Regeneration of tracheal neotissue in partially decellularized scaffolds

Liver tissue engineering using decellularized scaffolds: Current progress, challenges, and opportunities

Liver transplantation represents the only definitive treatment for patients with end-stage liver disease. However, the shortage of liver donors provokes a dramatic gap between available grafts and patients on the waiting list. Whole liver bioengineering, an emerging field of tissue engineering, holds great potential to overcome this gap. This approach involves two main steps; the first is liver decellularization and the second is recellularization. Liver decellularization aims to remove cellular and nuclear materials from the organ, leaving behind extracellular matrices containing different structural proteins and growth factors while retaining both the vascular and biliary networks. Recellularization involves repopulating the decellularized liver with appropriate cells, theoretically from the recipient patient, to reconstruct the parenchyma, vascular tree, and biliary network. The aim of this review is to identify the major advances in decellularization and recellularization strategies and investigate obstacles for the clinical application of bioengineered liver, including immunogenicity of the designed liver extracellular matrices, the need for standardization of scaffold fabrication techniques, selection of suitable cell sources for parenchymal repopulation, vascular, and biliary tree reconstruction. In vivo transplantation models are also summarized for evaluating the functionality of bioengineered livers. Finally, the regulatory measures and future directions for confirming the safety and efficacy of bioengineered liver are also discussed. Addressing these challenges in whole liver bioengineering may offer new solutions to meet the demand for liver transplantation and improve patient outcomes.

Proteomic Analysis of Surgery-induced Stress Post-Tracheal Transplantation Highlights Changes in Matrisome

OBJECTIVE

Investigate the impact of Surgery-induced stress (SIS) on the normal airway repair process after airway reconstruction using a mouse microsurgery model, mass spectrometry (MS), and bioinformatic analysis.

METHODS

Tracheal tissue from non-surgical (N = 3) and syngeneic tracheal grafts at 3 months post-replacement (N = 3) were assessed using mass spectrometry. Statistical analysis was done using MASCOT via Proteome Discoverer™. Proteins were categorized into total, dysregulated, suppressed, and evoked proteins in response to SIS. Dysregulated proteins were identified using cut-off values of -1 1 and t-test (p value <0.05). Enriched pathways were determined using STRING and Metascape.

RESULTS

At the three-month post-operation mark, we noted a significant increase in submucosal cellular infiltration (14343 ± 1286 cells/mm2, p = 0.0003), despite reduced overall thickness (30 ± 3 μm, p = 0.01), compared to Native (4578 ± 723 cells/mm2; 42 ± 6 μm). Matrisome composition remained preserved, with proteomic analysis identifying 193 commonly abundant proteins, encompassing 7.2% collagens, 34.2% Extracellular matrix (ECM) glycoproteins, 6.2% proteoglycans, 33.2% ECM regulators, 14.5% Extracellular matrix-affiliated, and 4.7% secreted factors. Additionally, our analysis unveiled a unique proteomic signature of 217 "Surgery-evoked proteins" associated with SIS, revealing intricate connections among neutrophils, ECM remodeling, and vascularization through matrix metalloproteinase-9 interaction.

CONCLUSIONS

Our study demonstrated the impact of SIS on the extracellular matrix, particularly MMP9, after airway reconstruction. The novel identification of MMP9 prompts further investigation into its potential role in repair.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:4052-4059, 2024.

Tissue-engineered tracheal implants: Advancements, challenges, and clinical considerations

Restoration of extensive tracheal damage remains a significant challenge in respiratory medicine, particularly in instances stemming from conditions like infection, congenital anomalies, or stenosis. The trachea, an essential element of the lower respiratory tract, constitutes a fibrocartilaginous tube spanning approximately 10-12 cm in length. It is characterized by 18 ± 2 tracheal cartilages distributed anterolaterally with the dynamic trachealis muscle located posteriorly. While tracheotomy is a common approach for patients with short-length defects, situations requiring replacement arise when the extent of lesion exceeds 1/2 of the length in adults (or 1/3 in children). Tissue engineering (TE) holds promise in developing biocompatible airway grafts for addressing challenges in tracheal regeneration. Despite the potential, the extensive clinical application of tissue-engineered tracheal substitutes encounters obstacles, including insufficient revascularization, inadequate re-epithelialization, suboptimal mechanical properties, and insufficient durability. These limitations have led to limited success in implementing tissue-engineered tracheal implants in clinical settings. This review provides a comprehensive exploration of historical attempts and lessons learned in the field of tracheal TE, contextualizing the clinical prerequisites and vital criteria for effective tracheal grafts. The manufacturing approaches employed in TE, along with the clinical application of both tissue-engineered and non-tissue-engineered approaches for tracheal reconstruction, are discussed in detail. By offering a holistic view on TE substitutes and their implications for the clinical management of long-segment tracheal lesions, this review aims to contribute to the understanding and advancement of strategies in this critical area of respiratory medicine.

Feasibility of tracheal reconstruction using silicone-stented aortic allografts

OBJECTIVES

Tracheal reconstruction post-extensive resection remains an unresolved challenge in thoracic surgery. This study evaluates the use of aortic allografts (AAs) for tracheal replacement and reconstruction in a rat model, aiming to elucidate the underlying mechanisms of tracheal regeneration.

METHODS

AAs from female rats were employed for tracheal reconstruction in 36 male rats, with the replacement exceeding half of the tracheal length. To avert collapse, silicone stents were inserted into the AA lumens. No immunosuppressive therapy was administered. The rats were euthanized biweekly, and the AAs were examined for neovascularization, cartilage formation, respiratory epithelial ingrowth, submucosal gland regeneration and the presence of the Sex-determining region of Y-chromosome (SRY) gene.

RESULTS

All procedures were successfully completed without severe complications. The AA segments were effectively integrated into the tracheal framework, with seamless distinction at suture lines. Histological analysis indicated an initial inflammatory response, followed by the development of squamous and mucociliary epithelia, new cartilage ring formation and gland regeneration. In situ hybridization identified the presence of the SRY gene in newly formed cartilage rings, confirming that regeneration was driven by recipient cells.

CONCLUSIONS

This study demonstrates the feasibility of AAs transforming into functional tracheal conduits, replicating the main structural and functional characteristics of the native trachea. The findings indicate that this approach offers a novel pathway for tissue regeneration and holds potential for treating extensive tracheal injuries.

Airway disease decreases the therapeutic potential of epithelial stem cells

BACKGORUND

Tissue-engineered tracheal grafts (TETG) can be recellularized by the host or pre-seeded with host-derived cells. However, the impact of airway disease on the recellularization process is unknown.

METHODS

In this study, we determined if airway disease alters the regenerative potential of the human tracheobronchial epithelium (hTBE) obtained by brushing the tracheal mucosa during clinically-indicated bronchoscopy from 48 pediatric and six adult patients.

RESULTS

Our findings revealed that basal cell recovery and frequency did not vary by age or region. At passage 1, all samples produced enough cells to cellularize a 3.5 by 0.5 cm2 graft scaffold at low cell density (~ 7000 cells/cm2), and 43.75% could cellularize a scaffold at high cell density (~ 100,000 cells/cm2). At passage 2, all samples produced the number of cells required for both recellularization models. Further evaluation revealed that six pediatric samples (11%) and three (50%) adult samples contained basal cells with a squamous basal phenotype. These cells did not form a polarized epithelium or produce differentiated secretory or ciliated cells. In the pediatric population, the squamous basal cell phenotype was associated with degree of prematurity (< 28 weeks, 64% vs. 13%, p = 0.02), significant pulmonary history (83% vs. 34%, p = 0.02), specifically with bronchopulmonary dysplasia (67% vs. 19%, p = 0.01), and patients who underwent previous tracheostomy (67% vs. 23%, p = 0.03).

CONCLUSIONS

In summary, screening high-risk pediatric or adult population based on clinical risk factors and laboratory findings could define appropriate candidates for airway reconstruction with tracheal scaffolds.

LEVEL OF EVIDENCE

Level III Cohort study.