The MC4 receptor agonist RO27-3225 inhibits NLRP1-dependent neuronal pyroptosis via the ASK1/JNK/p38 MAPK pathway in a mouse model of intracerebral haemorrhage

To protect or adversely affect? The dichotomous role of the NLRP1 inflammasome in human disease

NLRP1 is an inflammasome forming pattern recognition receptor (PRR). When activated by pathogen- and damage- associated molecular patterns (PAMPS/DAMPS), NLRP1 inflammasome formation leads to inflammation through the production of proinflammatory cytokines IL-18 and IL-1β. As with other inflammasome forming NLR family members, NLRP1 also regulates cell death processes, termed pyroptosis. The domain structure of NLRP1 differs between mice and humans, making it possible for the function of the inflammasome to differ between species and adds complexity to the study of this NLR family member. In humans, mutations in both coding and non-coding regions of the NLRP1 gene are linked to a variety of diseases. Likewise, interruption of NLRP1 inhibitors or changes in the prevalence of NLRP1 activators can also impact disease pathobiology. Adding to its complexity, the NLRP1 inflammasome plays a dichotomous role in human diseases, functioning to either attenuate or augment miscellaneous biological processes in a tissue specific manner. For example, NLRP1 plays a protective role in the gastrointestinal tract by modulating the microbiome composition; however, it augments neurological disorders, cardio-pulmonary diseases, and cancer through promoting inflammation. Thus, it is critical that the role of NLRP1 in each of these disease processes be robustly defined. In this review, we summarize the current research landscape to provide a better understanding of the mechanisms associated with NLRP1 function and dysfunction in human disease pathobiology. We propose that a better understanding of these mechanisms will ultimately result in improved insight into immune system dysfunction and therapeutic strategies targeting inflammasome function in multiple human diseases.

DKK3 attenuates JNK and AP-1 induced inflammation via Kremen-1 and DVL-1 in mice following intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) is the most devastating stroke subtype, with a poor prognosis and few proven treatments. Neuroinflammation is associated with ICH-induced brain injury and unfavorable outcomes. There is growing evidence that Dickkopf (DKK) 3 plays a key role in the adaptive anti-inflammatory and neuroprotective responses following intracerebral hemorrhage. This study aimed to evaluate the protective effects of DKK3 against brain edema and neuroinflammation in a mice model of ICH.

METHODS

Male, adult CD1 mice were subjected to sham or ICH surgery using a collagenase injection model. ICH animals received either recombinant DKK3, Kremen-1 siRNA, or DVL-1 siRNA. The neurobehavioral deficits were evaluated at 24 h, 72 h, and 28 days after ICH induction. Western blot and immunofluorescence were employed to examine the expression and localization of DKK3, Kremen-1, Dishevelled-1 (DVL-1), c-JUN N-terminal kinase (JNK), Activator protein-1 (AP-1), cleaved caspase-1, NF-κB, and IL-1β in the brain.

RESULTS

The expression of endogenous DKK3 and DVL-1 was transiently decreased after ICH compared to that in the sham group. Compared to the mice of ICH, exogenous rDKK3 administration reduced the brain water content and affected the neurological functions in ICH mice. Moreover, DKK3 was colocalized with Kremen-1 in microglia. Using a Kremen-1 or DVL-1 siRNA-induced in vivo knockdown approach, we demonstrated that the effects of DKK3 against ICH were mediated, at least partly, by the Kremen-1 and DVL-1 pathways.

CONCLUSIONS

DKK3 improves the neurological outcomes, potentially by decreasing JNK/AP-1-mediated inflammation, thereby ameliorating the short- and long-term sequelae after ICH.

Programmed Cell Deaths and Potential Crosstalk With Blood-Brain Barrier Dysfunction After Hemorrhagic Stroke

Hemorrhagic stroke is a life-threatening neurological disease characterized by high mortality and morbidity. Various pathophysiological responses are initiated after blood enters the interstitial space of the brain, compressing the brain tissue and thus causing cell death. Recently, three new programmed cell deaths (PCDs), necroptosis, pyroptosis, and ferroptosis, were also found to be important contributors in the pathophysiology of hemorrhagic stroke. Additionally, blood-brain barrier (BBB) dysfunction plays a crucial role in the pathophysiology of hemorrhagic stroke. The primary insult following BBB dysfunction may disrupt the tight junctions (TJs), transporters, transcytosis, and leukocyte adhesion molecule expression, which may lead to brain edema, ionic homeostasis disruption, altered signaling, and immune infiltration, consequently causing neuronal cell death. This review article summarizes recent advances in our knowledge of the mechanisms regarding these new PCDs and reviews their contributions in hemorrhagic stroke and potential crosstalk in BBB dysfunction. Numerous studies revealed that necroptosis, pyroptosis, and ferroptosis participate in cell death after subarachnoid hemorrhage (SAH) and intracerebral hemorrhage (ICH). Endothelial dysfunction caused by these three PCDs may be the critical factor during BBB damage. Also, several signaling pathways were involved in PCDs and BBB dysfunction. These new PCDs (necroptosis, pyroptosis, ferroptosis), as well as BBB dysfunction, each play a critical role after hemorrhagic stroke. A better understanding of the interrelationship among them might provide us with better therapeutic targets for the treatment of hemorrhagic stroke.

Effects of RO27-3225 on neurogenesis, PDGFRβ+ cells and neuroinflammation after cerebral infarction

Cerebral infarction causes severe social and economic burdens to patients due to its high morbidity and mortality rates, and the available treatments are limited. RO27-3225 is a highly selective melanocortin receptor 4 agonist that alleviates damage in many nervous system diseases, such as cerebral hemorrhage, traumatic brain injury and chronic neurodegenerative diseases. However, the effect of RO27-3225 on cerebral infarction remains unclear. In this study, we used a mouse model of transient middle cerebral artery occlusion (tMCAO) and administered RO27-3225 or saline to the mice through intraperitoneal injection. RO27-3225 increased the number of Nestin⁺/BrdU⁺ cells and doublecortin (DCX)⁺/BrdU⁺ cells in the subventricular zone (SVZ) and the number of DCX⁺/BrdU⁺ cells in the peri-infarct area on day 7 after tMCAO. Furthermore, RO27-3225 decreased the number of activated microglia (Iba1⁺ cells with a specific morphology) and the expression levels of Iba1, TNFα, IL6, and iNOS proteins and increased the number of PDGFRβ⁺ cells in the peri-infarct region on day 3 after tMCAO. Finally, RO27-3225-treated mice exhibited significantly decreased infarct volumes, brain water contents, and neurological deficits after cerebral infarction. Thus, RO27-3225 can improve the outcomes following cerebral infarction, partially by regulating neurogenesis in the SVZ, PDGFRβ⁺ cell survival and neuroinflammation in the peri-infarct zone. Our research reveals that RO27-3225 is a potential new treatment for cerebral infarction.

The MC4 receptor agonist RO27-3225 inhibits NLRP1-dependent neuronal pyroptosis via the ASK1/JNK/p38 MAPK pathway in a mouse model of intracerebral haemorrhage

BACKGROUND AND PURPOSE

Inflammasome-mediated pyroptosis is an important neuronal cell death mechanism. Previous studies reported that activation of melanocortin MC₄ receptor exerted neuroprotection in several neurological diseases. Here, we have investigated the role of MC₄ receptor activation with RO27-3225 in suppressing neuronal pyroptosis after experimental intracerebral haemorrhage (ICH) and the underlying mechanism.

EXPERIMENTAL APPROACH

One hundred and sixty-nine male CD1 mice were used. ICH was induced by injection of bacterial collagenase into the right-side basal ganglia. RO27-3225, a selective agonist of MC₄ receptor, was injected intraperitoneally at 1 hr after ICH. To elucidate the underlying mechanism, we used the specific MC₄ receptor antagonist HS024 and NQDI-1, a specific inhibitor of the apoptosis signalling-regulating kinase 1 (ASK1). Neurological tests, Western blot, Fluoro-Jade C, TUNEL, and immunofluorescence staining were conducted.

KEY RESULTS

Expression of MC₄ receptor and the NOD-like receptor family, pyrin domain containing 1 (NLRP1) inflammasome in brain were increased after ICH. RO27-3225 treatment decreased neuronal pyroptosis and neurobehavioural deficits at 24 and 72 hr after ICH. RO27-3225 reduced the expression of p-ASK1, p-JNK, p-p38 MAPK, NLRP1 inflammasome, cleaved caspase-1, and IL-1β after ICH. HS024 pretreatment prevented the effects of RO27-3225. Similar to RO27-3225, NQDI-1 alone improved neurological functions and down-regulated ASK1/JNK/p38MAPK expression after ICH.

CONCLUSIONS AND IMPLICATIONS

RO27-3225 suppressed NLRP1-dependent neuronal pyroptosis and improved neurological function, possibly mediated by activation of MC₄ receptor and inhibition of ASK1/JNK/p38 MAPK signalling pathways, after experimental ICH in mice. The MC₄ receptor may be a promising therapeutic target for the management of ICH.