The Role of Oncostatin M and Its Receptor Complexes in Cardiomyocyte Protection, Regeneration, and Failure.

Oncostatin M (OSM), a member of the interleukin-6 family, functions as a major mediator of cardiomyocyte remodeling under pathological conditions. Its involvement in a variety of human cardiac diseases such as aortic stenosis, myocardial infarction, myocarditis, cardiac sarcoidosis, and various cardiomyopathies make the OSM receptor (OSMR) signaling cascades a promising therapeutic target. However, the development of pharmacological treatment strategies is highly challenging for many reasons. In mouse models of heart disease, OSM elicits opposing effects via activation of the type II receptor complex (OSMR/gp130). Short-term activation of OSMR/gp130 protects the heart after acute injury, whereas chronic activation promotes the development of heart failure. Furthermore, OSM has the ability to integrate signals from unrelated receptors that enhance fetal remodeling (dedifferentiation) of adult cardiomyocytes. Because OSM strongly stimulates the production and secretion of extracellular proteins, it is likely to exert systemic effects, which in turn, could influence cardiac remodeling. Compared with the mouse, the complexity of OSM signaling is even greater in humans because this cytokine also activates the type I leukemia inhibitory factor receptor complex (LIFR/gp130). In this article, we provide an overview of OSM-induced cardiomyocyte remodeling and discuss the consequences of OSMR/gp130 and LIFR/gp130 activation under acute and chronic conditions.

Long-term results after mitral valve surgery using minimally invasive versus sternotomy approach: a propensity matched comparison of a large single-center series.

BACKGROUND: Mitral valve (MV) surgery has traditionally been performed by conventional sternotomy (CS), but more recently minimally invasive surgery (MIS) has become another treatment option. The aim of this study is to compare short- and long-term results of MV surgery after CS and MIS. METHODS: This study was a retrospective propensity-matched analysis of MV operations between January 2005 and December 2015. RESULTS: Among 1357 patients, 496 underwent CS and 861 MIS. Matching resulted in 422 patients per group. The procedure time was longer with MIS than CS (192 vs. 185 min; p = 0.002) as was cardiopulmonary bypass time (133 vs. 101 min; p < 0.001) and X-clamp time (80 vs. 71 min; p < 0.001). 'Short-term' successful valve repair was higher with MIS (96.0% vs. 76.0%, p < 0.001). Length of hospital stay was shorter in MIS than CS patients (10 vs. 11 days; p = 0.001). There was no difference in the overall 30-day mortality rate. Cardiovascular death was lower after MIS (1.2%) compared with CS (3.8%; OR 0.30; 95%CI 0.11-0.84). The difference did not remain significant after adjustment for procedural differences (aOR 0.40; 95%CI 0.13-1.25). Pacemaker was required less often after MIS (3.3%) than CS (11.2%; aOR 0.31; 95%CI 0.16-0.61), and acute renal failure was less common (2.1% vs. 11.9%; aOR 0.22; 95%CI 0.10-0.48). There were no significant differences with respect to rates of stroke, myocardial infarction or repeat MV surgery. The 7-year survival rate was significantly better after MIS (88.5%) than CS (74.8%; aHR 0.44, 95%CI 0.31-0.64). CONCLUSION: This study demonstrates that good results for MV surgery can be obtained with MIS, achieving a high MV repair rate, low peri-procedural morbidity and mortality, and improved long-term survival.

Myocardial Accumulations of Reg3A, Reg3γ and Oncostatin M Are Associated with the Formation of Granulomata in Patients with Cardiac Sarcoidosis.

Cardiac sarcoidosis (CS) is a poorly understood disease and is characterized by the focal accumulation of immune cells, thus leading to the formation of granulomata (GL). To identify the developmental principles of fatal GL, fluorescence microscopy and Western blot analysis of CS and control patients is presented here. CS is visualized macroscopically by positron emission tomography (PET)/ computed tomography (CT). A battery of antibodies is used to determine structural, cell cycle and inflammatory markers. GL consist of CD68+, CD163+ and CD206+ macrophages surrounded by T-cells within fibrotic areas. Cell cycle markers such as phospho-histone H3, phospho-Aurora and Ki67 were moderately present; however, the phosphorylated ERM (ezrin, radixin and moesin) and Erk1/2 proteins, strong expression of the myosin motor protein and the macrophage transcription factor PU.1 indicate highly active GL. Mild apoptosis is consistent with PI3 kinase and Akt activation. Massive amounts of the IL-1R antagonist reflect a mild activation of stress and inflammatory pathways in GL. High levels of oncostatin M and the Reg3A and Reg3γ chemokines are in accordance with macrophage accumulation in areas of remodeling cardiomyocytes. We conclude that the formation of GL occurs mainly through chemoattraction and less by proliferation of macrophages. Furthermore, activation of the oncostatin/Reg3 axis might help at first to wall-off substances but might initiate the chronic development of heart failure.

Comparison of flexible, open with semi-rigid, closed annuloplasty-rings for mitral valve repair.

BACKGROUND: Mitral regurgitation is a frequent valvular disease, with an increasing prevalence. We analysed the long-term outcomes of mitral valve repair procedures conducted over the last 10 years in our clinic using almost exclusively two different annuloplasty ring types. METHODS: A single-centre, retrospective analysis of mitral valve surgeries conducted between January 2005 and December 2015 for patients undergoing first-line mitral valve repair with either open (Cosgrove) or closed (CE Physio / Physio II) annuloplasty (OA or CA, respectively) rings. RESULTS: In total, 1120 patient documentations were available of which 528 underwent OA and 592 patients CA. The median age of patients was 64.0 years and 41.1% were female. The majority of these patients underwent the procedure because of degenerative valve disease. Rates of successful repair were about 90%, 72 h procedural mortality was 0.6% and the rate of re-intervention was 0.6% within the first 30 days. Functional (mitral regurgitation, left ventricular ejection fraction, left ventricular end-diastolic and systolic diameter and New York Heart Association class) as well as hard outcomes were comparable. 77.7 and 74.4% of patients were alive at the 10-year follow-up in the OA and CA groups, respectively. Upon multivariable adjustment, the hazard ratio was 0.926 (95% CI: 0.642-1.3135; p = 0.681). CONCLUSIONS: The functional outcome and survival rates up to 10 years after mitral valve repair were comparable using open and closed annuloplasty rings. Whether this means these rings are interchangeable or a carefully selection of the best-for-the-patient devices will be subject of future investigations.

Minimally invasive left atrial appendage (LAA) clip insertion after challenging LAA occluder implantation to minimize the risk of stroke.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia, requiring lifelong anticoagulation or interventional, transseptal left atrial appendage (LAA) occluder implantation to minimize stroke risk. Incomplete LAA closure post implantation is a frequent observation. Incomplete LAA occlusion after transseptal occluder implantation necessitates anticoagulation in cases of persistent AF to minimze risk of embolism and/or apoplexy. Patients with contraindications to lifelong anticoagulation therapy are challenging to treat and alternative options are needed. We present a case of a patient with persistent AF who underwent frustraneous LAA occluder implantation. The patient's anatomy necessitated surgical closure of the LAA, which was accomplished with an LAA clip 4 weeks after implantation. The patient was discharged in excellent clinical status 5 days after the surgery. No further complications were observed within the following year.

Pulmonary herniation after minimally invasive cardiac surgery: review and implications from a series of 20 cases.

Minimally invasive cardiac surgery (MICS) via right lateral mini thoracotomy is the gold standard treatment approach for mitral and tricuspid valve disorders. Other selected procedures (e.g. transapical aortic valve implantation, MIDCAB) require a left lateral mini thoracotomy for surgical access. Advantages of MICS over complete sternotomy are well known, but access-related complications post MICS, such as pulmonary herniation, are often underestimated/overlooked. In males, a pulmonary herniation in the proximity of the former thoracotomy is often clinically visible, especially when the intrathoracic pressure rises (e.g. during coughing). In females, clinical symptoms may be hidden by the breast and patients often have unspecific complaints or occasional pain when coughing, making identification of a lung herniation more difficult. Chest computed tomography is the diagnostic tool of choice for pulmonary herniations. Using a series of 20 patients with pulmonary herniation post MICS, we report our findings in diagnosis and treatment of this condition.

Long-term results of endoclamping in patients undergoing minimally invasive mitral valve surgery where external aortic clamping cannot be used - a propensity matched analysis.

BACKGROUND: Minimally invasive mitral valve surgery is standard of care in many centres and it is commonly associated with the need for cardiopulmonary bypass. Conventional external aortic clamping (exoclamping) is not always feasible, so endoaortic clamping (endoclamping) has evolved as a viable alternative. The aim of this study is to compare endoclamping (Intraclude™, Edwards Lifesciences) with exoclamping (Chitwood) during minimally invasive mitral valve procedures. METHODS: This single-centre study included 822 consecutive patients undergoing minimally invasive mitral valve procedures. The endoclamp was used in 64 patients and the exoclamp in 758. Propensity-score (PS) matching was performed resulting in 63 patients per group. Outcome measures included procedural variables, length of intensive care unit (ICU) and hospital stay, major adverse cardiac and cerebrovascular events (MACCE) and repeat surgery. RESULTS: The mean age was similar in the two group (62.2 [endoclamp] vs. 63.5 [exoclamp] years; p = 0.554), as were the cardiopulmonary bypass (145 vs. 156 min; p = 0.707) and the procedure time (203 vs. 211 min; p = 0.648). The X-clamp time was significantly shorter in the endoclamp group (88 vs. 99 min; p = 0.042). Length of ICU stay (25.0 vs. 23.0 h) and length of hospital stay (10.0 vs. 9.0 days) were slightly longer in the endoclamp group, but without statistical significance. There were nominal but no statistically significant differences between the groups in the rates of stroke, vascular complications, myocardial infarction or repeat mitral valve surgery. The conversion rate to open sternotomy approach was 2.4% without difference between groups. The estimated 7-year survival rate was similar for both groups (89.9% [endoclamp]; 84.0% [exoclamp]) with a hazard ratio of 1.291 (95% CI 0.453-3.680). CONCLUSIONS: Endoaortic clamping is an appropriate and reasonably safe alternative to the conventional Chitwood exoclamp for patients in which the exoclamp cannot be used because the ascending aorta cannot be safely mobilised.

The MEK/ERK Module Is Reprogrammed in Remodeling Adult Cardiomyocytes.

Fetal and hypertrophic remodeling are hallmarks of cardiac restructuring leading chronically to heart failure. Since the Ras/Raf/MEK/ERK cascade (MAPK) is involved in the development of heart failure, we hypothesized, first, that fetal remodeling is different from hypertrophy and, second, that remodeling of the MAPK occurs. To test our hypothesis, we analyzed models of cultured adult rat cardiomyocytes as well as investigated myocytes in the failing human myocardium by western blot and confocal microscopy. Fetal remodeling was induced through endothelial morphogens and monitored by the reexpression of Acta2, Actn1, and Actb. Serum-induced hypertrophy was determined by increased surface size and protein content of cardiomyocytes. Serum and morphogens caused reprogramming of Ras/Raf/MEK/ERK. In both models H-Ras, N-Ras, Rap2, B- and C-Raf, MEK1/2 as well as ERK1/2 increased while K-Ras was downregulated. Atrophy, MAPK-dependent ischemic resistance, loss of A-Raf, and reexpression of Rap1 and Erk3 highlighted fetal remodeling, while A-Raf accumulation marked hypertrophy. The knock-down of B-Raf by siRNA reduced MAPK activation and fetal reprogramming. In conclusion, we demonstrate that fetal and hypertrophic remodeling are independent processes and involve reprogramming of the MAPK.

Radixin Relocalization and Nonmuscle α-Actinin Expression Are Features of Remodeling Cardiomyocytes in Adult Patients with Dilated Cardiomyopathy.

BACKGROUND: Pediatric patients show an impressive capacity of cardiac regeneration. In contrast, severely deteriorated adult hearts do usually not recover. Since cardiac remodeling-involving the expression of fetal genes-is regarded as an adaptation to stress, we compared hearts of adult patients suffering from dilated cardiomyopathy (DCM) with remodeling of cultured neonatal (NRC) as well as adult (ARC) rat cardiomyocytes and the developing postnatal myocardium. METHODS: NRC and ARC were stimulated with serum and cardiac morphogens derived from DCM hearts. Protein synthesis (PS) as well as protein accumulation (PA) was measured, and cell survival was determined under ischemic conditions. Fetal markers were investigated by Western blot. Biomarkers of remodeling were analyzed in controls, DCM, and 2- to 6-month-old children with tetralogy of Fallot as well as in neonatal and adult rats by immunofluorescence. RESULTS: In NRC, serum and morphogens strongly stimulated PS and PA and the reestablishment of cell-cell contacts (CCC). In ARC, both stimulants increased PS and CCC, but PA was only elevated after serum stimulation. In contrast to serum, morphogen treatment resulted in the expression of fetal genes in ARC as determined by nonmuscle α-actinin-1 and α-actinin-4 expression (NM-actinins) and was associated with increased survival under ischemia. NM-actinins were present in cardiomyocytes of DCM in a cross-striated pattern reminiscent of sarcomeres as well as in extensions of the area of the intercalated disc (ID). NM-actinins are expressed in NRC and in the developing heart. Radixin staining revealed remodeling of the area of the ID in DCM almost identical to stimulated cultured ARC. CONCLUSIONS: Remodeling was similar in ARC and in cardiomyocytes of DCM suggesting evolutionary conserved mechanisms of regeneration. Despite activation of fetal genes, the atrophy of ARC indicates differences in their regenerative capacity from NRC. Cardiac-derived factors induced NM-actinin expression and increased survival of ischemic ARC while circulating molecules were less effective. Identification of these cardiac-derived factors and determination of their individual capacity to heal or damage are of particular importance for a biomarker-guided therapy in adult patients.

Long-term outcomes of concomitant tricuspid valve repair in patients undergoing mitral valve surgery.

BACKGROUND: We aimed to find out how the concomitant performance of tricuspid valve repair (TVR) affects outcomes of patients undergoing mitral valve surgery (MVS). METHODS: Single-centre, retrospective analysis of 1357 patients who underwent MVS between January 2005 and December 2015, including 1165 patients with isolated MVS and 192 patients with MVS plus TVR. We used propensity scores to match patients for baseline characteristics other than valve related parameters and arrived at a matched sample of 182 patients per group. RESULTS: The overall procedure duration was longer in the MVS + TVR (224 min) versus the MVS group (176 min; p < 0.001), as were the duration of mechanical ventilation (13 vs. 11 h; p < 0.001), X-clamp (90.5 vs. 66 min; p < 0.001) and cardiopulmonary bypass time (136 vs. 95.5 min; p < 0.001). Rates of procedural complications were not different between groups with the exception of pacemaker rates which were 16.0% in the MVS + TVR group and 8.8% in the isolated MVS group (p = 0.037). There was no difference in death rates within 30 days, stroke, myocardial infarction or repeat MVS. The long-term survival rate was 60.8% in the MVS + TVR vs. 57.5% in the isolated MVS group (HR 1.048; 95%CI 0.737-1.492; p = 0.794). The rate of grade III/IV tricuspid regurgitation (TR) remained low after MVS + TVR during long-term follow-up while the rate of grade ≥ II TR increased slightly in the isolated MVS group. CONCLUSION: The data show that the concomitant performance of TVR in patients undergoing MVS is a safe and effective procedure with good long-term outcomes. Patients can undergo MVS + TVR with confidence as it improves their prognosis up to the level of patients undergoing isolated MVS.

Macrophages represent the major pool of IL-7Rα expressing cells in patients with myocarditis.

Myocarditis is characterized by infiltration and activation of cytokine as well as chemokine receptors frequently producing heart failure. Causes are often infections triggering inflammatory and immune responses but these initial lines of defense might be finally disastrous. To identify mediators we screened various receptors by confocal microscopy and identified cardiac interleukin-7 (IL-7) receptor-α (IL-7Rα) expressing cells in patients with myocarditis. IL-7Rα+ cells were analyzed by markers for leukocytes (CD45), B cells (CD19), T cells (CD3, CD4, CD8) and macrophages (CD68, CD163, CD206). Immune cells were hardly detected in controls. In patients with myocarditis main inflammatory populations consisted of macrophages and T cells. B cells were hardly present. 90% of CD68+ macrophages but less than 20% of CD3+ T cells were IL-7Rα+. This was surprising since T and B lymphocytes are generally regarded as the major IL-7Rα+ cells. Since IL-7 acts as a chemokine, the expression of its receptor might orchestrate cardiac macrophage infiltration. In contrast, consumption of IL-7 by IL-7Rα+ cardiac macrophages might potentially prevent a certain overshooting immune reaction and sepsis by reducing proliferation and survival of lymphocytes. Our data suggest a participation of IL-7Rα+ macrophages in the development of myocarditis and heart failure.

Mitral valve repair for posterior leaflet prolapse: Long-term comparison of loop implantation vs resection.

BACKGROUND: Resection (triangular or quadrangular) is considered the gold standard for the treatment of posterior leaflet prolapse and loop implantation a more recent alternative. We aimed to compare the long-term outcomes of triangular or quadrangular resection vs loop implantation. METHODS: Single-centre, retrospective analysis of mitral valve (MV) surgeries conducted from January 2005 to December 2015. Propensity score matching was based on seven key baseline variables. RESULTS: Data from 721 patients were analyzed; 358 patients received loop implantation and 363 patients underwent resection. Patients had a mean age of 62 years, 33.0% were female and 50.6% had hypertension. Propensity score matching resulted in a matched group of 263 patients who received loop implantation or underwent resection, respectively. Postoperatively, the patients' mitral insufficiency was reduced from grade III/IV to either zero or trace (45.8%) or I (49.8%) and New York Heart Association class reduced from 66.9% in class III/IV preoperatively to 8.3% with no significant differences between groups. Fewer patients receiving loops had procedure-related complications. Fewer patients in the loop implantation group required permanent pacemaker implantation at 30 days (8.4% vs 2.3%; P = .002). The 10-year survival for patients in the resection (88.0%) and loop implantation (89.3%) groups had a hazard ratio of 1.224 (95% confidence interval, 0.633-2.367). CONCLUSION: Our study showed that both loop implantation and resection were associated with comparable long-term survival in patients with posterior leaflet prolapse. Loop implantation is associated with a significantly higher rate of a successful repair, a significantly lower rate of MV replacement after repair failure, fewer procedure-related complications and better 30-day at comparable long-term outcomes.

Explantation and reimplantation of a breast implant to facilitate minimally invasive mitral valve surgery and cryoablation of atrial fibrillation.

Clinicians can feel confident about performing mitral repair/replacement in patients who have previously undergone mammoplasty. It may also have applications in performing atrial septal defect closure, Maze procedures for atrial fibrillation, and tricuspid valve surgery in patients with breast implants.

Long-term outcome after mitral valve replacement using biological versus mechanical valves.

BACKGROUND: This study compared long-term outcomes of biological and mechanical mitral valve replacement (MVR) in patients requiring replacement of the mitral valve where repair was not feasible. METHODS: A single-centre registry of patients receiving MVR between 2005 and 2015 was established. Thirty-day mortality and long-term outcomes were analysed and compared. RESULTS: Three hundred twenty four patients underwent MVR (265 biological; 59 mechanical valves). Patients receiving biological valves were older (p < 0.001), had a higher log EuroSCORE (p < 0.001) and received less minimally invasive surgery (p < 0.001). Immediate procedural mortality was 1.9%, which only occurred in the biological valve group. At 30 days, 9.0% of patients had died, 4.0% experienced stroke, 8.0% received a pacemaker and 10.5% suffered an acute renal failure. The rate of re-thoracotomy (14.2%) was lower in the biological (12.5%) than in the mechanical valve group (22.0%; adjOR 0.45 [0.20-1.00]; p = 0.050). Frequent long-term complications were stroke (9.2%) and bleeding (4.8%), with bleeding complications being higher in the mechanical valve group (p = 0.009). During the follow-up period biological valves showed a numerically higher survival rate during the first years, which shifted after 3 years in favour of mechanical valves. At 10 years, survival rates were 62.4% vs. 77.1% in the biological and mechanical valve groups (p = 0.769). Hazard ratio after adjustment was 0.833 (95% CI 0.430-1.615). CONCLUSION: These data confirm that mechanical valve implantation is associated with an increased risk of bleeding. While there was a potential survival benefit during the first years after surgery for patients receiving a biological valves the difference became insignificant after a follow-up of 10 years.

Atresia of the inferior vena cava in a patient undergoing mitral and tricuspid valve surgery.

We report on a 61-year-old man with a previously unknown interruption of the inferior vena cava who was scheduled to undergo minimally invasive mitral and tricuspid valve surgery. We aimed to establish a cardiopulmonary bypass using femorofemoral cannulation under transoesophageal echocardiography. In spite of multiple attempts, the positioning of the venous wire in the right atrium was not accomplished. The intervention was subsequently performed by an open sternotomy. Further to the intervention, the patient underwent thoraco-abdominal multislice computed tomography that excluded the presence of an abdominal tumour or vena cava thrombosis but revealed atresia of the inferior vena cava.

Combined mitral valve repair and heart transplantation.

In times of donor organ shortage, organs with extended allocation criteria, for example, valve pathologies, have to be taken into consideration for transplantation. The donor pool can be extended to hearts with mitral valve insufficiency. Mitral valve repair can rapidly be performed in the donor heart on the back table with excellent results.

The MEK1 inhibitors UO126 and PD98059 block PDGF-AB induced phosphorylation of threonine 292 in porcine smooth muscle cells.

PDGF-AB and FGF-2 (GFs) induce smooth muscle cell (SMC) proliferation which is indispensible for arteriogenesis. While there is common agreement that GFs stimulate SMC proliferation through phosphorylation (P-) of MEK1/2 at Ser218/222, we previously demonstrated that the MEK inhibitors PD98059 and UO126 did not inhibit P-Ser218/222 as originally proposed but caused strong hyperphosphorylation. Here, we demonstrate that GFs increased phosphorylation of MEK1 at Thr292 while UO126 and PD98059 blocked this phosphorylation. This was again surprising since phosphorylation of Thr292 is regarded as a negative feedback loop. Our findings suggest that inhibition of Thr292 phosphorylation in combination with hyperphosphorylation of Ser218/222 serves as an "off" switch of SMC proliferation and potentially of arteriogenesis.

Increased levels of interleukin-33 in gingival crevicular fluids of patients with chronic periodontitis.

The purpose of this clinical study is to comparatively investigate the interleukin-33 (IL-33) levels in gingival crevicular fluid (GCF), saliva and plasma of patients with periodontal disease as well as periodontally healthy subjects and the association between these levels and clinical parameters. GCF, saliva and plasma samples were collected from systemically healthy, non-smoker chronic periodontitis patients (CP group, n = 20), gingivitis patients (G group, n = 20) and periodontally healthy control groups (H group, n = 20). Full-mouth clinical periodontal parameters were also recorded. IL-33 levels were determined by ELISA. The total amount of GCF IL-33 was greater in the G and CP groups compared to the H group (p < 0.05). The GCF IL-33 concentration was significantly lower in the CP group than in the H and G groups (p < 0.001). Salivary or plasma IL-33 levels were similar in the study groups. The total amount of GCF IL-33 was positively correlated with the GI, PI and BOP (%) (p < 0.05). Considering the present findings, the increase in total amounts of GCF IL-33 may have a role in the pathogenesis of periodontal disease.

Implication of C-type natriuretic peptide-3 signaling in glycosaminoglycan synthesis and chondrocyte hypertrophy during TGF-ß1 induced chondrogenic differentiation of chicken bone marrow-derived mesenchymal stem cells.

This study investigated the involvement of CNP-3, chick homologue for human C-type natriuretic peptide (CNP), in TGF-ß1 induced chondrogenic differentiation of chicken bone marrow-derived mesenchymal stem cells (MSCs). Chondrogenic differentiation of MSCs in pellet cultures was induced by TGF-ß1. Chondrogenic differentiation and glycosaminoglycan synthesis were analyzed on the basis of basic histology, collagen type II expression, and Alcian blue staining. Antibodies against CNP and NPR-B were used to block their function during these processes. Results revealed that expression of CNP-3 and NPR-B in MSCs were regulated by TGF-ß1 in monolayer cultures at mRNA level. In pellet cultures of MSCs, TGF-ß1 successfully induced chondrogenic differentiation and glycosaminoglycan synthesis. Addition of CNP into the TGF-ß1 supplemented chondrogenic differentiation medium further induced the glycosaminoglycan synthesis and hypertrophy of differentiated chondrocytes in these pellets. Pellets induced with TGF-ß1 and treated with antibodies against CNP and NPR-B, did show collagen type II expression, however, Alcian blue staining showing glycosaminoglycan synthesis was significantly suppressed. In conclusion, CNP-3/NPR-B signaling may strongly be involved in synthesis of glycosaminoglycans of the chondrogenic matrix and hypertrophy of differentiated chondrocytes during TGF-ß1 induced chondrogenic differentiation of MSCs.