Lymphoblastoid Cell Lines as Models to Study Mitochondrial Function in Neurological Disorders, 2021, Annesley and Fisher

[Sly Saint]

Abstract
Neurological disorders, including neurodegenerative diseases, are collectively a major cause of death and disability worldwide. Whilst the underlying disease mechanisms remain elusive, altered mitochondrial function has been clearly implicated and is a key area of study in these disorders.

Studying mitochondrial function in these disorders is difficult due to the inaccessibility of brain tissue, which is the key tissue affected in these diseases. To overcome this issue, numerous cell models have been used, each providing unique benefits and limitations. Here, we focussed on the use of lymphoblastoid cell lines (LCLs) to study mitochondrial function in neurological disorders.

LCLs have long been used as tools for genomic analyses, but here we described their use in functional studies specifically in regard to mitochondrial function. These models have enabled characterisation of the underlying mitochondrial defect, identification of altered signalling pathways and proteins, differences in mitochondrial function between subsets of particular disorders and identification of biomarkers of the disease. The examples provided here suggest that these cells will be useful for development of diagnostic tests (which in most cases do not exist), identification of drug targets and testing of pharmacological agents, and are a worthwhile model for studying mitochondrial function in neurological disorders.

8. Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)
ME/CFS is a complex disorder characterised by fatigue lasting greater than 6 months, and, in most classification systems, an overwhelming post-exertional malaise (PEM). The exertion itself can be relatively minor, could be either physical or cognitive, and the malaise can occur immediately following the exertion or up to 3 days later. PEM is defined as an exacerbation of the individual’s ME/CFS symptoms. Patients suffer from a range of symptoms which include severe fatigue, musculoskeletal pain, headaches, recurrent flu-like symptoms, gastrointestinal problems, sensory sensitivity, concentration/memory difficulties and unrefreshing sleep [114].

Mitochondrial dysfunction has been investigated in ME/CFS using blood cells, muscle tissue, urine and saliva and in most cases, a defect in mitochondrial function was suggested, but no precise mechanism was identified. Direct measures of respiration in non-proliferating, quiescent cells, such as PBMCs and muscle cells, revealed no clear, consistent differences between patients compared with healthy controls [115,116,117,118]. However, studies using LCLs generated from ME/CFS patients unveiled a clear and specific defect in the efficiency of the final complex in mitochondrial respiration, Complex V [44]. It seems likely that this defect was able to be observed due to the cell model used—LCLs. LCLs are actively proliferating and therefore, metabolism, including respiration, is occurring at an elevated rate, so the differences between patient and control groups can be identified [44].

The patient cells also had increased activity of a key stress sensing regulator called Target of Rapamycin Complex 1 (TORC1 or, in mammalian cells, mTORC1 [44]). TORC1 is able to activate transcription factors and separately upregulate the translation of many proteins, including mitochondrial proteins. All five mitochondrial respiratory complexes were indeed upregulated, as were enzymes involved in the TCA cycle, fatty acid uptake, β-oxidation and other pathways that serve as alternatives to glycolysis involved in provisioning the mitochondria with oxidizable substrates [59]. This elevation of expression may represent a cellular “attempt” to compensate for the inefficiency of Complex V. The upregulation of mitochondrial proteins was also reported in non-immortalised lymphocytes and saliva, supporting the utility of LCLs as a model system for this disease [60,118,119].

Using measures of mitochondrial function and TORC1 activity in LCLs in combination with a cell death rate assay in frozen lymphocytes, the authors showed that these parameters could be used to identify or diagnose ME/CFS patients from healthy controls with a nearly 100% specificity and sensitivity [120]. If further validated, this could be developed into the world’s first diagnostic test for ME/CFS.

https://www.mdpi.com/1422-0067/22/9/4536/htm