The Ideal Recipe for Cartilage from Stem Cells


Researchers at Case Western Reserve and Harvard University will use a 5-year, $2-million NIH grant to build a microfactory that bangs out the optimal formula for joint cartilage. Such an end product could one day potentially benefit many of the tens of thousands of people in the United States who suffer from cartilage loss or damage.

Joint cartilage or articular cartilage caps the ends of long bones and bears the loads, absorbs shocks and, in combination with lubricating synovial fluid, helps knees, hips, shoulders, and other joints to smoothly bend, lift, and rotate. Unfortunately, this tissue has little capacity to regenerate, which means that there is a critical need for new therapeutic strategies.

Artificial substitutes cannot match real cartilage and attempts to engineer articular cartilage have been stymied by the complexities of directing stem cells to differentiate into chondrocytes and form the right kind of cartilage.

Stem cells are quite responsive to the environmental cues presented to them from their surroundings. What this research project hopes to determine are those specific cue that drive stem cells to differentiate into chondrocytes that make the right kind of cartilage with the right kind of microarchitecture that resembles natural, articular cartilage. To do this, they will engage in a systematic study of the effects of cellular micro-environmental factors that influence stem cell differentiation and cartilage formation.

Bone marrow- and fat-derived mesenchymal stem cells have been differentiated into cartilage-making chondrocytes in the laboratory. These two stem cell populations are distinct, however, and required different conditions in order to drive them to differentiate into chondrocytes. This research group, however, has designed new materials with unique physical properties, cell adhesive capabilities, and have the capacity to deliver bioactive molecules.

By controlling the presentation of these signals to cells, independently and in combination with mechanical cues, this group hopes to identify those most important cues for driving cells to differentiate into chondrocytes.

Ali Khademhosseini specializes in microfabrication and micro-and nano-scale technologies to control cell behavior. He and his team will develop a microscale high-throughput system at his laboratory that will accelerate the testing and analysis of materials engineered in another laboratory.

This research cooperative hopes to test and analyze more than 3,000 combinations of factors that may influence cell development, including differentiation, amounts of biochemicals, extracellular matrix properties, compressive stresses, and more. Khademhosseini and his colleagues hope to begin testing comditions identified from these studies in animal models by the of the grant term.

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Human articular cartilage defects can be treated with nasal septum cells


A report from collaborating research teams from the University and the University Hospital of Basel specifies that cells isolated from the nasal septum cartilage can adapt to the environment the knee and repair articular cartilage defects. The ability of nasal cartilage cells to self-renew and adapt to the joint environment is associated with the expression of genes know as HOX genes. This research was published in the journal Science Translational Medicine in combination with reports of the first patients treated with their own nasal cartilage.

Lesions in articular or joint-specific cartilage is a degenerative that tends to occur in older people or younger athletes who engage in impact-heavy sports. Sometimes people who have experienced accidents can also suffer from cartilage lesions. Cartilage lesions present several challenges for orthopedic surgeons to repair. These surgeries are often complicated, and the recovery times are also long. However, Prof. Ivan Martin, professor of tissue engineering, and Prof. Marcel Jakob, Head of Traumatology, from the Department of Biomedicine at the University and the University Hospital of Basel have presented a new treatment option for cartilage lesions that includes the use of nasal cartilage cells to replace cartilage cells in joints.

When grown in cell culture, cartilage cells extracted from the nasal septum (also known as nasal chondrocytes) have a remarkable ability to generate new cartilage tissue after their growth in culture. In an ongoing clinical study, the Basal research group have taken small biopsies (6 millimeters in diameter) from the nasal septa of seven of 25 patients below the age of 55 years. After isolating the cartilage cells from these cartilage samples, they cultured these cells and expanded them and applied them to a three-dimensional scaffold in order to engineer a cartilage graft with a specific size (30 x 40 millimeters).

Martin and his colleagues used these very cartilage grafts to treat the cartilage lesions in human patients. After removing the damaged cartilage tissue from the knee of several patients, their knees were treated with the engineered, tailored tissue from their noses.

Two previous experiments demonstrated the potential efficacy of this procedure. First, a previous clinical study conducted in cooperation with plastic surgeons and the Basel group used the same method to successfully reconstruct nasal wings affected by tumors.

Secondly, a preclinical study with goats whose knees were implanted with nasal cartilage cells showed that these cells were not only compatible with the knee-joint, but also successfully reconstituted the joint cartilage. Lead author of this study, Karoliina Pelttari, and her colleagues were quite surprised that the implanted nasal cartilage cells, which originate from a completely different set of embryonic cell types than the knee-joint were compatible. Nasal septum cells develop from neuroectodermal cells, which also form the nervous system and their self-renewal capacity is attributed to their lack of expression of some homeobox (HOX) genes. However, these same HOX genes are expressed in articular cartilage cells that are formed by mesodermal cells in the embryo.

“The findings from the basic research and the preclinical studies on the properties of nasal cartilage cells and the resulting engineered transplants have opened up the possibility to investigate an innovative clinical treatment of cartilage damage,” says Prof. Ivan Martin about the results. Several studies have confirmed that human nasal cells maintain their capacity to grow and form new cartilage despite the age of the patient. This means that older people could also benefit from this new method, as could patients with large articular cartilage defects.

The primary target of the ongoing clinical study at the University Hospital of Basel is to confirm the safety, efficacy and feasibility of nasal cartilage grafts transplanted into joints, the clinical effectiveness of this procedure, from the data presently in hand, is highly promising.

Mesenchymal Stem Cells Repair Cartilage Defects in Cynomolgus Monkeys


Repairing cartilage defects in the knee represents one of the primary goals of orthopedic regenerative medicine. Cartilage that covers the joints, otherwise known as articular cartilage, has a limited capacity for repair, which leads to further degeneration of the cartilage when it is damaged if it remains untreated. A number of surgical options for treating cartilage defects include microfracture, osteochondral grafting, and cell-based techniques such as autologous chondrocyte implantation (ACI). Each of these procedures have been used in clinical settings. Unfortunately cartilage injuries treated with microfracturing deteriorate with time, since the cartilage made by microfracturing has a high proportion of softer. less durable fibrocartilage.  Also osteochondral grafting suffers from a lack of lateral integration between host and donor cartilage.

Alternatively, tissue engineering has shown some promise when it comes to the healing of cartilage defects.  Mesenchymal stem cells (MSCs) are multipotent progenitor cells that have the ability to differentiate into several different cell lineages including cartilage-making chondrocytes.  MSCs have theoretical advantages over implanted chondrocytes when it come to healing potential.  MSCs have the ability to proliferate without losing their ability to differentiate into mature chondrocytes and produce collagen II and aggrecan. In the short-term, bone marrow-derived MSCs combined with scaffolds have been successful in cartilage repair using animal models such as rabbits (Dashtdar H, et al., J Orthop Res 2011; 29: 1336-42) sheep (Zscharnack M, et al., Am J Sports Med 2010; 38: 185769) and horses (Wilke MM, et al.,l J Orthop Res 2007; 25: 9132).  

In a recent study, Kazumasa Ogasawara and Yoshitaka Matsusue and their colleagues from Shiga University of Medical Science in Shiga, Japan, tested the ability of expanded bone marrow-derived MSCs that had been placed in a collagen scaffold to improve healing of cartilage defects in cynomolgus macaques (type of monkey).  Before this study, there were no previous studies using MSCs from primates for cartilage repair.  The monkey MSCs were shown to properly differentiate into fat, bone, or cartilage in culture, and then were transplanted into the injured cartilage in the cynomolgus macaque.  The efficacy of these cells were ascertained at 6, 12, and 24 weeks after transplantation.

In culture, the cynomolgus MSCs were able to differentiate into fat, bone, and cartilage.

Characteristics of bone marrow-derived MSCs. Panel (a) demonstrates the colony-forming properties of MSCs isolated from bone marrow of cynomolgus macaques using the present protocol (arrows). Bar: 1 cm. Panel (b) shows the adipogenetic properties of MSC-derived cells from staining of lipid droplets with oil red O (arrowheads). Bar: 20 μm. Panel (c) confirms the osteoblastic properties of MSC-derived cells with alkaline phosphatase staining (arrowheads). Bar: 30 μm. Panel (d) confirms the chondrogenetic properties from immunostaining of type-II collagen. Type-II collagen-positive matrix is stained red. Bar: 0.5 mm. Read More: http://informahealthcare.com/doi/full/10.3109/17453674.2014.958807.
Characteristics of bone marrow-derived MSCs. Panel (a) demonstrates the colony-forming properties of MSCs isolated from bone marrow of cynomolgus macaques using the present protocol (arrows). Bar: 1 cm. Panel (b) shows the adipogenetic properties of MSC-derived cells from staining of lipid droplets with oil red O (arrowheads). Bar: 20 μm. Panel (c) confirms the osteoblastic properties of MSC-derived cells with alkaline phosphatase staining (arrowheads). Bar: 30 μm. Panel (d) confirms the chondrogenetic properties from immunostaining of type-II collagen. Type-II collagen-positive matrix is stained red. Bar: 0.5 mm.
Read More: http://informahealthcare.com/doi/full/10.3109/17453674.2014.958807.

Upon transplantation into cartilage defects in the knee cartilage of cynomolgus monkeys, MSCs were compared with collagen gel devoid of MSCs.  The knees that received the transplantations did not show any signs of irritation, bone spurs or infection.  All of the animals had so-called “full-thickness cartilage defects,” and those in the non-treated group showed cartilage defects that did not change all that much.  The cartilage defects of the gel group had sharp edges at 6 weeks that were thinly covered with reparative tissue by 12 weeks, and at 24 weeks, the defect was covered with thick tissue, but the central region of the defects often remained uncovered, with a hollow-like deformity.  In the cartilage defects of those animals treated with MSCs plus the collagen gel, the sharp edges of the defects were visible at 6 weeks after the operation, but at 12 weeks, the defects were evenly covered with yellowish reparative tissue.  At 24 weeks, the defects were covered with watery hyaline cartilage-like tissue that was very similar to the neighboring naïve cartilage.

Macroscopic observations of the repaired defects in the 3 groups at 6 weeks (a, d, g), 12 weeks (b, e, h), and 24 weeks (c, f, i) after implantation. Scale bar: 5 mm. Arrow in (d): the sharp edge of the defect is visible at 6 weeks in the gel group. Arrow in (f): a hollow-like deformity remains in the central region of the defect, despite thick coverage by the reparative tissue. Arrow in (g): the sharp edge of the defect is also visible in the MSC group at 6 weeks. Read More: http://informahealthcare.com/doi/full/10.3109/17453674.2014.958807.
Macroscopic observations of the repaired defects in the 3 groups at 6 weeks (a, d, g), 12 weeks (b, e, h), and 24 weeks (c, f, i) after implantation. Scale bar: 5 mm. Arrow in (d): the sharp edge of the defect is visible at 6 weeks in the gel group. Arrow in (f): a hollow-like deformity remains in the central region of the defect, despite thick coverage by the reparative tissue. Arrow in (g): the sharp edge of the defect is also visible in the MSC group at 6 weeks.
Read More: http://informahealthcare.com/doi/full/10.3109/17453674.2014.958807.

When evaluated at the tissue level, Ogasawara and Matsusue and others used a stain called toluidine blue to visualize the amount of cartilage made by each treatment.  As you can see in the picture below, the non-treated group didn’t do so well.  In the full-thickness defect the region below the cartilage was filled with amorphous stuff 6 weeks after the procedure, and at 12 weeks, amorphous stuff faintly stained with toluidine blue, which reflects the conversion of the amorphous stuff into bone.  At 24 weeks, bone tissue reappeared below the cartilage zone, even though the bone did not look all that normal (no trabecular structure but woven bone-like structure).

In the gel group, cartilage-like tissue is seen at 6 weeks, and at 12 weeks, the faintly stained layer covered the cartilage defect. At 24 weeks, the defect was covered with the cartilage-like stuff, even though the central region had only a little cartilage, as ascertained by toluidine blue staining.  The bone underneath the cartilage looked crummy and there was excessive growth of cartilage into the region underneath the cartilage layer.

In the MSC group, the bone underneath the cartilage healed normally, and at 12 weeks, the boundary between the articular cartilage and the bone layer beneath it had reappeared.  At 24 weeks, the thickness of the toluidine blue-stained cartilage layer was comparable to that of the neighboring naïve cartilage.

Even though the gel group showed most cartilage-rich tissue covering the defect, this was due to the formation of excessive cartilage extruding through the abnormal lower bone layer.  Despite the lower amount of new cartilage produced, the MSC group showed better-quality cartilage with a regular surface, seamless integration with neighboring naïve cartilage, and reconstruction of the bone underneath the cartilage layer.

Histological findings after toluidine blue staining in the 3 groups at 6 weeks (a, d, g), 12 weeks (b, e, h), and 24 weeks (c, f, i) after implantation. Scale bar: 2 mm. Dotted line in (a): amorphous reparative tissue filling the subchondral region. Arrowheads in (b): faint toluidine blue staining that reflects involvement of endochondral ossification. Arrowhead in (c): toluidine blue-negative reparative tissue covering the defect. Dotted line in (c): reconstructed subchondral bone consisting of woven bone-like structure. Arrowhead in (d): toluidine blue-positive cartilaginous tissue. Arrowhead in (e): thin faintly toluidine blue-positive layer covering the defect. Arrowhead in (f): the unstained central region of the cartilaginous layer covering the defect. Arrow in (f): excessive cartilage extruding through the deficient tidemark. Dotted line in (g): woven bone-like subchondral bone already re-appearing at 6 weeks. Arrowhead in (h): reconstructed tidemark distinctly discriminating the articular cartilage from the subchondral bone.
Histological findings after toluidine blue staining in the 3 groups at 6 weeks (a, d, g), 12 weeks (b, e, h), and 24 weeks (c, f, i) after implantation. Scale bar: 2 mm. Dotted line in (a): amorphous reparative tissue filling the subchondral region. Arrowheads in (b): faint toluidine blue staining that reflects involvement of endochondral ossification. Arrowhead in (c): toluidine blue-negative reparative tissue covering the defect. Dotted line in (c): reconstructed subchondral bone consisting of woven bone-like structure. Arrowhead in (d): toluidine blue-positive cartilaginous tissue. Arrowhead in (e): thin faintly toluidine blue-positive layer covering the defect. Arrowhead in (f): the unstained central region of the cartilaginous layer covering the defect. Arrow in (f): excessive cartilage extruding through the deficient tidemark. Dotted line in (g): woven bone-like subchondral bone already re-appearing at 6 weeks. Arrowhead in (h): reconstructed tidemark distinctly discriminating the articular cartilage from the subchondral bone.

This protocol has been nicely optimized by Ogasawara and Matsusue and their research team.  From these data, they conclude:  “Application in larger defects is certainly in line with future clinical use. If MSCs—under optimized conditions—turn out to be superior to chondrocyte implantation in experimental cartilage repair, the procedure should be introduced to clinical practice after well-controlled randomized clinical trials.”  Hopefully, clinical trials will commence before long.  This procedure uses a patient’s own MSCs, and if such a procedure could reduce or delay the number of knee replacements, then it would surely be a godsend to clinicians and patients alike.

Stem Cell Therapy Following Meniscus Knee Surgery Reduces Pain and Regenerates Meniscus


According to a new study published in the January issue of the Journal of Bone and Joint Surgery (JBJS), a single stem cell injection after meniscus knee surgery can provide pain relief and aid in meniscus regrowth.

In the US alone, over one million knee arthroscopy procedures are performed each year. These surgeries are usually prescribed to treat tears to the wedge-shaped piece of cartilage on either side of the knee called the “meniscus.” The meniscus acts as an important shock absorber between the thighbone (femur) and the shinbone (tibia) at the knee-joint.

Knee-Ligament-Pain-and-Strains-Meniscus-Tear-and-Pain

This novel study, “Adult Human Mesenchymal Stem Cells (MSC) Delivered via Intra-Articular Injection to the Knee, Following Partial Medial Meniscectomy,” examined 55 patients who had undergone a surgical removal or all or part of a torn meniscus (known as a partial medial meniscectomy). Each patient was randomly assigned to one of three treatment groups: Groups A, B and C. The 18 patients in group A received a “low-dose” injection of 50 million stem cells within seven to 10 days after their meniscus surgery. Another 18 patients in group B received a higher dose of 150 million stem cells seven to ten days after their knee surgery. The controls group consisted of 19 patients who received injections of sodium hyaluronate only (no stem cells). All patients were evaluated to determine the safety of the procedure, the degree of meniscus regeneration (i.e. with MRI and X-ray images), the overall condition of the knee-joint, and the clinical outcomes through two years. Most of the patients enrolled in this study had some arthritis, but patients with severe (level three or four) arthritis, were excluded from the study.

Most of the patients who had received stem cell treatments reported a significant reduction in pain. 24 percent of the patients in one MSC group and 6 percent of the other showed at least a 15 percent increase in meniscal volume at one year. Unfortunately, there was no additional increase in meniscal volume at year two.

“The results demonstrated that high doses of mesenchymal stem cells can be safely delivered in a concentrated manner to a knee-joint without abnormal tissue formation,” said lead study author C. Thomas Vangsness, Jr., MD. “No one has ever done that before.” In addition, “the patients with arthritis got strong improvement in pain” and some experienced meniscal regrowth.

The key findings of this study are that there no abnormal (ectopic) tissue formation or “clinically important” safety issues identified. Also, 24 percent of the patients in the low-dose injection group (A) and six percent of the high-dose injection group (B) at one year showed “significantly increased meniscal volume,” as determined by an MRI, and this increase did not continue into the second year, but remained stable (should future studies try a second injection of MSCs?). Third, none of the patients in the control group (non-MSC group) showed significant meniscus regrowth. Finally, patients with osteoarthritis experienced a reduction in pain in the stem cell treatment groups, but there was no reduction in pain in the control (non-MSC group).

“The results of this study suggest that mesenchymal stem cells have the potential to improve the overall condition of the knee joint,” said Dr. Vangsness. “I am very excited and encouraged” by the results. With the success of a single injection, “it begs the question: What if we give a series of injections?”

Muscle-Derived Stem Cells And Platelet-Rich Plasma Improve Cartilage Formation


Skeletal muscle contains a stem cell population called muscle derived stem cells or MDSCs that might have tremendous therapeutic potential. MDSCs have been isolated from skeletal muscle by means of their ability to adhere to culture flasks coated with collagen. Samples of muscle taken from a biopsy are mechanically mashed and then treated with enzymes the separate the cells. These cells are plated onto collagen-coated dishes and the cells either adhere quickly (fibroblasts and myoblasts), or slowly (MDSC-enriched fraction).

Skeletal muscle contains another cell population known as satellite cells. Satellite cells can divide and form muscle progenitor cells known as myoblasts that fuse to form myotubes. MDSCs, however, as distinct from satellite cells. They express different sets of genes: satellite cells typically express Pax7, whereas MDSCs are more heterogeneous but express Sca-1 consistently and often express CD34.

Studies in culture and in living animals have established that MDSCs can self-renew and differentiate into multiple lineages. They also have the potential to regenerate various adult tissues. See Usas A, et al Medicina (Kaunas) 2011;47:469–479; Cao B, et al Nat Cell Biol. 2003;5:640–646; Deasy BM, et al Blood Cells Mol Dis. 2001;27:924–933.

MDSCs also display a superior regenerative capacity relative to satellite cells following transplantation into mice with a form of rodent muscular dystrophy (mdx mice). MDSCs are at least partially invisible to the immune system. When transplanted into mdx mice and left for at least 3 months, no sign of immune rejection was detected.

The laboratory of Johnny Huard at the University of Pittsburgh has been genetically engineering MDSCs from mouse for use as cartilage making cells to treat rodents with osteoarthritis. In 2009, Huard’s group published an intriguing paper in the journal Arthritis and Rheumatism in which they genetically engineered MDSCs with two genes: Bone Morphogenetic Protein 4 (BMP-4) and Soluble Flt-1. If you are wondering what the heck these two genes encode, then you are not alone. BMP-4 is a secreted signaling protein that is very important for bone healing, but it also plays a central role in helping cartilage-making cells (chondrocytes) survive and divide. Flt-1 is one of the receptor proteins that binds the growth factor VEGF (vascular endothelial growth factor).  Normally, VEGF forms blood vessels and remodels existing blood vessels.  However, when it comes to cartilage, VEGF tends to cause cartilage to die back.  Therefore, Huard’s group used a soluble version of Flt-1, which scavenged the available VEGF in the environment and bound it up.

In their 2009 paper, Huard and others showed that BMP-4/soluble Flt-1-expressing MDSCs did a remarkable job of making new cartilage and repairing damage joint cartilage in rodents.  See Tomoyuki Matsumoto, et al ARTHRITIS & RHEUMATISM Vol. 60, No. 5, May 2009, pp 1390–1405.

A and B, Macroscopic (A) and histologic (B) evaluation of representative joints from rats injected with muscle-derived stem cells (MDSCs) transduced with soluble Flt-1 (sFlt-1) and bone morphogenetic protein 4 (BMP-4 [B4]) (sFlt-1/BMP-4–MDSC), MDSCs transduced with vascular endothelial growth factor (VEGF) and BMP-4 (VEGF/BMP-4–MDSC), MDSCs transduced with BMP-4 alone (BMP-4–MDSC), nontransduced MDSCs (MDSC), or phosphate buffered saline (PBS) alone, 4 and 12 weeks after transplantation. Four weeks after transplantation, the sFlt-1/BMP-4–MDSC and BMP-4–MDSC groups macroscopically and histologically showed smooth joint surface with well-repaired articular cartilage and Safranin O–positive hyaline-like cartilage (red staining in B). However, the other groups showed marked arthritic progression, synovial hypertrophy, and osteophyte formation (arrows). Twelve weeks after transplantation, although the sFlt-1/BMP-4–MDSC group still showed well-repaired articular cartilage, the other groups exhibited more severe arthritis compared with 4 weeks. (Original magnification  100.) C, Semiquantitative histologic scores for all groups, 4 and 12 weeks following transplantation. The sFlt-1/BMP-4–MDSC group had the lowest (best) scores of all groups. Bars show the mean and SEM.   P   0.05 versus all other groups;   P   0.05 versus the VEGF/BMP-4–MDSC, MDSC, and PBS groups.
A and B, Macroscopic (A) and histologic (B) evaluation of representative joints from rats injected with muscle-derived stem cells (MDSCs) transduced with soluble Flt-1 (sFlt-1) and bone morphogenetic protein 4 (BMP-4 [B4]) (sFlt-1/BMP-4–MDSC), MDSCs transduced with vascular endothelial growth factor (VEGF) and BMP-4 (VEGF/BMP-4–MDSC), MDSCs transduced with BMP-4 alone (BMP-4–MDSC), nontransduced MDSCs (MDSC), or phosphate buffered saline (PBS) alone, 4 and 12 weeks after transplantation. Four weeks after transplantation, the sFlt-1/BMP-4–MDSC and BMP-4–MDSC groups macroscopically and histologically showed smooth joint surface with well-repaired articular cartilage and Safranin O–positive hyaline-like cartilage (red staining in B). However, the other groups showed marked arthritic progression, synovial hypertrophy, and osteophyte formation (arrows). Twelve weeks after transplantation, although the sFlt-1/BMP-4–MDSC group still showed well-repaired articular cartilage, the other groups exhibited more severe arthritis compared with 4 weeks. (Original magnification  100.) C, Semiquantitative histologic scores for all groups, 4 and 12 weeks following transplantation. The sFlt-1/BMP-4–MDSC group had the lowest (best) scores of all groups. Bars show the mean and SEM.   =P<0.05 versus all other groups;  =P<0.05 versus the VEGF/BMP-4–MDSC, MDSC, and PBS groups.
In another paper that came out in January of this year, Huard has used platelet-rich plasma with his engineered MDSCs to determine with platelet-rich plasma (PRP) can increase the cartilage-making activity of engineered MDSCs.

Since PRP has been reported to promote the synthesis of collagen and cell proliferation, and increase cartilage repair, it is possible that, when paired with the right stem cells, PRP can enhance cartilage repair.  To test this suspicion, MDSCs expressing BMP-4 and sFlt1 were mixed with PRP and injected into the knees of rats whose immune system did not work properly that had osteoarthritis.  Osteoarthritis can be chemically induced in rats rather easily, and the rats were treated with MDSCs expressing BMP-4 and sFlt1 or MDSCs expressing BMP-4 and sFlt1 plus PRP.  Tissue assessments of the arthritic joints were performed 4 and 12 weeks after cell transplantation.  Other tests conducted in culture determined the cell proliferation, adhesion, migration and cartilage-making capacities of cells in culture.

The results showed that addition of PRP to MDSCs expressing BMP-4 and sFlt1 significantly improved joint cartilage repair at week 4 compared to MDSCs expressing BMP-4 and sFlt1 alone.  The joints showed higher numbers of cells producing type II collagen and lower levels of chondrocyte cell death were observed by MDSCs expressing BMP-4 and sFlt1 and mixed with PRP.  In culture, the addition of PRP promoted proliferation, adhesion and migration of the MDSCs.  When pellets of cells were induced to make cartilage in culture, PRP tended to increase the number of type II collagen producing cells.

From this, Huard and his colleagues concluded that PRP can promote the cartilage-repairing capacities of MDSCs that express BMP-4 and sFlt1.  This enhancement involves the promotion of collagen synthesis, the suppression of chondrocyte cell death, and by enhancing the integration of the transplanted cells in the repair process.

See Mifune Y, et al Osteoarthritis Cartilage. 2013 Jan;21(1):175-85. doi: 10.1016/j.joca.2012.09.018.