Chondrocytes from iPSC will restore articular cartilage
Pain in the knee and other joints significantly worsens the quality of life not only of the elderly, but also, in some cases, of young people. Very often, the cause of joint pain is the destruction of hyaline cartilage that is unable to regenerate independently. Hyaline cartilages consist of chondrocytes and extracellular matrix proteins secreted by them – collagens of types II and XI. The composition of these cartilages does not include type I collagen, which is the main component of fibrous cartilage or scar tissue. Therefore, the secret of successful restoration of the destroyed hyaline cartilage is the introduction of chondrocytes into it, secreting only collagens of types II and XI.
One of the most common strategies for treating hyaline cartilage damage is autologous chondrocyte transplantation. This technique involves the isolation of a fragment of hyaline cartilage by biopsy and its transplantation into the area of damage. Since the transplanted fragment is usually smaller than the damage zone, chondrocytes must multiply, which is impossible without enzymatic cleavage of extracellular matrix proteins. Unfortunately, in the process of division, chondrocytes actually lose their chondrogenic potential and begin to synthesize type I collagen, which inevitably leads to the formation of scar tissue.
In search of a solution to this problem, Japanese researchers from Kyoto University, working under the guidance of Professor Noriyuki Tsumaki, have developed a protocol that allows using induced pluripotent stem cells (iPSCs) as the starting material, not chondrocytes.
At the first stage, human iPSCs were propagated under laboratory conditions until a sufficiently large population was obtained. After that, they were placed in a specially developed medium containing bone morphogenetic protein-2 (BMP2), transforming growth factor-beta-1 (TGF-beta1) and growth and differentiation factor-5 (GDF5). This combination of growth factors provided targeted chondrogenic differentiation of iPSCs. After six weeks of cultivation in suspension culture, the cells stopped dividing and formed homogeneous cartilage particles with a diameter of 1-2 mm (Fig. 1).
Here and below are the pictures – Professor Noriyuki Tsumaki / Stem Cell Research
The proteins synthesized by them were exclusively proteins of the extracellular matrix of hyaline cartilage. These particles, each of which consisted of approximately 70,000 chondrocytes, were isolated from culture and transplanted into animal models (Fig. 2).
The researchers used immunodeficient mice, immunodeficient rats and immunodeficient mini-pigs as animal models. During subcutaneous transplantation to immunodeficient mice, cartilage particles formed hyaline cartilage expressing type II collagen and non-expressing type I collagen. At the same time, transplantation into joint defects of other immunodeficient models demonstrated the ability of the emerging new cartilage tissue to survive in the conditions of the recipient's body and integrate into his own cartilage tissue (Fig. 3). At the same time, the formation of tumors or fragments of ectopic tissue was not detected in animals.
The researchers note that the direct production of chondrocytes from iPSC cancels the need for the breakdown of extracellular matrix proteins, avoiding the problem of formation of fibrous scar tissue and ensuring the formation of hyaline cartilage.
In addition, the new approach makes it possible to abandon the use of artificial scaffolds used in other studies with chondrocytes obtained from embryonic and induced stem cells. Such cells, as a rule, were transplanted together with a framework supporting them before they began to independently produce extracellular matrix proteins. However, the researchers believe that artificial scaffold materials may interfere with the optimal integration of the transplanted material into the recipient's tissue.
According to the authors, it takes about a million chondrocytes to restore a 1 cm2 piece of cartilage. The size of cartilage damage in human joints is usually 2-10 cm2, which requires transplantation of 30-150 cartilage particles, which can be obtained using the developed technique is quite realistic. In general, the developers are very pleased with the results of the experiments, but emphasize their preliminary nature and the need for research on larger animal models.
Article by Akihiro Yamashita et al. Generation of scaffold hyaline cartoonish tissue from human iPS cells is published in the journal Stem Cell Reports.
Evgeniya Ryabtseva
Portal "Eternal youth" http://vechnayamolodost.ru based on the materials of the Center for IPS cell research and application,
Kyoto University: Scaffold-free iPS cell-based hyaline cartilage for joint repair.
02.03.2015