK has provided pilot funding for a number of projects at Newcastle University exploring the mechanisms underlying this symptom, and one key study took a close look at muscle cell function using biopsies obtained from ME/CFS patients.
These muscle cells were cultured and examined in standardised laboratory conditions by applying a series of electrical pulses to simulate the muscle contraction that occurs during exercise.
The researchers found that the activation of AMP-activated protein kinase (AMPK) and the uptake of glucose were both impaired in these cells. AMPK has an important role in regulating energy in the cell and is normally activated during muscle contraction, while glucose is an important energy source.
Although AMPK was not activated by simulated muscle contraction in these cells from ME/CFS patients, later experiments indicated that it could be activated by treatment with metformin. This raises the possibility of whether a drug such as this could improve muscle function in patients.
To look at these abnormalities in more detail, and potentially to trace where they occur in the signalling pathway, the Newcastle team began a series of experiments funded by ME Research UK.
The first part of this work, published in Bioscience Reports, used a similar methodology to that in their previous study to investigate whether AMPK and glucose uptake in muscle cells from ME/CFS patients could be activated by treatment with pharmacological agents.
Skeletal muscle cells were obtained from eight patients with ME/CFS and from seven healthy control subjects. The cultured cells were then treated with metformin or with compound 991. Metformin is a drug commonly used to treat diabetes, and is known to activate AMPK indirectly via other mechanisms. Compound 991, on the other hand, was designed specifically as a direct activator of AMPK.
Treatment with metformin increased both AMPK activation and glucose uptake, and this was true for muscle cells from ME/CFS patients and from healthy control subjects. Similarly, compound 991 treatment also significantly increased both parameters in patient and control cells, and the effect on glucose uptake was similar to that expected following treatment with insulin.
Therefore, while AMPK in muscle cells from ME/CFS patients is not activated by electrical stimulation of the cells, it can be activated pharmacologically, and there are two important conclusions that might be drawn from these findings.
Firstly, this abnormality in signalling can potentially be bypassed by pharmacological treatment, and the investigators suggest that this adds further support to the idea of conducting a clinical trial of an AMPK activator in ME/CFS patients. Secondly, their results indicate that the signalling defect lies further up the molecular chain, possibly involving upstream enzymes such as LKB1 or CaMKK.
These findings represent the fascinating first steps of this project, which will continue to look more closely at the mechanisms underlying muscle fatigue in ME/CFS, and hopefully to identify potential targets for therapy.