ncRNAs and Their Impact on Dopaminergic Neurons: Autophagy Pathways in Parkinson's Disease

Parkinson's Disease (PD) is a complex neurological illness that causes severe motor and non-motor symptoms due to a gradual loss of dopaminergic neurons in the substantia nigra. The aetiology of PD is influenced by a variety of genetic, environmental, and cellular variables. One important aspect of this pathophysiology is autophagy, a crucial cellular homeostasis process that breaks down and recycles cytoplasmic components. Recent advances in genomic technologies have unravelled a significant impact of ncRNAs on the regulation of autophagy pathways, thereby implicating their roles in PD onset and progression. They are members of a family of RNAs that include miRNAs, circRNA and lncRNAs that have been shown to play novel pleiotropic functions in the pathogenesis of PD by modulating the expression of genes linked to autophagic activities and dopaminergic neuron survival. This review aims to integrate the current genetic paradigms with the therapeutic prospect of autophagy-associated ncRNAs in PD. By synthesizing the findings of recent genetic studies, we underscore the importance of ncRNAs in the regulation of autophagy, how they are dysregulated in PD, and how they represent novel dimensions for therapeutic intervention. The therapeutic promise of targeting ncRNAs in PD is discussed, including the barriers that need to be overcome and future directions that must be embraced to funnel these ncRNA molecules for the treatment and management of PD.

Review on the interactions between dopamine metabolites and α-Synuclein in causing Parkinson's disease

Parkinson's disease (PD) is characterized by an abnormal post-translational modifications (PTM) in amino acid sequence and aggregation of alpha-synuclein (α-Syn) protein. It is generally believed that dopamine (DA) metabolite in dopaminergic (DAergic) neurons promotes the aggregation of toxic α-Syn oligomers and protofibrils, whereas DA inhibits the formation of toxic fibers and even degrades the toxic fibers. Therefore, the study on interaction between DA metabolites and α-Syn oligomers is one of the current hot topics in neuroscience, because this effect may have direct relevance to the selective DAergic neuron loss in PD. Several mechanisms have been reported for DA metabolites induced α-Syn oligomers viz. i) The reactive oxygen species (ROS) released during the auto-oxidation or enzymatic oxidation of DA changes the structure of α-Syn by the oxidation of amino acid residue leading to misfolding, ii) The oxidized DA metabolites directly interact with α-Syn through covalent or non-covalent bonding leading to the formation of oligomers, iii) DA interacts with lipid or autophagy related proteins to decreases the degradation efficiency of α-Syn aggregates. However, there is no clear-cut mechanism proposed for the interaction between DA and α-Syn. However, it is believed that the lysine (Lys) side chain of α-Syn sequence is the initial trigger site for the oligomer formation. Herein, we review different chemical mechanism involved during the interaction of Lys side chain of α-Syn with DA metabolites such as dopamine-o-quinone (DAQ), dopamine-chrome (DAC), dopamine-aldehyde (DOPAL) and neuromelanin. This review also provides the promotive effect of divalent Cu²⁺ ions on DA metabolites induced α-Syn oligomers and its inhibition effect by antioxidant glutathione (GSH).

Dihydromyricetin ameliorates liver fibrosis via inhibition of hepatic stellate cells by inducing autophagy and natural killer cell-mediated killing effect

Background

This study investigated the mechanisms underlying the preventive effect of dihydromyricetin (DHM) against liver fibrosis involving hepatic stellate cells (HSCs) and hepatic natural killer (NK) cells.

Methods

A carbon tetrachloride (CCl₄)-induced liver fibrosis model was established in C57BL/6 mice to study the antifibrotic effect of DHM based on serum biochemical parameters, histological and immunofluorescence stainings, and the expression of several fibrosis-related markers. Based on the immunoregulatory role of DHM, the effect of DHM on NK cell activation ex vivo was evaluated by flow cytometry. Then, we investigated whether DHM-induced autophagy was involved in HSCs inactivation using enzyme-linked immunosorbent assays, transmission electron microscopy, and western blot analysis. Thereafter, the role of DHM in NK cell-mediated killing was studied by in vitro coculture of NK cells and HSCs, with subsequent analysis by flow cytometry. Finally, the mechanism by which DHM regulates NK cells was studied by western blot analysis.

Results

DHM ameliorated liver fibrosis in C57BL/6 mice, as characterized by decreased serum alanine transaminase and aspartate transaminase levels, decreased expressions of collagen I alpha 1 (CoL-1α1), collagen I alpha 2 (CoL-1α2), tissue inhibitor of metalloproteinases 1 (TIMP-1), α-smooth muscle actin (α-SMA) and desmin, as well as increased expression of matrix metalloproteinase 1 (MMP1). Interestingly, HSCs activation was significantly inhibited by DHM in vivo and in vitro. As expected, DHM also upregulated autophagy-related indicators in liver from CCl₄-treated mice. DHM also prevented TGF-β1-induced activation of HSCs in vitro by initiating autophagic flux. In contrast, the autophagy inhibitor 3-methyladenine markedly abolished the antifibrotic effect of DHM. Surprisingly, the frequency of activated intrahepatic NK cells was significantly elevated by DHM ex vivo. Furthermore, DHM enhanced NK cell-mediated killing of HSCs by increasing IFN-γ expression, which was abolished by an anti-IFN-γ neutralizing antibody. Mechanistically, DHM-induced IFN-γ expression was through AhR-NF-κB/STAT3 pathway in NK cells.

Conclusion

These results demonstrated that DHM can ameliorate the progression of liver fibrosis and inhibition of HSCs activation by inducing autophagy and enhancing NK cell-mediated killing through the AhR-NF-κB/STAT3-IFN-γ signaling pathway, providing new insights into the preventive role of DHM in liver fibrosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12986-021-00589-6.

Resveratrol attenuates endothelial oxidative injury by inducing autophagy via the activation of transcription factor EB

Background

Endothelial oxidative injury is a key event in the pathogenesis of atherosclerosis (AS). Resveratrol (RSV) attenuates the oxidative injury in human umbilical vein endothelial cells (HUVECs). Autophagy is critical for the RSV-induced protective effects. However, the exact underlying mechanisms haven’t been completely elucidated. Thus, we aimed to explore the role of autophagy of the anti-oxidation of RSV and the underlying mechanism in palmitic acid (PA)-stimulated HUVECs.

Methods

HUVECs were pretreated with 10 μM of RSV for 2 h and treated with 200 μM of PA for an additional 24 h. Cell viability, intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels were estimated with a microplate reader and confocal microscope. Autophagosomes were analyzed by transmission electron microscopy, while lysosomes by confocal microscopy. The expression of transcription factor EB (TFEB) and related genes were quantified by qRT-PCR assay. Furthermore, TFEB levels, autophagy, and lysosomes were examined by western blot assay.

Results

RSV pretreatment suppressed the PA-induced decline in cell viability and elevation in ROS and MDA levels in HUVECs. RSV pretreatment also increased LC3 production and P62 degradation while promoted the autophagosomes formation. However, 3-methyladenine (3-MA) treatment attenuated RSV-induced autophagy. RSV pretreatment upregulated the TFEB and TFEB-modulated downstream genes expression in a concentration-dependent manner. Additionally, in cells transfected with TFEB small interfering RNA, RSV-induced TFEB expression and subsequent autophagy were abolished. Meanwhile, the TFEB-modulated genes expression, the lysosomes formation and the RSV-induced anti-oxidation were suppressed.

Conclusions

In HUVECs, RSV attenuates endothelial oxidative injury by inducing autophagy in a TFEB-dependent manner.

Recent advances in the mechanisms of neuroinflammation and their roles in neurodegeneration

Neuroinflammation is associated with the pathogenesis of many neurological disorders including Parkinson's disease, Alzheimer's disease, Amyotrophic lateral sclerosis and Huntington disease. Current studies in this area have advanced the mechanism of neuroinflammation and its role in neurodegeneration. Studies from epidemiologic, clinical and animal models also contributed in the various new mechanisms of neuroinflammation. In this line, activation of monocytes is an important emerging mechanism that has a, profound role in neuroinflammation and neurodegeneration. Ion channels, matrix metalloproteases and microRNAs are also found to be the key players in the pathogenesis of neuroinflammation. In particular, microRNA-32 regulates microglia-mediated neuroinflammation and thus neurodegeneration. Notably, some important studies describe the role of Th17 cells in neuroinflammation, but, very little knowledge is available about their mechanism of action. Particularly, the role of autophagy gets emphasized, which plays a very critical role in protein aggregation and neurodegeneration. In this review, we highlight and discuss the mechanisms of these mediators of inflammation by which they contribute to the disease progression. In conclusion, we focus on the various newer molecular mechanisms that are associated with the basic understanding of neuroinflammation in neurodegeneration.

Imaging Lysosomal pH Alteration in Stressed Cells with a Sensitive Ratiometric Fluorescence Sensor

The organelle-specific pH is crucial for cell homeostasis. Aberrant pH of lysosomes has been manifested in myriad diseases. To probe lysosome responses to cell stress, we herein report the detection of lysosomal pH changes with a dual colored probe (CM-ROX), featuring a coumarin domain with "always-on" blue fluorescence and a rhodamine-lactam domain activatable to lysosomal acidity to give red fluorescence. With sensitive ratiometric signals upon subtle pH changes, CM-ROX enables discernment of lysosomal pH changes in cells undergoing autophagy, cell death, and viral infection.

Substance P prevents 1-methyl-4-phenylpyridinium-induced cytotoxicity through inhibition of apoptosis via neurokinin-1 receptors in MES23.5 cells

[Sar9, Met(O2)11] termed Substance P (SP), is an effective and selective agonist for the neurokinin‑1 (NK‑1) receptors, which are synthetic peptides, similar in structure to SP. SP is an important neurotransmitter or neuromodulator mediated by neurokinin receptors, namely the SP receptor in the central nervous system. The excitatory effects induced by SP may be selectively inhibited by a neurokinin‑1 receptor antagonist, such as SR140333B. It has been proposed that Parkinson's disease (PD) is primarily caused by the loss of trophic peptidergic neurotransmitter, possibly SP, which may lead to the degeneration of neurons. In previous studies, 1‑methyl‑4‑phenylpyridinium (MPP+) has been frequently utilized to establish animal or cell models of PD. In the present study, to further investigate the effects of SP in PD, MPP+ was employed to investigate the promising anti‑apoptotic effects of SP, and examine the underlying mechanisms of the pathology in the MES23.5 dopaminergic cell line. The results indicated that MPP+‑triggered apoptosis was prevented by treatment with SP. SP treatment also decreased the MPP+‑triggered Ca2+ influx, caspase‑3 re‑activity, reactive oxygen species production and mitochondrial membrane potential decrease. Treatment with MPP+ also induced phosphorylation of c‑Jun N‑terminal kinase and p38 mitogen‑activated protein kinase. In addition, treatment with SP inhibited the MPP+‑triggered neurotoxicity in MES23.5 cells. However, no changes were observed in SR140333B+SP+MPP+‑treated MES23.5 cell lines. In conclusion, SP could protect the cells from MPP+‑induced cytotoxicity by inhibiting the apoptosis via NK-1 receptors.

Chaperone-mediated autophagy and neurodegeneration: connections, mechanisms, and therapeutic implications

Lysosomes degrade dysfunctional intracellular components via three pathways: macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). Unlike the other two, CMA degrades cytosolic proteins with a recognized KFERQ-like motif in lysosomes and is important for cellular homeostasis. CMA activity declines with age and is altered in neurodegenerative diseases. Its impairment leads to the accumulation of aggregated proteins, some of which may be directly tied to the pathogenic processes of neurodegenerative diseases. Its induction may accelerate the clearance of pathogenic proteins and promote cell survival, representing a potential therapeutic approach for the treatment of neurodegenerative diseases. In this review, we summarize the current findings on how CMA is involved in neurodegenerative diseases, especially in Parkinson's disease.

Resveratrol attenuates vascular endothelial inflammation by inducing autophagy through the cAMP signaling pathway

Inflammation participates centrally in all stages of atherosclerosis (AS), which begins with inflammatory changes in the endothelium, characterized by expression of the adhesion molecules. Resveratrol (RSV) is a naturally occurring phytoalexin that can attenuate endothelial inflammation; however, the exact mechanisms have not been thoroughly elucidated. Autophagy refers to the normal process of cell degradation of proteins and organelles, and is protective against certain inflammatory injuries. Thus, we intended to determine the role of autophagy in the antiinflammatory effects of RSV in human umbilical vein endothelial cells (HUVECs). We found that RSV pretreatment reduced tumor necrosis factor ? (TNF/TNF?)-induced inflammation and increased MAP1LC3B2 (microtubule-associated protein 1 light chain 3 ? 2) expression and SQSTM1/p62 (sequestosome 1) degradation in a concentration-dependent manner. A bafilomycin A 1 (BafA1) challenge resulted in further accumulation of MAP1LC3B2 in HUVECs. Furthermore, autophagy inhibitors 3-methyladenine (3-MA), chloroquine as well as ATG5 and BECN1 siRNA significantly attenuated RSV-induced autophagy, which, subsequently, suppressed the downregulation of RSV-induced inflammatory factors expression. RSV also increased cAMP (cyclic adenosine monophosphate) content, the expression of PRKA (protein kinase A) and SIRT1 (sirtuin 1), as well as the activity of AMPK (AMP-activated protein kinase). RSV-induced autophagy in HUVECs was abolished in the presence of inhibitors of ADCY (adenylyl cyclase, KH7), PRKA (H-89), AMPK (compound C), or SIRT1 (nicotinamide and EX-527), as well as ADCY, PRKA, AMPK, and SIRT1 siRNA transfection, indicating that the effects of RSV on autophagy induction were dependent on cAMP, PRKA, AMPK and SIRT1. In conclusion, RSV attenuates endothelial inflammation by inducing autophagy, and the autophagy in part was mediated through the activation of the cAMP-PRKA-AMPK-SIRT1 signaling pathway.

Resveratrol-activated AMPK/SIRT1/autophagy in cellular models of Parkinson's disease

Excessive misfolded proteins and/or dysfunctional mitochondria, which may cause energy deficiency, have been implicated in the etiopathogenesis of Parkinson's disease (PD). Enhanced clearance of misfolded proteins or injured mitochondria via autophagy has been reported to have neuroprotective roles in PD models. The fact that resveratrol is a known compound with multiple beneficial effects similar to those associated with energy metabolism led us to explore whether neuroprotective effects of resveratrol are related to its role in autophagy regulation. We tested whether modulation of mammalian silent information regulator 2 (SIRT1) and/or metabolic energy sensor AMP-activated protein kinase (AMPK) are involved in autophagy induction by resveratrol, leading to neuronal survival. Our results showed that resveratrol protected against rotenone-induced apoptosis in SH-SY5Y cells and enhanced degradation of α-synucleins in α-synuclein-expressing PC12 cell lines via autophagy induction. We found that suppression of AMPK and/or SIRT1 caused decrease of protein level of LC3-II, indicating that AMPK and/or SIRT1 are required in resveratrol-mediated autophagy induction. Moreover, suppression of AMPK caused inhibition of SIRT1 activity and attenuated protective effects of resveratrol on rotenone-induced apoptosis, further suggesting that AMPK-SIRT1-autophagy pathway plays an important role in the neuroprotection by resveratrol on PD cellular models.

Differential effects of rapamycin on rods and cones during light-induced stress in albino mice

PURPOSE

Autophagy is a lysosomal machinery-dependent process that catabolizes cellular components/organelles and proteins in an autophagic vacuole (AV)-dependent and -independent manner, respectively. Short-term exposure of the retina to bright light results in shortening of the outer segments, concomitant with AV formation. Autophagy is also induced by continuous long-term light damage, leading to photoreceptor cell death. Here the authors examined two questions: is autophagy induced during light damage proapoptotic or antiapoptotic, and are rods and cones affected differently? To this end, Balb/c mice exposed to light damage were treated with rapamycin to increase autophagy.

METHODS

Balb/c and GFP-LC3 mice were treated with rapamycin/vehicle. Photoreceptor degeneration was induced by 10-day light damage. Autophagy was documented by histologic, biochemical, and molecular tools; rod and cone survival was assessed by histology and electroretinography.

RESULTS

Light damage resulted in rod, but not cone, cell loss. Autophagy and AV formation was elicited in response to light damage, which was amplified by rapamycin. Rapamycin treatment significantly improved rod survival and function, reduced apoptosis, and normalized cytokine production that was increased in light damage. However, AV formation in GFP-LC3 mice revealed that light damage or rapamycin treatment induced AVs in cones, concomitant with reduced cone-mediated electroretinograms.

CONCLUSIONS

Systemic rapamycin treatment provided rod protection; however, AV formation was induced only in cones. Thus, rapamycin may act differentially in stressed photoreceptors; rapamycin might protect rods by normalizing cytokine production, removing damaged proteins by AV-independent autophagy, or both, whereas cones might be protected by AV-dependent autophagy, possibly involving reduced photon capture.

Mitochondrial dynamics, cell death and the pathogenesis of Parkinson's disease

The structure and function of the mitochondrial network is regulated by mitochondrial biogenesis, fission, fusion, transport and degradation. A well-maintained balance of these processes (mitochondrial dynamics) is essential for neuronal signaling, plasticity and transmitter release. Core proteins of the mitochondrial dynamics machinery play important roles in the regulation of apoptosis, and mutations or abnormal expression of these factors are associated with inherited and age-dependent neurodegenerative disorders. In Parkinson's disease (PD), oxidative stress and mitochondrial dysfunction underlie the development of neuropathology. The recessive Parkinsonism-linked genes PTEN-induced kinase 1 (PINK1) and Parkin maintain mitochondrial integrity by regulating diverse aspects of mitochondrial function, including membrane potential, calcium homeostasis, cristae structure, respiratory activity, and mtDNA integrity. In addition, Parkin is crucial for autophagy-dependent clearance of dysfunctional mitochondria. In the absence of PINK1 or Parkin, cells often develop fragmented mitochondria. Whereas excessive fission may cause apoptosis, coordinated induction of fission and autophagy is believed to facilitate the removal of damaged mitochondria through mitophagy, and has been observed in some types of cells. Compensatory mechanisms may also occur in mice lacking PINK1 that, in contrast to cells and Drosophila, have only mild mitochondrial dysfunction and lack dopaminergic neuron loss. A better understanding of the relationship between the specific changes in mitochondrial dynamics/turnover and cell death will be instrumental to identify potentially neuroprotective pathways steering PINK1-deficient cells towards survival. Such pathways may be manipulated in the future by specific drugs to treat PD and perhaps other neurodegenerative disorders characterized by abnormal mitochondrial function and dynamics.

LRRK2 signaling pathways: the key to unlocking neurodegeneration?

Mutations in PARK8, encoding leucine-rich repeat kinase 2 (LRRK2), are a major cause of Parkinson's disease. We contrast data suggesting that changes in LRRK2 activity cause alterations in mitogen-activated protein kinase, translational control, tumor necrosis factor α/Fas ligand and Wnt signaling pathways with the cell biological functions of LRRK2 such as vesicle trafficking. Despite scarce in vivo data on cell signaling, involvement in diverse cell biological functions suggests a role for LRRK2 as an upstream regulator in events leading to neurodegeneration. To stimulate discussion and give direction for future research, we further suggest that despite the importance of the catalytic activity for cytotoxicity, the main cellular function of LRRK2 is linked to assembly of signaling complexes.

A new perspective in Parkinson's disease, chaperone-mediated autophagy

Parkinson's disease (PD) is an age-related neurodegenerative disease characterized by loss of dopaminergic neurons and aggregation of alpha-synuclein. Although the role of alpha-synuclein in the pathology of PD is still unclear, the fact that its aggregation contributes to the loss of dopaminergic neurons has been confirmed. Therefore, controlling the alpha-synuclein protein level may be critical for PD pathogenesis and may provide potential therapeutics. Wild-type alpha-synuclein is physiologically degraded by chaperone-mediated autophagy (CMA), and dysfunction of CMA results in alpha-synuclein aggregation and compensative macroautophagy activation which finally leads to cell death. Therefore, CMA may participate in PD pathogenesis as a very important factor, and up-regulating CMA activity could degrade overloaded alpha-synuclein. In view of potential compensative effects, maintenance of the balance of CMA activity will be another major challenge in the future development of the therapeutic strategy. Herein we review the current knowledge of the role of CMA in PD.

Apoptosis-inducing factor mediates dopaminergic cell death in response to LPS-induced inflammatory stimulus: evidence in Parkinson's disease patients

We show that intranigral lipopolysaccharide (LPS) injection, which provokes specific degeneration of DA neurons, induced caspase-3 activation in the rat ventral mesencephalon, which was mostly associated with glial cells. In contrast, nigral DA neurons exhibited AIF nuclear translocation in response to LPS. A significant decrease of the Bcl-2/Bax ratio in nigral tissue after LPS injection was observed. We next developed an in vitro co-culture system with the microglial BV2 and the DA neuronal MN9D murine cell lines. The silencing of caspase-3 or AIF by small interfering RNAs exclusively in the DA MN9D cells demonstrated the key role of AIF in the LPS-induced death of DA cells. In vivo chemical inhibition of caspases and poly(ADP-ribose)polymerase-1, an upstream regulator of AIF release and calpain, proved the central role of the AIF-dependent pathway in LPS-induced nigral DA cell death. We also observed nuclear translocation of AIF in the ventral mesencephalon of Parkinson's disease subjects.

The mechanism for the neuroprotective effect of melatonin against methamphetamine-induced autophagy

Methamphetamine (METH) is a common drug of abuse that induces toxicity in the central nervous system and is connected to neurological disorders such as Parkinson's disease. METH neurotoxicity is induced by reactive oxygen species (ROS) production and apoptosis. Moreover, autophagy is an alternative to cell death and a means for eliminating dysfunctional organelles. In other cases, autophagy can end up in cell death. Nonetheless, it is not clear whether autophagy is also correlated with apoptotic signaling in drug-induced neurotoxicity. Therefore, we hypothesized that METH-generated toxicity associated with initiating the apoptotic signaling cascade can also increase the autophagic phenotype in neuronal cells. Using the SK-N-SH dopaminergic cell line as our model system, we found that METH-induced autophagy by inhibiting dissociation of Bcl-2/Beclin 1 complex and its upstream pathway that thereby led to cell death. We uncovered a novel function for the anti-apoptotic protein Bcl-2, as it played a role in negatively regulating autophagy by blocking an essential protein in the signaling pathway, Beclin 1. Furthermore, Bcl-2 was activated by c-Jun N-terminal kinase 1 (JNK 1), which is upstream of Bcl-2 phosphorylation, to induce Bcl-2/Beclin 1 dissociation. Furthermore, we demonstrated a novel role for melatonin in protecting cells from autophagic cell death triggered by the Bcl-2/Beclin 1 pathway by inhibiting the activation of the JNK 1, Bcl-2 upstream pathway. This study provides information regarding the link between apoptosis and autophagy signaling, which could lead to the development of therapeutic strategies that exploit the neurotoxicity of drugs of abuse.

Chaperone-mediated autophagy: machinery, regulation and biological consequences

Degradation of dysfunctional intracellular components in the lysosome system can occur through three different pathways, i.e., macroautophagy, microautophagy and chaperone-mediated autophagy (CMA). In this review, we focus on CMA, a type of autophagy distinct from the other two autophagic pathways owing to its selectivity, saturability and competitivity by which a subset of long-lived cytosolic soluble proteins are directly delivered into the lysosomal lumen via specific receptors. CMA participates in quality control to maintain normal cell functions by clearing "old" proteins and provides energy to cells under nutritional stress. Deregulation of CMA has recently been shown to underlie some diseases, especially neurodegenerative disorders for which the decline with age in the activity of CMA may become a major aggravating factor. Therefore, targeting aberrant alteration in CMA under pathological conditions could serve as a potential therapeutic strategy for treating related diseases.