Chronic cerebral hypoperfusion in rats causes proteasome dysfunction and aggregation of ubiquitinated proteins

miR-30a-5p mediates ferroptosis of hippocampal neurons in chronic cerebral hypoperfusion-induced cognitive dysfunction by modulating the SIRT1/NRF2 pathway

OBJECTIVE

Chronic cerebral hypoperfusion (CCH) is a common cause of brain dysfunction. As a microRNA (also known as miRNAs or miRs), miR-30a-5p participates in neuronal damage and relates to ferroptosis. We explored the in vivo and in vitro effects and functional mechanism of miR-30a-5p in CCH-triggered cognitive impairment through the silent information regulator 1 (SIRT1)/nuclear factor erythroid 2-related factor 2 (NRF2) pathway.

METHODS

After 1 month of CCH modeling through bilateral common carotid artery stenosis, mice were injected with 2 μL antagomir (also known as anti-miRNAs) miR-30a-5p, with cognitive function evaluated by Morris water maze and novel object recognition tests. In vitro HT-22 cell oxygen glucose deprivation (OGD) model was established, followed by miR-30a-5p inhibitor and/or si-SIRT1 transfections, with Fe2+ concentration, malonaldehyde (MDA) and glutathione (GSH) contents, reactive oxygen species (ROS), miR-30a-5p and SIRT1 and glutathione peroxidase 4 (GPX4) protein levels, NRF2 nuclear translocation, and miR-30a-5p-SIRT1 targeting relationship assessed.

RESULTS

CCH-induced mice showed obvious cognitive impairment, up-regulated miR-30a-5p, and down-regulated SIRT1. Ferroptosis occurred in hippocampal neurons, manifested by elevated Fe2+ concentration and ROS and MDA levels, mitochondrial atrophy, and diminished GSH content. Antagomir miR-30a-5p or miR-30a-5p inhibitor promoted SIRT1 expression and NRF2 nuclear translocation, increased GPX4, cell viability and GSH content, and reduced Fe2+ concentration and ROS and MDA levels. miR-30a-5p negatively regulated SIRT1. In vitro, miR-30a-5p knockout increased NRF2 nuclear translocation by up-regulating SIRT1, inhibiting OGD-induced ferroptosis in HT-22 cells.

CONCLUSION

miR-30a-5p induces hippocampal neuronal ferroptosis and exacerbates post-CCH cognitive dysfunction by targeting SIRT1 and reducing NRF2 nuclear translocation.

Chronic Cerebral Hypoperfusion-Induced Disturbed Proteostasis of Mitochondria and MAM Is Reflected in the CSF of Rats by Proteomic Analysis

Declining cerebral blood flow leads to chronic cerebral hypoperfusion which can induce neurodegenerative disorders, such as vascular dementia. The reduced energy supply of the brain impairs mitochondrial functions that could trigger further damaging cellular processes. We carried out stepwise bilateral common carotid occlusions on rats and investigated long-term mitochondrial, mitochondria-associated membrane (MAM), and cerebrospinal fluid (CSF) proteome changes. Samples were studied by gel-based and mass spectrometry-based proteomic analyses. We found 19, 35, and 12 significantly altered proteins in the mitochondria, MAM, and CSF, respectively. Most of the changed proteins were involved in protein turnover and import in all three sample types. We confirmed decreased levels of proteins involved in protein folding and amino acid catabolism, such as P4hb and Hibadh in the mitochondria by western blot. We detected reduced levels of several components of protein synthesis and degradation in the CSF as well as in the subcellular fractions, implying that hypoperfusion-induced altered protein turnover of brain tissue can be detected in the CSF by proteomic analysis.

Ambiguous Effects of Autophagy Activation Following Hypoperfusion/Ischemia

Autophagy primarily works to counteract nutrient deprivation that is strongly engaged during starvation and hypoxia, which happens in hypoperfusion. Nonetheless, autophagy is slightly active even in baseline conditions, when it is useful to remove aged proteins and organelles. This is critical when the mitochondria and/or proteins are damaged by toxic stimuli. In the present review, we discuss to that extent the recruitment of autophagy is beneficial in counteracting brain hypoperfusion or, vice-versa, its overactivity may per se be detrimental for cell survival. While analyzing these opposite effects, it turns out that the autophagy activity is likely not to be simply good or bad for cell survival, but its role varies depending on the timing and amount of autophagy activation. This calls for the need for an appropriate autophagy tuning to guarantee a beneficial effect on cell survival. Therefore, the present article draws a theoretical pattern of autophagy activation, which is hypothesized to define the appropriate timing and intensity, which should mirrors the duration and severity of brain hypoperfusion. The need for a fine tuning of the autophagy activation may explain why confounding outcomes occur when autophagy is studied using a rather simplistic approach.

Inhibition of excessive autophagy and mitophagy mediates neuroprotective effects of URB597 against chronic cerebral hypoperfusion

URB597 (URB) has therapeutic potential for treating chronic cerebral hypoperfusion (CCH)-induced neuronal death. The present study investigated the protective effects of URB on autopahgy and mitophagy in a CCH model as well as the underlying mechanisms. The ultrastructural changes were examined by electron microscopy. The mitochondrial membrane potential was assessed by immunofluorescence. The expressions of autophagy-related proteins (beclin-1, p62, and LC3), lysosome-related proteins (CTSD and LAMP1), and mitophagy-related proteins (BNIP3, cyt C and parkin) were evaluated by western blotting, and the interaction of beclin-1 and Bcl-2 were determined by immunoprecipitation. CCH significantly decreased the protein expression of p62, CTSD, and LAMP1 and increased the protein expression of beclin-1, parkin, and BNIP3, the LC3-II to LC3-I ratio, and the release of cyt C from mitochondria to cytoplasm. Furthermore, CCH induced the accumulation of ubiquitinated proteins in PSDs. However, URB significantly reversed these results. Besides, URB significantly inhibited the beclin-1 from beclin-1/Bcl-2 complex to whole-cell lysates. The above results indicate that URB could inhibit impaired autophagy degradation and the disruption of beclin-1/Bcl-2 complex and subsequently cut off BNIP3-cyt C- and parkin-required mitophagy, finally preventing the abnormal excessive autophagy and mitophagy. These findings provide new insights that URB is a promising agent for therapeutic management of CCH.

Neuroprotection Targeting Protein Misfolding on Chronic Cerebral Hypoperfusion in the Context of Metabolic Syndrome

Metabolic syndrome (MetS) is a cluster of risk factors that lead to microvascular dysfunction and chronic cerebral hypoperfusion (CCH). Long-standing reduction in oxygen and energy supply leads to brain hypoxia and protein misfolding, thereby linking CCH to Alzheimer's disease. Protein misfolding results in neurodegeneration as revealed by studying different experimental models of CCH. Regulating proteostasis network through pathways like the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), chaperone-mediated autophagy (CMA), and macroautophagy emerges as a novel target for neuroprotection. Lipoxin A4 methyl ester, baclofen, URB597, N-stearoyl-L-tyrosine, and melatonin may pose potential neuroprotective agents for rebalancing the proteostasis network under CCH. Autophagy is one of the most studied pathways of proteostatic cell response against the decrease in blood supply to the brain though the role of the UPR-specific chaperones and the UPS system in CCH deserves further research. Pharmacotherapy targeting misfolded proteins at different stages in the proteostatic pathway might be promising in treating cognitive impairment following CCH.

Transport of c-MYC by Kinesin-1 for proteasomal degradation in the cytoplasm

c-MYC is an oncogenic transcription factor that is degraded by the proteasome pathway. However, the mechanism that regulates delivery of c-MYC to the proteasome for degradation is not well characterized. Here, the results show that the motor protein complex Kinesin-1 transports c-MYC to the cytoplasm for proteasomal degradation. Inhibition of Kinesin-1 function enhanced ubiquitination of c-MYC and induced aggregation of c-MYC in the cytoplasm. Transport studies showed that the c-MYC aggregates moved from the nucleus to the cytoplasm and KIF5B is responsible for the transport in the cytoplasm. Furthermore, inhibition of the proteasomal degradation process also resulted in an accumulation of c-MYC aggregates in the cytoplasm. Moreover, Kinesin-1 was shown to interact with c-MYC and the proteasome subunit S6a. Inhibition of Kinesin-1 function also reduced c-MYC-dependent transformation activities. Taken together, the results strongly suggest that Kinesin-1 transports c-MYC for proteasomal degradation in the cytoplasm and the proper degradation of c-MYC mediated by Kinesin-1 transport is important for transformation activities of c-MYC. In addition, the results indicate that Kinesin-1 transport mechanism is important for degradation of a number of other proteins as well.

Effects of N-stearoyl-L-tyrosine on the hippocampal ubiquitin-proteasome system in rats with chronic cerebral hypoperfusion

OBJECTIVES

Chronic cerebral hypoperfusion (CCH) leads to neurodegeneration and cognitive impairment. Ubiquitinated protein aggregates are commonly present in neurodegenerative disorders and are believed to cause neuronal degeneration. Here, we investigated the effects of N-stearoyl-L-tyrosine (NSTyr) on the hippocampal ubiquitin-proteasome system (UPS) in rats with CCH.

METHODS

After induction of CCH, NSTyr was intraperitoneally administered daily for 3 months. Protein aggregation was analyzed by ethanolic phosphotungstic acid (EPTA) electron microscopy (EM), immunogold EM, laser-scanning confocal microscopy, and Western blot. Proteasome peptidase activity was measured by peptidase activity assays.

RESULTS

By using EPTA EM, immunogold EM and high-resolution laser-scanning confocal microscopy, we found that CCH resulted in the accumulation of ubiquitinated protein aggregates in rat hippocampal CA1 neurons. Western blot revealed that the levels of free ubiquitin were significantly reduced and that the levels of ubiquitinated proteins were markedly increased in the hippocampus of CCH rats. Direct activity measurements demonstrated that proteasome peptidase activity in the hippocampal region of rats was decreased after CCH induction. In the hippocampal tissue of CCH rats treated with NSTyr, however, ubiquitinated protein aggregates decreased and proteasome peptidase activity increased.

DISCUSSION

These data indicate that NSTyr may exert protective effects on rat hippocampal UPS function via endogenous regulation.

Cognitive and MRI correlates of orthostatic hypotension in Parkinson's disease

Orthostatic hypotension (OH) is a frequent nonmotor feature of Parkinson's disease (PD), and its occurrence has been associated with cognitive impairment. The underlying mechanism could be mediated by development of cerebrovascular disease induced by chronic or episodic hypoperfusion, but the extent of brain vascular load in PD patients with OH has never been investigated. This study aimed to assess the relationship between OH and cognitive function in PD patients and to investigate the contribution of brain vascular lesions. Forty-eight PD patients underwent a tilt table test (TT) to assess supine and orthostatic blood pressure as well as an extensive neuropsychological evaluation to evaluate cognitive function. Brain magnetic resonance imaging was acquired in 44/48 patients and analyzed by a visual semiquantitative scale. Twenty-three patients presented OH at TT (13/23 were symptomatic), and 25 did not. There were no differences in motor severity or disease duration between patients with and without OH. In patients with OH we found significantly worse cognitive performance in specific tasks, such as sustained attention, visuospatial and verbal memory, compared with patients without OH. However, there were no differences in vascular burden between the two groups. Our study confirms that there is an association between OH and selective cognitive deficits in PD, but rebuts the hypothesis that this is underlined by the development of cerebrovascular disease.