MyD88 Deficiency Accelerates Retinal Degeneration and Alters Microglial Dynamics in Retinitis Pigmentosa Mouse Model
Background
Retinitis Pigmentosa (RP) is a group of inherited retinal diseases leading to progressive vision loss due to photoreceptor degeneration. Neuroinflammation, mediated by activated microglia and astrocytes, is increasingly recognized as a key driver in RP progression. The Toll-like receptor (TLR)/MyD88 pathway is a crucial mediator of inflammatory signaling, recognizing damage-associated molecular patterns (DAMPs) and initiating immune responses. However, the precise role of MyD88 in modulating retinal degeneration and neuroinflammation within RP remains incompletely understood, representing a critical gap in potential therapeutic strategies.
Study Design
Researchers investigated MyD88's role by crossing rd10 mice, a model of retinitis pigmentosa, with Myd88-/- mice to generate rd10; Myd88-/- mice. Retinal degeneration was assessed using TUNEL staining for apoptotic cells, hematoxylin and eosin (H&E) staining for outer nuclear layer (ONL) thickness, and electroretinography (ERG) to measure retinal function. Microglial dynamics were evaluated by immunostaining with Iba-1. Neuroinflammatory mRNA profiles were analyzed using a NanoString Neuroinflammation panel to identify changes in gene expression.
Results
MyD88 deficiency significantly worsened retinal degeneration in rd10 mice. > Myd88-/- mice showed an increased number of TUNEL-positive cells in the outer nuclear layer (ONL) and exacerbated ONL thinning at postnatal day 18 and 21 (P < 0.01, each). Consistent with these structural changes, scotopic electroretinogram (ERG) recordings revealed significantly lower b-wave amplitudes in rd10; Myd88-/- mice compared to rd10 controls (P < 0.01). Microglial infiltration into the outer retina exhibited an early but transient increase at P18, followed by a reduction at P21 in rd10; Myd88-/- mice, suggesting altered microglial dynamics. Furthermore, retinal mRNA profiling indicated increased expression of Ifitm3 and Serpina3n, which are markers associated with astrocytic glia, in the rd10; Myd88-/- mice. Immunostaining confirmed the upregulation of IFITM3 and SERPINA3N proteins in astrocytes and Müller cells, corroborating the gene expression findings.
Key Findings
- MyD88 deficiency increased
TUNEL-positive cells in the ONL ofrd10mice at P18 and P21 (P < 0.01). Myd88-/-mice exhibited exacerbated ONL thinning at P18 and P21 (P < 0.01).- Scotopic
ERGb-wave amplitudes were significantly lower inrd10; Myd88-/-mice (P < 0.01). - Microglial infiltration showed an early, transient increase at P18 but reduced at P21 in
Myd88-/-mice. - Retinal mRNA profiling revealed increased
Ifitm3andSerpina3nexpression inrd10; Myd88-/-mice.
Why It Matters
This study highlights the complex and potentially detrimental role of MyD88 signaling in Retinitis Pigmentosa progression, suggesting that simply blocking MyD88 may not be a straightforward therapeutic approach. Understanding the precise timing and context of MyD88 activation is crucial for future interventions. While MyD88 is often associated with pro-inflammatory responses, its deficiency here accelerated degeneration, implying a protective or regulatory role in certain contexts of chronic retinal disease. This suggests that modulating, rather than ablating, MyD88 activity or downstream pathways might be a more nuanced strategy for preserving retinal function, potentially guiding the development of targeted therapies that consider the dual nature of neuroinflammation in RP.
retinitis-pigmentosa
myd88
neuroinflammation
retinal-degeneration
microglia
tlr