Elastin-Like Recombinamer Hydrogels for Improved Skeletal Muscle Healing Through Modulation of Macrophage Polarization

Abstract

Large skeletal muscle injuries, such as a volumetric muscle loss (VML), often result in an incomplete regeneration due to the formation of a non-contractile fibrotic scar tissue. This is, in part, due to the outbreak of an inflammatory response, which is not resolved over time, meaning that type-1 macrophages (M1, pro-inflammatory) involved in the initial stages of the process are not replaced by pro-regenerative type-2 macrophages (M2). Therefore, biomaterials that promote the shift from M1 to M2 are needed to achieve optimal regeneration in VML injuries. In this work, we used elastin-like recombinamers (ELRs) as biomaterials for the formation of non-(physical) and covalently (chemical) crosslinked bioactive and biodegradable hydrogels to fill the VML created in the tibialis anterior (TA) muscles of rats. These hydrogels promoted a higher infiltration of M2 within the site of injury in comparison to the non-treated control after 2 weeks (p<0.0001), indicating that the inflammatory response resolves faster in the presence of both types of ELR-based hydrogels. Moreover, there were not significant differences in the amount of collagen deposition between the samples treated with the chemical ELR hydrogel at 2 and 5 weeks, and this same result was found upon comparison of these samples with healthy tissue after 5 weeks, which implies that this treatment prevents fibrosis. The macrophage modulation also translated into the formation of myofibers that were morphologically more similar to those present in healthy muscle. Altogether, these results highlight that ELR hydrogels provide a friendly niche for infiltrating cells that biodegrades over time, leaving space to new muscle tissue. In addition, they orchestrate the shift of macrophage population toward M2, which resulted in the prevention of fibrosis in the case of the chemical hydrogel treatment and in a more healthy-like myofiber phenotype for both types of hydrogels. Further studies should focus in the assessment of the regeneration of skeletal muscle in larger animal models, where a more critical defect can be created and additional methods can be used to evaluate the functional recovery of skeletal muscle.

Combining tunable proteolytic sequences and a VEGF-mimetic peptide for the spatiotemporal control of angiogenesis within Elastin-Like Recombinamer scaffolds

“…This indicated an inverse correlation between cleavage kinetics and macrophage content, with no differences upon conjugation with the QK-peptide. In addition, the M1/M2 ratio confirmed an equilibrated presence of both types of macrophages with a slight tendency towards pro-healing macrophages (M2) over time, and without signs of chronic inflammation or fibrotic tissue formation, in agreement with previously described protease-sensitive ELR hydrogels [20,25]. Thus, in terms of macrophage-related immunogenicity, these hydrogels and scaffolds can be safely used for TERM applications that require the formation of a complex vascular structure.…”

“…This technique has reported the formation of biocompatible ELR hydrogels [20] that promoted the regeneration of different tissues, thanks to their bioinspired ECM-like nature and to the inclusion of bioactive sequences [21]. For instance, they have shown to enable the regeneration of bone [22], cartilage [23,24], skeletal muscle [25], cornea [26] and cardiovascular tissues [27][28][29]. In addition, ELRs have demonstrated a non-immunogenic response, promoting the shift from type-1 macrophages (M1, pro-inflammatory) towards type-2 macrophages (M2, pro-regenerative), thus preventing fibrosis and inducing an improved healing of the damaged tissue [25].…”

“…For instance, they have shown to enable the regeneration of bone [22], cartilage [23,24], skeletal muscle [25], cornea [26] and cardiovascular tissues [27][28][29]. In addition, ELRs have demonstrated a non-immunogenic response, promoting the shift from type-1 macrophages (M1, pro-inflammatory) towards type-2 macrophages (M2, pro-regenerative), thus preventing fibrosis and inducing an improved healing of the damaged tissue [25].…”

Harnessing the ECM Microenvironment to Ameliorate Mesenchymal Stromal Cell-Based Therapy in Chronic Lung Diseases

“…growth factors, RGD domains, and ECM proteins. Recombinantly produced biomaterials such as the elastin-like recombinamer polymer allows for the precise composition of structural and chemical properties, with gene technology introducing sequences for cell attachment and MMP degradation and at the same time exposing functional groups for binding of for example growth factors to promote or maintain the MSC therapeutic effect (Ibáñez-Fonseca et al, 2020). De Santis et al recently demonstrated the functional outcome of a 3D bioprinted hybrid hydrogel combining decellularized lung tissue with alginate to form human airways containing primary human airway epithelial progenitor cells (De Santis et al, 2020).…”

Thixotropic Hydrogels Composed of Self-Assembled Nanofibers of Double-Hydrophobic Elastin-Like Block Polypeptides

“…Catalyst-free click reactions occured on mixing these ELPs, yielding a hydrogel. The click hydrogels, with cell-adhesive and biodegradable properties, were successful in tissue regeneration, in animal models of volumetric muscle loss [ 14 ], myocardial infarction [ 15 ], and critical limb ischemia [ 16 ].…”