Structured wound angiogenesis instructs mesenchymal barrier compartments in the regenerating nerve

The ROX@PDA@PCL vascularized bionic nerve conduit facilitates the restoration of nerve defects

Previous research has highlighted the pivotal role of angiogenesis in facilitating nerve function repair following nerve injury. In this study, we employed polydopamine (PDA) to modify polycaprolactone (PCL) and subsequently loaded it with roxadustat (ROX), thereby constructing a vascularized nerve conduit for the repair of a 10 mm sciatic nerve defect in rats. At 2 weeks post-surgery, new blood vessels were evaluated by immunofluorescence staining. Twelve weeks post-surgery, a comprehensive suite of assessments was conducted to evaluate the efficacy of the conduit, including gait analysis, determination of gastrocnemius muscle wet weight recovery, electrophysiological examination of gastrocnemius compound action potential (CMAP), Masson staining to evaluate gastrocnemius muscle fiber cross-sectional area, toluidine blue staining to assess the total number of regenerated myelinated nerve fibers, and electron microscopic observation of myelin sheath thickness. Our findings revealed that ROX@PDA@PCL could promote the proliferation of vascular endothelial cells and significantly enhance angiogenesis in regenerated nerves (p < 0.05). Regarding the recovery of neurological function, compared to the PDA@PCL and PCL groups, the ROX@PDA@PCL group exhibited significantly superior outcomes in the sciatic functional index (SFI), CMAP, gastrocnemius muscle wet weight ratio, muscle fiber cross-sectional area, total number of regenerated myelinated nerve fibers, and myelin sheath thickness. These indices approached those of the autologous group, but were still lower than in the autograft group (p < 0.05). The study underscores the potential of the vascularized nerve graft (ROX@PDA@PCL), constructed through PDA-mediated loading of ROX onto PCL, to enhance functional nerve recovery. Our findings present a promising new therapeutic approach for the clinical repair of peripheral nerve defects.

In vivo programming of adult pericytes aids axon regeneration by providing cellular bridges for SCI repair

Pericytes are contractile cells of the microcirculation that participate in wound healing after spinal cord injury (SCI). Thus far, the extent to which pericytes cause or contribute to axon growth and regeneration failure after SCI remains controversial. Here, we found that SCI leads to profound changes in vasculature architecture and pericyte coverage. We demonstrated that pericytes constrain sensory axons on their surface, causing detrimental structural and functional changes in adult dorsal root ganglion neurons that contribute to axon regeneration failure after SCI. Perhaps more excitingly, we discovered that in vivo programming of adult pericytes via local administration of platelet-derived growth factor BB (PDGF-BB) effectively promotes axon regeneration and recovery of hindlimb function by contributing to the formation of cellular bridges that span the lesion. Ultrastructural analysis showed that PDGF-BB induced fibronectin fibril alignment and extension, effectively converting adult pericytes into a permissive substrate for axon growth. In addition, PDGF-BB localized delivery positively affects the physical and chemical nature of the lesion environment, thereby creating more favorable conditions for SCI repair. Thus, therapeutic manipulation rather than wholesale ablation of pericytes can be exploited to prime axon regeneration and SCI repair.

Organoid-Like Neurovascular Spheroids Promote the Recovery of Hypoxic-Ischemic Skin Flaps Through the Activation of Autophagy

Crosstalk between nerves and blood vessels plays a crucial role in flap development, injury repair, and homeostasis maintenance. However, in most flap transplantation strategies, the interactions between nerves and blood vessels have been ignored, leading to unsatisfactory repair effects. In this study, highly sprouting organoid-like neurovascular spheroids (NVUs) with P34HB porous microsphere cores embedding in a supportive microenvironment of Gelatin Methacryloyl hydrogel are developed. Cell-laden porous microspheres successfully recapitulated neurovascular coupling by providing a biomimetic extracellular microenvironment for neural and vascular cells at an in vivo cell density. The results demonstrated that neurovascular spheres formed complex vascular plexuses and secreted extracellular matrix, improving in vivo regeneration of skin flap. Autophagy activation regulated by nerves is detected along with the assembly of vascular networks, suggesting its role in neovascularization. By incorporating fibroblasts, highly biomimetic organoid-like models composed of dermis, vasculature, and innervation are facilely developed to mimic dermal tissues. This stable and highly reproducible in vitro model can be utilized for organ repair and mechanistic exploration.

A MEF2C transcription factor network regulates proliferation of glomerular endothelial cells in diabetic kidney disease

The maintenance of a healthy epithelial-endothelial juxtaposition requires cross-talk within glomerular cellular niches. We sought to understand the spatially-anchored regulation and transition of endothelial and mesangial cells from health to injury in DKD. From 74 human kidney samples, an integrated multi-omics approach was leveraged to identify cellular niches, cell-cell communication, cell injury trajectories, and regulatory transcription factor (TF) networks in glomerular capillary endothelial (EC-GC) and mesangial cells. Data were culled from single nucleus RNA and ATAC sequencing and three orthogonal spatial transcriptomic technologies for correlation with histopathological and clinical trial data. We identified a cellular niche in diabetic glomeruli enriched in a proliferative endothelial cell subtype (prEC) and altered vascular smooth muscle cells (VSMCs). Cellular communication within this niche maintained pro-angiogenic signaling with loss of anti-angiogenic factors. We identified a TF network of MEF2C, MEF2A, and TRPS1 which regulated SEMA6A and PLXNA2, a receptor-ligand pair opposing angiogenesis. In silico knockout of the TF network accelerated the transition from healthy EC-GCs toward a degenerative (injury) endothelial phenotype, with concomitant disruption of EC-GC and prEC expression patterns. Glomeruli enriched in the prEC niche had histologic evidence of neovascularization. MEF2C activity was increased in diabetic glomeruli with nodular mesangial sclerosis. The gene regulatory network (GRN) of MEF2C was dysregulated in EC-GCs of patients with DKD, but sodium glucose transporter-2 inhibitor (SGLT2i) treatment reversed the MEF2C GRN effects of DKD. The MEF2C, MEF2A, and TRPS1 TF network carefully balances the fate of the EC-GC in DKD. When the TF network is "on" or over-expressed in DKD, EC-GCs may progress to a prEC state, while TF suppression leads to cell death. SGLT2i therapy may restore the balance of MEF2C activity.

TFEB/3 Govern Repair Schwann Cell Generation and Function Following Peripheral Nerve Injury

TFEB and TFE3 (TFEB/3), key regulators of lysosomal biogenesis and autophagy, play diverse roles depending on cell type. This study highlights a hitherto unrecognized role of TFEB/3 crucial for peripheral nerve repair. Specifically, they promote the generation of progenitor-like repair Schwann cells after axonal injury. In Schwann cell-specific TFEB/3 double knock-out mice of either sex, the TFEB/3 loss disrupts the transcriptomic reprogramming that is essential for the formation of repair Schwann cells. Consequently, mutant mice fail to populate the injured nerve with repair Schwann cells and exhibit defects in axon regrowth, target reinnervation, and functional recovery. TFEB/3 deficiency inhibits the expression of injury-responsive repair Schwann cell genes, despite the continued expression of c-jun, a previously identified regulator of repair Schwann cell function. TFEB/3 binding motifs are enriched in the enhancer regions of injury-responsive genes, suggesting their role in repair gene activation. Autophagy-dependent myelin breakdown is not impaired despite TFEB/3 deficiency. These findings underscore a unique role of TFEB/3 in adult Schwann cells that is required for proper peripheral nerve regeneration.

Guiding axon regeneration: Instructions from blood vessels

In this issue of Neuron, Bhat et al.1 unveil the temporary reawakening of an embryonic guidance program, which facilitates the alignment of blood neovessels, creating a supportive "bridge" microenvironment for axon regrowth and tissue regeneration after peripheral nervous system (PNS) injury.