Blood tissue Plasminogen Activator (tPA) of liver origin contributes to neurovascular coupling involving brain endothelial N-Methyl-D-Aspartate (NMDA) receptors

Improving stroke outcomes in hyperglycemic mice by modulating tPA/NMDAR signaling to reduce inflammation and hemorrhages

ABSTRACT

The pharmacological intervention for ischemic stroke hinges on intravenous administration of the recombinant tissue-type plasminogen activator (rtPA, Alteplase/Actilyse) either as a standalone treatment or in conjunction with thrombectomy. However, despite its clinical significance, broader use of rtPA is constrained because of the risk of hemorrhagic transformations (HTs). Furthermore, the presence of diabetes or chronic hyperglycemia is associated with an elevated risk of HT subsequent to thrombolysis. This detrimental impact of tPA on the neurovascular unit in patients with hyperglycemia has been ascribed to its capacity to induce endothelial N-methyl-D-aspartate receptor (NMDAR) signaling, contributing to compromised blood-brain barrier integrity and neuroinflammatory processes. In a mouse model of thromboembolic stroke with chronic hyperglycemia, we assessed the effectiveness of rtPA and N-acetylcysteine (NAC) as thrombolytic agents. We also tested the effect of blocking tPA/NMDAR signaling using a monoclonal antibody, Glunomab. Magnetic resonance imaging, speckle contrast imaging, flow cytometry, and behavioral tasks were used to evaluate stroke outcomes. In hyperglycemic animals, treatment with rtPA resulted in lower recanalization rates and increased HTs. Conversely, NAC treatment reduced lesion sizes while mitigating HTs. After a single administration, either in standalone or combined with rtPA-induced thrombolysis, Glunomab reduced brain lesion volumes, HTs, and neuroinflammation after stroke, translating into improved neurological outcomes. Additionally, we demonstrated the therapeutic efficacy of Glunomab in combination with NAC or as a standalone strategy in chronic hyperglycemic animals. Counteracting tPA-dependent endothelial NMDAR signaling limits ischemic damages induced by both endogenous and exogenous tPA, including HTs and inflammatory processes after ischemic stroke in hyperglycemic animals.

Parabiosis Discriminates the Circulating, Endothelial, and Parenchymal Contributions of Endogenous Tissue-Type Plasminogen Activator to Stroke

BACKGROUND

Intravenous injection of alteplase, a recombinant tPA (tissue-type plasminogen activator) as a thrombolytic agent has revolutionized ischemic stroke management. However, tPA is a more complex enzyme than expected, being for instance able to promote thrombolysis, but at the same time, also able to influence neuronal survival and to affect the integrity of the blood-brain barrier. Accordingly, the respective impact of endogenous tPA expressed/present in the brain parenchyma versus in the circulation during stroke remains debated.

METHODS

To address this issue, we used mice with constitutive deletion of tPA (tPANull [tPA-deficient mice]) or conditional deletion of endothelial tPA (VECad [vascular endothelial-Cadherin-Cre-recombinase]-Cre∆tPA). We also developed parabioses between tPANull and wild-type mice (tPAWT), anticipating that a tPAWT donor would restore levels of tPA to normal ones, in the circulation but not in the brain parenchyma of a tPANull recipient. Stroke outcomes were investigated by magnetic resonance imaging in a thrombo-embolic or a thrombotic stroke model, induced by local thrombin injection or FeCl3 application on the endothelium, respectively.

RESULTS

First, our data show that endothelial tPA, released into the circulation after stroke onset, plays an overall beneficial role following thrombo-embolic stroke. Accordingly, after 24 hours, tPANull/tPANull parabionts displayed less spontaneous recanalization and reperfusion and larger infarcts compared with tPAWT/tPAWT littermates. However, when associated to tPAWT littermates, tPANull mice had similar perfusion deficits, but less severe brain infarcts. In the thrombotic stroke model, homo- and hetero-typic parabionts did not differ in the extent of brain damages and did not differentially recanalize and reperfuse.

CONCLUSIONS

Together, our data reveal that during thromboembolic stroke, endogenous circulating tPA from endothelial cells sustains a spontaneous recanalization and reperfusion of the tissue, thus, limiting the extension of ischemic lesions. In this context, the impact of endogenous parenchymal tPA is limited.

Rejuvenation of cerebromicrovascular function in aged mice through heterochronic parabiosis: insights into neurovascular coupling and the impact of young blood factors

Age-related impairment of neurovascular coupling (NVC; "functional hyperemia") is a critical factor in the development of vascular cognitive impairment (VCI). Recent geroscience research indicates that cell-autonomous mechanisms alone cannot explain all aspects of neurovascular aging. Circulating factors derived from other organs, including pro-geronic factors (increased with age and detrimental to vascular homeostasis) and anti-geronic factors (preventing cellular aging phenotypes and declining with age), are thought to orchestrate cellular aging processes. This study aimed to investigate the influence of age-related changes in circulating factors on neurovascular aging. Heterochronic parabiosis was utilized to assess how exposure to young or old systemic environments could modulate neurovascular aging. Results demonstrated a significant decline in NVC responses in aged mice subjected to isochronic parabiosis (20-month-old C57BL/6 mice [A-(A)]; 6 weeks of parabiosis) when compared to young isochronic parabionts (6-month-old, [Y-(Y)]). However, exposure to young blood from parabionts significantly improved NVC in aged heterochronic parabionts [A-(Y)]. Conversely, young mice exposed to old blood from aged parabionts exhibited impaired NVC responses [Y-(A)]. In conclusion, even a brief exposure to a youthful humoral environment can mitigate neurovascular aging phenotypes, rejuvenating NVC responses. Conversely, short-term exposure to an aged humoral milieu in young mice accelerates the acquisition of neurovascular aging traits. These findings highlight the plasticity of neurovascular aging and suggest the presence of circulating anti-geronic factors capable of rejuvenating the aging cerebral microcirculation. Further research is needed to explore whether young blood factors can extend their rejuvenating effects to address other age-related cerebromicrovascular pathologies, such as blood-brain barrier integrity.