Rubidium-Containing Calcium Alginate Hydrogel for Antibacterial and Diabetic Skin Wound Healing Applications.

Rubidium (Rb) is an important microelement for the human body, which can kill and inhibit bacteria. Rubidium-containing polyhydrated ionogens have been applied to treat refractory wounds. In this work, for the first time, Rb was added into calcium alginate hydrogel (Rb-CA gel) and then made into a dressing by freeze-drying. The addition of Rb to CA maintained a well-ordered porous structure with only slightly reduced swelling and storage modulus and increased roughness and in vitro degradation rate. Experiments in vitro demonstrated that Rb-CA gels could not only inhibit the growth of Staphylococcus aureus and Pseudomonas aeruginosa ubiquitous but were nontoxic and even conducive to human umbilical vein endothelial cells (HUVECs), fibroblasts, and keratinocytes. HUVECs exposed to Rb-CA gels exhibited enhanced migration and tubule formation ability, increased vascular endothelial growth factor secretion, and improved activation of the nuclear factor (erythroid-derived 2)-like 2 (NRF2)/heme-oxygenase-1 (HO-1) signaling pathway. Rb-CA gels also promoted the migration of fibroblasts and keratinocytes. In vivo, in a type II diabetic male Sprague-Dawley rat wound model, neovascularization, re-epithelialization, and collagen deposition were all improved greatly by the Rb-CA gel, with the upregulation of NRF2 and HO-1 protein secretion that inhibited the oxidative stress reaction in the wound sites. Moreover, the Rb-CA gel exhibited a strong anti-inflammatory effect on the wound. In summary, the application of Rb-CA gel dressings to diabetic wounds could produce various synergetic enhancements in terms of angiogenesis, re-epithelialization, and collagen deposition. Hence, Rb-CA gels can be used as a novel therapeutic strategy to promote the healing of diabetic wounds.

Decellularised extracellular matrix-derived peptides from neural retina and retinal pigment epithelium enhance the expression of synaptic markers and light responsiveness of human pluripotent stem cell derived retinal organoids.

Tissue specific extracellular matrices (ECM) provide structural support and enable access to molecular signals and metabolites, which are essential for directing stem cell renewal and differentiation. To mimic this phenomenon in vitro, tissue decellularisation approaches have been developed, resulting in the generation of natural ECM scaffolds that have comparable physical and biochemical properties of the natural tissues and are currently gaining traction in tissue engineering and regenerative therapies due to the ease of standardised production, and constant availability. In this manuscript we report the successful generation of decellularised ECM-derived peptides from neural retina (decel NR) and retinal pigment epithelium (decel RPE), and their impact on differentiation of human pluripotent stem cells (hPSCs) to retinal organoids. We show that culture media supplementation with decel RPE and RPE-conditioned media (CM RPE) significantly increases the generation of rod photoreceptors, whilst addition of decel NR and decel RPE significantly enhances ribbon synapse marker expression and the light responsiveness of retinal organoids. Photoreceptor maturation, formation of correct synapses between retinal cells and recording of robust light responses from hPSC-derived retinal organoids remain unresolved challenges for the field of regenerative medicine. Enhanced rod photoreceptor differentiation, synaptogenesis and light response in response to addition of decellularised matrices from RPE and neural retina as shown herein provide a novel and substantial advance in generation of retinal organoids for drug screening, tissue engineering and regenerative medicine.

Extracellular matrix component expression in human pluripotent stem cell-derived retinal organoids recapitulates retinogenesis in vivo and reveals an important role for IMPG1 and CD44 in the development of photoreceptors and interphotoreceptor matrix.

The extracellular matrix (ECM) plays an important role in numerous processes including cellular proliferation, differentiation, migration, maturation, adhesion guidance and axonal growth. To date, there has been no detailed analysis of the ECM distribution during retinal ontogenesis in humans and the functional importance of many ECM components is poorly understood. In this study, the expression of key ECM components in adult mouse and monkey retina, developing and adult human retina and retinal organoids derived from human pluripotent stem cells was studied. Our data indicate that basement membrane ECMs (Fibronectin and Collagen IV) were expressed in Bruch's membrane and the inner limiting membrane of the developing human retina, whilst the hyalectins (Versican and Brevican), cluster of differentiation 44 (CD44), photoreceptor-specific ECMs Interphotoreceptor Matrix Proteoglycan 1 (IMPG1) and Interphotoreceptor Matrix Proteoglycan 2 (IMPG2) were detected in the developing interphotoreceptor matrix (IPM). The expression of IMPG1, Versican and Brevican in the developing IPM was conserved between human developing retina and human pluripotent stem cell-derived retinal organoids. Blocking the action of CD44 and IMPG1 in pluripotent stem cell derived retinal organoids affected the development of photoreceptors, their inner/outer segments and connecting cilia and disrupted IPM formation, with IMPG1 having an earlier and more significant impact. Together, our data suggest an important role for IMPG1 and CD44 in the development of photoreceptors and IPM formation during human retinogenesis. STATEMENT OF SIGNIFICANCE: The expression and the role of many extracellular matrix (ECM) components during human retinal development is not fully understood. In this study, expression of key ECM components (Collagen IV, Fibronectin, Brevican, Versican, IMPG1 and IMPG2) was investigated during human retinal ontogenesis. Collagen IV and Fibronectin were expressed in Bruch's membrane; whereas Brevican, Versican, IMPG1 & IMPG2 in the developing interphotoreceptor matrix (IPM). Retinal organoids were successfully generated from pluripotent stem cells. The expression of ECM components was examined in the retinal organoids and found to recapitulate human retinal development in vivo. Using functional blocking experiments, we were able to highlight an important role for IMPG1 and CD44 in the development of photoreceptors and IPM formation.