Role of MicroRNAs on Age and Contraction-induced Skeletal Muscle Growth

The age-associated loss of skeletal muscle mass and function (sarcopenia) is associated with
substantial social and economic costs. The plasticity and adaptability of skeletal muscle to
contraction (ie. resistance-exercise) is a fundamental physiological event leading to larger
and more robust skeletal muscle. However, muscle growth in response to resistance exercise
(RE), like other anabolic stimuli, is attenuated in older adults. The cause of aberrant
muscle adaptation with aging is complex. Recent work has revealed a novel role for small
non-coding RNAs, called microRNAs (miRNA) in the regulation of gene expression. Using an
integrated bioinformatics analysis of protein-coding gene and miRNA array data from young and
older men, I identified ten specific miRNAs as important regulators of muscle plasticity
(Plasticity Related miRs [PR-miRs]) leading to the transcriptional response to exercise and
lean mass in young and older men. However, the precise mechanisms underlying the expression
of PR-miRs on age-related changes in muscle anabolism and sarcopenia are currently unknown.

Thus, the overall objective of this K01 application will be to determine the mechanistic
role(s) of these PR-miRs in skeletal muscle adaptation to anabolic stimulation in:

1. healthy young,

2. sarcopenic older and

3. age- and functionally-matched non-sarcopenic older males and females.

This will be accomplished by determine the differences in expression of PR-miRs with aging
and sarcopenia in response to anabolic stimulation (AIM 1). Mechanistically determine the
extent to which manipulation of PR-miR levels in vitro, in human primary myocytes, can
reverse anabolic resistance observed with age and sarcopenia (AIM 2) and the effect of
altering PR-miRs levels on skeletal muscle growth and development (AIM 3). This project will
improve our understanding of the molecular mechanisms that contribute to the loss of skeletal
muscle and eventually leading to the development of drug therapies for the treatment of
sarcopenia in the ever growing aging population.

Inclusion Criteria:

- Male and Female

- 20-30 or 70-85 years of age

- Sedentary: Must not participate in any regular exercise sessions (participants who
walk regularly or walk for exercise are eligible)

- Individuals must confirm good health

- BMI must be between 19-35 kg/m2

- Individuals must be fluent in English

- Willing to come to the HNRCA laboratory for study visits

- Short Physical Performance Battery of less than 9 (70-85 years of age cohort)

- 10 subjects with Normal Muscle Mass and 10 subjects with Low Muscle Mass as determined
by DXA scan (70-85 years of age cohort) Low Muscle Mass is defined as Class I
Sarcopenia, Skeletal Muscle Index within 1 to 2 standard deviations from the
sex-specific mean of young adults

Exclusion Criteria:

- Lost or gained 7.5% or more of their body weight in the past 6 months

- Acute or terminal disease

- Significant immune disorder

- Types I and II Diabetes mellitus

- Uncontrolled hypertension (>180/100 mmHg)

- Neuromuscular disease

- Subjects must also not be participating in any regular endurance or resistance
training exercise during the previous six months.

- Mini-mental state examination (MMSE) score of <23

- Because of the DXA scan and the unknown risk associated with the muscle biopsy
procedure, women who are pregnant, planning to become pregnant, or are breastfeeding
will be excluded from the study.

Subjects with a history of any of the following within the past 6 months will be excluded:

- Myocardial infarction in the past 6 months, or other symptomatic coronary artery
disease.

- Surgery in previous 6 months

- Upper or lower extremity fracture in the previous 6 months

- Allergy to lidocaine

Subjects currently taking any of the following drugs or classes of drugs will be excluded:

- Anticoagulant therapy (Warfarin, Coumadin, or Plavix)

- ACE inhibitors

- Drugs that affects neuromuscular function

- Angiotensin receptor blockers

- Androgen or estrogen therapy or other hormone replacement therapy

- Low dose aspirin with known cardiovascular disease (e.g.: reported coronary artery
disease, peripheral vascular disease, or previous stroke, or history of transient
ischemic attacks)

- Diabetes medications (ie. metformin, insulin therapy, thiazolidinediones,
sulfonylureas etc.)

- Chronic corticosteroid therapy

Laboratory blood test exclusions:

- Estimated GFR <30 mL/min/1.73m2

- Other abnormal screening lab values will be at the discretion of the study physician