Takeaway: Fibroblasts remodel fascia, creating or removing collagen based on physical supply and demand.

Wherever you live, it’s almost certain you have a Public Works Department. Public works cares for much of the local infrastructure, including things like streetlights, sidewalks, and roadside gardens and trees. But chances are, you don’t think about public works except when they’re inconveniencing you. You’ll see workers in their brightly colored, fluorescent garb digging up a street to fix a water line and creating a detour that’s going to make you late to work. But they’re out there, doing a necessary—and mostly thankless—job. They’re a lot like the fibroblast, my favorite cell of the more than 200 cell types we have in our bodies.

Required Maintenance

Fibroblasts make up our inner public works department; they maintain our collagen infrastructure by building, demolishing, cleaning up, and even rendering emergency aid when there’s an injury like a cut on the skin. 

Fibroblasts are the most abundant cells in fascia. They arise primarily from the mesoderm (the middle layer of the embryo). I use the term layer here because some regard the mesoderm as not a layer at all, but rather a liminal space between the inner endoderm and the outer ectoderm. But it’s useful to think of the mesoderm as a layer, since it functions to create the biological collagen scaffold that gives structure to our insides (e.g., our organs) as well as our outsides (our head, limbs, nervous system, and skin), and keeps them separate but also interconnected.

The fibroblasts are the cells dressed in fluorescent-colored shirts, and they’re always busy. They produce the fibers of collagen and elastin in the connective tissue matrix as well as the components of ground substance, the gel-like base of all connective tissue. When we cut ourselves, fibroblasts in the area will suddenly express strong contractile properties—called myofibroblasts—to help close the wound.

Furthermore, the fibroblasts are connected to each other via long cellular extensions called filopodia. If you imagine the fascial matrix as a body-wide web, the fibroblasts are the spiders that are responsible for the production and maintenance of that web. All these spiders are also connected to each other, forming their own network of connections within the interconnected web of fascia. In essence, the fibroblasts form a body-wide signaling network.

While the fibroblasts are also involved in inflammation and immune function, too much fibroblast and myofibroblast activity is implicated in both fibrosis and chronic contracture conditions like Dupuytren’s disease. However, what’s most interesting to us is how they decide whether to produce more collagen or to secrete an enzyme—collagenase—to remove unneeded collagen. While this can be influenced by physiologic and metabolic functions, fibroblasts do this primarily through a non-neuronal process—no nervous system required. That’s because fibroblasts are equipped with a primary cilium, a hair-like antenna whose job is to listen (or rather feel) for two mechanical messages: pressure and vibration.

POWER IN NUMBERS

Imagine you want to take up a new hobby of jumping on one leg, for which you practice every day. For one hour a day, seven days a week, your right knee is flexed and you’re bouncing up and down with your left leg. Over a 3- to 6-month period, you would strengthen quite a few muscles, but you would also completely remodel the fascial network in both legs and hips. For example, the fibroblasts in the fascia of your right leg would create more collagen in your right knee to support the constant flexion, and the fascia surrounding the hamstrings, quadriceps, and hip flexors would be affected too. 

The left side would be affected not only to allow for more bounce but also to create tougher collagen along the path up the left side from the foot to the spine, as a result of the constant mechanical pressure (or force transmission). And, of course, the bones would also be affected.

Patterns of bone strength and formation follow Wolff’s Law, which states that bone will adapt to regular loading, growing stronger over time. This is a lifelong process. It also explains why simple weight lifting (within reason) can halt or even reverse osteoporosis. The opposite is also true, like when astronauts in prolonged microgravity actually lose bone mass and need to undergo a strengthening regimen upon their return to Earth.

While I’m not aware of anyone measuring astronauts’ soft tissue, fascia is thought to follow Davis’s Law, which states that soft tissue also models and remodels based on physical loading and stresses. Davis’s Law is named after Henry Gasset Davis, an orthopedic surgeon from the 1800s who developed a number of traction-based, nonsurgical therapies to induce changes in soft tissue.

Given that fibroblasts respond to pressure and vibration, we can conclude they are also direction sensitive, so it’s reasonable to extrapolate that certain forms of manual therapy and massage have the potential to affect the behavior of fibroblasts. The collagen changes are initially small, with recent estimates suggesting 1 cm of length change per month, but when you consider the body-wide interconnectedness of most people’s compensation patterns, lengthening by a centimeter here and there can make a big difference. This difference recapitulates itself on the cellular level every time that person moves and bears weight slightly differently than before treatment, because your inner public works department—your fibroblasts—are on the job, receiving slightly different pressure signals than before the treatment and responding accordingly. 

Resources

Grinnell, F. “Fibroblast Mechanics in Three-Dimensional Collagen Matrices.” Journal of Bodywork and Movement Therapies 12, no. 3 (July 2008): 191–3. https://doi.org/10.1016/j.jbmt.2008.03.005.

Langevin, H. “Connective Tissue: A Body-Wide Signaling Network?” Medical Hypotheses 66, no. 6 (2006): 1,074–7. https://doi.org/10.1016/j.mehy.2005.12.032.

 Langevin, H., C. J. Cornbrooks, and D. J. Taatjes. “Fibroblasts Form a Body-Wide Cellular Network.” Histochemistry and Cell Biology 122 (2004): 7–15. https://doi.org/10.1007/s00418-004-0667-z.

‌Nelson, M. E., and S. Wernick. 2000. Strong Women Stay Young. New York: Bantam Books.