Methylene blue promotes survival and GAP-43 expression of retinal ganglion cells after optic nerve transection

CX3CL1-CX3CR1 axis protects retinal ganglion cells by inhibiting microglia activation in a distal optic nerve trauma model

BACKGROUND

The chemokine CX3CL1 has been reported to play an important role in optic nerve protection, but the underlying mechanism is still unclear. CX3CR1, the only receptor of CX3CL1, is specifically expressed on retinal microglia, whose activation plays a role in the pathological process of optic nerve injury. This study aimed to evaluate whether CX3CL1 exerts optic neuroprotection by affecting the activation of microglia by combining with CX3CR1.

METHODS

A mouse model of distal optic nerve trauma (ONT) was used to evaluate the effects of the CX3CL1-CX3CR1 axis on the activation of microglia and survival or axonal regeneration of retinal ganglion cells (RGCs). The activation of microglia, loss of RGCs, and damage to visual function were detected weekly till 4 weeks after modeling. CX3CL1 was injected intravitreally immediately or delayed after injury and the status of microglia and RGCs were examined.

RESULTS

Increases in microglia activation and optic nerve damage were accompanied by a reduced production of the CX3CL1-CX3CR1 axis after the distal ONT modeling. Both immediate and delayed intravitreal injection of CX3CL1 inhibited microglia activation, promoted survival of RGCs, and improved axonal regenerative capacity. Injection with CX3CL1 was no longer effective after 48 h post ONT. The CX3CL1-CX3CR1 axis promotes survival and axonal regeneration, as indicated by GAP43 protein and gene expression, of RGCs by inhibiting the microglial activation after ONT.

CONCLUSIONS

The CX3CL1-CX3CR1 axis could promote survival and axonal regeneration of RGCs by inhibiting the microglial activation after optic nerve injury. The CX3CL1-CX3CR1 axis may become a potential target for the treatment of optic nerve injury. Forty-eight hours is the longest time window for effective treatment after injury. The study is expected to provide new ideas for the development of targeted drugs for the repair of optic nerve.

Associations of Growth-Associated Protein 43 with Cerebral Microbleeds: A Longitudinal Study

Background

Cerebral microbleeds (CMB) play an important role in neurodegenerative pathology.

Objective

The present study aims to test whether cerebrospinal fluid (CSF) growth-associated protein 43 (GAP-43) level is linked to CMBs in elderly people.

Methods

A total of 750 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) who had measurements of GAP-43 and CMBs were included in the study. According to the presence and extent of CMBs, participants were stratified into different groups. Regression analyses were used to assess cross-sectional and longitudinal associations between GAP-43 and CMBs.

Results

Participants with CMB were slightly older and had higher concentrations of CSF GAP43. In multivariable adjusted analyses for age, gender, APOEɛ4 status, and cognitive diagnoses, higher CSF GAP-43 concentrations were modestly associated with CMB presence (OR = 1.169, 95% CI = 1.001-1.365) and number (β= 0.020, SE = 0.009, p = 0.027). Similarly, higher CSF GAP43 concentrations were accrual of CMB lesions, associated with higher CMB progression (OR = 1.231, 95% CI = 1.044-1.448) and number (β= 0.017, SE = 0.005, p = 0.001) in the follow up scan. In stratified analyses, slightly stronger associations were noted in male participants, those 65 years and older, carriers of APOEɛ4 alleles, and with more advanced cognitive disorders.

Conclusions

CSF GAP-43 was cross-sectionally associated with the presence and extent of CMBs. GAP-43 might be used as a biomarker to track the dynamic changes of CMBs in elderly persons.

Hypoxic preconditioned MSCs-derived small extracellular vesicles for photoreceptor protection in retinal degeneration

Photoreceptor apoptosis is an important pathogenesis of retinal degeneration and a primary cause of vision loss with limited treatment methods. Mesenchymal stem/stromal cells-derived small extracellular vesicles (MSC-sEVs) have shown therapeutic value in various ocular disorders. Recent studies have revealed that hypoxic preconditioning can improve the effectiveness of MSC-sEVs in tissue regeneration. However, whether hypoxic preconditioned MSC-sEVs (Hyp-sEVs) exert superior effects on photoreceptor protection relative to normoxic conditioned MSC-sEVs (Nor-sEVs) remains unclear. Here, we reported that Hyp-sEVs further improved retinal structure, recovered retinal function, and suppressed photoreceptor apoptosis in N-methyl-N-nitrosourea (MNU)-induced mouse model compared with Nor-sEVs. Hyp-sEVs also exhibited enhanced anti-apoptotic roles in MNU-provoked 661 W cell injury in vitro. We then analyzed the protein profiles of Nor-sEVs and Hyp-sEVs by LC-MS/MS and found that growth-associated protein 43 (GAP43) was enriched in Hyp-sEVs. The knockdown of GAP43 abolished the retinal therapeutic effects of Hyp-sEVs. Mechanistically, hypoxic stimulation-induced hypoxia-inducible factor-1α (HIF-1α) activation was responsible for preventing tripartite motif-containing protein 25 (TRIM25)-mediated GAP43 ubiquitination and degradation, leading to the upregulation of GAP43 in Hyp-sEVs. Together, our findings uncover the efficacy and mechanism of Hyp-sEVs-based photoreceptor protection and highlight the potential of Hyp-sEVs as optimized therapeutics for retinal degeneration.

[Protective effect of Epothilone D against traumatic optic nerve injury in rats]

OBJECTIVE

To investigate the therapeutic effect of Epothilone D on traumatic optic neuropathy (TON) in rats.

METHODS

Forty-two SD rats were randomized to receive intraperitoneal injection of 1.0 mg/kg Epothilone D or DMSO (control) every 3 days until day 28, and rat models of TON were established on the second day after the first administration. On days 3, 7, and 28, examination of flash visual evoked potentials (FVEP), immunofluorescence staining and Western blotting were performed to examine the visual pathway features, number of retinal ganglion cells (RGCs), GAP43 expression level in damaged axons, and changes of Tau and pTau-396/404 in the retina and optic nerve.

RESULTS

In Epothilone D treatment group, RGC loss rate was significantly decreased by 19.12% (P=0.032) on day 3 and by 22.67% (P=0.042) on day 28 as compared with the rats in the control group, but FVEP examination failed to show physiological improvement in the visual pathway on day 28 in terms of the relative latency of N2 wave (P=0.236) and relative amplitude attenuation of P2-N2 wave (P=0.441). The total Tau content in the retina of the treatment group was significantly increased compared with that in the control group on day 3 (P < 0.001), showing a consistent change with ptau-396/404 level. In the optic nerve axons, the total Tau level in the treatment group was significantly lower than that in the control group on day 7 (P=0.002), but the changes of the total Tau and pTau-396/404 level did not show an obvious correlation. Epothilone D induced persistent expression of GAP43 in the damaged axons, detectable even on day 28 of the experiment.

CONCLUSION

Epothilone D treatment can protect against TON in rats by promoting the survival of injured RGCs, enhancing Tau content in the surviving RGCs, reducing Tau accumulation in injured axons, and stimulating sustained regeneration of axons.

Pretreatment with combined low-level laser therapy and methylene blue improves learning and memory in sleep-deprived mice

Low-level laser therapy (LLLT) and methylene blue (MB) were proved to have neuroprotective effects. In this study, we evaluated the preventive effects of LLLT and MB alone and in combination to examine their efficacy against sleep deprivation (SD)-induced cognitive impairment. Sixty Balb/c male mice were randomly divided into five groups as follows: wide platform (WP), SD, LLLT, MB, LMB (treatment with both LLLT and MB). Daily MB (0.5 mg/kg) was injected for ten consecutive days. An 810-nm, 10-Hz pulsed laser was used in LLLT every other day. We used the T-maze test, social interaction test (SIT), and shuttle box to assess learning and memory and PSD-95, GAP-43, and synaptophysin (SYN) markers to examine synaptic proteins levels in the hippocampus. Our results showed that SD decreased alternation rate in the T-maze test, sociability and social novelty in SIT, and memory index in the shuttle box. Single treatments were not able to reverse these in most of the behavioral parameters. However, behavioral tests showed a significant difference between combined therapy and the SD group. The levels of synaptic plasticity markers were also significantly reduced after SD. There was a significant difference between the MB group and SD animals in GAP-43 and SYN biomarkers. Combination treatment with LLLT and MB also increased GAP-43, PSD-95, and SYN compared to the SD group. We found that the combined use of LLLT and MB pretreatment is more effective in protecting SD-induced cognitive impairment, which may be imparted via modulation of synaptic proteins.