Novel biomimetics promote dynamic cell-driven remodeling of their microenvironment

Three-dimensional (3D) cell culture systems have been extensively used to mimic the complexity of human tissues and organs in vitro. They represent a powerful biomedical technology for disease modeling, tissue engineering and regenerative medicine. Organoids consist of a 3D collection of cells able to self-renew and self-organize that recapitulate key features of developed organs; they are explored for drug design and screening assays. Biological cell models strongly rely on biomaterials to recreate a microenvironment with compatible properties that resemble the extracellular matrix (ECM). Biomimetic materials are the materials developed by taking inspiration from nature to support a complete or a portion of a living structure that accomplishes, enhances, or substitutes a natural function. These biomaterials are usually engineered for medical biotechnology and pharmaceutical applications. Several concerted efforts have been made in the area of synthetic biomaterials for tunning bioactivity through mixing of materials, degradable crosslinks, and adoption of adhesive molecules such as RGD. Unfortunately, integrin-mediated cell adhesion and proteolytic matrix degradation are known to contribute only a fraction of features of extracellular matrix reported to mediate cell behavior.

During extracellular matrix modelling, the matrix is degraded and deposited, thereby allowing cells to alter the structure and composition of nearby extracellular matrix. Also, extracellular matrix serves as a hub for biochemical cues and growth factors that are presented to cells as tethered molecules. The limitations of current biomaterials present the need for clinically translational synthetic biomimetics with controllable biomechanics that recapitulate the structural features and biological functions of the native extracellular matrix and the possibility of sequestering growth factors.

Biomimetic hydrogel-based cultures can serve as a treatment option for infertility caused by cancer radio- and chemotherapies by supporting the growth and maturation of ovarian follicles to yield fertilizable eggs. These therapies are cytotoxic to ovarian follicles, and it’s impossible to regenerate the non-renewable ovarian follicular reserves once degraded. The only viable yet experimental fertility preservation option which would be applicable to a broad range of cancer survivors is ovarian tissue cryopreservation before the anti-cancer treatments, succeeded by culture and maturation of follicles to obtain fertilizable oocytes. This option could also help avoid the potential transfer of cancer cells back into the patient in the case of leukemia and ovarian cancer.

Despite the impressive progress made in the culture of large murine follicles adopting biomaterials such as degradable poly(ethylene-glycol) hydrogels, it’s still challenging to culture small follicles and achieve clinical translation by yielding supreme oocytes. The lack of endogenous extracellular matrix in the current systems is partly to blame for this shortfall.

To address these challenges, University of Michigan researchers, Claire Tomaszewski, Katarina DiLillo, Brendon Baker, Kelly Arnold, and led by Professor Ariella Shikanov proposed that peptides from native extracellular matrix or growth factors and tethered to a poly(ethylene-glycol) (PEG) hydrogel would sequester and retain extracellular matrix molecules secreted by an encapsulated follicle. They designed these hydrogels with an objective of recapitulating the native extracellular matrix for culture and maturation of follicular organoid. Their research is published in the journal Acta Biomaterialia.

To regenerate the extracellular matrix of ovarian tissues, the authors adopted four peptides, laminin-derived peptide (AG73), heparin-binding peptide (HBP), basement membrane binder (BMB) peptide and the extracellular matrix binding region of placental growth factor 2 (RRR). The authors observed that the peptides they adopted considerably improved ovarian follicle growth, survival, and maturation compared to an inert control, PEG-Cys. By performing an immunohistochemical analysis of the hydrogels near the cultured follicles, the authors were able to see sequestration and retention of laminin, fibronectin, perlecan, and collagen I in the ECM-sequestering hydrogels but not in the bioinert hydrogels.

The research team demonstrated that follicles cultured in hydrogels functionalized with AG73, BMB, or RRR peptides posted higher concentrations of follicle development regulating factors than PEG-Cys. AG73 and BMB peptides were the most crucial in enhancing follicle maturation mainly because they take after basement membrane activity, which is necessary for follicle development.

The outcomes of the study report improved folliculogenesis, presenting a fertility preservation avenue for women put under anti-cancer treatments. They also give a potential solution for other tissue engineering options, for it was possible for encapsulated cells to reinstate their native microenvironments in vitro.