Neurovascular injury associated non-apoptotic endothelial caspase-9 and astroglial caspase-9 mediate inflammation and contrast sensitivity decline

Abstract

Retinal neurovascular injuries are a leading cause of vision loss in young adults presenting unmet therapeutic needs. Neurovascular injuries damage homeostatic communication between endothelial, pericyte, glial, and neuronal cells through signaling pathways that remain to be established. To understand the mechanisms that contribute to neuronal death, we use a mouse model of retinal vein occlusion (RVO). Using this model, we previously discovered that after vascular damage, there was non-apoptotic activation of endothelial caspase-9 (EC Casp9); knock-out of EC Casp9 led to a decrease in retinal edema, capillary ischemia, and neuronal death. In this study, we aimed to explore the role of EC Casp9 in vision loss and inflammation. We found that EC Casp9 is implicated in contrast sensitivity decline, induction of inflammatory cytokines, and glial reactivity. One of the noted glial changes was increased levels of astroglial cl-caspase-6, which we found to be activated cell intrinsically by astroglial caspase-9 (Astro Casp9). Lastly, we discovered that Astro Casp9 contributes to capillary ischemia and contrast sensitivity decline after RVO (P-RVO). These findings reveal specific endothelial and astroglial non-apoptotic caspase-9 roles in inflammation and neurovascular injury respectively; and concomitant relevancy to contrast sensitivity decline.

Caspase-9 inhibition confers stronger neuronal and vascular protection compared to VEGF neutralization in a mouse model of retinal vein occlusion

“…The standard of care for RVO is therapy with injections of anti-VEGF. We have shown that targeting caspase-9 in a mouse model of RVO provides substantial morphologic, cellular and functional protection ( Avrutsky et al, 2020 ; Colon Ortiz et al, 2022 ). To compare the efficacy of inhibiting caspase-9, vs. blocking VEGF, mice were followed for 8 days following induction of RVO and treatment with either caspase-9 inhibitor eyedrops (Pen1-XBir3), or intravitreal injection of anti-VEGF antibody.…”

“…This study represents a framework for comparing in vivo efficacy of experimental treatments against a clinically-established mechanism of action (VEGF-neutralization) in a mouse model of RVO. Our prior work has shown that non-apoptotic activation of caspase-9 regulates edema, gliosis and neuronal dysfunction in a well-defined mouse model of RVO (Avrutsky et al, 2020;Colon Ortiz et al, 2022). Here, Orthogonal measures capture different dimensions of RVO pathology in response to caspase-9 inhibition, VEGF-neutralization, or a combination treatment.…”

“…Consistent with clinical findings, inhibiting VEGF signaling attenuates retinal edema and improves retinal nonperfusion following experimental RVO ( Fuma et al, 2017 ). One novel mediator of retinal injury in RVO is caspase-9, which acts as a multimodal instigator of neurovascular and astroglial dysfunction ( Avrutsky et al, 2020 ; Colon Ortiz et al, 2022 ). Selective in vivo inhibition of caspase-9 can be achieved through administration of Pen1-XBir3 ( Akpan et al, 2011 ; Avrutsky et al, 2020 ), a formulation containing the caspase-9-inhibitory domain of XIAP protein (BIR3) ( Denault et al, 2007 ) crosslinked to a cell penetrating peptide, Penetratin-1 ( Dupont et al, 2011 ).…”

Exploring laser-induced acute and chronic retinal vein occlusion mouse models: Development, temporal in vivo imaging, and application perspectives

“…Cascade activation of multiple signaling pathways induced by excitotoxicity, oxidative stress, inflammation, and mitochondrial dysfunction is implicated in chronic cerebral under-perfusion, leading to immune cell recruitment and activation, and necrosis/apoptosis of vascular endothelial and supportive cells, as well as neurons [ 49 , 50 ]. Some of these mechanisms have been validated in the retina, offering novel therapeutic targets for RVO [ 6 , 17 , 51 , 52 ].…”

“…Venous recanalization initiates at 1 to 3 days after RVO, progressing to 2/3 to all individuals approximately a week later [3, 5-7, 9, 10, 15]. Some studies specified a 24-hour duration of venous occlusion, with subsequent venous recanalization no longer being considered an exclusion criterion [6,[15][16][17][18].…”