Li Lin

BACKGROUND: Resident microglia and macrophages are the predominant contributors to neuroinflammation and immune reactions, which play a critical role in the pathogenesis of ischemic brain injury. Controlling inflammatory responses is considered a promising therapeutic approach for stroke. Recombinant human fibroblast growth factor 21 (rhFGF21) presents anti-inflammatory properties by modulating microglia and macrophages; however, our knowledge of the inflammatory modulation of rhFGF21 in focal cerebral ischemia is lacking. Therefore, we investigated whether rhFGF21 improves ischemic outcomes in experimental stroke by targeting microglia and macrophages. METHODS: C57BL/6 mice were subjected to middle cerebral artery occlusion (MCAO) and randomly divided into groups that received intraperitoneal rhFGF21 or vehicle daily starting at 6 h after reperfusion. Behavior assessments were monitored for 14 days after MCAO, and the gene expression levels of inflammatory cytokines were analyzed via qRT-PCR. The phenotypic variation of microglia/macrophages and the presence of infiltrated immune cells were examined by flow cytometry and immunostaining. Additionally, magnetic cell sorting (MACS) in combination with fluorescence-activated cell sorting (FACS) was used to purify microglia and macrophages. RESULTS: rhFGF21 administration ameliorated neurological deficits in behavioral tests by regulating the secretion of pro-inflammatory and anti-inflammatory cytokines. rhFGF21 also attenuated the polarization of microglia/macrophages toward the M1 phenotype and the accumulation of peripheral immune cells after stroke, accompanied by a temporal evolution of the phenotype of microglia/macrophages and infiltration of peripheral immune cells. Furthermore, rhFGF21 treatment inhibited M1 polarization of microglia and pro-inflammatory cytokine expression through its actions on FGF receptor 1 (FGFR1) by suppressing nuclear factor-kappa B (NF-κB) and upregulating peroxisome proliferator-activated receptor-γ (PPAR-γ). CONCLUSIONS: rhFGF21 treatment promoted functional recovery in experimental stroke by modulating microglia/macrophage-mediated neuroinflammation via the NF-κB and PPAR-γ signaling pathways, making it a potential anti-inflammatory agent for stroke treatment.

Wound therapy remains a clinical challenge. Incorporation of growth factors (GFs) into heparin-functionalized polymer hydrogel is considered as a promising strategy to improve wound healing efficiency. However, different GFs incorporation into the same heparin-based hydrogels often lead to different wound healing effects, and the underlying GF-induced wound healing mechanisms still remain elusive. Herein, we developed a thermos-sensitive heparin-poloxamer (HP) hydrogel to load and deliver different GFs (aFGF and bFGF) for wound healing in vivo. The resulting GFs-based hydrogels with and without HP hydrogels were systematically evaluated and compared for their wound healing efficiency by extensive in vivo tests, including wound closure rate, granulation formation, re-epithelization, cell proliferation, collagen, and angiogenesis expressions. While all GFs-based dressings with and without HP hydrogels exhibited better wound healing efficacy than controls, both HP-aFGF and HP-bFGF hydrogels demonstrated their superior healing activity to improve wound closure, granulation formation, re-epithelization, and blood vessel density by up-regulation of PCNA proliferation and collagen synthesis, as compared to GF dressings alone. More importantly, HP-aFGF dressings exhibited the higher healing efficacy than HP-bFGF dressings, indicating that different a/bFGF surface properties lead to different binding and release behaviors in HP hydrogels, both of which will affect different wound healing efficiency. On the basis of experimental observations, the working mechanisms of different healing effects of HP-GFs on full skin removal wound were proposed. This work provides different views of the design and development of an effective hydrogel-based delivery system for GFs toward rapid wound healing.

Defensive responses to threatening stimuli are crucial to the survival of species. While expression of these responses is considered to be instinctive and unconditional, their magnitude may be affected by environmental and internal factors. The neural circuits underlying this modulation are still largely unknown. In mice, looming-evoked defensive responses are mediated by the superior colliculus (SC), a subcortical sensorimotor integration center. We found that repeated stress caused an anxiety-like state in mice and accelerated defensive responses to looming. Stress also induced c-fos activation in locus coeruleus (LC) tyrosine hydroxylase (TH)+ neurons and modified adrenergic receptor expression in SC, suggesting a possible Th::LC-SC projection that may be involved in the accelerated defensive responses. Indeed, both anterograde and retrograde neural tracing confirmed the anatomical Th::LC-SC projection and that the SC-projecting TH+ neurons in LC were activated by repeated stress. Optogenetic stimulation of either LC TH+ neurons or the Th::LC-SC fibers also caused anxiety-like behaviors and accelerated defensive responses to looming. Meanwhile, chemogenetic inhibition of LC TH+ neurons and the infusion of an adrenergic receptor antagonist in SC abolished the enhanced looming defensive responses after repeated stress, confirming the necessity of this pathway. These findings suggest that the Th::LC-SC pathway plays a key role in the sophisticated adjustments of defensive behaviors induced by changes in physiological states.