Sometimes a new critical study is found which helps me and the other researchers understand a little better just how chondrocytes in cartilage turn into volumetrically growing bones and cartilage like growth plates. This is one of those studies. it may not seem like a lot for the person who just wants the step-by-step manual on how to grow taller, but for the researchers, this study is in my opinion one of the most insightful studies written due to the fact it shows just how the growth plates seem to be formed as a function of the overall volumetric shape or form that they are in.
Center of Molecular Medicine, Department of Women and Child Health, Karolinska Institutet and University Hospital Stockholm, Sweden
Abstract
Longitudinal bone growth occurs at the growth plate, which is located near the ends of long bones. At the growth plate, cartilage expansion, through chondrocyte proliferation, hypertrophy and matrix production results in elongation of the bone. This process is orchestrated by the interaction of a large number of endocrine and paracrine factors. The study of these complex interactions has been limited by the lack of well characterized chondrocyte culture models and that growth plate chondrocytes cultured in mono-layer rapidly de-differentiate into fibroblast-like cells with high expression of Collagen type I (Col1) and minimal expression of chondrocytic markers, Collagen type II (Col2) and X (Col10). Dedifferentiated rat growth plate chondrocytes in monolayer were trypsinized and centrifuged to form high-density pellets. The cells rapidly (within 3 days) redifferentiated into Col2-expressing chondrocytes as evidenced by a more than 200-fold increase in Col2 expression, up to a level of expression similar to that of growth plate chondrocytesin vivo. We then assessed expression of newly identified resting (Sfrp5) and proliferative zone (Prelp) markers. With prolonged culture, these chondrocytes underwent a reproducible differentiation program characterized by an early rise in expression of resting zone marker Sfrp5, followed by a rise in the proliferation marker Prelp, and finally an increase in hypertrophic zone markers Indian hedgehog and Col10 expression. Our findings suggest that growth plate chondrocytes cultured in high-density pellets undergo a sequential differentiation program similar to growth plate chondrocytes in vivo. These findings may thus help to improve in vitro studies aimed at clarifying the interactions of endocrine and paracrine factors in the regulation of longitudinal bone growth at the growth plate.
Analysis
One of the things that keeps happening to us as any type of scientific researchers is that once we reach a certain level (usually extremely) of study, the understanding on how a phenomena of a physical mechanism actually happens is impossible. For the study of how the mechanism of growth plate process work at a microscopic level, it is the same as well. We just don’t know many things.
It does seem however that if chondrocyte cultures and growth plate chondrocytes are made into monolayers, they actually de-differentiate into a type of cell known as fibroblast-like cells with express only Collegen Type I, not the Type II and Type X which is seen in hyaline cartilage and hypertrophic epiphyseal zones.
The researchers either intentionally or accidently did something that resulted in the fibroblast-like cells to re-differentiate back into growth plate chondrocytes found in vivo. They ” trypsinized and centrifuged to form high-density pellets.” So it seems that they added some type of protein or enzyme called trypsin and took the monolayer cell cultures and spinned them until they turned into 3-D pellets that had the cells in a high density concentration.
The process took just 3 days for the fibroblasts-like cells to turn back into chondrocytes. This was checked with analysis of Collagen Type II testing, which showed a 200 times increase.
In addition, the researchers tested for certain “markers” which signify that a certain zone in growth plates were around
- Resting Zone Markers – Sfrp5
- Proliferation Zone Markers – Prelp
- Hypertrophy Zone Markers – indian hedgehog and Collagen Type X
They state, “Our findings suggest that growth plate chondrocytes cultured in high-density pellets undergo a sequential differentiation program similar to growth plate chondrocytes in vivo.”
This shows an important point which we will need to understand if we ever plan to create a type of research program or do any type of laboratory experiments to get a type of cartilage tissue that functions almost exactly like the growth plates found in human bodies.
We need to form 3-D pellets for growth plates to work, not monolayers. Any type of cartilage structure we decide to create must have a 3-D form, not something very thin.
Pellets with the diameter large enough to be re-implanted into lab rabbits to test to see if they restart the longitudinal growth process will be done first. That was proven to be successful in studies done by a group of researchers in Hong Kond.
Eventually one day that pellet must be big enough in width, and have the right thickness as well as structure strength to be implanted back into an adult human’s tibia or femur to get them to start growing their bone longer again.
