Morphological and Functional Changes of Human Vocal Fold Fibroblasts with Hepatocyte Growth Factor

Dual growth factor-immobilized bioactive injection material for enhanced treatment of glottal insufficiency

With increasing demand for treatment of glottal insufficiency, several injection materials have been examined. However, biological resorption, degradation of injected materials, and the subsequent need to perform multiple injections still remain major clinical problems. In this study, we fabricated two different growth factor (GF) [single basic fibroblast growth factor (bFGF), single hepatocyte growth factor (HGF), or dual bFGF/HGF]-immobilized polycaprolactone (PCL)/Pluronic F127 microspheres. These materials were investigated for their potential use as bioactive injection laryngoplasty agents. HGF was found to be continuously released over 20 days and the bFGF was found to be continuously released over 25 days, as demonstrated by ELISA assay. Human vocal fold fibroblasts (hVFFs) showed significantly higher proliferative ability on dual GF-immobilized microspheres. GF-immobilized microspheres (bFGF, HGF, and dual GF) were injected into paralyzed vocal folds of New Zealand white rabbits. Through endoscopic observation and H&E staining, we identified that the microspheres remained localized at the injection site, resulting in constant volume augmentation of the paralyzed vocal fold without significant loss of the initial volume after 4 weeks. The expression of genes related to the extracellular matrix (ECM) in the vocal fold was upregulated by dual GF-immobilized microspheres. Furthermore, dual GF-immobilized microspheres inhibited muscle degeneration and upregulation of myogenic-related genes. In conclusion, dual GF-immobilized microspheres passively augmented the volume of the paralyzed vocal fold while actively inducing ECM synthesis at the injected vocal fold and preserving muscle tissue. Dual GF-immobilized microspheres could be a new and promising injection material for paralyzed vocal folds. STATEMENT OF SIGNIFICANCE: Limitation of prolonged augmentation of vocal fold and degeneration of vocal fold tissue still remain as major clinical problems in the treatment of vocal fold paralysis. Herein, we fabricated the polycaprolactone (PCL)/Pluronic F127 microspheres to augment volume of paralyzed vocal folds. On top of that, we additionally immobilized the growth factors (bFGF, HGF, or dual bFGF/HGF) on the surface of these microspheres. We highlight the efficacy of the dual GF-immobilized microspheres which augmented the volume of the paralyzed vocal fold passively, induced ECM synthesis actively at the injected vocal fold and preserved laryngeal muscle tissue. Our results suggest that the dual GF-immobilized microsphere could be a new promising injection material for injection laryngoplasty to treat paralyzed vocal fold.

Identifying the Growth Factors for Improving Neointestinal Regeneration in Rats through Transcriptome Analysis Using RNA-Seq Data

Using our novel surgical model of simultaneous intestinal adaptation "A" and neointestinal regeneration "N" conditions in individual rats to determine feasibility for research and clinical application, we further utilized next generation RNA sequencing (RNA-Seq) here in normal control tissue and both conditions ("A" and "N") across time to decipher transcriptome changes in neoregeneration and adaptation of intestinal tissue at weeks 1, 4, and 12. We also performed bioinformatics analyses to identify key growth factors for improving intestinal adaptation and neointestinal regeneration. Our analyses indicate several interesting phenomena. First, Gene Ontology and pathway analyses indicate that cell cycle and DNA replication processes are enhanced in week 1 "A"; however, in week 1 "N", many immune-related processes are involved. Second, we found some growth factors upregulated or downregulated especially in week 1 "N" versus "A". Third, based on each condition and time point versus normal control tissue, we found in week 1 "N" BMP2, BMP3, and NTF3 are significantly and specifically downregulated, indicating that the regenerative process may be inhibited in the absence of these growth factors. This study reveals complex growth factor regulation in small neointestinal regeneration and intestinal adaptation and provides potential applications in tissue engineering by introducing key growth factors identified here into the injury site.

The Effect of Fibroblast Growth Factors in Grafted Fascia into the Vocal Fold of Rabbits

Introduction  The human larynx is a very important organ for communication. Many conditions lead to scarring of the vocal folds, decreasing voice quality. Objective  We aimed to determine whether fibroblast growth factors (FGFs) may influence tissue integration of grafted fascia into the vocal folds of an animal model. Methods  This is an experimental animal study with 12 adult rabbits that were submitted to a grafting fragment obtained from superficial cervical fascia into the vocal fold lamina propria, bilaterally. The right vocal fold was injected with FGFs. The animals were sacrificed after 1 month or 12 months, depending on the group they were assigned to, and a histological analysis of their vocal folds was performed. We analyzed the histological changes (such as the presence of fibrosis and neovascularization) induced by the acute or chronic inflammatory reactions. Results  The FGFs induced acute inflammatory changes in all animals after 1 month of the initial experiment. The presence of FGFs triggered more fibrosis than the expected due to the surgical procedure itself when compared with the control side of all animals after 12 months of the initial experiment. Conclusions  Fibroblast growth factors alone do not represent a good therapeutic option in phonosurgery, since we observed higher levels of fibrosis in the vocal fold lamina propria. Further studies combining more substances may be necessary to elucidate the best option to be used in this kind of surgery.

Characterization of aged rat vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

To elucidate the aging physiology of the vocal folds, we examined the characters of aged vocal fold fibroblasts (VFFs) in various conditions.

STUDY DESIGN

In vitro study.

METHODS

VFFs from young (12-week-old) and aged (19-month-old) Sprague-Dawley rats were compared. Proliferative capacity, ratio of myofibroblast to fibroblast, myofibroblast function, and extracellular matrix production were examined in the following conditions: naïve, basic fibroblast growth factor (bFGF) supplemented, and hepatocyte growth factor (HGF) supplemented.

RESULTS

Aged VFFs demonstrated reduced proliferation by cell counting, though the ratio of Ki-67-positive cells showed no difference. Aged VFFs exhibited an increased expression of α-smooth muscle actin (α-SMA); however, they demonstrated no enhanced contractile ability in a gel contraction assay. Type I collagen protein was increased age dependently, accompanied with decreased Mmp1 and unchanged Col1a1 transcription. Type I collagen protein and α-SMA represented quite similar reduction patterns to bFGF or HGF administration.

CONCLUSIONS

The following possible characteristics of aged VFFs were implied: long duration of mitosis, increased myofibroblast population size with certain dysfunctions, reduced type I collagen turnover, and correlation between α-SMA expression and type I collagen metabolism. Further investigations of these features will help to clarify presbyphonia's pathology and establish treatment strategies.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:E94-E101, 2019.

Evaluation of the Grafted Fascia in the Vocal Fold of Dogs: A Histologic Study

INTRODUCTION

There is no consensus on the ideal graft for medialization surgery of the vocal folds in the literature. One of the most favorable proposals is the use of autologous fascia, which seems limited by the lack of information regarding the integration of grafted tissue. Our study aims to evaluate the degree of fully engrafted fascia integration in the vocal fold lamina propria of dogs.

MATERIALS AND METHODS

Fourteen adult mongrel dogs that underwent intravenous general anesthesia were selected and kept under spontaneous ventilation. A fascia lata fragment of 4 cm² was obtained from the right leg of each dog. The dogs underwent laryngoscopy; a 3 mm incision was made in the vocal process, next to the vestibular process, and the fascia was grafted into the right vocal fold. The left vocal fold was used as a control. The animals were divided into two groups: group A, evaluated after 2 months of the procedure, and group B, evaluated after 6 months of the procedure. Histologic analysis was made semiquantitatively regarding the presence of inflammatory reaction, fibrosis, and neovascularization.

RESULTS

Our final studied group comprised 12 dogs. Microscopic examination of the larynx revealed the absence of any detectable inflammation in the incision site. The lamina propria of the grafted vocal fold showed identifiable compact, thick, and eosinophilic collagen bands. The surrounding tissue showed thin collagen bands with some organization, similar to the contralateral vocal fold.

CONCLUSION

The grafted fascia integrates into the vocal fold lamina propria and seems not to cause inflammatory reaction response.

Hyaluronic Acid Behavior in the Lamina Propria of the Larynx with Advancing Age

Objectives

To analyze the hyaluronic acid behavior in the lamina propria of the larynx with advancing age.

Study Design

Prospective study.

Setting

UNESP-Univ Estadual Paulista, Botucatu Medical School, Brazil.

Subjects and Methods

Thirty vocal folds were obtained at necropsy from 10 adult males (30–50 years old) and 20 geriatric males (10: 60–75 years old; 10: over 76 years old). Midmembranous vocal fold sections were subjected to immunohistochemical reactions. Digital imaging software (ImageJ) was used to quantify the hyaluronic acid distribution over the lamina propria of vocal folds, from superficial to deep layers.

Results

Hyaluronic acid distribution was homogeneous for the larynges, at both superficial and deep layers (41.6 and 38.5, respectively). For both 30- to 50-year-old men geriatric age groups, hyaluronic acid level was lower at both layers.

Conclusion

Hyaluronic acid level in the lamina propria of the larynx of geriatric men decreases with advancing age at both layers of the lamina.

Restoration of scarred vocal folds using 5 amino acid-deleted type hepatocyte growth factor

OBJECTIVES/HYPOTHESIS

Our previous studies demonstrated a regenerative effect of recombinant human hepatocyte growth factor (HGF) on vocal fold scarring using full-length HGF. However, clinical application has not yet been achieved because of the lack of a good manufacturing practice (GMP) for full-length HGF. Another natural form of human HGF, 5 amino acid-deleted type HGF (dHGF), has been newly produced under a GMP procedure. In the current study, we investigated the effect of dHGF in comparison with full-length HGF for the treatment of vocal fold scars using a canine model.

STUDY DESIGN

Prospective animal experiment.

METHODS

The vocal folds of nine beagles were unilaterally injured. Four weeks after injury, the vocal folds were treated with an intracordal injection of full-length HGF (full HGF group), dHGF (dHGF group), or phosphate-buffered saline (sham group). Vibratory and histological examinations were performed for each group 6 months after injury.

RESULTS

Vibratory examinations demonstrated significantly lower phonation threshold pressure and a higher ratio of normalized mucosal wave amplitude in both the full HGF and dHGF groups as compared to the sham group. Histological examination showed restoration of hyaluronic acid in both the full HGF and dHGF groups as compared to the sham group. No significant differences were observed for each parameter between the full HGF group and the dHGF group.

CONCLUSIONS

dHGF showed the same potential for regenerative effects on vocal fold scars as full-length HGF. dHGF should be applicable for human clinical trials in patients with vocal fold scars.

CD34-positive fibroblasts in Reinke's edema

OBJECTIVES/HYPOTHESIS

To elucidate whether and to what extent CD34+ fibroblasts (so-called CD34+ fibrocytes, CD34+ dendritic cells, and CD34+ stromal cells) occur in normal human vocal folds and in Reinke's edema.

STUDY DESIGN

Histological study.

METHODS

Conventional, immunohistochemical, and ultrastructural procedures were performed in histological blocks of 18 selected cases of Reinke's edema (with typical findings including acellular edematous spaces in the subepithelial connective tissue of vocal folds, and disarrangement of elastic, collagen, and reticular fibers). For control purposes, four normal vocal folds were analyzed.

RESULTS

In normal vocal folds, most stromal cells were spindle-shaped CD34+ fibroblasts. In Reinke's edema, increased density and changes in the morphology and size of this subpopulation of fibroblasts were demonstrated in the connective tissue surrounding the edematous spaces, particularly in their borders, where together with some macrophages they formed boundaries, mimicking the walls of distended lymphatic vessels when conventional stains were used. These activated CD34+ fibroblasts acquired a dendritic morphology (with long, moniliform, often bifurcated, overlapping multipolar processes), and their cytoplasmic organelles were increased in number. In addition to CD34, they expressed vimentin, CD10 and CD99, but no α-smooth muscle actin (α-SMA), CD31, CD117, CD68, h-caldesmon, desmin, or S-100 protein.

CONCLUSIONS

CD34+ fibroblasts are a major cell component in the stroma of vocal folds in Reinke's edema, and their activation, with increased density and morphologic changes around the edematous spaces, occurs without immunophenotypic transformation toward myofibroblasts (no expression of α-SMA). The mechanisms by which these cells act in Reinke's edema require further study.

[Treatment of glottal gap]

Glottal gaps can be either physiological or pathological. The latter are multifactorial, predominantly organic in origin and occasionally functional. Organic causes include vocal fold paralysis or scarring, as well as a deficiency or excess of tissue. In addition to loss of the mucosal wave, the degree of hoarseness is primarily determined by the circumferential area of the glottal gap. It is thus important to quantify the extent of glottal insufficiency. Although a patient's symptoms form the basis for treatment decisions, these may be subjective and inadequately reflected by the results of auditory-perceptual evaluation, voice analysis and voice performance tests. The therapeutic approach should always combine phonosurgery with conventional voice therapy methods. Voice therapy utilises all the resources made available by the sphincter model of the aerodigestive tract and knowledge on the mechanism of voice production. The aim of phonosurgery is medialization, reconstruction or reinnervation by injection laryngoplasty or larynx framework surgery. These different methods can be combined and often applied directly after vocal fold surgery (primary reconstruction). In conclusion, the techniques described here can be effectively employed to compensate for glottal gaps.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Using growth factor conditioning to modify the properties of human cell derived extracellular matrix

We have recently reported on a bench-top approach for isolating extracellular matrix (ECM) from pure populations of cells grown in culture using sacrificial, open-celled foams to concentrate and capture the ECM. To increase both the accumulation and the strength of the ECM harvested, cell-seeded polyurethane (PU) foams were cultured in media supplemented with either transforming growth factor β-1 (TGFβ1) or hepatocyte growth factor (HGF). At the end of a 3-week culture period, ECM yield was significantly increased for samples conditioned in supplemented media. Control foams yielded 48 ± 12 mg of material for every gram of PU foam seeded. Yield values increased to 102 ± 21 and 243 ± 25 mg for HGF and TGFβ1-treated samples, respectively. HGF supplementation increased the modulus by 59%, while TGFβ1 treatment increased the elastic modulus by 204%. TGFβ1-stimulated material was organized into a network that was markedly denser than control material, with HGF-stimulated network density intermediate to TGFβ1 and controls. Our study showed that TGFβ1-treated samples were collagen enriched while HGF samples had an increased gylcosaminoglycan concentration. The results demonstrate that growth factor supplementation, particularly with TGFβ1, can significantly alter the biomechanical properties of cell-derived ECM that may be used for therapeutic applications.

Implantation of an atelocollagen sponge with autologous bone marrow-derived mesenchymal stromal cells for treatment of vocal fold scarring in a canine model

OBJECTIVES

Vocal fold scarring remains a therapeutic challenge. A new regenerative approach is needed to restore disorganized extracellular matrix. Tissue regeneration requires appropriate cells and a scaffold. Bone marrow-derived mesenchymal stromal cells (BMSCs) are multipotent and secrete many kinds of growth factors to regenerate tissues. Atelocollagen sponges have many large pores that permit cell entry. The present study was performed to evaluate whether implantation of an atelocollagen sponge plus BMSCs is effective for the treatment of vocal fold scarring.

METHODS

Twelve beagles underwent implantation of an atelocollagen sponge or of an atelocollagen sponge with autologous BMSCs (1.0 x 10(6) cells) in the subepithelial pockets of scarred vocal folds. Six months after the operation, vibratory examinations and histologic examinations were performed.

RESULTS

Mucosal vibrations improved significantly for the atelocollagen sponge-implanted vocal folds. Histologic analyses revealed favorable restoration of the extracellular matrix in the lamina propria. Increased distribution of hyaluronic acid and decreased dense collagen deposition were also noted. These improvements were enhanced by implantation of BMSCs.

CONCLUSIONS

Implantation of atelocollagen sponges with autologous BMSCs into scarred vocal folds significantly increased hyaluronic acid distribution and decreased dense collagen deposition in the lamina propria, leading to better mucosal vibration.

Prostaglandin (PG)E2 exhibits antifibrotic activity in vocal fold fibroblasts

OBJECTIVES/HYPOTHESIS

Prostaglandin (PG)E2 has been implicated in a variety of disease processes. It has been described as antifibrotic in the lower airway, yet scar-inducing in the skin. We seek to describe the effects of PGE2 on vocal fold fibroblasts and its interactions with transforming growth factor (TGF)-β1. In addition, we describe a novel organotypic model, a critical step in the development of therapeutic trials.

STUDY DESIGN

In vitro, ex vivo.

METHODS

Collagen secretion by human vocal fold fibroblasts (HVFF) was assayed in response to TGF-β1, PGE2 , and specific EP receptor agonists. Basal HVFF migratory rate was also quantified in response to PGE2 . TGF-β1 induced COX-2 mRNA expression/PGE2 secretion was assayed. Excised vocal folds were subjected to exogenous IL-1β; PGE2 secretion into the supernatant was then assayed.

RESULTS

TGF-β1-induced collagen secretion was blunted in a dose-dependent manner in response to PGE2 . This effect appears to be mediated primarily through the EP1 and EP2 receptors. TGF-β1 induced COX-2 mRNA expression and PGE2 secretion. In our organ culture model, IL-1β stimulated PGE2 secretion in a dose-dependent manner.

CONCLUSIONS

PGE2 is antifibrotic; this finding suggests that the upper airway response to this inflammatory mediator differs significantly from the lower airway. These data have important clinical implications for a variety of pathological processes. Furthermore, exogenous TGF-β1 elicits induction of COX-2, suggesting inherent complexity regarding these processes and PGE2 signaling, specifically. In addition, our organ culture model may prove useful as a means to quantify biological phenomena in the vocal folds.

Controlled release of hepatocyte growth factor from a bovine acellular scaffold for vocal fold reconstruction

A bovine acellular scaffold was found to facilitate tissue remodeling in a rat model of vocal fold injury, whereas hepatocyte growth factor (HGF) has been shown to have an antiscarring effect in the larynx. This study examined the loading and release kinetics of HGF in vitro, and the potential of the acellular scaffold as a timed-release system for the delivery of HGF in vivo. Bilateral wounds were created in the posterior vocal folds of 20 rats, with HGF-loaded acellular scaffolds implanted into the wounds unilaterally, and scaffolds without HGF implanted into the contralateral vocal folds as control. The rats were humanely sacrificed after 3, 7, 30, and 90 days and their larynges were examined histologically and immunohistochemically. Expressions of key matrix proteins in the vocal fold coronal sections were quantified by digital image analysis. Results demonstrated a gradual, sustained release of HGF for at least 7 days in vitro, consistent with the detection of glycosaminoglycans inherent of the scaffold. In rat vocal folds implanted with HGF-loaded scaffolds, apparently fewer inflammatory cells were observed 3 days after surgery when compared to the control. The mean relative densities of collagen III and hyaluronic acid were significantly lower than those of the control 7 days after surgery. Scaffold implants were apparently degraded by 3 months in all animals, with no evidence of fibrosis or calcification. These data suggested that the bovine acellular scaffold could be promising for the exogenous delivery of select growth factors in vivo.

Vocal quality of patients treated for laryngeal tuberculosis, before and after speech therapy

Objectives:

To evaluate dysphonia in patients treated for laryngeal tuberculosis, and to assess the effect of speech therapy on patients' vocal quality.

Materials and methods:

Seven of 23 patients with a confirmed diagnosis of laryngeal tuberculosis, treated at the Evandro Chagas Institute of Clinical Research, Oswaldo Cruz Foundation, underwent speech therapy for six months. These seven patients were evaluated by videolaryngoscopy and vocal acoustic analysis, before, during and after a course of speech therapy.

Results:

The 23 patients with laryngeal tuberculosis comprised five women and 18 men, with ages ranging from 25 to 83 years (mean 41.3 years). Dysphonia was present in 91.3 per cent of these laryngeal tuberculosis patients, being present as the first symptom in 82.6 per cent. In laryngeal tuberculosis patients with dysphonia, laryngeal tuberculosis treatment resulted in dysphonia resolution in only 15.8 per cent. After speech therapy, dysphonia patients had better vocal quality, as demonstrated by statistical analysis of jitter, shimmer, fundamental frequency variability, maximum phonation time, and the ratio between maximum phonation time for voiceless and voiced fricative sounds.

Conclusions:

Following treatment of laryngeal tuberculosis, the incidence of dysphonia was very high. Speech therapy improved patients' vocal quality.

Reinke's edema: investigations on the role of MIB-1 and hepatocyte growth factor

Reinke's edema is a benign disease of the human vocal fold, which mainly affects the sub-epithelial layer of the vocal fold. Microscopic observations show a strongly oedematous epithelium with loosened intercellular junctions, a disruption of the extracellular connections between mucosal epithelium and connective tissue, closely adherent to the thyroarytenoid muscle. Thickening of the basal layer of epithelium, known as Reinke's space, high deposition of fibronectin and chronic inflammatory infiltration it is also visible. We analyzed, together with the hepatocyte growth factor (HGF), the expression level of MIB-1 in samples harvested from patients affected by Reinke's edema, in order to define its biological role and consider it as a possible prognostic factor in the follow-up after surgical treatment. We observed a moderate expression of HGF in the lamina propria of the human vocal fold and in the basal membrane of the mucosal epithelium. Our finding suggests that this growth factor acts as an anti - fibrotic agent in Reinke's space and affects the fibronectin deposition in the lamina propria. MIB-1, on the contrary, showed a weak expression in the basement membrane of the mucosal epithelium and a total absence in the lamina propria deep layer, thus suggesting that only the superficial layer is actively involved in the reparatory process with a high regenerative capacity, together with a high deposition of fibronectin. The latter is necessary for the cellular connections reconstruction, after the inflammatory infiltration.

Liver-derived extracellular matrix as a biologic scaffold for acute vocal fold repair in a canine model

OBJECTIVES/HYPOTHESIS

The objective of the study was to evaluate a naturally derived liver extracellular matrix (L-ECM) scaffold for repair of an acute injury to the vocal fold lamina propria in a canine model.

METHODS

The vocal fold lamina propria was removed bilaterally in four dogs. One vocal fold in each dog was repaired with a porcine L-ECM scaffold, which was chosen because it contains hepatocyte growth factor, an antifibrotic growth factor that aids the healing of vocal folds. The other vocal fold was left untreated. At 3 months after surgery, morphologic and histologic analysis was performed to assess the vocal fold shape, collagen density, collagen composition, elastic fiber content, and glycosaminoglycan content.

RESULTS

The L-ECM-treated vocal fold showed increased collagen density in the superficial aspect of the vocal fold (P < .05). The L-ECM-treated vocal fold also showed an increased collagen III/I ratio as compared to the nontreated group (P < .05). However, the elastic fiber content was found to be increased in both groups, and the glycosaminoglycan content was decreased in both groups as compared to the normal vocal fold (P < .05) with no differences detected between groups.

CONCLUSIONS

The L-ECM scaffold did not restore the biochemical composition or histologic appearance of the injured vocal fold as compared to normal. However, the increased ratio of collagen III/I and elastic fiber content suggests that L-ECM leads to formation of connective tissue that may be more pliable as compared to no treatment. Additional investigation, including functional assessment, is warranted.

Functional morphology of the sound-generating labia in the syrinx of two songbird species

In songbirds, two sound sources inside the syrinx are used to produce the primary sound. Laterally positioned labia are passively set into vibration, thus interrupting a passing air stream. Together with subsyringeal pressure, the size and tension of the labia determine the spectral characteristics of the primary sound. Very little is known about how the histological composition and morphology of the labia affect their function as sound generators. Here we related the size and microstructure of the labia to their acoustic function in two songbird species with different acoustic characteristics, the white-crowned sparrow and zebra finch. Histological serial sections of the syrinx and different staining techniques were used to identify collagen, elastin and hyaluronan as extracellular matrix components. The distribution and orientation of elastic fibers indicated that the labia in white-crowned sparrows are multi-layered structures, whereas they are more uniformly structured in the zebra finch. Collagen and hyaluronan were evenly distributed in both species. A multi-layered composition could give rise to complex viscoelastic properties of each sound source. We also measured labia size. Variability was found along the dorso-ventral axis in both species. Lateral asymmetry was identified in some individuals but not consistently at the species level. Different size between the left and right sound sources could provide a morphological basis for the acoustic specialization of each sound generator, but only in some individuals. The inconsistency of its presence requires the investigation of alternative explanations, e.g. differences in viscoelastic properties of the labia of the left and right syrinx. Furthermore, we identified attachments of syringeal muscles to the labia as well as to bronchial half rings and suggest a mechanism for their biomechanical function.

Effect of exogenous hepatocyte growth factor on vocal fold fibroblasts

OBJECTIVES

We have previously demonstrated the therapeutic potential of hepatocyte growth factor (HGF) in the treatment of vocal fold scarring, although how exogenous HGF affects gene expression of endogenous HGF or extracellular matrix components in the vocal fold fibroblasts remains unclear. In this in vitro study, we aimed to clarify this aspect in order to better understand the effects of HGF on the vocal folds.

METHODS

Fibroblasts were obtained from the lamina propria of the vocal folds of 5 Sprague-Dawley rats and were cultured with HGF at concentrations of 100, 10, 1, and 0 ng/mL. The cells were collected on days 1, 3, and 7, and the expression of endogenous HGF, its receptor c-Met, transforming growth factor-beta1 (TGF-beta1), procollagen types I and III, and hyaluronic acid synthase (HAS)-1 and HAS-2 messenger RNAs (mRNAs) was examined by real-time reverse transcription-polymerase chain reaction.

RESULTS

The expression of endogenous HGF and HAS-1 mRNAs increased significantly when exogenous HGF was administered at a concentration of 1 ng/mL. On day 1, the expression of TGF-beta1 and HAS-2 mRNAs increased significantly in response to 1 ng/mL HGF.

CONCLUSIONS

Exogenous HGF triggered the up-regulation of endogenous HGF, TGF-beta1, HAS-1, and HAS-2 mRNAs in vocal fold fibroblasts.

Effects of transforming growth factor-beta1 on human vocal fold fibroblasts

OBJECTIVES

We studied the effect of transforming growth factor (TGF)-beta on immortalized human vocal fold fibroblasts.

METHODS

Normal human vocal fold fibroblasts were subjected to sequential lentiviral transduction with genes for human telomerase (hTERT) and SV40 large T antigen in order to produce an "immortalized" cell line of normal phenotype. After confirmation of vocal fold fibroblast transfection, these cells, referred to as HVOX, were treated with various concentrations of exogenous TGF-beta1 and assayed for collagen secretion, migration, and proliferation. In addition, components of the TGF-beta signaling pathway were examined in this cell line.

RESULTS

TGF-beta stimulated collagen secretion and migration without altering proliferation of HVOX. HVOX constitutively expressed type I and II TGF-beta receptors, as well as messenger RNA for the Smad signaling proteins and for all TGF-beta isoforms. Exogenous TGF-beta1 induced temporally dependent alterations in Smad2 and Smad3 gene expression. TGF-beta increased Smad7 expression at both 4 and 24 hours. Prolonged exposure to TGF-beta decreased TGF-beta1 gene expression.

CONCLUSIONS

Insight into the underlying pathophysiology of vocal fold fibrosis is likely to yield improved therapeutic strategies to mitigate vocal fold scarring. Our data suggest that TGF-beta signaling may be both paracrine and autocrine in this vocal fold fibroblast cell line, and we therefore propose that TGF-beta may be a reasonable target for therapies to prevent and/or treat vocal fold fibrosis, given its putative role in both acute and chronic vocal fold injury, as well as its effects on vocal fold fibroblasts.

Age-related changes in the murine larynx: initial validation of a mouse model

OBJECTIVES

Changes in voice are commonly associated with aging (presbyphonia). Age-related voice change significantly impairs elderly individuals' ability to communicate meaningfully with others and affects their quality of life. With changing age demographics in our society and increasing emphasis on quality of life, treatment of presbylaryngis is becoming more paramount.

METHODS

We used 9 aged and 9 young mice to validate a mouse model for the aging larynx. We stained the larynges with Alcian blue to determine the hyaluronic acid content, trichrome stain to determine the collagen content, and immunohistochemical stain for alpha smooth muscle actin to determine the myofibroblast content. Morphometric measurements were performed for muscle area, muscle thickness, and muscle fiber diameter.

RESULTS

Statistically significant differences in the density measurements of hyaluronic acid and collagen reflected decreased hyaluronic acid and increased collagen content in the aging larynx. We found alpha smooth muscle actin-labeled myofibroblasts only in the aged larynges. No statistically significant differences were found in the morphometric measurements.

CONCLUSIONS

Aged mice may make a practical model for the age-related changes in the vocal folds that can be used further in studies aiming to correct these changes.

Vocal Fold Wound Healing: A Review for Clinicians

SUMMARY

The basic science of wound healing is largely omitted from the curriculum of many voice clinicians. This fact is relatively disheartening as most therapeutic manipulation in the realm of laryngology and voice disorders deals with injured tissue. Therefore, the selection of therapeutic tasks for persons with vocal injury should ideally be informed by basic science in wound healing. Recently, several investigators have initiated lines of research to determine the course of vocal fold wound healing and the potential role of therapeutic agents, including behavioral agents. The current review seeks to provide a foundation of basic wound healing science and present the most current data regarding the wound healing process in the vocal folds.

Dependence of phonation threshold pressure on vocal tract acoustics and vocal fold tissue mechanics

Analytical and computer simulation studies have shown that the acoustic impedance of the vocal tract as well as the viscoelastic properties of vocal fold tissues are critical for determining the dynamics and the energy transfer mechanism of vocal fold oscillation. In the present study, a linear, small-amplitude oscillation theory was revised by taking into account the propagation of a mucosal wave and the inertive reactance (inertance) of the supraglottal vocal tract as the major energy transfer mechanisms for flow-induced self-oscillation of the vocal fold. Specifically, analytical results predicted that phonation threshold pressure (Pth) increases with the viscous shear properties of the vocal fold, but decreases with vocal tract inertance. This theory was empirically tested using a physical model of the larynx, where biological materials (fat, hyaluronic acid, and fibronectin) were implanted into the vocal fold cover to investigate the effect of vocal fold tissue viscoelasticity on Pth. A uniform-tube supraglottal vocal tract was also introduced to examine the effect of vocal tract inertance on Pth. Results showed that Pth decreased with the inertive impedance of the vocal tract and increased with the viscous shear modulus (G") or dynamic viscosity (eta') of the vocal fold cover, consistent with theoretical predictions. These findings supported the potential biomechanical benefits of hyaluronic acid as a surgical bioimplant for repairing voice disorders involving the superficial layer of the lamina propria, such as scarring, sulcus vocalis, atrophy, and Reinke's edema.

Transdifferentiation of vocal-fold stellate cells and all-trans retinol-induced deactivation

The maculae flavae of the human vocal folds include dense extracellular matrices and compacted cells with a stellate morphology. These vocal-fold stellate cells are thought to participate in the metabolism of extracellular matrices essential in maintaining vocal-fold viscoelasticity required for phonation. We have isolated and cultured these new cells and have tested the hypothesis that they maintain a distinct cellular and biochemical phenotype. We have compared proliferation rates, changes on immunophenotype, and intracellular lipid and vitamin A storage. Vocal-fold stellate cells undergo culture-induced transdifferentiation to a myofibroblast-like phenotype with an altered phenotype resembling, but not identical to, activated hepatic and pancreatic stellate cells. Our results reveal that these cells are capable of responding to exogenous all-trans retinol in culture. Exposure to this synthetic co-factor causes deactivation characterized by decreased proliferation, loss of the activated stellate cell marker, alpha-smooth muscle actin, and restoration of intracellular lipid and vitamin A metabolite storage. These data establish a new and distinct cellular target for future investigations of the viscoelastic properties of the vocal-fold mucosa during normal phonation, aging, vocal-fold scarring, laryngeal fibrosis, and myofibroblastoma.

Current understanding and review of the literature: vocal fold scarring

Vocal fold scarring is the greatest cause of poor voice after vocal fold injury. Scarring causes a disruption of the viscoelastic layered structure of the lamina propria, an increase in stiffness of the vibratory structure, and glottic incompetence. Current treatments for this complex condition are inconsistent and often produce suboptimal results. Research investigating this condition has dramatically increased over the last several years. The literature has been directed toward understanding vocal fold scarring at the biological level and translating this to the clinical forum. We present an up-to-date, thorough, and scholarly review of the literature in vocal fold scarring since 1996.