Cytisine is neuroprotective in female but not male 6-hydroxydopamine lesioned parkinsonian mice and acts in combination with 17-β-estradiol to inhibit apoptotic endoplasmic reticulum stress in dopaminergic neurons

A novel mechanism of PHB2-mediated mitophagy participating in the development of Parkinson's disease

JOURNAL/nrgr/04.03/01300535-202408000-00037/figure1/v/2023-12-16T180322Z/r/image-tiff Endoplasmic reticulum stress and mitochondrial dysfunction play important roles in Parkinson's disease, but the regulatory mechanism remains elusive. Prohibitin-2 (PHB2) is a newly discovered autophagy receptor in the mitochondrial inner membrane, and its role in Parkinson's disease remains unclear. Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is a factor that regulates cell fate during endoplasmic reticulum stress. Parkin is regulated by PERK and is a target of the unfolded protein response. It is unclear whether PERK regulates PHB2-mediated mitophagy through Parkin. In this study, we established a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of Parkinson's disease. We used adeno-associated virus to knockdown PHB2 expression. Our results showed that loss of dopaminergic neurons and motor deficits were aggravated in the MPTP-induced mouse model of Parkinson's disease. Overexpression of PHB2 inhibited these abnormalities. We also established a 1-methyl-4-phenylpyridine (MPP+)-induced SH-SY5Y cell model of Parkinson's disease. We found that overexpression of Parkin increased co-localization of PHB2 and microtubule-associated protein 1 light chain 3, and promoted mitophagy. In addition, MPP+ regulated Parkin involvement in PHB2-mediated mitophagy through phosphorylation of PERK. These findings suggest that PHB2 participates in the development of Parkinson's disease by interacting with endoplasmic reticulum stress and Parkin.

IRE1/JNK Is the Leading UPR Pathway in 6-OHDA-Induced Degeneration of Differentiated SH-SY5Y Cells

Parkinson's disease (PD) is a neurodegenerative disorder which affects dopaminergic neurons of the midbrain. Accumulation of α-synuclein or exposure to neurotoxins like 6-hydroxydopamine (6-OHDA) induces endoplasmic reticulum (ER) stress along with the unfolded protein response (UPR), which executes apoptosis via activation of PERK/CHOP or IRE1/JNK signaling. The present study aimed to determine which of these pathways is a major contributor to neurodegeneration in an 6-OHDA-induced in vitro model of PD. For this purpose, we have applied pharmacological PERK and JNK inhibitors (AMG44 and JNK V) in differentiated SH-SY5Y cells exposed to 6-OHDA. Inhibition of PERK and JNK significantly decreased genotoxicity and improved mitochondrial respiration, but only JNK inhibition significantly increased cell viability. Gene expression analysis revealed that the effect of JNK inhibition was dependent on a decrease in MAPK10 and XBP1 mRNA levels, whereas inhibition of either PERK or JNK significantly reduced the expression of DDIT3 mRNA. Western blot has shown that JNK inhibition strongly induced the XBP1s protein, and inhibition of each pathway attenuated the phosphorylation of eIF2α and JNK, as well as the expression of CHOP. Collectively, our data suggests that targeting the IRE1/JNK pathway of the UPR is a more effective option for PD treatment as it simultaneously affects more than one pro-apoptotic pathway.

ER stress in mouse serotonin neurons triggers a depressive phenotype alleviated by ketamine targeting eIF2α signaling

Depression is a devastating mood disorder that causes significant disability worldwide. Current knowledge of its pathophysiology remains modest and clear biological markers are lacking. Emerging evidence from human and animal models reveals persistent alterations in endoplasmic reticulum (ER) homeostasis, suggesting that ER stress-related signaling pathways may be targets for prevention and treatment. However, the neurobiological basis linking the pathways involved in depression-related ER stress remains unknown. Here, we report that an induced model of ER stress in mouse serotonin (5-HT) neurons is associated with reduced Egr1-dependent 5-HT cellular activity and 5-HT neurotransmission, resulting in neuroplasticity deficits in forebrain regions and a depressive-like phenotype. Ketamine administration engages downstream eIF2α signaling to trigger rapid neuroplasticity events that rescue the depressive-like effects. Collectively, these data identify ER stress in 5-HT neurons as a cellular pathway involved in the pathophysiology of depression and show that eIF2α is critical in eliciting ketamine's fast antidepressant effects.

Strategies targeting endoplasmic reticulum stress to improve Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder with motor symptoms, which is caused by the progressive death of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc). Accumulating evidence shows that endoplasmic reticulum (ER) stress occurring in the SNpc DA neurons is an early event in the development of PD. ER stress triggers the activation of unfolded protein response (UPR) to reduce stress and restore ER function. However, excessive and continuous ER stress and UPR exacerbate the risk of DA neuron death through crosstalk with other PD events. Thus, ER stress is considered a promising therapeutic target for the treatment of PD. Various strategies targeting ER stress through the modulation of UPR signaling, the increase of ER's protein folding ability, and the enhancement of protein degradation are developed to alleviate neuronal death in PD models. In this review, we summarize the pathological role of ER stress in PD and update the strategies targeting ER stress to improve ER protein homeostasis and PD-related events.

Extracellular S100B inhibits A-type voltage-gated potassium currents and increases L-type voltage-gated calcium channel activity in dopaminergic neurons

Parkinson's disease (PD) is associated with an increase in secreted S100B within the midbrain and cerebrospinal fluid. In addition, S100B overexpression in mice accelerates the loss of substantia nigra pars compacta dopaminergic (DA) neurons, suggesting a role for this protein in PD pathogenesis. We found that in the mouse SNc, S100B labeled astrocytic processes completely envelop the somata of tyrosine hydroxylase (TH) expressing DA neurons only in male mice. These data suggest that an increase in S100B secretion by astrocytes within the midbrain could play a role in DA dysfunction during early PD. We therefore asked if acute exposure to extracellular S100B alters the activity of identified TH expressing DA neurons in primary mouse midbrain cultures. Acute exposure to 50 pM S100B specifically inhibited A-type voltage-gated potassium currents in TH+ , but not TH- neurons. This was accompanied by ~2-fold increases in the frequency of both intrinsic firing, as well as L-type voltage-gated calcium channel (VGCC)-mediated calcium fluxes only in TH+ neurons. Further, exposure to 100 μM 4-aminopyridine (4-AP), an A-type voltage-gated potassium channel inhibitor, mimicked the S100B mediated increase in intrinsic firing and L-type VGCC-mediated calcium fluxes in TH+ neurons. Taken together, our finding that extracellular S100B alters the activity of native DA neurons via an inhibition of A-type voltage-gated potassium channels has important implications for understanding the pathophysiology of early PD.

Inflammasome Activation in Parkinson’s Disease

Chronic sterile inflammation and persistent immune activation is a prominent pathological feature of Parkinson’s disease (PD). Inflammasomes are multi-protein intracellular signaling complexes which orchestrate inflammatory responses in immune cells to a diverse range of pathogens and host-derived signals. Widespread inflammasome activation is evident in PD patients at the sites of dopaminergic degeneration as well as in blood samples and mucosal biopsies. Inflammasome activation in the nigrostriatal system is also a common pathological feature in both neurotoxicant and α-synuclein models of PD where dopaminergic degeneration occurs through distinct mechanisms. The NLRP3 (NLR Family Pyrin Domain Containing 3) inflammasome has been shown to be the primary driver of inflammatory neurotoxicity in PD and other neurodegenerative diseases. Chronic NLRP3 inflammasome activation is triggered by pathogenic misfolded α-synuclein aggregates which accumulate and spread over the disease course in PD. Converging lines of evidence suggest that blocking inflammasome activation could be a promising therapeutic strategy for disease modification, with both NLRP3 knockout mice and CNS-permeable pharmacological inhibitors providing robust neuroprotection in multiple PD models. This review summarizes the current evidence and knowledge gaps around inflammasome activation in PD, the pathological mechanisms by which persistent inflammasome activation can drive dopaminergic degeneration and the therapeutic opportunities for disease modification using NLRP3 inhibitors.

Omarigliptin attenuates rotenone-induced Parkinson's disease in rats: Possible role of oxidative stress, endoplasmic reticulum stress and immune modulation

The current study aimed to explore the potential neuroprotective effect of omarigliptin (OG), an antidiabetic drug that crosses the blood-brain barrier (BBB), in a Parkinson's disease (PD) rotenone-based rat-model. Results showed that OG attenuated motor impairment, histological aberrations, α-synuclein accumulation, and rescued the dopaminergic neurons in rotenone-administered rats. Furthermore, OG halted rotenone-induced oxidative stress; as shown by reduced lipid peroxidation, decline in the oxidative stress sensor (nuclear factor erythroid 2-related factor 2) and its downstream heme oxygenase-1. In addition, OG abrogated neuroinflammation and apoptosis in rotenone-treated rats. Moreover, OG ameliorated endoplasmic reticulum (ER) stress in rotenone-administered rats; as evidenced by reduced levels of ER resident proteins such as glucose-regulated protein 78, C/EBP homologous protein and apoptotic caspase-12. In conclusion, this study implies repurposing of OG, as a novel neuroprotective agent due to its antioxidant properties, its effects on ER stress in addition to its anti-inflammatory and anti-apoptotic activities.

Female Rats Are Resistant to Cognitive, Motor and Dopaminergic Deficits in the Reserpine-Induced Progressive Model of Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. The main symptoms are motor signs such as resting tremor and difficulty in initializing movements. Non-motor alterations, such as cognitive deficits, can precede the motor symptoms. PD is more frequent in men than women. The mechanisms related to this difference are not completely understood. There is evidence that females present distinct characteristics in dopaminergic function compared to males. While the severity of motor impairments is often compared between sexes, little is known about sex differences in the prodromal stage. Most animal models of PD present acute severe motor impairment, which precludes the study of non-motor symptoms. Our research group have proposed an adaptation of the classic reserpine protocol, using low doses in a chronic treatment. This method allows the observation of progressive motor impairment as well as premotor deficits. Here we investigate possible behavioral and neuronal sex differences in the effects of the repeated treatment with a low dose of reserpine in rats. Male and female Wistar rats received 10–15 injections of reserpine (0.1 mg/kg) or vehicle, on alternate days. We followed-up the estrous cycle phases and conducted motor and cognitive assessments (catalepsy, open field, oral movements and object recognition tests). The euthanasia occurred 48 h after the 10th or 15th injections, with the collection of blood for the quantification of sex hormones and brains for tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compact (SNpc). Reserpine induced progressive catalepsy, involuntary oral movements and cognitive deficits in male rats. The behavioral effects of reserpine were attenuated (motor) or absent (cognitive) in females. Reserpine decreased TH immunoreactivity in males, but not in females. Estrogen levels in females negatively correlated with catalepsy duration. Our findings show that females present a delay and/or a prevention in the reserpine-induced motor alterations in the progressive PD model, compatible with the lower prevalence of this disease in women. Further, females were protected from the deficit in object recognition at the prodromal stage. The absence of reserpine-induce decrease in TH immunoreactivity suggests that differences in dopaminergic function/plasticity are related to this protection in female sex.

17β-oestradiol alleviates endoplasmic reticulum stress injury induced by chronic cerebral hypoperfusion through the Haemoglobin/HIF 1α signalling pathway in ovariectomized rats

Endoplasmic reticulum stress (ERS) is known to be an essential target in protecting against ischaemic brain injury. In this study, using a vascular dementia (VaD) animal model induced by bilateral common carotid artery occlusion (BCCAO), we evaluated the effect and mechanism of 17β-oestradiol (E2) against VaD by inhibiting ERS at the early stage (14 d, 21 d, 28 d) and late stage (3 m) after BCCAO in the hippocampal CA1 region of ovariectomized rats. The results showed that the activation of the PERK-eIF2α-ATF4-CHOP axis, a typical ERS pathway, was significantly increased at the early and late stages after BCCAO. JNK (c-Jun N-terminal kinase)-cJun, a pro-death pathway, also displayed the same pattern as the ERS axis. E2 treatment profoundly suppressed the impairments caused by BCCAO. Further mechanistic studies revealed that cerebral blood flow (CBF) was sharply decreased at 14 d and returned to the normal level at 21 d after BCCAO. E2 could not change CBF, while it unexpectedly enhanced the ability to carry oxygen. This is evidenced by the fact that the protein expression of haemoglobin α/β (Hα/β), an oxygen carrier, robustly increased at BCCAO 21 d and 3 m after E2 treatment. The oxygen carrier increased strongly after 21 d and 3 m of BCCAO treated with E2. Moreover, E2 correspondingly enhanced the protein expression of hypoxia-inducible factor 1α (HIF 1α) in both the early and late stage after BCCAO in the hippocampal CA1 region. Finally, E2 administration markedly decreased the activities of caspase-8, caspase-3, and caspase-12 and increased the number of NeuN-positive cells. These findings suggest that E2 serves as a neuroprotectant to alleviate VaD by suppressing ERS injury involving the haemoglobin/HIF 1α signalling pathway.