Macrophage-based delivery of interleukin-13 improves functional and histopathological outcomes following spinal cord injury

Amelioration of functional and histopathological consequences after spinal cord injury through phosphodiesterase 4D (PDE4D) inhibition

Spinal cord injury (SCI) is a life-changing event that severely impacts the patient's quality of life. Modulating neuroinflammation, which exacerbates the primary injury, and stimulating neuro-regenerative repair mechanisms are key strategies to improve functional recovery. Cyclic adenosine monophosphate (cAMP) is a second messenger crucially involved in both processes. Following SCI, intracellular levels of cAMP are known to decrease over time. Therefore, preventing cAMP degradation represents a promising strategy to suppress inflammation while stimulating regeneration. Intracellular cAMP levels are controlled by its hydrolyzing enzymes phosphodiesterases (PDEs). The PDE4 family is most abundantly expressed in the central nervous system (CNS) and its inhibition has been shown to be therapeutically relevant for managing SCI pathology. Unfortunately, the use of full PDE4 inhibitors at therapeutic doses is associated with severe emetic side effects, hampering their translation toward clinical applications. Therefore, in this study, we evaluated the effect of inhibiting specific PDE4 subtypes (PDE4B and PDE4D) on inflammatory and regenerative processes following SCI, as inhibitors selective for these subtypes have been demonstrated to be well-tolerated. We reveal that administration of the PDE4D inhibitor Gebr32a, even when starting 2 dpi, but not the PDE4B inhibitor A33, improved functional as well as histopathological outcomes after SCI, comparable to results obtained with the full PDE4 inhibitor roflumilast. Furthermore, using a luminescent human iPSC-derived neurospheroid model, we show that PDE4D inhibition stabilizes neural viability by preventing apoptosis and stimulating neuronal differentiation. These findings strongly suggest that specific PDE4D inhibition offers a novel therapeutic approach for SCI.

Berberine inhibits NLRP3 inflammasome activation and proinflammatory macrophage M1 polarization to accelerate peripheral nerve regeneration

Berberine (BBR) has demonstrated potent anti-inflammatory effects by modulating macrophage polarization. Nevertheless, the precise mechanisms through which berberine regulates post-injury inflammation within the peripheral nerve system remain elusive. This study seeks to elucidate the role of BBR and its underlying mechanisms in inflammation following peripheral nerve injury (PNI). Adult male C57BL/6J mice subjected to PNI were administered daily doses of berberine (0, 60, 120, 180, 240 ​mg/kg) via gavage from day 1 through day 28. Evaluation of the sciatic function index (SFI) and paw withdrawal threshold revealed that BBR dose-dependently enhanced both motor and sensory functions. Immunofluorescent staining for anti-myelin basic protein (anti-MBP) and anti-neurofilament-200 (anti-NF-200), along with histological staining comprising hematoxylin-eosin (HE), luxol fast blue (LFB), and Masson staining, demonstrated that BBR dose-dependently promoted structural regeneration. Molecular analyses including qRT-PCR, Western blotting, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence confirmed that inactivation of the NLRP3 inflammasome by MCC950 shifted macrophages from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype, while also impeding macrophage infiltration. Furthermore, BBR significantly downregulated the expression of the NLRP3 inflammasome and its associated molecules in macrophages, thereby mitigating NLRP3 inflammasome activation-induced macrophage M1 polarization and inflammation. In summary, BBR's neuroprotective effects were concomitant with the suppression of inflammation after PNI, achieved through the inhibition of NLRP3 inflammasome activation-induced macrophage M1 polarization.

α-Gal Nanoparticles in CNS Trauma: I. In Vitro Activation of Microglia Towards a Pro-Healing State

BACKGROUND

Macrophages and microglia play critical roles after spinal cord injury (SCI), with the pro-healing, anti-inflammatory (M2) subtype being implicated in tissue repair. We hypothesize that promoting this phenotype within the post-injured cord microenvironment may provide beneficial effects for mitigating tissue damage. As a proof of concept, we propose the use of nanoparticles incorporating the carbohydrate antigen, galactose-α-1,3-galactose (α-gal epitope) as an immunomodulator to transition human microglia (HMC3) cells toward a pro-healing state.

METHODS

Quiescent HMC3 cells were acutely exposed to α-gal nanoparticles in the presence of human serum and subsequently characterized for changes in cell shape, expression of anti or pro-inflammatory markers, and secretion of phenotype-specific cytokines.

RESULTS

HMC3 cells treated with serum activated α-gal nanoparticles exhibited rapid enlargement and shape change in addition to expressing CD68. Moreover, these activated cells showed increased expression of anti-inflammatory markers like Arginase-1 and CD206 without increasing production of pro-inflammatory cytokines TNF-α or IL-6.

CONCLUSION

This study is the first to show that resting human microglia exposed to a complex of α-gal nanoparticles and anti-Gal (from human serum) can be activated and polarized toward a putative M2 state. The data suggests that α-gal nanoparticles may have therapeutic relevance to the CNS microenvironment, in both recruiting and polarizing macrophages/microglia at the application site. The immunomodulatory activity of these α-gal nanoparticles post-SCI is further described in the companion work (Part II).

Effects of Recombinant IL-13 Treatment on Gut Microbiota Composition and Functional Recovery after Hemisection Spinal Cord Injury in Mice

In recent years, the gut-central nervous system axis has emerged as a key factor in the pathophysiology of spinal cord injury (SCI). Interleukin-13 (IL-13) has been shown to have anti-inflammatory and neuroprotective effects in SCI. The aim of this study was to investigate the changes in microbiota composition after hemisection injury and to determine whether systemic recombinant (r)IL-13 treatment could alter the gut microbiome, indirectly promoting functional recovery. The gut microbiota composition was determined by 16S rRNA gene sequencing, and correlations between gut microbiota alterations and functional recovery were assessed. Our results showed that there were no changes in alpha diversity between the groups before and after SCI, while PERMANOVA analysis for beta diversity showed significant differences in fecal microbial communities. Phylogenetic classification of bacterial families revealed a lower abundance of the Bacteroidales S24-7 group and a higher abundance of Lachnospiraceae and Lactobacillaceae in the post-SCI group. Systemic rIL-13 treatment improved functional recovery 28 days post-injury and microbiota analysis revealed increased relative abundance of Clostridiales vadin BB60 and Acetitomaculum and decreased Anaeroplasma, Ruminiclostridium_6, and Ruminococcus compared to controls. Functional assessment with PICRUSt showed that genes related to glyoxylate cycle and palmitoleate biosynthesis-I were the predominant signatures in the rIL-13-treated group, whereas sulfolactate degradation super pathway and formaldehyde assimilation-I were enriched in controls. In conclusion, our results indicate that rIL-13 treatment promotes changes in gut microbial communities and may thereby contribute indirectly to the improvement of functional recovery in mice, possibly having important implications for the development of novel treatment options for SCI.

Type 2 cytokines promote angiogenesis in ischemic muscle via endothelial IL-4Rα signaling

Peripheral arterial disease (PAD) is one of the leading causes of cardiovascular morbidity and mortality worldwide, yet current trials on therapeutic angiogenesis remain suboptimal. Type 2 immunity is critical for post-ischemic regeneration, but its regulatory role in revascularization is poorly characterized. Here, we show that type 2 cytokines, interleukin-4 (IL-4) and interleukin-13 (IL-13), are the key mediators in post-ischemic angiogenesis. IL-4/IL-13-deficient mice exhibit impaired reperfusion and muscle repair in an experimental model of PAD. We find that deletion of IL-4Rα in the endothelial compartment, rather than the myeloid compartment, leads to remarkable impairment in revascularization. Mechanistically, IL-4/IL-13 promote endothelial cell proliferation, migration, and tube formation via IL-4Rα/STAT6 signaling. Furthermore, attenuated IL-4/IL-13 expression is associated with the angiogenesis deficit in the setting of diabetic PAD, while IL-4/IL-13 treatment rescues this defective regeneration. Our findings reveal the therapeutic potential of type 2 cytokines in treating patients with muscle ischemia.

Oxidative DNA Damage in the Pathophysiology of Spinal Cord Injury: Seems Obvious, but Where Is the Evidence?

Oxidative stress occurs at various phases of spinal cord injury (SCI), promoting detrimental processes such as free radical injury of proteins, nucleic acids, lipids, cytoskeleton, and organelles. Oxidative DNA damage is likely a major contributor to the pathogenesis of SCI, as a damaged genome cannot be simply turned over to avert detrimental molecular and cellular outcomes, most notably cell death. Surprisingly, the evidence to support this hypothesis is limited. There is some evidence that oxidative DNA damage is increased following SCI, mainly using comet assays and immunohistochemistry. However, there is great variability in the timing and magnitude of its appearance, likely due to differences in experimental models, measurement techniques, and the rigor of the approach. Evidence indicates that 8-oxodG is most abundant at 1 and 7 days post-injury (dpi), while DNA strand breaks peak at 7 and 28 dpi. The DNA damage response seems to be characterized by upregulation of PCNA and PARP1 but downregulation of APEX1. Significant improvements in the analysis of oxidative DNA damage and repair after SCI, including single-cell analysis at time points representative for each phase post-injury using new methodologies and better reporting, will uncover the role of DNA damage and repair in SCI.