ABSTRACT:

Purpose: To identify long-term or persistent impairments in cognitive, psychosocial, oculomotor, and balance performances following mild traumatic brain injury (mTBI) as well as to investigate peripheral blood DNA methylation markers associated with such functional impairment.

Background: The lack of accurate and sensitive measures to assess mTBI, which does not necessarily involve detectable changes in the brain cells, may increase the risk of repetitive head injuries and persistent functional impairments. We proposed to use post-mTBI peripheral DNA methylation markers as well as objective cognitive and sensorimotor functional measures based on the integrative and multidisciplinary bioengineering approach.

Methods: Young male and female adult participants were recruited from the Las Vegas community for 2 separate studies, Study A and Study B. Overall, the participants were assessed for cognitive (by NIH toolbox or CNS-Vital Signs [CNS-VS]), psychological (by PROMIS), visual function (by King-Devick or EyeLink eye-tracking systems), and postural balance performance (by mobile health system or a force plate). Blood DNA methylations markers post- mTBI—global DNA methylation ratio (5-mC%) or whole-genome blood DNA methylation—were also examined.

Results: In Study 1 on multiple persistent functional impairments post-mTBI, 35 volunteers participated and provided informed consents based on procedures approved by the UNLV Institutional Review Board. mTBI cases consisted of 21 individuals (65% males; age, 26.8±5.04 years of age) with a self-reported history of single or multiple injuries (75% multiple), including sports-related activities and military operations. Controls consisted of 14 individuals (36% males; 22.0±4.13 years old). Only age was statistically different between the 2 groups (p=.006) among all demographic variables. mTBI cases reported significantly poorer episodic memory, severer anxiety, more sleep disturbance problems, a wider range of body movements during walking, and higher blood global methylation ratio (5-mC%) (all p’s<.05). From Study 2 on persistent cognitive declines post-injury, based on CNS-VS—processing speed scores at the baseline and the next 1 or up to 3 years, 4 professional fighters with cognitive declines (‘decliners’) and 5 without (‘non-decliners’) were selected for whole-genome methylation analysis using methylation sequencing. Mean age was 32.4 (±6.41) years old and professional fighting experience ranged from 0 to 14 (6.2±5.26) years. No significant differences were found in demographic and fighting variables between the 2 groups. Compared to non-decliners, decliners had significantly hypermethylated (i.e., dysregulated) genes of axonal dysfunction signaling (e.g., ADAM17, GRB10, PRKD1, and FGFR2) and neurological disorder (e.g., Pka, PI3K, LDL, LDLR, and Pkc(s)) at the baseline.

Implications: We observed persistent cognitive, psychosocial, and sensorimotor functional impairments, even long after mTBI, along with altered (higher) peripheral global methylation ratio and hypermethylated axonal degeneration genes associated with the subsequent cognitive declines in next 1 to 3 years. Our findings provide evidence to use peripheral methylation markers, in particular, of axonal degeneration-related genes, and clinically sensitive and more objective screening tools of post-mTBI persistent status.