The effect of chemical modification of amino acid side-chains on collagen degradation by enzymes

Expanding the chemical repertoire of protein-based polymers for drug-delivery applications

Expanding the chemical repertoire of natural and artificial protein-based polymers (PBPs) can enable the production of sequence-defined, yet chemically diverse, biopolymers with customized or new properties that cannot be accessed in PBPs composed of only natural amino acids. Various approaches can enable the expansion of the chemical repertoire of PBPs, including chemical and enzymatic treatments or the incorporation of unnatural amino acids. These techniques are employed to install a wide variety of chemical groups-such as bio-orthogonally reactive, cross-linkable, post-translation modifications, and environmentally responsive groups-which, in turn, can facilitate the design of customized PBP-based drug-delivery systems with modified, fine-tuned, or entirely new properties and functions. Here, we detail the existing and emerging technologies for expanding the chemical repertoire of PBPs and review several chemical groups that either demonstrate or are anticipated to show potential in the design of PBP-based drug delivery systems. Finally, we provide our perspective on the remaining challenges and future directions in this field.

Rap1a Regulates Cardiac Fibroblast Contraction of 3D Diabetic Collagen Matrices by Increased Activation of the AGE/RAGE Cascade

Cardiovascular disease is a common diabetic complication that can arise when cardiac fibroblasts transition into myofibroblasts. Myofibroblast transition can be induced by advanced glycated end products (AGEs) present in the extracellular matrix (ECM) activating RAGE (receptor for advanced glycated end products) to elicit intracellular signaling. The levels of AGEs are higher under diabetic conditions due to the hyperglycemic conditions present in diabetics. AGE/RAGE signaling has been shown to alter protein expression and ROS production in cardiac fibroblasts, resulting in changes in cellular function, such as migration and contraction. Recently, a small GTPase, Rap1a, has been identified to overlap the AGE/RAGE signaling cascade and mediate changes in protein expression. While Rap1a has been shown to impact AGE/RAGE-induced protein expression, there are currently no data examining the impact Rap1a has on AGE/RAGE-induced cardiac fibroblast function. Therefore, we aimed to determine the impact of Rap1a on AGE/RAGE-mediated cardiac fibroblast contraction, as well as the influence isolated diabetic ECM has on facilitating these effects. In order to address this idea, genetically different cardiac fibroblasts were embedded in 3D collagen matrices consisting of collagen isolated from either non-diabetic of diabetic mice. Fibroblasts were treated with EPAC and/or exogenous AGEs, which was followed by assessment of matrix contraction, protein expression (α-SMA, SOD-1, and SOD-2), and hydrogen peroxide production. The results showed Rap1a overlaps the AGE/RAGE cascade to increase the myofibroblast population and generation of ROS production. The increase in myofibroblasts and oxidative stress appeared to contribute to increased matrix contraction, which was further exacerbated by diabetic conditions. Based off these results, we determined that Rap1a was essential in mediating the response of cardiac fibroblasts to AGEs within diabetic collagen.

Atomic force microscopy in the production of a biovital skin graft based on human acellular dermal matrix produced in-house and in vitro cultured human fibroblasts

The most efficient method in III° burn treatment is the use of the autologous split thickness skin grafts that were donated from undamaged body area. The main limitation of this method is lack of suitable donor sites. Tissue engineering is a useful tool to solve this problem. The goal of this study was to find the most efficient way of producing biovital skin substitute based on in house produced acellular dermal matrix ADM and in vitro cultured fibroblasts. Sixty samples of sterilized human allogeneic skin (that came from 10 different donors) were used to examine the influence of decellularizing substances on extracellular matrix and clinical usefulness of the test samples of allogeneic human dermis. Six groups of acellular dermal matrix were studied: ADM-1 control group, ADM-2 research group (24 h incubation in 0.05% trypsin/EDTA solution), ADM-3 research group (24 h incubation in 0.025% trypsin/EDTA solution), ADM-4 research group (24 h incubation in 0.05% trypsin/EDTA solution and 4 h incubation in 0,1% SDS), ADM-5 research group (24 h incubation in 0.025% trypsin/EDTA solution and 4 h incubation in 0,1% SDS), and ADM-6 research group (24 h incubation in 0,1% SDS). Obtained ADMs were examined histochemically and by atomic force microscopy (AFM). ADMs were settled by human fibroblasts. The number of cultured cells and their vitality were measured. The obtained results indicated that the optimal method for production of living skin substitutes is colonization of autologous fibroblasts on the scaffold prepared by the incubation of human allogeneic dermis in 0.05% trypsin/EDTA. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 726-733, 2018.

Effects of different crosslinking conditions on the chemical-physical properties of a novel bio-inspired composite scaffold stabilised with 1,4-butanediol diglycidyl ether (BDDGE)

Serious cartilage lesions (Outerbridge III, IV) may be successfully treated with a three-layered gradient scaffold made by magnesium-doped hydroxyapatite and type I collagen, manufactured through a bio-inspired process and stabilised by a reactive bis-epoxy (1,4-butanediol diglycidyl ether, BDDGE). Each layer was analysed to elucidate the effects of crosslinking variables (concentration, temperature and pH). The chemical stabilisation led to an homogeneous and aligned collagenous matrix: the fibrous structures switched to a laminar foils-based arrangement and organic phases acquired an highly coordinated 3D-organization. These morphological features were strongly evident when crosslinking occurred in alkaline solution, with BDDGE concentration of at least 1 wt%. The optimised crosslinking conditions did not affect the apatite nano-crystals nucleated into self-assembling collagen fibres. The present work allowed to demonstrate that acting on BDDGE reaction parameters might be an useful tool to control the chemical-physical properties of bio-inspired scaffold suitable to heal wide osteochondral defects, even through arthroscopic procedure.

Bioengineered matrices--part 1: attaining structural success in biologic skin substitutes

Skin defect closure after injury or disease may present significant reconstructive challenges. Traditional epidermal coverage alone in the form of skin grafts often fall short in providing stable cover to restore structure and function of the skin. Excessive wound contraction and scar formation, particularly in defects of dermis and epidermis, may create functional and aesthetic problems. Progress in our understanding of molecular biology and tissue engineering have produced major advances in skin substitute technology, particularly relating to the dynamic cellular/extracellular matrix interaction that is critical to successful incorporation of a skin substitute. However, currently available skin substitutes still exhibit a range of problems including excessive wound contraction and scar formation, poor host tissue incorporation, revascularization and, in some cases, structural deficiencies in matrix design. The design principles and structural composition of the matrix must take into account collagenous forms, inherent resistance, porosity, and hydration. The ultimate matrix should be one that promotes intrinsic regeneration by encouraging cellular incorporation and cellular/extracellular cross communication. Attention to basic structural details rather than reliance on specialized cellular or peptide additions to the mix may well produce the advances we seek in improved incorporation of bioengineered skin substitutes.

Diabetes-induced alterations in the extracellular matrix and their impact on myocardial function

Diabetes is an increasing public health problem that is expected to escalate in the future due to the growing incidence of obesity in the western world. While this disease is well known for its devastating effects on the kidneys and vascular system, diabetic individuals can develop cardiac dysfunction, termed diabetic cardiomyopathy, in the absence of other cardiovascular risk factors such as hypertension or atherosclerosis. While much effort has gone into understanding the effects of elevated glucose or altered insulin sensitivity on cellular components within the heart, significant changes in the cardiac extracellular matrix (ECM) have also been noted. In this review article we highlight what is currently known regarding the effects diabetes has on both the expression and chemical modification of proteins within the ECM and how the fibrotic response often observed as a consequence of this disease can contribute to reduced cardiac function.