Myosin 1f-mediated activation of microglia contributes to the photoreceptor degeneration in a mouse model of retinal detachment

Role of MYO1F in neutrophil and macrophage recruitment and pro-inflammatory cytokine production in Aspergillus fumigatus keratitis

PURPOSE

Myosin 1f (Myo1f), an unconventional long-tailed class Ⅰ myosin, plays significant roles in immune cell motility and innate antifungal immunity. This study was aimed to assess the expression and role of Myo1f in Aspergillus fumigatus (AF) keratitis.

METHODS

Myo1f expression in the corneas of mice afflicted with AF keratitis and in AF keratitis-related cells was assessed using protein mass spectrometry, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and immunofluorescence. Myo1f expression following pre-treatment with inhibitors of dendritic cell-associated C-type lectin-1 (Dectin-1), Toll-like receptor 4 (TLR-4), and lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) was also examined. In AF keratitis mouse models, Myo1f small interfering RNA (siRNA) was administered via subconjunctival injection to observe disease progression, inflammatory cell recruitment, and protein production using slit lamp examination, immunofluorescence, hematoxylin-eosin (HE) staining, and western blotting.

RESULTS

Myo1f expression was upregulated in both AF keratitis mouse models and AF keratitis-related cells. Dectin-1, TLR-4, and LOX-1 were found to be essential for the production of Myo1f in response to the infection with AF. In mice with AF keratitis, knockdown of Myo1f reduced disease severity, decreased the recruitment of neutrophils alongside macrophages to inflammatory areas, suppressed the myeloid differentiation factor 88 (MyD88)/ nuclear factor-kappaB (NF-κB) signaling pathway, and decreased the production of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, along with IL-6. Additionally, Myo1f was associated with apoptosis and pyroptosis in mice with AF keratitis.

CONCLUSIONS

These findings demonstrated that Myo1f contributed to the recruitment of neutrophils and macrophages, the production of pro-inflammatory cytokines, and was associated with apoptosis and pyroptosis during AF keratitis.

Caspase-1 Inhibition Ameliorates Photoreceptor Damage Following Retinal Detachment by Inhibiting Microglial Pyroptosis

Retinal detachment (RD) is a sight-threatening condition that occurs in several retinal diseases. Microglia that reside in retina are activated after RD and play a role in the death of photoreceptor cells. The involvement of microglial pyroptosis in the early pathological process of RD is still unclear. VX-765, an inhibitor of caspase-1, may exert neuroprotective effects by targeting microglial pyroptosis in nervous system disease; however, whether it plays a role in RD is uncertain. This study detected and localized pyroptosis to specific cells by immunofluorescence co-staining and flow cytometry in rat RD models. The majority of gasdermin D N-terminal (GSDMD-N)-positive cells exhibited IBA1-positive or P2RY12-positive microglia in the early stage of RD, indicating the pyroptosis of microglia. Administration of VX-765 shifted the microglia phenotype from M1 to M2, inhibited microglial migration toward the outer nuclear layer (ONL) post-RD, and most importantly, inhibited microglial pyroptosis. The thickness of ONL increased with VX-765 administration, and the photoreceptors were more structured and orderly under hematoxylin and eosin staining and transmission electron microscopy, revealing the protective effects of VX-765 on photoreceptors. Overall, this study demonstrated that inflammation induced by pyroptosis of microglia is the early pathological process of RD. VX-765 may serve as a candidate therapeutic approach for the treatment of RD by targeting microglia.

Microglia in Cultured Porcine Retina: Qualitative Immunohistochemical Analyses of Reactive Microglia in the Outer Retina

A late stage of several retinal disorders is retinal detachment, a complication that results in rapid photoreceptor degeneration and synaptic damages. Experimental retinal detachment in vivo is an invasive and complicated method performed on anesthetized animals. As retinal detachment may result in visual impairment and blindness, research is of fundamental importance for understanding degenerative processes. Both morphological and ethical issues make the porcine retina a favorable organotypic model for studies of the degenerative processes that follow retinal detachment. In the cultured retina, photoreceptor degeneration and synaptic injuries develop rapidly and correlate with resident microglial cells' transition into a reactive phenotype. In this immunohistochemical study, we have begun to analyze the transition of subsets of reactive microglia which are known to localize close to the outer plexiform layer (OPL) in degenerating in vivo and in vitro retina. Biomarkers for reactive microglia included P2Ry12, CD63 and CD68 and the general microglial markers were CD11b, Iba1 and isolectin B₄ (IB₄). The reactive microglia markers labeled microglia subpopulations, suggesting that protective or harmful reactive microglia may be present simultaneously in the injured retina. Our findings support the usage of porcine retina cultures for studies of photoreceptor injuries related to retinal detachment.