Push-Through Myringoplasty Versus External Auditory Canal Flap Tympanoplasty for Chronic Marginal Perforations

OBJECTIVE

We compared the operation times, graft success rates, and hearing gains between push-through (PT) myringoplasty and external auditory canal (EAC) flap tympanoplasty in patients with chronic marginal perforations.

MATERIALS AND METHODS

A total of 77 patients with chronic marginal perforations were randomly allocated to endoscopic perichondrium-cartilage myringoplasty with raising of the EAC flaps (n = 39) and PT technique (n = 38) groups. The graft outcomes, mean operation times, and postoperative complications were compared 6 months after operation.

RESULTS

The graft success rate was 97.4% (38/39) in the EAC group and 81.6% (31/38) in the PT group; the difference was significant (P = .056). The mean operation time was 40.7 ± 10.4 min in the EAC group and 42.4 ± 8.3 min in the PT group (P = .741). In the EAC group, the mean pre- and postoperative air-bone gap (ABG)s were 29.3 (range: 28.4 ± 8.6) and 12.1 (range: 11.8 ± 2.4) dB (P < .01), respectively; the respective values were 29.5 (range: 29.1 ± 5.4) and 12.6 (range: 12.0 ± 1.3) dB (P < .01) in the PT group. No significant group difference was observed in the pre- (P = .794) or postoperative (P = .689) ABG values or mean ABG gain (16.7 ± 5.3 vs 17.1 ± 7.7 dB; P = .526). In addition, graft medialization occurred in 7.9% patients in the PT group. However, graft lateralization, significant blunting, deteriorative sensorineural hearing loss, vertigo, or tinnitus were not encountered in either group. No taste change was reported and no inclusion cholesteatoma was seen in the EAC group.

CONCLUSION

Endoscopic perichondrium-cartilage myringoplasty with raising of an EAC flap is useful and minimally invasive to repair chronic marginal perforations; the technique is simple, has a high graft success rate in comparison to the PT technique.

Hes1 marks peri-condensation mesenchymal cells that generate both chondrocytes and perichondrial cells in early bone development

Bone development starts with condensations of undifferentiated mesenchymal cells that set a framework for future bones within the primordium. In the endochondral pathway, mesenchymal cells inside the condensation differentiate into chondrocytes and perichondrial cells in a SOX9-dependent mechanism. However, the identity of mesenchymal cells outside the condensation and how they participate in developing bones remain undefined. Here we show that mesenchymal cells surrounding the condensation contribute to both cartilage and perichondrium, robustly generating chondrocytes, osteoblasts, and marrow stromal cells in developing bones. Single-cell RNA-seq analysis of Prrx1-cre-marked limb bud mesenchymal cells at E11.5 reveals that Notch effector Hes1 is expressed in a mutually exclusive manner with Sox9 that is expressed in pre-cartilaginous condensations. Analysis of a Notch signaling reporter CBF1:H2B-Venus reveals that peri-condensation mesenchymal cells are active for Notch signaling. In vivo lineage-tracing analysis using Hes1-creER identifies that Hes1+ early mesenchymal cells surrounding the SOX9+ condensation at E10.5 contribute to both cartilage and perichondrium at E13.5, subsequently becoming growth plate chondrocytes, osteoblasts of trabecular and cortical bones, and marrow stromal cells in postnatal bones. In contrast, Hes1+ cells in the perichondrium at E12.5 or E14.5 do not generate chondrocytes within cartilage, contributing to osteoblasts and marrow stromal cells only through the perichondrial route. Therefore, Hes1+ peri-condensation mesenchymal cells give rise to cells of the skeletal lineage through cartilage-dependent and independent pathways, supporting the theory that early mesenchymal cells outside the condensation also play important roles in early bone development.

The Effect of Perichondrium and Graft Modification on the Viability of Conchal Cartilage Graft: An Experimental Study in Rabbit

OBJECTIVE

Cartilage grafts are widely used in reconstructing nasal deformity for structural and aesthetic purposes. Despite being immunologically privileged, cartilage grafts are susceptible to volume loss with high risk of resorption over time. Therefore, experts opt for cartilage handling modification to resolve this issue through graft dicing, wrapping, or perichondrium preservation. This study will evaluate the effect cartilage graft preparations on graft viability.

DESIGN

Single-randomized post-test-only study design.

SETTING

Animal Hospital at Bogor Agricultural Institute.

PARTICIPANTS

Six New Zealand, male, Hycole rabbits.

INTERVENTION

Conchal cartilage grafts were retrieved from 6 experimental rabbits and distributed into 3 treatment groups: diced cartilage graft (DC; control), one-sided perichondrium-attached scored cartilage (OPSC), and tube-shaped perichondrium-wrapped diced cartilage (TPDC).

MAIN OUTCOME MEASURES

Macroscopic (weight and contour) and microscopic (chondroblast proliferation, graft thickness, apoptotic cells) evaluation through histological measures were recorded on week 12. Statistical analysis was done to compare between groups.

RESULTS

Diced cartilage and OPSC groups showed significant weight changes on week 12 (P < .05) with OPSC presenting with the biggest difference. Diced cartilage and OPSC group showed moderate cell proliferation on week 12 while TPDC displayed most abundant apoptotic cells (5.8%; P < .05). Diced cartilage group had the highest cartilage thickness ratio (P < .05).

DISCUSSION

Bare DC technique promoted graft thickness while perichondrium-attached scored cartilage showed the most abundant chondroblast proliferation and the least apoptotic cells. Perichondrium contributes to enhanced new cartilage formation.

CONCLUSION

Diced cartilage graft is suitable for masking irregularity and volume augmentation, while perichondrium-attached cartilage graft is better for structural support in nasal reconstruction.

7-Tesla MRI Evaluation of the Knee, 25 Years after Cartilage Repair Surgery: The Influence of Intralesional Osteophytes on Biochemical Quality of Cartilage

OBJECTIVE

To evaluate the morphological and biochemical quality of cartilage transplants and surrounding articular cartilage of patients 25 years after perichondrium transplantation (PT) and autologous chondrocyte transplantation (ACT) as measured by ultra-high-field 7-Tesla (7T) magnetic resonance imaging (MRI) and to present these findings next to clinical outcome.

DESIGN

Seven PT patients and 5 ACT patients who underwent surgery on the femoral condyle between 1986 and 1996 were included. Patient-reported outcome measures (PROMs) were assessed by the clinical questionnaires: Knee injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC), and Visual Analogue Scale (VAS) for knee pain. The morphological (MOCART score) and biochemical quality (glycosaminoglycans [GAGs] content and collagen integrity) of cartilage transplants and surrounding articular cartilage were analyzed by 7T MRI. The results of the PT and ACT patients were compared. Finally, a detailed morphological analysis of the grafts alone was performed.

RESULTS

No statistically significant difference was found for the PROMs and MOCART scores of PT and ACT patients. Evaluation of the graft alone showed poor repair tissue quality and high prevalence of intralesional osteophyte formation in both the PT and ACT patients. Penetration of the graft surface by the intralesional osteophyte was related to biochemically damaged opposing tibial cartilage; GAG content was significantly lower in patients with an osteophyte penetrating the graft surface.

CONCLUSIONS

Both PT and ACT patients have a high incidence of intralesional osteophyte formation 25 years after surgery. The resulting biochemical damage to the opposing tibial cartilage might be dependent on osteophyte morphology.

Regenerative Potential of Perichondrium: A Tissue Engineering Perspective

The clinical relevance of perichondrium was recognized more than a century ago. In children and adolescents, perichondrium is essential for the formation and growth of the cartilaginous part of craniofacial features and must be considered during reconstructive surgery in the head and neck area. Also in adults, perichondrium must be preserved during surgical intervention for adequate postoperative healing and cartilage maintenance. Furthermore, the regenerative function of perichondrium in the ribs enables the harvesting of the rib cartilage tissue for reconstruction of craniofacial features. With the advancement of tissue engineering, renewed attention has been focused on the perichondrium, because without this crucial tissue, the function of cartilage engineered for craniofacial reconstruction is incomplete and may not be suitable for long-term reconstructive goals. Furthermore, interest in the perichondrium was revived owing to its possible role as a microenvironment containing stem and progenitor cells. Here we will revisit seminal studies on the perichondrium and review the current literature to provide a holistic perspective on the importance of this tissue in the context of regenerative medicine. We will also highlight the functional significance of perichondrium for cartilage tissue engineering.

Double-Layered (Cartilage Island + Extra Perichondrium) Graft for Type 1 Tympanoplasty

OBJECTIVE

To compare the graft success rates and hearing results of single-layered (composite island) grafting (SLG) vs double-layered (composite plus second layer of perichondrium) grafting (DLG) for over-under type 1 tympanoplasty techniques.

STUDY DESIGN

Retrospective chart review.

SETTINGS

Tertiary center otorhinolaryngology clinic.

SUBJECTS AND METHODS

Medical charts of the patients who underwent type 1 tympanoplasty via the microscopic technique by a single surgeon between 2015 and 2019 were analyzed.

RESULTS

A total of 48 patients were included. The DLG (n = 26) group had higher graft take rates as compared to the SLG group (n = 22) for all patients (P = .038) and for moderate- to high-risk patients according to Middle Ear Risk Index (MERI) scores (P = .029) but not for patients with mild disease (P = .429) or myringosclerotic patients (P = .242). The DLG group exhibited higher air-bone gap closure (C-ABG) values as compared to the SLG group for all patients (P = .018). However, there was no noticeable difference in C-ABG values within the patients with successful grafting (P = .217). Only graft success status had a significant effect on C-ABG values when the multivariate linear regression was performed. (P = .016). Higher MERI scores and presence of myringosclerosis were related to the unsuccessful grafting (P < .01).

CONCLUSION

DLG tympanoplasty is encouraged, especially for patients with higher MERI scores, to increase the graft success rates. Better hearing outcomes of DLG tympanoplasty were related to the higher graft success status of this technique; DLG had no additional hearing effect for patients with successful grafting. Higher MERI scores and presence of myringosclerosis were related to graft failure.

Biomarker Signatures of Quality for Engineering Nasal Chondrocyte-Derived Cartilage

The definition of quality controls for cell therapy and engineered product manufacturing processes is critical for safe, effective, and standardized clinical implementation. Using the example context of cartilage grafts engineered from autologous nasal chondrocytes, currently used for articular cartilage repair in a phase II clinical trial, we outlined how gene expression patterns and generalized linear models can be introduced to define molecular signatures of identity, purity, and potency. We first verified that cells from the biopsied nasal cartilage can be contaminated by cells from a neighboring tissue, namely perichondrial cells, and discovered that they cannot deposit cartilaginous matrix. Differential analysis of gene expression enabled the definition of identity markers for the two cell populations, which were predictive of purity in mixed cultures. Specific patterns of expression of the same genes were significantly correlated with cell potency, defined as the capacity to generate tissues with histological and biochemical features of hyaline cartilage. The outlined approach can now be considered for implementation in a good manufacturing practice setting, and offers a paradigm for other regenerative cellular therapies.

Is type 1 tympanoplasty effective in elderly patients? Comparison of fascia and perichondrium grafts

Background: Tympanoplasty is regularly performed in various ages but data about the procedure in elderly is insufficient. Objectives: To compare the success rates and hearing outcomes of fascia and perichondrium grafts used for tympanoplasty in patients >65 years and to evaluate the prognostic factors affecting the success of tympanoplasty. Methods: Reviewing records of 49 elderly patients underwent tympanoplasty, two groups were constituted: perichondrium (25 patients) and fascia (24 patients) groups. Ages, genders, perforation sides, type and location of perforation, graft success rates, functional success rates and air-bone gap (ABG) gains were compared. Results: Overall graft success rate was 85.7%. After a mean follow-up of 23.3 ± 8.32 months, overall mean ABG gain was 11.33 ± 8.42 dB. Overall median postoperative ABG value (9 dB) was significantly lower compared to the median preoperative value (24 dB) (p < .001). Graft success rate was higher in perichondrium group (96%) compared to fascia group (75%) (p = .04). Functional success rate did not significantly differ between perichondrium (68%) and fascia groups (62.5%) (p = .68). Conclusion and significance: Tympanoplasty is an effective procedure with a graft success rate of 85.7% in elderly. Both fascia and perichondrium are suitable materials; however, perichondrium had higher success rate.

The in vivo chondrogenesis of cartilage stem/progenitor cells from auricular cartilage and the perichondrium

Bone marrow-derived stem cells are commonly studied for cartilage tissue engineering and regeneration medicine applications, but their ossification tendency and their limited capacity for chondrogenic differentiation depending on the donor age limit their clinical application. Cartilage stem/progenitor cells are ideal seeding cells, as cartilage stem/progenitor cells from auricular cartilage and the perichondrium have the inherent advantages of chondrogenesis capacity and an easy and nontraumatic harvesting process, displaying promise for applications. The identification and comparison of cartilage stem/progenitor cells from auricular cartilage and the perichondrium in vitro were explored in our previous study, but the in vivo chondrogenesis of these cells has not been fully examined. In the current study, we explored the ectopic chondrogenesis of cartilage stem progenitor/cells from auricular cartilage and the perichondrium after chondrogenic induction in vitro. Our results suggest that stem/progenitor cells from auricular cartilage exhibit significantly better chondrogenesis than those from the perichondrium in vivo, with upregulated chondrogenic genes and a stable cartilage phenotype, as well as good mechanical properties, indicating that stem/progenitor cells from auricular cartilage could be one type of ideal seeding cells for cartilage tissue engineering.

[Application of thin-ribbed cartilage with the perichondrium in correction of secondary cleft lip nasal deformity as lateral crural onlay graft]

Objective

To explore the application and effectiveness of thin-ribbed cartilage with the perichondrium in the correction of secondary cleft lip nasal deformity as the lateral crural onlay graft.

Methods

A retrospective study was performed based on the data of 28 patients with secondary nasal deformity of cleft lip between October 2015 and April 2017. There were 16 males and 12 females with an average age of 24 years (range, 18-31 years). There were 11 cases with secondary nasal deformities on the left side, 13 cases on the right side, and 4 cases on both sides. Three-dimensional stereotaxy of the nasolabial muscles was used to correct the deformity. The costal cartilage as the support was used to perform nasal columella and nasal dorsum while the thin-ribbed cartilage with the perichondrium was used as wing cartilage support. The photography of nasal position was taken before operation and at 6-8 months after operation. The midpoint of the junction between the nasal columella and the upper lip was marked point O; the lateral horizontal line passing through the point O was marked as X-line, and the longitudinal line (the midline) as Y-line. The distance of the highest point of the affected nostril to the X-line, the distance of the nostril's outermost point to the Y-line, the symmetries of both the most lateral and the highest point of the bilateral nostrils, and the distance of the highest point of the nasal tip to the X-line were measured.

Results

All incisions healed by first intention. All patients were followed up 6 to 24 months with an average of 12 months. The size and shape of the noses were stable, and no compli cation, such as cartilage exposure, hematoma, or infection occurred during the postoperative follow-up. There were 4 cases with obvious incision scars, 3 cases with nostril and alar asymmetry, and 1 case of lateral side of the nose without well positioned. The symmetry of the highest points of bilateral nostrils was 57.643%±27.491% before operation and 90.246%±18.769% after operation. The symmetry of the most lateral points of the bilateral nostrils was 77.391%±30.628% before operation and 92.373%±21.662% after operation. And there were significant differences between pre- and post-operation ( P<0.05). There were also significant differences in the distance of highest point of the affected nostril to the X-line, the distance of the nostril's outermost point to the Y-line, and the distance of the highest point of the nasal tip to the X-line ( P<0.05). No thoracic contour change occurred at the costal cartilage donor site.

Conclusion

The thin-ribbed cartilage with the perichondrium has good support and long-term stability, and it can be used as one of the ideal materials for nasal alar cartilage transplantation for nasal deformity secondary to cleft lip.

Histological study of costal cartilage after transplantation and reasons for avoidance of postoperative resorption and retention of cartilage structure in rats

BACKGROUND

Limited information is available on the biological status of transplanted cartilage from which the perichondrium has been removed. This article describes the histological and three-dimensional structural picture of cartilage, using green fluorescent protein (GFP) transgenic rats and normal wild rats.

METHODS

Three sections of costal cartilage were harvested from 10-week-old wild rats. One section was used as a specimen while two were subcutaneously collected from the dorsal region of 10-week-old GFP rats at 4 and 8 weeks post-transplant. The experiment was performed in two randomized groups. The perichondrium was removed from transplanted cartilage in the first group and perichondrium of transplanted cartilage remained intact in the second group. Histology and focused ion beam/scanning electron microscope (FIB/SEM) tomography were used to evaluate the transplanted cartilage.

RESULTS

All 40 transplanted sections were harvested and no infections, exposure or qualitative change of cartilage matrix were seen following transplant. Histological analyses showed that the surface layer of the GFP-negative transplanted cartilage was replaced with GFP-positive chondrocytes 8 weeks post-transplant in the first group. A three-dimensional layer of perichondrium-like tissue reconstructed around the cartilage at 8 weeks was confirmed, resembling normal perichondrium. However, the GFP-positive chondrocytes were not replaced in the second group.

CONCLUSIONS

The cell renewal of chondrocytes is necessary for subcutaneously transplanted cartilage to maintain its tissue composition over a long period of time. The histological and ultrastructural analyses revealed that cells from recipient tissue generated new chondrocytes even when cartilage was implanted after removing the perichondrium.

Integration Capacity of Human Induced Pluripotent Stem Cell-Derived Cartilage

New cell and tissue sources are needed for the regenerative treatment of articular cartilage damage. Human induced pluripotent stem cells (hiPSCs) are an abundant cell source due to their self-renewal capacity. Hyaline cartilage tissue particles derived from hiPSCs (hiPS-Carts), 1–3 mm in diameter, are one candidate source that can be used for transplantation. When transplanted to fill the defects of articular cartilage, hiPS-Carts form a repair tissue by integrating with each other and with adjacent host tissue. In this study, we analyzed the integration capacity using an in vitro model and found that hiPS-Carts spontaneously integrate with each other in vitro. hiPS-Carts consist of cartilage at the center and perichondrium-like membrane that wraps around the cartilage. The integration started at the perichondrium-like membrane at around 1 week. Then, the integration progressed to the cartilage within 4–8 weeks. RNA sequencing analysis identified a higher expression of FGF18 in the perichondrium-like membrane in hiPS-Carts compared with the central cartilage. The addition of FGF18 to the model accelerated the integration of hiPS-Carts, whereas the addition of a FGFR inhibitor inhibited it. These results suggest that FGF18 secreted from the perichondrium-like membrane plays a role in the integration of hiPS-Carts. Understanding the integration mechanism of hiPS-Carts is expected to contribute to the realization of regenerative treatment for patients with articular cartilage damage.

Costal cartilage graft with perichondrium, a possible anti-adhesive material

BACKGROUND

Adhesion occurs as a part of the wound healing process, but it sometimes compromises patients' daily activities. The authors were looking for materials and methods that could prevent adhesion, and noticed that the costal cartilage has possibility. The anti-adhesive property of the costal cartilage was examined histologically.

METHODS

Thirty-five patients with microtia who provided consent for participating in this study were enrolled between April 2008 and March 2015. In the first stage of microtia reconstruction surgery, the excess cartilage was used to create these three types of specimens: (A) a piece of cartilage retaining the perichondrium on one side, (B) a piece of only cartilage parenchyma sliced with a plane parallel to the long axis of costal cartilage, and (C) the costal cartilage in a plane perpendicular to the long axis sliced pieces. These specimens were implanted into the subcutaneous fat of the chest. After at least 6 months in the second stage of surgery (i.e. auricular elevation), these specimens, wearing a little around the adipose tissue, we removed and examined histologically.

RESULT

A fibrosis formation of the perichondrium side of Specimen A was thicker significantly than that of the cartilage side. A fibrosis formation of Specimen B was thicker significantly than that of the cartilage side of Specimen A.

CONCLUSION

It was suggested that, if there is perichondrium, the costal cartilage parenchyma surface makes less adhesion with surrounding tissues. Costal cartilage with unilateral perichondrium is likely to be an effective surgical material for adhesion prevention.

[The application of U-shaped cartilage-perichondrium tympanoplastyfor subtotal tympanic membrane perforation]

Objective:To evaluate the anatomical and functional results of U-shaped cartilage-perichondrium tympanoplasty for subtotal tympanic membrance perforation.Method:A retrospective study was carried out 45 patients(45 ears) with chronic otitis media treated with U-shaped cartilage-perichondrium tympanoplasty.Patients were followed up to assess anatomic and functional results and the data was analyzed statistically.Result:Forty-five cases were followed up successfully,all cases had a tympanic membrane with no irregularities(100%),and the average air-bone gaps of pure tone audiometry of 0.25,0.50,1.00,2.00,4.00 kHz were reduced significantly(P<0.05).Conclusion:U-shaped cartilage-perichondrium tympanoplasty for subtotal tympanic membrane perforation is good with high survival rate and better results of hearing.

Isolation, identification, and comparison of cartilage stem progenitor/cells from auricular cartilage and perichondrium

Auricular cartilage loss or defect remains a challenge to plastic surgeons, and cartilage regenerative medicine provides a novel method to solve the problem. However, ideal seeding cells seem to be the key point in the development of cartilage regeneration. Although bone marrow-mesenchymal stem cells were considered as the ideal seeding cells in cartilage regeneration, regenerative cartilage differentiated from bone marrow-mesenchymal stem cells still faces some problems. It is reported that many tissues and organs contain a certain number of adult progenitor or stem cells that can replace cells that die or restore tissues and organs after injury. Therefore, we tried to use a fibronectin differential adhesion assay to isolate cartilage stem/progenitor cells from auricular cartilage and perichondrium. Flow cytometric analysis demonstrated the two cell populations expressed mesenchyme stem cell positive surface marker. Meanwhile, the cells differentiate into osteogenic line, chondrogenic line and adipogenic line under different induction conditions. The proliferation of cartilage stem/progenitor cells derived from perichondrium was higher than cartilage stem/progenitor cells derived from auricular cartilage. In addition, there is a difference on osteogenic differentiation, chondrogenic differentiation and adipogenic differentiation between these two cell populations. In conclusion, auricular cartilage and perichondrium both contain cartilage stem/progenitor cells, which may provide an ideal seeding cells for cartilage regeneration.

Differentiating the extent of cartilage repair in rabbit ears using nonlinear optical microscopy

Nonlinear optical microscopy (NLOM) was used as a noninvasive and label-free tool to detect and quantify the extent of the cartilage recovery. Two cartilage injury models were established in the outer ears of rabbits that created a different extent of cartilage recovery based on the presence or absence of the perichondrium. High-resolution NLOM images were used to measure cartilage repair, specifically through spectral analysis and image texture. In contrast to a wound lacking a perichondrium, wounds with intact perichondria demonstrated significantly larger TPEF signals from cells and matrix, coarser texture indicating the more deposition of type I collagen. Spectral analysis of cells and matrix can reveal the matrix properties and cell growth. In addition, texture analysis of NLOM images showed significant differences in the distribution of cells and matrix of repaired tissues with or without perichondrium. Specifically, the decay length of autocorrelation coefficient based on TPEF images is 11.2 ± 1.1 in Wound 2 (with perichondrium) and 7.5 ± 2.0 in Wound 1 (without perichondrium), indicating coarser image texture and faster growth of cells in repaired tissues with perichondrium (p < 0.05). Moreover, the decay length of autocorrelation coefficient based on collagen SHG images also showed significant difference between Wound 2 and 1 (16.2 ± 1.2 vs. 12.2 ± 2.1, p < 0.05), indicating coarser image texture and faster deposition of collagen in repaired tissues with perichondrium (Wound 2). These findings suggest that NLOM is an ideal tool for studying cartilage repair, with potential applications in clinical medicine. NLOM can capture macromolecular details and distinguish between different extents of cartilage repair without the need for labelling agents.

Genetic interactions between Shox2 and Hox genes during the regional growth and development of the mouse limb

The growth and development of the vertebrate limb relies on homeobox genes of the Hox and Shox families, with their independent mutation often giving dose-dependent effects. Here we investigate whether Shox2 and Hox genes function together during mouse limb development by modulating their relative dosage and examining the limb for nonadditive effects on growth. Using double mRNA fluorescence in situ hybridization (FISH) in single embryos, we first show that Shox2 and Hox genes have associated spatial expression dynamics, with Shox2 expression restricted to the proximal limb along with Hoxd9 and Hoxa11 expression, juxtaposing the distal expression of Hoxa13 and Hoxd13. By generating mice with all possible dosage combinations of mutant Shox2 alleles and HoxA/D cluster deletions, we then show that their coordinated proximal limb expression is critical to generate normally proportioned limb segments. These epistatic interactions tune limb length, where Shox2 underexpression enhances, and Shox2 overexpression suppresses, Hox-mutant phenotypes. Disruption of either Shox2 or Hox genes leads to a similar reduction in Runx2 expression in the developing humerus, suggesting their concerted action drives cartilage maturation during normal development. While we furthermore provide evidence that Hox gene function influences Shox2 expression, this regulation is limited in extent and is unlikely on its own to be a major explanation for their genetic interaction. Given the similar effect of human SHOX mutations on regional limb growth, Shox and Hox genes may generally function as genetic interaction partners during the growth and development of the proximal vertebrate limb.

Concurrent elevation of the upper lateral cartilage perichondrium and nasal bone periosteum for management of dorsum: the perichondro-periosteal flap

A meticulous nasal dorsal dissection is an indispensable tool for a successful rhinoplasty. To achieve an aesthetically pleasing dorsum, fine dissection of the upper lateral cartilages (ULC), nasal bones, and keystone area is crucial. In this Featured Operative Technique article, the author describes a different concept of nasal dorsal skeletonization: the perichondro-periosteal flap technique. This technique has several advantages in restoring the nasal dorsum after hump reduction. Namely, the preparation and protection of the perichondrium and the periosteum of the nasal dorsum as a single entity allows a healthier, separate-layer closure over the osseocartilaginous dorsum.

Perichondrium phenotype and border function are regulated by Ext1 and heparan sulfate in developing long bones: a mechanism likely deranged in Hereditary Multiple Exostoses

During limb skeletogenesis the cartilaginous long bone anlagen and their growth plates become delimited by perichondrium with which they interact functionally. Yet, little is known about how, despite being so intimately associated with cartilage, perichondrium acquires and maintains its distinct phenotype and exerts its border function. Because perichondrium becomes deranged and interrupted by cartilaginous outgrowths in Hereditary Multiple Exostoses (HME), a pediatric disorder caused by EXT mutations and consequent heparan sulfate (HS) deficiency, we asked whether EXT genes and HS normally have roles in establishing its phenotype and function. Indeed, conditional Ext1 ablation in perichondrium and lateral chondrocytes flanking the epiphyseal region of mouse embryo long bone anlagen - a region encompassing the groove of Ranvier - caused ectopic cartilage formation. A similar response was observed when HS function was disrupted in long bone anlagen explants by genetic, pharmacological or enzymatic means, a response preceded by ectopic BMP signaling within perichondrium. These treatments also triggered excess chondrogenesis and cartilage nodule formation and overexpression of chondrogenic and matrix genes in limb bud mesenchymal cells in micromass culture. Interestingly, the treatments disrupted the peripheral definition and border of the cartilage nodules in such a way that many nodules overgrew and fused with each other into large amorphous cartilaginous masses. Interference with HS function reduced the physical association and interactions of BMP2 with HS and increased the cell responsiveness to endogenous and exogenous BMP proteins. In sum, Ext genes and HS are needed to establish and maintain perichondrium's phenotype and border function, restrain pro-chondrogenic signaling proteins including BMPs, and restrict chondrogenesis. Alterations in these mechanisms may contribute to exostosis formation in HME, particularly at the expense of regions rich in progenitor cells including the groove of Ranvier.

Cartilage-specific β-catenin signaling regulates chondrocyte maturation, generation of ossification centers, and perichondrial bone formation during skeletal development

The WNT/β-catenin signaling pathway is a critical regulator of chondrocyte and osteoblast differentiation during multiple phases of cartilage and bone development. Although the importance of β-catenin signaling during the process of endochondral bone development has been previously appreciated using a variety of genetic models that manipulate β-catenin in skeletal progenitors and osteoblasts, genetic evidence demonstrating a specific role for β-catenin in committed growth-plate chondrocytes has been less robust. To identify the specific role of cartilage-derived β-catenin in regulating cartilage and bone development, we studied chondrocyte-specific gain- and loss-of-function genetic mouse models using the tamoxifen-inducible Col2Cre(ERT2) transgene in combination with β-catenin(fx(exon3)/wt) or β-catenin(fx/fx) floxed alleles, respectively. From these genetic models and biochemical data, three significant and novel findings were uncovered. First, cartilage-specific β-catenin signaling promotes chondrocyte maturation, possibly involving a bone morphogenic protein 2 (BMP2)-mediated mechanism. Second, cartilage-specific β-catenin facilitates primary and secondary ossification center formation via the induction of chondrocyte hypertrophy, possibly through enhanced matrix metalloproteinase (MMP) expression at sites of cartilage degradation, and potentially by enhancing Indian hedgehog (IHH) signaling activity to recruit vascular tissues. Finally, cartilage-specific β-catenin signaling promotes perichondrial bone formation possibly via a mechanism in which BMP2 and IHH paracrine signals synergize to accelerate perichondrial osteoblastic differentiation. The work presented here supports the concept that the cartilage-derived β-catenin signal is a central mediator for major events during endochondral bone formation, including chondrocyte maturation, primary and secondary ossification center development, vascularization, and perichondrial bone formation.

Nfatc2 is a primary response gene of Nell-1 regulating chondrogenesis in ATDC5 cells

Nell-1 is a growth factor required for normal skeletal development and expression of extracellular matrix proteins required for bone and cartilage cell differentiation. We identified the transcription factor nuclear factor of activated T cells (Nfatc2) as a primary response gene of Nell-1 through a microarray screen, with validation using real-time polymerase chain reaction (PCR). We investigated the effects of recombinant Nell-1 protein on the chondrogenic cell line ATDC5 and primary mouse chondrocytes. The osteochondral transcription factor Runx2 was investigated as a possible intermediary between Nell-1 and Nfatc2 using adenoviral overexpression of wild-type and dominant-negative Runx2. Nell-1 transiently induced both transcription and translation of Nfatc2, an effect inhibited by transduction of dominant-negative Runx2, suggesting that Runx2 was necessary for Nfatc2 induction. Differentiation assays revealed inhibitory effects of Nell-1 on ATDC5 cells. Although proliferation was unaffected, expression of chondrocyte-specific genes was decreased, and cartilage nodule formation and proteoglycan accumulation were suppressed. siRNA knockdown of Nfatc2 significantly reversed these inhibitory effects. To elucidate the relationship between Nell-1, Runx2, and Nfatc2 in vivo, their presence and distribution were visualized in femurs of wild-type and Nell1-deficient mice at both neonatal and various developmental stages using immunohistochemistry. All three proteins colocalized in the perichondrium of wild-type femurs but stained weakly or were completely absent in Nell1-deficient femurs at neonatal stages. Thus Nfatc2 likely plays an important role in Nell-1-mediated osteochondral differentiation in vitro and in vivo. To our knowledge, this is the first demonstration that Nfatc2 is a primary response gene of Nell-1.

A cellular lineage analysis of the chick limb bud

The chick limb bud has been used as a model system for studying pattern formation and tissue development for more than 50 years. However, the lineal relationships among the different cell types and the migrational boundaries of individual cells within the limb mesenchyme have not been explored. We have used a retroviral lineage analysis system to track the fate of single limb bud mesenchymal cells at different times in early limb development. We find that progenitor cells labeled at stage 19-22 can give rise to multiple cell types including clones containing cells of all five of the major lateral plate mesoderm-derived tissues (cartilage, perichondrium, tendon, muscle connective tissue, and dermis). There is a bias, however, such that clones are more likely to contain the cell types of spatially adjacent tissues such as cartilage/perichondrium and tendon/muscle connective tissue. It has been recently proposed that distinct proximodistal segments are established early in limb development; however our analysis suggests that there is not a strict barrier to cellular migration along the proximodistal axis in the early stage 19-22 limb buds. Finally, our data indicate the presence of a dorsal/ventral boundary established by stage 16 that is inhibitory to cellular mixing. This boundary is demarcated by the expression of the LIM-homeodomain factor lmx1b.

Expression of parathyroid hormone-related peptide (PthrP) and its receptor (PTH1R) during the histogenesis of cartilage and bone in the chicken mandibular process

The purpose of this study was to examine the expression and actions of parathyroid hormone-related protein (PTHrP) when skeletal histogenesis occurs in the chicken mandible. Prior to the appearance of skeletal tissues, PTHrP and PTH1R were co-expressed by cells in the ectoderm, skeletal muscle, peripheral nerve and mesenchyme. Hyaline cartilage was first observed at HH stage 27 when many but not all chondroblasts expressed PTHrP and PTH1R. By stage 34, PTHrP and PTH1R were not detected in chondrocytes but were expressed in the perichondrium. Alkaline phosphatase (AP)-positive preosteoblasts and woven bone appeared at stages 31 and 34, respectively. Preosteoblasts, osteoblasts and osteocytes co-expressed PTHrP and PTH1R. Treatment with chicken PTHrP (1-36) increased cAMP in mesenchyme from stage 26 embryos. Continuous exposure to chicken PTHrP (1-36) for 14 days increased cartilage nodule number and decreased AP while intermittent exposure did not affect cartilage nodule number and increased AP in cultures of stage 26 mesenchymal cells. Adding a neutralizing anti-PTHrP antibody to the cultures reduced cartilage nodule number and did not affect AP. These findings show that PTHrP and PTH1R are co-expressed by extraskeletal and skeletal cells before and during skeletal tissue histogenesis, and that PTHrP may influence skeletal tissue histogenesis by affecting the differentiation of mandibular mesenchymal cells into chondroblasts and osteoblasts.

Parathyroid hormone-related peptide (PTHrP)-dependent and -independent effects of transforming growth factor beta (TGF-beta) on endochondral bone formation

Previously, we showed that expression of a dominant-negative form of the transforming growth factor beta (TGF-beta) type II receptor in skeletal tissue resulted in increased hypertrophic differentiation in growth plate and articular chondrocytes, suggesting a role for TGF-beta in limiting terminal differentiation in vivo. Parathyroid hormone-related peptide (PTHrP) has also been demonstrated to regulate chondrocyte differentiation in vivo. Mice with targeted deletion of the PTHrP gene demonstrate increased endochondral bone formation, and misexpression of PTHrP in cartilage results in delayed bone formation due to slowed conversion of proliferative chondrocytes into hypertrophic chondrocytes. Since the development of skeletal elements requires the coordination of signals from several sources, this report tests the hypothesis that TGF-beta and PTHrP act in a common signal cascade to regulate endochondral bone formation. Mouse embryonic metatarsal bone rudiments grown in organ culture were used to demonstrate that TGF-beta inhibits several stages of endochondral bone formation, including chondrocyte proliferation, hypertrophic differentiation, and matrix mineralization. Treatment with TGF-beta1 also stimulated the expression of PTHrP mRNA. PTHrP added to cultures inhibited hypertrophic differentiation and matrix mineralization but did not affect cell proliferation. Furthermore, terminal differentiation was not inhibited by TGF-beta in metatarsal rudiments from PTHrP-null embryos; however, growth and matrix mineralization were still inhibited. The data support the model that TGF-beta acts upstream of PTHrP to regulate the rate of hypertrophic differentiation and suggest that TGF-beta has both PTHrP-dependent and PTHrP-independent effects on endochondral bone formation.