P15 peptide stimulates chondrogenic commitment and endochondral ossification

The Osteogenic Peptide P-15 for Bone Regeneration: A Narrative Review of the Evidence for a Mechanism of Action

Bone regeneration is a complex multicellular process involving the recruitment and attachment of osteoprogenitors and their subsequent differentiation into osteoblasts that deposit extracellular matrixes. There is a growing demand for synthetic bone graft materials that can be used to augment these processes to enhance the healing of bone defects resulting from trauma, disease or surgery. P-15 is a small synthetic peptide that is identical in sequence to the cell-binding domain of type I collagen and has been extensively demonstrated in vitro and in vivo to enhance the adhesion, differentiation and proliferation of stem cells involved in bone formation. These events can be categorized into three phases: attachment, activation and amplification. This narrative review summarizes the large body of preclinical research on P-15 in terms of these phases to describe the mechanism of action by which P-15 improves bone formation. Knowledge of this mechanism of action will help to inform the use of P-15 in clinical practice as well as the development of methods of delivering P-15 that optimize clinical outcomes.

The Role of Extracellular Matrix (ECM) Adhesion Motifs in Functionalised Hydrogels

To create functional tissue engineering scaffolds, biomaterials should mimic the native extracellular matrix of the tissue to be regenerated. Simultaneously, the survival and functionality of stem cells should also be enhanced to promote tissue organisation and repair. Hydrogels, but in particular, peptide hydrogels, are an emerging class of biocompatible scaffolds which act as promising self-assembling biomaterials for tissue engineering and regenerative therapies, ranging from articular cartilage regeneration at joint defects, to regenerative spinal cord injury following trauma. To enhance hydrogel biocompatibility, it has become imperative to consider the native microenvironment of the site for regeneration, where the use of functionalised hydrogels with extracellular matrix adhesion motifs has become a novel, emerging theme. In this review, we will introduce hydrogels in the context of tissue engineering, provide insight into the complexity of the extracellular matrix, investigate specific adhesion motifs that have been used to generate functionalised hydrogels and outline their potential applications in a regenerative medicine setting. It is anticipated that by conducting this review, we will provide greater insight into functionalised hydrogels, which may help translate their use towards therapeutic roles.

Chondroinductive Peptides for Cartilage Regeneration

Inducing and maintaining a hyaline cartilage phenotype is the greatest challenge for cartilage regeneration. Synthetic chondroinductive biomaterials might be the answer to the unmet clinical need for a safe, stable, and cost-effective material capable of inducing true hyaline cartilage formation. The past decade witnessed an emergence of peptides to achieve chondrogenesis, as peptides have the advantages of versatility, high target specificity, minimized toxicity and immunogenicity, and ease of synthesis. Here, we review peptides as the basis for creating promising synthetic chondroinductive biomaterials for in situ scaffold-based cartilage regeneration. We provide a thorough review of peptides evaluated for cartilage regeneration while distinguishing between peptides reported to induce chondrogenesis independently, and peptides reported to act in synergy with other growth factors to induce cartilage regeneration. Additionally, we highlight that most peptide studies have been in vitro, and appropriate controls are not always present. A few rigorously-performed in vitro studies have proceeded to in vivo studies, but the peptides in those in vivo studies were mainly introduced via systemic, subcutaneous, or intraarticular injections, with a paucity of studies employing in situ defects with appropriate controls. Clinical translation of peptides will require the evaluation of these peptides in well-controlled in vivo cartilage defect studies. In the decade ahead, we may be poised to leverage peptides to design devices that are safe, reproducible, cost-efficient, and scalable biomaterials, which are themselves chondroinductive to achieve true hyaline cartilage regeneration without the need for growth factors and other small molecules.