Astrocytic Glutamate Transporters and Migraine

Targeting Na,K-ATPase-Src signaling to normalize cerebral blood flow in a murine model of familial hemiplegic migraine

Familial hemiplegic migraine type 2 (FHM2) is linked to Na,K-ATPase α2 isoform mutations, including that of G301R. Mice heterozygous for this mutation (α 2 + / G3 0 1R ) show cerebrovascular hypercontractility associated with amplified Src kinase signaling, and exaggerated neurovascular coupling. This study hypothesized that targeting Na,K-ATPase-dependent Src phosphorylation with pNaKtide would normalize cerebral perfusion and neurovascular coupling in α 2 + / G3 0 1R mice. The effect of pNaKtide on cerebral blood flow and neurovascular coupling was assessed using laser speckle contrast imaging in awake, head-fixed mice with cranial windows in a longitudinal study design. At baseline, compared to wild type, α 2 + / G3 0 1R mice exhibited increased middle cerebral artery tone; with whisker stimulation leading to an exaggerated increase in sensory cortex blood flow. No difference between genotypes in telemetrically assessed blood pressure occurred. The exaggerated neurovascular coupling in α 2 + / G3 0 1R mice was associated with increased Kir2.1 channel expression in cerebrovascular endothelium. Two weeks pNaKtide treatment normalized cerebral artery tone, endothelial Kir2.1 expression, and neurovascular coupling in α 2 + / G3 0 1R mice. Inhibition of the Na,K-ATPase-dependent Src kinase signaling with pNaKtide prevented excessive vasoconstriction and disturbances in neurovascular coupling in α 2 + / G3 0 1R mice. pNaKtide had only minor hypotensive effect similar in both genotypes. These results demonstrate a novel treatment target to normalize cerebral perfusion in FHM2.

Mechanisms underlying CSD initiation implicated by genetic mouse models of migraine

A key unanswered question in migraine neurobiology concerns the mechanisms that make the brain of migraineurs susceptible to cortical spreading depression (CSD, a spreading depolarization that underlies migraine aura and may trigger the migraine pain mechanisms). Important insights into this question can be obtained by studying the mechanisms of facilitation of CSD initiation in genetic mouse models of the disease. These models, all generated from families with hereditary migraine, allow the investigation of the functional consequences of disease-causing mutations at the molecular, cellular, synaptic and neural circuit levels. In this review, after describing the available genetic mouse models of migraine, which all share increased susceptibility to experimentally induced CSD, we will discuss the functional alterations in their cerebral cortex and the mechanisms underlying the facilitation of CSD initiation in their cortex, as well as the insights that these mechanisms may give into the mechanisms of initiation of spontaneous CSDs in migraine.

Na+-K+-ATPase/GLT-1 interaction participates in EGCG protection against cerebral ischemia-reperfusion injury in rats

BACKGROUND

In China, stroke is the primary cause of adult death and disability. Because of the increased rate of blood vessel reperfusion, it is important to prevent cerebral ischemia-reperfusion injury, in which glutamate (Glu) excitotoxicity plays a critical role. The most important Glu transporter, GLT-1, is essential for the regulation of Glu, which is dependent on Na+-K+-ATPase (NKA)-induced ion concentration gradient differences. EGCG, a substance found in tea polyphenols, can reduce infarct areas in ischemia-reperfusion models, reduce stroke incidence, and prolong life in which NKA is involved.

PURPOSE

In this study, we investigated the potential of EGCG in protecting against cerebral ischemia-reperfusion injury by regulating the interaction between NKA and GLT-1.

STUDY DESIGN

This study was designed to investigate the protective effects of EGCG against cerebral ischemia-reperfusion injury by modulating the interaction between NKA and GLT-1, utilizing both the rat middle cerebral artery occlusion/reperfusion (MCAO/R) model and the oxygen-glucose deprivation/reoxygenation (OGD/R) model in co-cultures of rat hippocampal neurons and astrocytes.

METHODS

The neuronal survival rate was assessed using CCK8, and the cerebral infarction area and neurological function were determined by TTC staining and neurological deficit scores. NKA activity was measured using an inorganic phosphorous detection method, and NKA and GLT-1 expression was detected using western blotting. The interaction between NKAα2 and GLT-1 was identified by co-immunoprecipitation (CoIP) assay, laser confocal microscopy, and Imaris 3D confocal rendering technology. An adenovirus vector with overexpression of NKAα2 was constructed, packaged, and injected into the rat lateral ventricle. Neurological function and the cerebral infarction area were identified, and the interaction between NKAα2 and GLT-1 was identified using CoIP assay.

RESULTS

EGCG reduced the infarction area and neurological deficit scores, restored NKA activity, alleviated the decrease in membrane NKAα2 and GLT-1 expression, and relieved the uncoupling of NKAα2 and GLT-1 in the hippocampal CA1 after rat MCAO/R injury. By promoting the coupling of NKAα2 and GLT-1 in rat MCAO/R models, overexpression of NKAα2 reduced the cerebral infarction area and neurological impairment scores.

CONCLUSION

EGCG improved cerebral ischemia-reperfusion injury by restoring NKA activity and increasing membrane GLT-1 expression due to NKA-GLT-1 interaction. For the first time, our findings demonstrate the critical role that NKA and GLT-1 colocalization plays in cerebral ischemia-reperfusion damage. Our findings provide new strategic directions for the pathogenesis and prevention of thrombolytic injury in the clinical treatment of stroke, while also serving as a basis for further development and utilization of EGCG.

1H-MRS reveals abnormal energy metabolism and excitatory-inhibitory imbalance in a chronic migraine-like state induced by nitroglycerin in mice

BACKGROUND

Chronic migraine is closely related to the dysregulation of neurochemical substances in the brain, with metabolic imbalance being one of the proposed causes of chronic migraine. This study aims to evaluate the metabolic changes between energy metabolism and excitatory and inhibitory neurotransmitters in key brain regions of mice with chronic migraine-like state and to uncover the dysfunctional pathways of migraine.

METHODS

A chronic migraine-like state mouse model was established by repeated administration of nitroglycerin (NTG). We used von Frey filaments to assess the mechanical thresholds of the hind paw and periorbital in wild-type and familial hemiplegic migraine type 2 mice. After the experiments, tissue was collected from five brain regions: the somatosensory cortex (SSP), hippocampus, thalamus (TH), hypothalamus, and the spinal trigeminal nucleus caudalis (TNC). Proton magnetic resonance spectroscopy (1H-MRS) was employed to study the changes in brain metabolites associated with migraine, aiming to explore the mechanisms underlying metabolic imbalance in chronic migraine-like state.

RESULTS

In NTG-induced chronic migraine-like state model, we observed a significant reduction in energy metabolism during central sensitization, an increase in excitatory neurotransmitters such as glutamate, and a tendency for inhibitory neurotransmitters like GABA to decrease. The TNC and thalamus were the most affected regions. Furthermore, the consistency of N-acetylaspartate levels highlighted the importance of the TNC-TH-SSP pathway in the ascending nociceptive transmission of migraine.

CONCLUSION

Abnormal energy metabolism and neurotransmitter imbalance in the brain region of NTG-induced chronic migraine-like state model are crucial mechanisms contributing to the chronicity of migraine.

Rare GPR37L1 Variants Reveal Potential Association between GPR37L1 and Disorders of Anxiety and Migraine

GPR37L1 is an orphan receptor that couples through heterotrimeric G-proteins to regulate physiological functions. Since its role in humans is not fully defined, we used an unbiased computational approach to assess the clinical significance of rare G-protein-coupled receptor 37-like 1 (GPR37L1) genetic variants found among 51,289 whole-exome sequences from the DiscovEHR cohort. Rare GPR37L1 coding variants were binned according to predicted pathogenicity and analyzed by sequence kernel association testing to reveal significant associations with disease diagnostic codes for epilepsy and migraine, among others. Since associations do not prove causality, rare GPR37L1 variants were functionally analyzed in SK-N-MC cells to evaluate potential signaling differences and pathogenicity. Notably, receptor variants exhibited varying abilities to reduce cAMP levels, activate mitogen-activated protein kinase (MAPK) signaling, and/or upregulate receptor expression in response to the agonist prosaptide (TX14(A)), as compared with the wild-type receptor. In addition to signaling changes, knock-out (KO) of GPR37L1 or expression of certain rare variants altered cellular cholesterol levels, which were also acutely regulated by administration of the agonist TX14(A) via activation of the MAPK pathway. Finally, to simulate the impact of rare nonsense variants found in the large patient cohort, a KO mouse line lacking Gpr37l1 was generated. Although KO animals did not recapitulate an acute migraine phenotype, the loss of this receptor produced sex-specific changes in anxiety-related disorders often seen in chronic migraineurs. Collectively, these observations define the existence of rare GPR37L1 variants associated with neuropsychiatric conditions in the human population and identify the signaling changes contributing to pathological processes.

Rare GPR37L1 variants reveal potential roles in anxiety and migraine disorders

GPR37L1 is an orphan receptor that couples through heterotrimeric G-proteins to regulate physiological functions. Since its role in humans is not fully defined, we used an unbiased computational approach to assess the clinical significance of rare GPR37L1 genetic variants found among 51,289 whole exome sequences from the DiscovEHR cohort. Briefly, rare GPR37L1 coding variants were binned according to predicted pathogenicity, and analyzed by Sequence Kernel Association testing to reveal significant associations with disease diagnostic codes for epilepsy and migraine, among others. Since associations do not prove causality, rare GPR37L1 variants were then functionally analyzed in SK-N-MC cells to evaluate potential signaling differences and pathogenicity. Notably, receptor variants exhibited varying abilities to reduce cAMP levels, activate MAPK signaling, and/or upregulate receptor expression in response to the agonist prosaptide (TX14(A)), as compared to the wild-type receptor. In addition to signaling changes, knockout of GPR37L1 or expression of certain rare variants altered cellular cholesterol levels, which were also acutely regulated by administration of the agonist TX14(A) via activation of the MAPK pathway. Finally, to simulate the impact of rare nonsense variants found in the large patient cohort, a knockout (KO) mouse line lacking Gpr37L1 was generated, revealing loss of this receptor produced sex-specific changes implicated in migraine-related disorders. Collectively, these observations define the existence of rare GPR37L1 variants in the human population that are associated with neuropsychiatric conditions and identify the underlying signaling changes that are implicated in the in vivo actions of this receptor in pathological processes leading to anxiety and migraine.

SIGNIFICANCE STATEMENT

G-protein coupled receptors (GPCRs) represent a diverse group of membrane receptors that contribute to a wide range of diseases and serve as effective drug targets. However, a number of these receptors have no identified ligands or functions, i.e., orphan receptors. Over the past decade, advances have been made, but there is a need for identifying new strategies to reveal their roles in health and disease. Our results highlight the utility of rare variant analyses of orphan receptors for identifying human disease associations, coupled with functional analyses in relevant cellular and animal systems, to ultimately reveal their roles as novel drug targets for treatment of neurological disorders that lack wide-spread efficacy.