The Search for Mechanisms Underlying Fatigue Through Gene Expression Profiling

2016    Kord Kober, PhD, is this year’s winner of the Fatigue Study Group’s Junior Investigator Award for his research on gene expression profiling of inflammation and immune response pathways in breast cancer patients undergoing chemotherapy. In July, Kord and his colleagues, including MASCC members Christine Miaskowski and Judy Mastick, published their paper, “Gene Expression Profiling of Evening Fatigue in Women Undergoing Chemotherapy for Breast Cancer,” in Biological Research for Nursing. The report contains extensive details regarding methodology and gene expression analyses that we cannot include here, but the paper is available for free download.*

Moderate-to-severe fatigue occurs in up to 94% of women undergoing treatment for breast cancer. The severity of fatigue can vary over the course of the day, with considerable variability among individuals. But morning and evening fatigue seem to be two distinct, though related, symptoms. And they are distinguished by different phenotypic and genotypic characteristics. In reviewing recent literature, the authors found, for instance, that having a higher number of comorbidities was associated with morning fatigue, while caring for children at home was more associated with evening fatigue. Genotypic associations have also been reported. For example variations in interleukin (IL) 8 and tumor necrosis factor alpha (TNFA) have been associated with the severity of morning fatigue, while variations in IL 1 receptor 2, IL4, IL6, and TNFA have been associated with the severity of evening fatigue. Kober et al. reasoned that a better understanding of the unique phenotypic and molecular characteristics associated with these two distinct fatigue patterns would help in identifying high-risk patients and in developing interventions to relieve fatigue.

To date, fatigue management has not been very effective. The authors contend that this is largely due to a lack of understanding of the mechanisms that underlie fatigue. While some previous research has shown that inflammation might be involved in the onset of fatigue, there may be many contributing factors. Kober et al. reasoned that one approach to identifying other mechanisms underlying fatigue is to investigate associated gene expression. They looked at differences in the phenotypic characteristics and gene expression (of peripheral leukocytes) in a sample of 44 women undergoing chemotherapy for breast cancer who reported either low (n=19) or high (n=25) levels of evening fatigue (Lee Fatigue Scale). Kober and his colleagues also assessed functional status (Karnofsky Performance Status scale), comorbidities (Self-administered Comorbidity Questionnaire), and prior cancer treatments. Gene-expression measurements were obtained via total RNA extraction, microarray hybridization, and microarray preprocessing and normalization. Analyses included methods to assess differential gene expression and pathway perturbation, transcript origin analysis, and whole-transcriptome pattern comparison to public expression datasets.

Consistent with previous reports, the authors found that women in the high-fatigue group had poorer functional status and more comorbidities (e.g., diabetes, arthritis). A more surprising finding was the association between fewer previous cancer treatments and higher evening fatigue. This could be due to altered perceptions or increased tolerance on the part of those with more previous treatments, or to selection bias among study volunteers, but the authors acknowledge that further study of this phenomenon is warranted.

In all, 12 genes were identified that distinguished between the low- and high-evening-fatigue groups. One gene was identified as upregulated and 11 as downregulated in the high-evening-fatigue group. Gene set analysis found 24 downregulated and 94 simultaneously up- and downregulated pathways between the two fatigue groups. Transcript origin analysis showed that differential expression originated primarily from monocytes and dendritic cell types. The whole-transcriptome differential expression profile is consistent with those reported in gene-expression studies of exhaustive physical exercise, and the profiles for the high-evening-fatigue group were consistent with those reported in studies of sickness behavior. Further, the differential expression genes and pathways identified in this study have similar biological qualities and are the genes involved in inflammation, mitochondrial dysfunction, circadian rhythm disruption, and serotonin regulation.

The differentially expressed genes have plausible inflammatory and immune mechanisms for evening fatigue. The authors also identified several pathways associated with immune cell recovery after chemotherapy, as well as cytokine pathways and inflammation-related pathways that were significantly differentially perturbed between the two fatigue groups. The findings of the study also have implications for the role of circadian rhythmicity, the regulation of neurotransmission, and energy metabolism in chemotherapy-related fatigue.

This study is the first to evaluate differences in gene expression and perturbed pathways in breast cancer patients who reported low versus high levels of evening fatigue during chemotherapy. The analyses suggest that several mechanisms may underlie fatigue in cancer patients and that inflammation, neurotransmitter regulation, and energy metabolism are likely to be involved. They also show that chemotherapy may contribute to fatigue among cancer patients. The authors suggest that the patterns of gene expression found in this study might be shared with other models of fatigue (e.g., physical exercise and pathogen-induced sickness behavior).

Most important, perhaps, the findings of this study suggest that the molecular mechanisms associated with evening fatigue are multifactorial and, moreover, that these mechanisms interact among themselves (for example, neurotransmitter regulation and inflammation, inflammation and mitochondrial dysfunction). Further research on the potential interplay among pathways can help to identify more exactly the mechanisms underlying evening fatigue.
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*Kober KM, Dunn L, Mastick J, Cooper B, Langford D, Melisko M, Venook A, Chen LM, Wright F, Hammer M3, Schmidt BL, Levine J, Miaskowski C, Aouizerat BE. Gene Expression Profiling of Evening Fatigue in Women Undergoing Chemotherapy for Breast Cancer. Biol Res Nurs. 2016 Jul;18(4):370-85. The paper is available for download from Sage Publications.

Kord Kober

Kord M. Kober earned his MA and PhD in Molecular Evolutionary Biology at the University of California, Santa Cruz, and is currently Assistant Professor of Physiological Nursing in the University of California, San Francisco’s School of Nursing. Kord’s research centers around using genomic, transcriptomic, and epigenetic data and bioinformatic analyses to improve our understanding of the molecular mechanisms underlying common symptoms, such as pain and fatigue, as well as treatment failure in patients with chronic medical conditions. He has authored or coauthored numerous papers in these areas, including cancer-related fatigue and pain, especially in breast cancer patients. He is also interested in the empirical evaluation of different processes underlying molecular evolution and quantification of their relative contributions (e.g., natural selection in HIV populations). Kord is the recipient of an NSF Doctoral Dissertation Improvement Grant in the Directorate for Biological Sciences (2010-2012) and a Regents' Fellowship, Department of Ecology and Evolutionary Biology, UCSC (2006-2007). He is a member of three MASCC Study Groups: Fatigue; Neutropenia, Infection & Myelosuppression; and Neurological Complications.