Fascia Is Able to Actively Contract and May Thereby Influence Musculoskeletal Dynamics: A Histochemical and Mechanographic Investigation

Abstract

Fascial tissues form a ubiquitous network throughout the whole body, which is usually regarded as a passive contributor to biomechanical behavior. We aimed to answer the question, whether fascia may possess the capacity for cellular contraction which, in turn, could play an active role in musculoskeletal mechanics. Human and rat fascial specimens from different body sites were investigated for the presence of myofibroblasts using immunohistochemical staining for α-smooth muscle actin (n = 31 donors, n = 20 animals). In addition, mechanographic force registrations were performed on isolated rat fascial tissues (n = 8 to n = 18), which had been exposed to pharmacological stimulants. The density of myofibroblasts was increased in the human lumbar fascia in comparison to fasciae from the two other regions examined in this study: fascia lata and plantar fascia [H(2) = 14.0, p < 0.01]. Mechanographic force measurements revealed contractions in response to stimulation by fetal bovine serum, the thromboxane A2 analog U46619, TGF-β1, and mepyramine, while challenge by botulinum toxin type C3-used as a Rho kinase inhibitor- provoked relaxation (p < 0.05). In contrast, fascial tissues were insensitive to angiotensin II and caffeine (p < 0.05). A positive correlation between myofibroblast density and contractile response was found (r _s = 0.83, p < 0.001). The hypothetical application of the registered forces to human lumbar tissues predicts a potential impact below the threshold for mechanical spinal stability but strong enough to possibly alter motoneuronal coordination in the lumbar region. It is concluded that tension of myofascial tissue is actively regulated by myofibroblasts with the potential to impact active musculoskeletal dynamics.

Keywords: connective tissue; contractility; contracture; myofibroblasts; stiffness.

FIGURE 1

Handling of rat thoracolumbar fascia. After removal of skin and subcutaneous connective tissue, the underlying dense layer of thoracolumbar fascia was made accessible (A). One long strip from the left side of the thoracolumbar spine (shown here in B) and also one from the other side were carefully dissected and cleaned of any attached muscle fibers. Some samples were then used for histochemical analysis while others were used for mechanographic registrations in an organ bath, as shown in (C). Here the bath solution was aerated with carbogen. Through a double-walled container, the bath was kept at a constant temperature. The upper end of the tissue was connected with a force transducer (FT).

FIGURE 2

Histological sections from samples of fascia. ASMA positive stress fiber bundles—used as a marker for MFBs—were stained in dark brown, while cell nuclei were stained in dark blue. (A) Section from rat lumbar fascia. (B) Section from human fascia lata with a very low MFB density. (C) Section from human lumbar fascia. Microscopic inspection shows obvious differences in ASMA density.

FIGURE 3

Immunofluorescence imaging of two representative sections of intramuscular fascia from the human lumbar region. Bright green: elements that are positively stained for the presence of ASMA. Note the apparently increased presence of MFBs in the perimysial zones (white arrows) as opposed to endomysial zones (black arrows) in both sections (A,B).

FIGURE 4

The MFB density of several samples of rat lumbar fascia was assessed (via immunostaining for ASMA) subsequent to their mechanographic examination in an organ bath environment. Statistical analysis revealed a strong positive correlation between the two factors, where higher MFB density was associated with more forceful contractile response (n = 14).

FIGURE 5

Force responses of rat lumbar fascia samples to exposure to different pharmacological agents. Error bars indicate interquartile range and ^∗ the total range. (A) Percentage of responders shown and their mean force responses during 30 min of substance exposure. Mep, mepyramin; Caff, caffeine; Ang, angiotensin II. (B) Responses to TGF-β1 and botulinum toxin type C3 occurred during much longer time periods. (C) Incubation with specific inhibitor substances prior to stimulation with U46619 led to the reduced force responses—compared with stimulation by U46619 alone—shown here. Repeated preparatory cycles of freezing and rapid thawing completely abolished force response.

FIGURE 6

Examples of force responses with repeated stimulation. (A) Fascia sample was treated with U46619 and then washed out thoroughly for 1 h before repeated stimulation with the same agent. (B) Preincubation with the Rho-kinase inhibitor Y-27632 led to a reduced force increase in response to the 2nd application of U46619.