Biochemical protective effect of 1,25-dihydroxyvitamin D3 through autophagy induction in the MPTP mouse model of Parkinson's disease

The neuroprotective effect of vitamin D in Parkinson's disease: association or causation

Parkinson's disease (PD) is a chronic neurodegenerative disease (NDD) due to the degeneration of dopaminergic neurons (DNs) in the substantia nigra (SN). PD is characterized by diverse motor symptoms such as rigidity, resting tremors, and bradykinesia, and non-motor symptoms such as cognitive dysfunction and sleep disturbances. Vitamin D (VD), VD receptor (VDR), and VD metabolites are present in the brain and play a role in maintaining the development, differentiation, and functions of the DNs. VDRs exert protective effects against PD neuropathology by modulating functional capacity and DNs neurotransmission in the SN. In virtue of its anti-inflammatory and antioxidant activities, VD could be effective in the prevention and treatment of PD. VD exerts a neuroprotective effect by reducing oxidative stress and mitochondrial dysfunction, and by increasing autophagy and brain-derived neurotrophic factor (BDNF). Low VD serum level is connected with cognitive dysfunction and the development of dementia in PD. The VD-mediated cognitive augmenting effect is interrelated to the safeguarding of synaptic plasticity and modulation of neurotransmitter release. VD deficiency is linked with the severity of olfactory dysfunction which precedes the progression of symptomatic PD. However, the precise role of VD in PD remains unidentified, and there is a conflict about whether treatment with VD can ameliorate PD or not.

Does vitamin D protect or treat Parkinson's disease? A narrative review

Parkinson's disease (PD) is a neurodegenerative brain disease (NBD) developed due to dopaminergic neuron loss in the substantia nigra (SN). Vitamin D (VD), VD receptor (VDR), and VD metabolites are highly expressed in the human brain and play a critical role in maintaining different brain functions. VDRs are highly expressed in the SN that regulates the activity of dopaminergic neurons and synaptic plasticity. VD exerts protective and therapeutic effects against the development of PD by modulating dopaminergic neurons of SN. VD reduces oxidative stress and neuroinflammation in PD because of its anti-inflammatory and antioxidant activities. Different studies revealed the protective effect of VD in the management of PD. However, the potential therapeutic effect of VD in well-established PD remains controversial. Therefore, this review aims to elucidate VD's preventive and therapeutic roles in PD. In conclusion, VD deficiency is associated with increased PD risk, but VD supplementation in well-established PD plays little role.

Nuclear and Cytoplasmatic Players in Mitochondria-Related CNS Disorders: Chromatin Modifications and Subcellular Trafficking

Aberrant mitochondrial phenotypes are common to many central nervous system (CNS) disorders, including neurodegenerative and neurodevelopmental diseases. Mitochondrial function and homeostasis depend on proper control of several biological processes such as chromatin remodeling and transcriptional control, post-transcriptional events, vesicle and organelle subcellular trafficking, fusion, and morphogenesis. Mutation or impaired regulation of major players that orchestrate such processes can disrupt cellular and mitochondrial dynamics, contributing to neurological disorders. The first part of this review provides an overview of a functional relationship between chromatin players and mitochondria. Specifically, we relied on specific monogenic CNS disorders which share features with mitochondrial diseases. On the other hand, subcellular trafficking is coordinated directly or indirectly through evolutionarily conserved domains and proteins that regulate the dynamics of membrane compartments and organelles, including mitochondria. Among these “building blocks”, longin domains and small GTPases are involved in autophagy and mitophagy, cell reshaping, and organelle fusion. Impairments in those processes significantly impact CNS as well and are discussed in the second part of the review. Hopefully, in filling the functional gap between the nucleus and cytoplasmic organelles new routes for therapy could be disclosed.

Assessing the Effects of Vitamin D on Neural Network Function in Patients With Parkinson's Disease by Measuring the Fraction Amplitude of Low-Frequency Fluctuation

Background: Recently, many studies have shown that low vitamin D (VD) levels may be related to an increased risk of Parkinson's disease (PD), but the underlying mechanisms remain unclear. Objective: To explore the relationship between PD and VD levels, as well as to analyze the effects of VD on spontaneous brain activity and explore the possible mechanism of its involvement in PD risk. Methods: In a cross-sectional study, we quantified the difference in VD levels between 330 PD patients and 209 healthy controls (HC) to explore the correlation between VD and PD risk. We also acquired resting-state Functional Magnetic Resonance Imaging (rs-fMRI) data from 46 PD patients and 21 HC. The PD patients were divided into three groups according to 25(OH)D levels: PD patients with VD deficiency (PD + VDD), PD patients with VD insufficiency (PD + VDI), and PD patients with normal VD (PD + NVD). The effect of VD status on spontaneous neuronal activity in the whole brain was analyzed by measuring the fraction amplitude of low-frequency fluctuation (fALFF). Results: Compared with HC, the PD patients had lower serum 25(OH)D levels (23.60 ± 7.27 vs. 25.60 ± 5.78, P < 0.001). The 25(OH)D level may have a potential dose-dependent effect on the risk of PD (P _trend = 0.007). A high risk of PD was associated with VD deficiency [25(OH)D < 20 ng/mL, OR = 2.319], and the lowest quartile of 25(OH)D concentration was associated with a high risk of PD (OR = 1.941). In the rs-fMRI study, PD + VDD patients had wider brain regions with altered fALFF than other PD groups when compared with the corresponding HC groups. Both PD + VDD and PD + VDI showed higher fALFF in the cuneus, left precuneus, calcarine cortex and right lingual, as well as lower fALFF in the left middle temporal gyrus. PD + VDD patients also showed higher fALFF in the left superior, middle and inferior frontal gyri, as well as the left precentral gyrus than HC. Among PD patients, there was only a statistically significant difference in fALFF between the PD + VDD and PD + NVD groups. Compared with the PD + NVD group, PD + VDD patients exhibited higher fALFF in the left precentral and left postcentral gyrus, as well as the left inferior parietal lobule. Conclusion: These results demonstrate that PD patients had lower serum VD levels than HC, and VD may have a potential dose-dependent effect on PD risk. Lower serum VD levels can affect the spontaneous neuronal activity of default-mode network (DMN) and visual pathway neurons in PD patients, providing a possible mechanism for its effect on PD risk.

Vitamin D in autophagy signaling for health and diseases: Insights on potential mechanisms and future perspectives

Vitamin D regulates the pleiotropic effect to maintain cellular homeostasis and epidemiological evidence establishes an association between vitamin D deficiency and various human diseases. Here, the role of autophagy, the cellular self-degradation process, in vitamin D-dependent function is documented in different cellular settings and discussed the molecular aspects for treating chronic inflammatory, infectious diseases, and cancer. Vitamin D activates autophagy through a genomic and non-genomic signaling pathway to influence a wide variety of physiological functions of different body organs along with bone health and calcium metabolism. Moreover, it induces autophagy as a protective mechanism to inhibit oxidative stress and apoptosis to regulate cell proliferation, differentiation, and immune modulation. Furthermore, vitamin D and its receptor regulate autophagy signaling to control inflammation and host immunity by activating antimicrobial defense mechanisms. Vitamin D has been revealed as a potent anticancer agent and induces autophagy to increase the response to radiation and chemotherapeutic drugs for potential cancer therapy. Increasing vitamin D levels in the human body through timely exposure to sunlight or vitamin D supplements could activate autophagy as part of the homeostasis mechanism to prevent multiple human diseases and aging-associated dysfunctions.

Calcitriol Alleviates MPP+- and MPTP-Induced Parthanatos Through the VDR/PARP1 Pathway in the Model of Parkinson's Disease

The pathogenesis of Parkinson’s disease (PD) is currently unclear. Recent studies have suggested a correlation between vitamin D and PD. Vitamin D and its analogs have protective effects in animal models of PD, but these studies have not clarified the mechanism. Parthanatos is a distinct type of cell death caused by excessive activation of poly (ADP-ribose) polymerase-1 (PARP1), and the activation of PARP1 in PD models suggests that parthanatos may exist in PD pathophysiology. 1,25-Dihydroxyvitamin D3 (calcitriol) is a potential inhibitor of PARP1 in macrophages. This study aimed to investigate whether calcitriol treatment improves PD models and its effects on the parthanatos pathway. A 1-methyl-4-phenylpyridinium (MPP⁺)-induced cell model and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) subacute animal model were selected as the in vitro and in vivo PD models, and calcitriol was applied in these models. Results showed that parthanatos existed in the MPP⁺-induced cell model and pretreatment with calcitriol improved cell viability, reduced the excessive activation of PARP1, and relieved parthanatos. The application of calcitriol in the MPTP subacute animal model also improved behavioral tests, restored the damage to dopamine neurons, and reduced the activation of PARP1-related signaling pathways. To verify whether calcitriol interacts with PARP1 through its vitamin D receptor (VDR), siRNA, and overexpression plasmids were used to downregulate or overexpress VDR. Following the downregulation of VDR, the expression and activation of PARP1 increased and PARP1 was inhibited when VDR was overexpressed. Coimmunoprecipitation verified the combination of VDR and PARP1. In short, calcitriol can substantially improve parthanatos in the MPP⁺-induced cell model and MPTP model, and the protective effect might be partly through the VDR/PARP1 pathway, which provides a new possibility for the treatment of PD.

Natural products as geroprotectors: An autophagy perspective

Over the past decade, significant attention has been given to repurposing Food and Drug Administration approved drugs to treat age-related diseases. In contrast, less consideration has been given to natural bioactive compounds. Consequently, there have been limited attempts to translate these compounds. Autophagy is a fundamental biological pathway linked to aging, and numerous strategies to enhance autophagy have been shown to extend lifespan. Interestingly, there are a number of natural products that are reported to modulate autophagy, and here we describe a number of them that activate autophagy through diverse molecular and cellular mechanisms. Among these, Urolithin A, Spermidine, Resveratrol, Fatty Acids and Phospholipids, Trehalose and Lithium are featured in detail. Finally, we outline possible strategies to optimise and increase the translatability of natural products, with the overall aim of delaying the ageing process and improving human healthspan.

The relationships of vitamin D, vitamin D receptor gene polymorphisms, and vitamin D supplementation with Parkinson's disease

In recent years, many studies have investigated the correlations between Parkinson's disease (PD) and vitamin D status, but the conclusion remains elusive. The present review focuses on the associations between PD and serum vitamin D levels by reviewing studies on the associations of PD with serum vitamin D levels and vitamin D receptor (VDR) gene polymorphisms from PubMed, Web of Science, Cochrane Library, and Embase databases. We found that PD patients have lower vitamin D levels than healthy controls and that the vitamin D concentrations are negatively correlated with PD risk and severity. Furthermore, higher vitamin D concentrations are linked to better cognitive function and mood in PD patients. Findings on the relationship between VDR gene polymorphisms and the risk of PD are inconsistent, but the FokI (C/T) polymorphism is significantly linked with PD. The occurrence of FokI (C/T) gene polymorphism may influence the risk, severity, and cognitive ability of PD patients, while also possibly influencing the effect of Vitamin D3 supplementation in PD patients. In view of the neuroprotective effects of vitamin D and the close association between vitamin D and dopaminergic neurotransmission, interventional prospective studies on vitamin D supplementation in PD patients should be conducted in the future.

A systematic review and meta-analysis of the associations of vitamin D receptor genetic variants with two types of most common neurodegenerative disorders

BACKGROUND

Whether vitamin D receptor (VDR) genetic variants influence individual susceptibility to neurodegenerative disorders remains controversial.

AIMS

This meta-analysis was conducted to analyze correlations of VDR genetic variants with two types of most common neurodegenerative disorders, Parkinson's disease (PD) and Alzheimer's disease (AD).

METHODS

Systematic literature research of PubMed and Embase was performed to identify eligible articles. Q test and I² statistic were employed to decide whether pooled analyses would be performed with random-effect models (REMs) or fixed-effect models (FEMs). All statistical analyses were conducted with Review Manager.

RESULTS

Totally sixteen studies were enrolled for analyses. Among these eligible studies, ten studies were about PD (2356 cases and 2815 controls) and six studies were about AD (1256 cases and 1205 controls). Pooled overall analyses suggested that VDR rs7975232 (additive model: p = 0.03, OR = 1.19, 95% CI 1.01-1.39) and rs2228570 (recessive model: p < 0.008, OR = 1.26, 95% CI 1.06-1.50; allele model: p < 0.001, OR = 0.80, 95% CI 0.71-0.91) variants were significantly correlated with PD, and VDR rs731236 (dominant model: p = 0.003, OR = 0.70, 95% CI 0.56-0.89; additive model: p = 0.02, OR = 1.32, 95% CI 1.06-1.66; allele model: p = 0.02, OR = 0.82, 95% CI 0.69-0.96) variant was significantly correlated with AD. Further subgroup analyses by ethnicity revealed that the positive results were mainly driven by the Asians, whereas no significant associations were observed in Caucasians.

CONCLUSION

Our meta-analysis suggested that VDR rs7975232 and rs2228570 variants might serve as genetic biomarkers of PD, whereas VDR rs731236 variant might serve as a genetic biomarker of AD.

Benefits of Vitamins in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the elderly, which is clinically characterized by bradykinesia, resting tremor, abnormal posture balance, and hypermyotonia. Currently, the pathogenic mechanism of PD remains unclear. Numerous clinical studies as well as animal and cell experiments have found a certain relationship between the vitamin family and PD. The antioxidant properties of vitamins and their biological functions of regulating gene expression may be beneficial for the treatment of PD. Current clinical evidence indicates that proper supplementation of various vitamins can reduce the incidence of PD in the general population and improve the clinical symptoms of patients with PD; nevertheless, the safety of regular vitamin supplements still needs to be highlighted. Vitamin supplementation may be an effective adjuvant treatment for PD. In this review, we summarized the biological correlations between vitamins and PD as well as the underlying pathophysiological mechanisms. Additionally, we elaborated the therapeutic potentials of vitamins for PD.

Anodal transcranial direct current stimulation prevents methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity by modulating autophagy in an in vivo mouse model of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the accumulation of protein inclusions and the loss of dopaminergic neurons. Transcranial direct current stimulation (tDCS) is a non-invasive brain-stimulating technique that has demonstrated promising results in clinical studies of PD. Despite accumulating evidence indicating that tDCS exerts a protective effect, the mechanism underlying its activity remains unknown. In the present study, we first investigated the neuroprotective effect of tDCS in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mouse model and then evaluated the effect of tDCS on the autophagy pathway. tDCS improved behavioral alterations, increased tyrosine hydroxylase protein levels and suppressed α-synuclein protein levels in MPTP-treated mice. MPTP-treated mice subjected to tDCS also had lower levels of autophagy-related proteins, such as microtubule-associated protein 1 light chain 3 and AMP-activated protein kinase, and higher levels of mechanistic target of rapamycin and p62. In addition, the protein levels of phosphoinositide 3-kinase and brain-derived neurotrophic factor were higher, and the levels of unc-51-like kinase 1 were lower in MPTP-treated mice subjected to tDCS. Our findings suggest that tDCS protected against MPTP-induced PD in a mouse model by modulating autophagy.

Promoting the clearance of neurotoxic proteins in neurodegenerative disorders of ageing

Neurodegenerative disorders of ageing (NDAs) such as Alzheimer disease, Parkinson disease, frontotemporal dementia, Huntington disease and amyotrophic lateral sclerosis represent a major socio-economic challenge in view of their high prevalence yet poor treatment. They are often called 'proteinopathies' owing to the presence of misfolded and aggregated proteins that lose their physiological roles and acquire neurotoxic properties. One reason underlying the accumulation and spread of oligomeric forms of neurotoxic proteins is insufficient clearance by the autophagic-lysosomal network. Several other clearance pathways are also compromised in NDAs: chaperone-mediated autophagy, the ubiquitin-proteasome system, extracellular clearance by proteases and extrusion into the circulation via the blood-brain barrier and glymphatic system. This article focuses on emerging mechanisms for promoting the clearance of neurotoxic proteins, a strategy that may curtail the onset and slow the progression of NDAs.

Serum Response Factor Promotes Dopaminergic Neuron Survival via Activation of Beclin 1-Dependent Autophagy

Serum response factor (SRF), a transcription factor highly expressed in neurons, is involved in neuronal survival and the pathogenesis of some neurodegenerative disorders. The ablation of SRF renders the midbrain dopaminergic (DA) neurons vulnerable to 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-induced neurotoxicity, however, the underlying mechanisms remain poorly understood. Here, we report decreased SRF levels in the substantia nigra (SN) of rotenone-treated rats that was associated with the loss of tyrosine hydroxylase (TH)-positive neurons. SRF expression was also reduced in rotenone-treated PC12 cells in vitro. In addition, Srf knockdown augmented rotenone-induced toxicity in PC12 cells. In contrast, overexpression of Srf attenuated the cells' sensitivity to rotenone and alleviated rotenone-induced α-synuclein accumulation. The protective effect of SRF was abolished when the expression of autophagy-related proteins Beclin 1 and Atg5 was suppressed. These results suggested that SRF may promote DA neuron survival by regulating autophagy, and thus serves as a critical molecule in PD progression.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)2 D3 and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)2 D3 have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)2 D3 , will focus on the potential crosstalk between sphingolipids and 1,25(OH)2 D3 in neural cells.

Autophagy is involved in the pathogenesis of experimental autoimmune neuritis in rats

Recent studies have shown that autophagy is involved in peripheral nervous system disease. However, the role of autophagy in the pathogenesis of experimental autoimmune neuritis (EAN) remains unclear. Therefore, EAN was induced by a subcutaneous injection into both hind footpads of synthetic neuritogenic P2(57-81) peptide in male Lewis rats. The clinical evaluation was completed using a 10-point scale method. The histological alteration of sciatic nerves was analyzed by hematoxylin and eosin and luxol fast blue staining. The ultrastructure of sciatic nerves was analyzed by transmission electron microscopy. Expressions of beclin-1 and microtubule-associated protein light chain-3 (LC3) and p62/SQSTM1 were determined by western blot. 3-Methyladenine, the inhibitor of autophagy, was used in this research. Results showed that the clinical scores were significantly increased from day 6 to day 16 after immunization compared with the control group. Compared with the control group, the number of inflammatory cells and the histological score of sciatic nerves were significantly increased, expressions of beclin-1 and LC3-II and the ratio of LC3-II/LC3-I in the sciatic nerve were significantly increased, and the expression of p62 was significantly decreased in the EAN model group. Considerable double-membrane autophagosomes in axons and myelin sheaths of sciatic nerves were observed and the number of autophagosomes in axons and myelin sheaths of sciatic nerves in the EAN model group was obviously increased compared with the control group. 3-Methyladenine ameliorated the neurologic severity of EAN. Our results suggest that autophagy activity in nerve tissue of EAN rats is increased, which may be associated with the pathogenesis of EAN.

Effects of calcitriol on experimental spinal cord injury in rats

STUDY DESIGN

Experimental, controlled, animal study.

OBJECTIVES

To evaluate the effects of calcitriol on oxidative stress, apoptosis, autophagy and locomotor recovery in rats after spinal cord injury (SCI).

SETTING

China.

METHODS

Ninety female rats were randomly divided into three groups. Laminectomy only was performed in the control group. The SCI group received laminectomy as well as spinal cord compression injury. In the calcitriol group, SCI rats received an intraperitoneal injection of calcitriol (2 μg kg(-1)day(-1)). Oxidative stress was assessed by the tissue superoxide dismutase (SOD) activity and the contents of glutathione (GSH) and malondialdehyde (MDA). The extent of apoptosis was assessed by immunohistochemistry for C-caspase3, TUNEL staining and western blotting for C-caspase3, Bax and Bcl2. Transmission electron microscopy was used to examine autophagosomes in the injured spinal cord of calcitriol-treated rats. Autophagy was detected by western blotting for LC3-II, Beclin1 and p62. Histological changes were assessed by haematoxylin and eosin staining and Nissl staining. Functional recovery was reflected by the Basso, Beattie and Bresnahan locomotion rating scale and the inclined plane test.

RESULTS

With calcitriol treatment, oxidative stress was decreased, SOD activity and GSH content were increased and MDA content was decreased. Moreover, apoptosis was inhibited in the SCI plus calcitriol group. However, a higher level of autophagy was detected in the lesions of the calcitriol group compared with the SCI group. Histological damage and neuron loss after SCI were reduced in calcitriol-treated rats, and functional recovery was significantly promoted in the calcitriol group compared with controls.

CONCLUSIONS

Calcitriol promotes locomotor recovery after SCI by reducing oxidative stress and inhibiting apoptosis, as well as promoting autophagy.