Protein synthesis rates of muscle, tendon, ligament, cartilage, and bone tissue in vivo in humans.
Level 4 - case-series / case-control
Cross-sectional human stable isotope tracer study with intraoperative tissue sampling
PubMed 31697717 · doi:10.1371/journal.pone.0224745
What was done
Six patients (mean age 62 ± 3 years) scheduled for unilateral total knee arthroplasty received primed continuous intravenous infusions of L-[ring-13C6]-Phenylalanine during surgery. Intraoperative biopsies were taken from skeletal muscle, tendon, cruciate ligaments, cartilage, bone, menisci, Hoffa's fat pad, and synovium. Fractional protein synthesis rates (%/h) were determined via isotopic tracer incorporation and compared with muscle protein synthesis using paired t-tests.
What was found
Skeletal muscle protein synthesis was 0.04 ± 0.01%/h. Tendon (0.06 ± 0.01%/h), bone (0.03 ± 0.01%/h), cartilage (0.04 ± 0.01%/h), Hoffa's fat pad (0.11 ± 0.03%/h), anterior cruciate ligament (0.07 ± 0.02%/h), posterior cruciate ligament (0.04 ± 0.01%/h), and menisci (0.04 ± 0.01%/h) did not differ significantly from muscle (P > 0.05). Synovium protein synthesis was significantly higher (0.13 ± 0.03%/h; P < 0.05) and intercondylar notch bone was significantly lower (0.03 ± 0.01%/h; P < 0.01) than muscle. Across all tissues, basal synthesis rates ranged between 0.02 and 0.13%/h.
Why it matters
This study provides direct in vivo human evidence that non-contractile joint and connective tissues maintain basal protein synthesis rates in the same range as skeletal muscle.
Limits
The sample size is very small (n = 6). All participants were older adults undergoing knee arthroplasty, so joint tissues may reflect osteoarthritic pathology rather than healthy tissue physiology. The study only measured basal fractional synthesis during surgery without assessing protein breakdown, net balance, or responses to exercise or feeding.
Cited by
- supports Protein synthesis rates of tissues in and around the knee—including cartilage, synovium, menisci, ACL, and PCL—are comparable in magnitude to the protein synthesis rate of skeletal muscle.