Related Experiment Video
Updated: Jun 26, 2025
A Magnetic Microbead Occlusion Model to Induce Ocular Hypertension-Dependent Glaucoma in Mice
Published on: March 23, 2016
Enantiomeric Agonists of the Type 2 Cannabinoid Receptor Reduce Retinal Damage during Proliferative Vitreoretinopathy
Alexander P Young1, Anna-Maria Szczesniak1, Karolynn Hsu1
1Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
Abstract:
Microglia are resident immune cells of the central nervous system (CNS) and propagate inflammation following damage to the CNS, including the retina. Proliferative vitreoretinopathy (PVR) is a condition that can emerge following retinal detachment and is characterized by severe inflammation and microglial proliferation. The type 2 cannabinoid receptor (CB2) is an emerging pharmacological target to suppress microglial-mediated inflammation when the eyes or brain are damaged. CB2-knockout mice have exacerbated inflammation and retinal pathology during experimental PVR. We aimed to assess the anti-inflammatory effects of CB2 stimulation in the context of retinal damage and also explore the mechanistic roles of CB2 in microglia function. To target CB2, we used a highly selective agonist, HU-308, as well as its enantiomer, HU-433, which is a putative selective agonist. First, β-arrestin2 and Gαi recruitment was measured to compare activation of human CB2 in an in vitro heterologous expression system. Both agonists were then utilized in a mouse model of PVR, and the effects on retinal damage, inflammation, and cell death were assessed. Finally, we used an in vitro model of microglia to determine the effects of HU-308 and HU-433 on phagocytosis, cytokine release, migration, and intracellular signaling. We observed that HU-308 more strongly recruited both β-arrestin2 and Gαi compared to HU-433. Stimulation of CB2 with either drug effectively blunted LPS- and IFNγ-mediated signaling as well as NO and TNF release from microglia. Furthermore, both drugs reduced IL-6 accumulation, total caspase-3 cleavage, and retinal pathology following the induction of PVR. Ultimately, this work supports that CB2 is a valuable target for drugs to suppress inflammation and cell death associated with infection or sterile retinopathy, although the magnitude of effector recruitment may not be predictive of anti-inflammatory capacity.
Insights
Stimulating the type 2 cannabinoid receptor (CB2) with HU-308 or HU-433 reduces inflammation and cell death in the retina. This suggests CB2 agonists are promising for treating retinopathy and CNS damage.
Area of Science:
- Neuroscience
- Immunology
- Ophthalmology
Background:
- Microglia, the central nervous system's immune cells, drive inflammation in conditions like proliferative vitreoretinopathy (PVR).
- The type 2 cannabinoid receptor (CB2) is a potential target for suppressing microglial inflammation in CNS and retinal damage.
- CB2-knockout mice show worsened inflammation and retinal pathology in experimental PVR.
Purpose of the Study:
- To evaluate the anti-inflammatory effects of CB2 stimulation in retinal damage models.
- To investigate the mechanistic roles of CB2 in microglial function.
- To assess the efficacy of CB2 agonists HU-308 and HU-433 in a mouse model of PVR.
Main Methods:
- Compared beta-arrestin2 and Gαi recruitment for human CB2 activation by HU-308 and HU-433 in vitro.
- Administered HU-308 and HU-433 in a mouse model of PVR to assess retinal damage, inflammation, and cell death.
- Utilized an in vitro microglia model to examine the effects of HU-308 and HU-433 on phagocytosis, cytokine release, migration, and intracellular signaling.
Main Results:
- HU-308 demonstrated stronger beta-arrestin2 and Gαi recruitment than HU-433.
- CB2 stimulation with either drug reduced microglial signaling, nitric oxide, and TNF release.
- Both HU-308 and HU-433 decreased IL-6, caspase-3 cleavage, and retinal pathology in the PVR model.
Conclusions:
- CB2 receptor stimulation effectively suppresses microglial-mediated inflammation and cell death in the context of retinal damage.
- HU-308 and HU-433 show therapeutic potential for treating inflammatory retinopathies and CNS injuries.
- The degree of effector recruitment by CB2 agonists may not directly predict their anti-inflammatory efficacy.
