Inflammatory Abnormalities in Muscle After Stroke: Effects of Exercise

Background: Stroke is the leading cause of disability in the United States. Biological
changes in hemiparetic skeletal muscle may further propagate the disability. We report gross
muscular atrophy and major shift to fast myosin heavy chain (MHC) isoform distribution in
hemiparetic thigh that are related to reduced fitness and slow walking speed. We also find
elevated inflammatory mediators, TNFa and NFkB in the paretic thigh muscle. No prior studies
have systematically examined the profile of hemiparetic muscle contractile proteins and
their relationship to function and fitness after stroke. Furthermore, the molecular
mechanisms underlying hemiparetic skeletal muscle atrophy and contractile protein
abnormalities are unknown.

We have investigated treadmill aerobic exercise (T-AEX), as a task-oriented training model.
This exercise model can reverse the alterations in MHC profile in hemiparetic leg muscles
after stroke. This T-AEX program also improves fitness levels, leg strength, and ambulatory
performance in chronic stroke. Moreover, post hoc analyses our randomized treadmill exercise
program show that specific features of the exercise prescription likely influence the nature
of exercise-mediated adaptations. Specifically, we find that the degree of training velocity
progression predicts gains in VO2 peak, but not walking function. In contrast, increasing
training duration is associated with improved 6-minute walking function, but not fitness
gains. These findings provide initial evidence that cardiovascular metabolic adaptations are
contingent upon advancing the training velocity, rather than training duration. These
exercise-mediated changes in MHC profiles and inflammation might be extremely important in
the context of muscle structure and function, ambulation and overall fitness.

Hypothesis: We propose a randomized clinical study to investigate the hypothesis that in
chronic stroke patients a 6 month velocity-based progressive T-AEX program is superior to
duration-based progressive T-AEX for improving HP leg skeletal muscle contractile protein
expression and reducing inflammatory markers to improve muscle function, fitness, and
ambulation.

Specific Aims: 1) Determine whether skeletal muscle MHC isoform expression is altered and
inflammatory mediators, TNF and markers of NFkB activation, present in the hemiparetic
vastus lateralis muscle, compared the non-paretic leg and matched non-stroke control leg
muscles, and related to muscle function, fitness, and gait performance. 2) Determine whether
6 months progressive T-AEX programs can attenuate this abnormal MHC profile and inflammatory
mediators to improve muscle structure and function.

Methods: At baseline, bilateral VL biopsies are obtained from chronically disabled, stroke
participants with hemiparetic gait to examine the HP and non-P thigh skeletal muscles for
alterations in MHC isoforms, key muscle contractile protein, and evidence for inflammation
(TNFa) and NFkB activation. Participants are randomized to 6 months of progressive
velocity-based or duration-based T-AEX training. Repeat VL muscle biopsies are obtained in
the HP limb only after exercise interventions to assess whether 6-month exercise
rehabilitation can restore MHC profile and attenuate activation of inflammatory pathways.
Expression of the specific MHC isoforms, TNF, and NFKB marker expression (mRNA and protein)
are investigated in these muscle tissues by real-time RT-PCR, Western Blot analysis, and
immunohistochemistry. We will explore relationships between T-AEX mediated changes in MHC
expression and inflammatory activation in skeletal muscle after stroke to improve muscle
strength, muscle performance, fitness and activity levels, ADL performance, and gait deficit
severity.

Anticipated Results and Relevance: The cross-sectional baseline data will provide the first
systematic study of a substantial cohort of stroke patients to define the relationship
between altered structural and contractile protein expression to both muscle physiology and
clinical measures of muscle performance, metabolic fitness, and rehabilitation mobility
outcomes. HP VL muscle will be directly compared to the non-P limb muscle within -subjects
and to non-stroke reference controls, in order to better understand the scope of skeletal
muscle inflammatory and metabolic abnormalities in the stroke population. The intervention
results will allow us to determine the specific requirements of treadmill training that are
optimal and crucial to produce the exercise-mediated adaptations in hemiparetic skeletal
muscle that lead to improved rehabilitation outcomes to reduce the disability of chronic
stroke.