Aβ1-42 oligomer induces alteration of tight junction scaffold proteins via RAGE-mediated autophagy in bEnd.3 cells

Blood-brain barrier biomarkers

The blood-brain barrier (BBB) is a dynamic interface that regulates the exchange of molecules and cells between the brain parenchyma and the peripheral blood. The BBB is mainly composed of endothelial cells, astrocytes and pericytes. The integrity of this structure is essential for maintaining brain and spinal cord homeostasis and protection from injury or disease. However, in various neurological disorders, such as traumatic brain injury, Alzheimer's disease, and multiple sclerosis, the BBB can become compromised thus allowing passage of molecules and cells in and out of the central nervous system parenchyma. These agents, however, can serve as biomarkers of BBB permeability and neuronal damage, and provide valuable information for diagnosis, prognosis and treatment. Herein, we provide an overview of the BBB and changes due to aging, and summarize current knowledge on biomarkers of BBB disruption and neurodegeneration, including permeability, cellular, molecular and imaging biomarkers. We also discuss the challenges and opportunities for developing a biomarker toolkit that can reliably assess the BBB in physiologic and pathophysiologic states.

T cell infiltration mediates neurodegeneration and cognitive decline in Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with pathological features of β-amyloid (Aβ) and hyperphosphorylated tau protein accumulation in the brain, often accompanied by cognitive decline. So far, our understanding of the extent and role of adaptive immune responses in AD has been quite limited. T cells, as essential members of the adaptive immune system, exhibit quantitative and functional abnormalities in the brains of AD patients. Dysfunction of the blood-brain barrier (BBB) in AD is considered one of the factors leading to T cell infiltration. Moreover, the degree of neuronal loss in AD is correlated with the quantity of T cells. We first describe the differentiation and subset functions of peripheral T cells in AD patients and provide an overview of the key findings related to BBB dysfunction and how T cells infiltrate the brain parenchyma through the BBB. Furthermore, we emphasize the risk factors associated with AD, including Aβ, Tau protein, microglial cells, apolipoprotein E (ApoE), and neuroinflammation. We discuss their regulation of T cell activation and proliferation, as well as the connection between T cells, neurodegeneration, and cognitive decline. Understanding the innate immune response is crucial for providing comprehensive personalized therapeutic strategies for AD.

Amyloid β oligomer induces cerebral vasculopathy via pericyte-mediated endothelial dysfunction

BACKGROUND

Although abnormal accumulation of amyloid beta (Aβ) protein is thought to be the main cause of Alzheimer's disease (AD), emerging evidence suggests a pivotal vascular contribution to AD. Aberrant amyloid β induces neurovascular dysfunction, leading to changes in the morphology and function of the microvasculature. However, little is known about the underlying mechanisms between Aβ deposition and vascular injuries. Recent studies have revealed that pericytes play a substantial role in the vasculopathy of AD. Additional research is imperative to attain a more comprehensive understanding.

METHODS

Two-photon microscopy and laser speckle imaging were used to examine cerebrovascular dysfunction. Aβ oligomer stereotactic injection model was established to explain the relationship between Aβ and vasculopathy. Immunofluorescence staining, western blot, and real-time PCR were applied to detect the morphological and molecular alternations of pericytes. Primary cultured pericytes and bEnd.3 cells were employed to explore the underlying mechanisms.

RESULTS

Vasculopathy including BBB damage, hypoperfusion, and low vessel density were found in the cortex of 8 to 10-month-old 5xFAD mice. A similar phenomenon accompanied by pericyte degeneration appeared in an Aβ-injected model, suggesting a direct relationship between Aβ and vascular dysfunction. Pericytes showed impaired features including low PDGFRβ expression and increased pro-inflammatory chemokines secretion under the administration of Aβ in vitro, of which supernatant cultured with bEND.3 cells led to significant endothelial dysfunction characterized by TJ protein deficiency.

CONCLUSIONS

Our results provide new insights into the pathogenic mechanism underlying Aβ-induced vasculopathy. Targeting pericyte therapies are promising to ameliorate vascular dysfunction in AD.

Extracellular vesicles derived from monomeric α-synuclein-treated microglia ameliorate neuroinflammation by delivery of miRNAs targeting PRAK

Parkinson's disease (PD) is characterized by the formation of Lewy body, which mainly contains misfolded α-synuclein. Microglial activation plays a role in neurodegeneration. The pathologically oligomeric α-synuclein promotes inflammatory microglia, while physiologically monomeric α-synuclein induces anti-inflammatory microglia, the relationship between these two forms in activating microglia and the molecular mechanism is essentially unknown. In this study, using in vivo and in vitro models, we challenged primary or BV2 microglia with exogenous stimuli including α-synuclein. We examined microglial activation and the underlying mechanism by Western blot, RT-PCR, ELISA, IF, FCM, miRNA sequencing and bioinformatic analysis. Oligomeric α-synuclein activatedmicroglia via theinvolvement of the PRAK/MK5 pathway. The specific PRAK inhibitor GLPG0259 could mitigate microglial activation insulted by oligomeric α-synuclein. Monomeric α-synuclein regulated theanti-inflammatory microglia by delivering microglia-derived extracellular vesicles (EVs) in vitro and in vivo. Furthersequencingand bioinformatic analysis of microglial EVs-associated miRNAs indicatedthatmost of these miRNAs targeted PRAK. These results suggest that PRAK serves as an intersection in microglial activation when challenged with conformationally different α-synuclein. EVs derived from microglia treated with monomeric α-synuclein promote anti-inflammatory microglia by delivering miRNAs that target PRAK into recipient microglia.

Enterogenic Stenotrophomonas maltophilia migrates to the mammary gland to induce mastitis by activating the calcium-ROS-AMPK-mTOR-autophagy pathway

BACKGROUND

Mastitis is an inflammatory disease of the mammary gland that has serious economic impacts on the dairy industry and endangers food safety. Our previous study found that the body has a gut/rumen-mammary gland axis and that disturbance of the gut/rumen microbiota could result in 'gastroenterogenic mastitis'. However, the mechanism has not been fully clarified. Recently, we found that long-term feeding of a high-concentrate diet induced mastitis in dairy cows, and the abundance of Stenotrophomonas maltophilia (S. maltophilia) was significantly increased in both the rumen and milk microbiota. Accordingly, we hypothesized that 'gastroenterogenic mastitis' can be induced by the migration of endogenous gut bacteria to the mammary gland. Therefore, this study investigated the mechanism by which enterogenic S. maltophilia induces mastitis.

RESULTS

First, S. maltophilia was labelled with superfolder GFP and administered to mice via gavage. The results showed that treatment with S. maltophilia promoted the occurrence of mastitis and increased the permeability of the blood-milk barrier, leading to intestinal inflammation and intestinal leakage. Furthermore, tracking of ingested S. maltophilia revealed that S. maltophilia could migrate from the gut to the mammary gland and induce mastitis. Subsequently, mammary gland transcriptome analysis showed that the calcium and AMPK signalling pathways were significantly upregulated in mice treated with S. maltophilia. Then, using mouse mammary epithelial cells (MMECs), we verified that S. maltophilia induces mastitis through activation of the calcium-ROS-AMPK-mTOR-autophagy pathway.

CONCLUSIONS

In conclusion, the results showed that enterogenic S. maltophilia could migrate from the gut to the mammary gland via the gut-mammary axis and activate the calcium-ROS-AMPK-mTOR-autophagy pathway to induce mastitis. Targeting the gut-mammary gland axis may also be an effective method to treat mastitis.

Local perfusion of capillaries reveals disrupted beta-amyloid homeostasis at the blood-brain barrier in Tg2576 murine Alzheimer's model

BACKGROUND

Parenchymal accumulation of beta-amyloid (Aβ) characterizes Alzheimer's disease (AD). Aβ homeostasis is maintained by two ATP-binding cassette (ABC) transporters (ABCC1 and ABCB1) mediating efflux, and the receptor for advanced glycation end products (RAGE) mediating influx across the blood-brain barrier (BBB). Altered transporter levels and disruption of tight junctions (TJ) were linked to AD. However, Aβ transport and the activity of ABCC1, ABCB1 and RAGE as well as the functionality of TJ in AD are unclear.

METHODS

ISMICAP, a BBB model involving microperfusion of capillaries, was used to assess BBB properties in acute cortical brain slices from Tg2576 mice compared to wild-type (WT) controls using two-photon microscopy. TJ integrity was tested by vascularly perfusing biocytin-tetramethylrhodamine (TMR) and quantifying its extravascular diffusion as well as the diffusion of FM1-43 from luminal to abluminal membranes of endothelial cells (ECs). To assess ABCC1 and ABCB1 activity, calcein-AM was perfused, which is converted to fluorescent calcein in ECs and gets actively extruded by both transporters. To probe which transporter is involved, probenecid or Elacridar were applied, individually or combined, to block ABCC1 and ABCB1, respectively. To assess RAGE activity, the binding of 5-FAM-tagged Aβ by ECs was quantified with or without applying FPS-ZM1, a RAGE antagonist.

RESULTS

In Tg2576 mouse brain, extravascular TMR was 1.8-fold that in WT mice, indicating increased paracellular leakage. FM1-43 staining of abluminal membranes in Tg2576 capillaries was 1.7-fold that in WT mice, indicating reduced TJ integrity in AD. While calcein was undetectable in WT mice, its accumulation was significant in Tg2576 mice, suggesting lower calcein extrusion in AD. Incubation with probenecid or Elacridar in WT mice resulted in a marked calcein accumulation, yet probenecid alone had no effect in Tg2576 mice, implying the absence of probenecid-sensitive ABC transporters. In WT mice, Aβ accumulated along the luminal membranes, which was undetectable after applying FPS-ZM1. In contrast, marginal Aβ fluorescence was observed in Tg2576 vessels, and FPS-ZM1 was without effect, suggesting reduced RAGE binding activity.

CONCLUSIONS

Disrupted TJ integrity, reduced ABCC1 functionality and decreased RAGE binding were identified as BBB alterations in Tg2576 mice, with the latter finding challenging the current concepts. Our results suggest to manage AD by including modulation of TJ proteins and Aβ-RAGE binding.

Methylglyoxal, a highly reactive dicarbonyl compound, as a threat for blood brain barrier integrity

The brain is a highly metabolically active organ requiring a large amount of glucose. Methylglyoxal (MGO), a by-product of glucose metabolism, is known to be involved in microvascular dysfunction and is associated with reduced cognitive function. Maintenance of the blood-brain barrier (BBB) is essential to maintain optimal brain function and a large amount of evidence indicates negative effects of MGO on BBB integrity. In this review, we summarized the current literature on the effect of MGO on the different cell types forming the BBB. BBB damage by MGO most likely occurs in brain endothelial cells and mural cells, while astrocytes are most resistant to MGO. Microglia on the other hand appear to be not directly influenced by MGO but rather produce MGO upon activation. Although there is clear evidence that MGO affects components of the BBB, the impact of MGO on the BBB as a multicellular system warrants further investigation. Diminishing MGO stress can potentially form the basis for new treatment strategies for maintaining optimal brain function.

Overexpression of ACE2 ameliorates Aβ-induced blood-brain barrier damage and angiogenesis by inhibiting NF-κB/VEGF/VEGFR2 pathway

BACKGROUND

Pathological angiogenesis and blood-brain barrier damage may play an important role in Alzheimer's disease (AD). ACE2 is mainly expressed on the surface of endothelial cells in brain. Recent studies have shown that the expression of ACE2 in AD is reduced, but its role in AD is still unclear.

METHOD

We induced AD damage in endothelial cells using Aβ25-35 and overexpressed ACE2 in bEend.3 cells through lentiviral transfection. We detected the effect of Aβ25-35 on cell viability using the CCK-8 assay and examined the effect of overexpressing ACE2 on angiogenesis using an angiogenesis assay. We used western blot and cell immunofluorescence to detect changes in the expression of the VEGF/VEGFR2 pathway, tight junction protein, and NF-κB pathway.

RESULTS

Aβ25-35 treatment significantly decreased the expression of ACE2 and reduced cell viability. ACE2 overexpression (1) reduced the number of branches and junctions in tube formation, (2) inhibited the activation of the VEGF/VEGFR2 pathway induced by Aβ25-35 , (3) increased the expression of TJPs, including ZO-1 and claudin-5, and (4) restored Aβ25-35 -induced activation of the NF-κB pathway.

CONCLUSION

Overexpression of ACE2 can improve pathological angiogenesis and blood-brain barrier damage in AD models in vitro by inhibiting NF-κB/VEGF/VEGFR2 pathway activity. ACE2 may therefore represent a therapeutic target for endothelial cell dysfunction in AD.

Sulforaphane attenuates microglia-mediated neuronal damage by down-regulating the ROS/autophagy/NLRP3 signal axis in fibrillar Aβ-activated microglia

The neuroinflammatory hypothesis of Alzheimer's disease (AD) posits that amyloid-beta (Aβ) phagocytosis along with subsequent lysosomal damage and NLRP3 inflammasome activation plays important roles in Aβ-induced microglia activation and microglia-induced neurotoxicity. Sulforaphane (SFN) has neuroprotective effects for AD. However, whether SFN can inhibit its cytotoxic autophagy and NLRP3 inflammasome activation in microglia remain unknown. In this study, results showed SFN played an indirect, protective role on neurons via a series of impacts on Aβ-activated microglia, including inhibition of autophagy initiation as well as autophagic lysosomal membrane permeability and subsequent NLRP3/caspase-1 inflammasomes activation. M1 phenotype polarization was also inhibited. Our results demonstrated that SFN could inhibit the cytostatic autophagy-induced NLRP3 signaling pathway in Aβ-activated microglia by decreasing reactive oxygen species (ROS) production. These results provide novel insight into the potential role of SFN in AD therapy.

Impaired autophagy in amyloid-beta pathology: A traditional review of recent Alzheimer's research

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder. The major pathological changes in AD progression are the generation and accumulation of amyloid-beta (Aβ) peptides as well as the presence of abnormally hyperphosphorylated tau proteins in the brain. Autophagy is a conserved degradation pathway that eliminates abnormal protein aggregates and damaged organelles. Previous studies have suggested that autophagy plays a key role in the production and clearance of Aβ peptides to maintain a steady-state of Aβ peptides levels. However, a growing body of evidence suggests that autophagy is significantly impaired in the pathogenesis of AD, especially in Aβ metabolism. Therefore, this article reviews the latest studies concerning the mechanisms of autophagy, the metabolism of Aβ peptides, and the defective autophagy in the production and clearance of Aβ peptides. Here, we also summarize the established and new strategies for targeting autophagy in vivo and through clinical AD trials to identify gaps in our knowledge and to generate further questions.

Relative Importance of Different Elements of Mitochondrial Oxidative Phosphorylation in Maintaining the Barrier Integrity of Retinal Endothelial Cells: Implications for Vascular-Associated Retinal Diseases

PURPOSE

Mitochondrial dysfunction is central to breaking the barrier integrity of retinal endothelial cells (RECs) in various blinding eye diseases such as diabetic retinopathy and retinopathy of prematurity. Therefore, we aimed to investigate the role of different mitochondrial constituents, specifically those of oxidative phosphorylation (OxPhos), in maintaining the barrier function of RECs.

METHODS

Electric cell-substrate impedance sensing (ECIS) technology was used to assess in real time the role of different mitochondrial components in the total impedance (Z) of human RECs (HRECs) and its components: capacitance (C) and the total resistance (R). HRECs were treated with specific mitochondrial inhibitors that target different steps in OxPhos: rotenone for complex I, oligomycin for complex V (ATP synthase), and FCCP for uncoupling OxPhos. Furthermore, data were modeled to investigate the effects of these inhibitors on the three parameters that govern the total resistance of cells: Cell-cell interactions (R_b), cell-matrix interactions (α), and cell membrane permeability (Cm).

RESULTS

Rotenone (1 µM) produced the greatest reduction in Z, followed by FCCP (1 µM), whereas no reduction in Z was observed after oligomycin (1 µM) treatment. We then further deconvoluted the effects of these inhibitors on the R_b, α, and C_m parameters. Rotenone (1 µM) completely abolished the resistance contribution of R_b, as the R_b became zero immediately after the treatment. Secondly, FCCP (1 µM) eliminated the resistance contribution of R_b only after 2.5 h and increased C_m without a significant effect on α. Lastly, of all the inhibitors used, oligomycin had the lowest impact on R_b, as evidenced by the fact that this value became similar to that of the control group at the end of the experiment without noticeable effects on C_m or α.

CONCLUSION

Our study demonstrates the differential roles of complex I, complex V, and OxPhos coupling in maintaining the barrier functionality of HRECs. We specifically showed that complex I is the most important component in regulating HREC barrier integrity. These observed differences are significant since they could serve as the basis for future pharmacological and gene expression studies aiming to improve the activity of complex I and thereby provide avenues for therapeutic modalities in endothelial-associated retinal diseases.

Yi-Zhi-Fang-Dai Formula Exerts Neuroprotective Effects Against Pyroptosis and Blood-Brain Barrier-Glymphatic Dysfunctions to Prevent Amyloid-Beta Acute Accumulation After Cerebral Ischemia and Reperfusion in Rats

Background: The dysfunctional blood–brain barrier (BBB)–glymphatic system is responsible for triggering intracerebral amyloid-beta peptide (Aβ) accumulation and acts as the key link between ischemic stroke and dementia dominated by Alzheimer’s disease (AD). Recently, pyroptosis in cerebral ischemia and reperfusion (I/R) injury is demonstrated as a considerable mechanism causing BBB–glymphatic dysfunctions and Aβ acute accumulation in the brain. Targeting glial pyroptosis to protect BBB–glymphatic functions after cerebral I/R could offer a new viewpoint to prevent Aβ accumulation and poststroke dementia. Yi-Zhi-Fang-Dai formula (YZFDF) is an herbal prescription used to cure dementia with multiple effects of regulating inflammatory responses and protecting the BBB against toxic Aβ-induced damage. Hence, YZFDF potentially possesses neuroprotective effects against cerebral I/R injury and the early pathology of poststroke dementia, which evokes our current study.

Objectives: The present study was designed to confirm the potential efficacy of YZFDF against cerebral I/R injury and explore the possible mechanism associated with alleviating Aβ acute accumulation.

Methods: The models of cerebral I/R injury in rats were built by the method of middle cerebral artery occlusion/reperfusion (MCAO/R). First, neurological function assessment and cerebral infarct measurement were used for confirming the efficacy of YZFDF on cerebral I/R injury, and the optimal dosage (YZFDF-H) was selected to conduct the experiments, which included Western blotting detections of pyroptosis, Aβ_1-42 oligomers, and NeuN, immunofluorescence observations of glial pyroptosis, aquaporin-4 (AQP-4), and Aβ locations, brain water content measurement, SMI 71 (a specific marker for BBB)/AQP-4 immunohistochemistry, and Nissl staining to further evaluate BBB–glymphatic functions and neuronal damage.

Results: YZFDF obviously alleviated neurological deficits and cerebral infarct after cerebral I/R in rats. Furthermore, YZFDF could inactivate pyroptosis signaling via inhibiting caspase-1/11 activation and gasdermin D cleavage, ameliorate glial pyroptosis and neuroinflammation, protect against BBB collapse and AQP-4 depolarization, prevent Aβ acute accumulation and Aβ_1-42 oligomers formation, and reduce neuronal damage and increase neurons survival after reperfusion.

Conclusion: Our study indicated that YZFDF could exert neuroprotective effects on cerebral I/R injury and prevent Aβ acute accumulation in the brain after cerebral I/R associated with inhibiting neuroinflammation-related pyroptosis and BBB–glymphatic dysfunctions.

GPR109A alleviate mastitis and enhances the blood milk barrier by activating AMPK/Nrf2 and autophagy

Mastitis causes great psychological and physical pain among women. Our previous studies found that niacin has anti-inflammatory effect, and the realization of this function depends on GPR109A. However, there are no previous reports about the anti-inflammatory function of GPR109A in mastitis. In our study, we observed the effect of niacin on the WT and GPR109A^-/- mice mastitis model. The results showed that administration of niacin to WT mice reduced the damage, proinflammatory mediators and protected the integrity of the blood milk barrier in mammary gland. While in GPR109A^-/- mice, there was no effect on the above indexes. In mammary epithelial cells, GPR109A was able to promote autophagy and Nrf2 nuclear import through AMPK. In LPS-induced mammary epithelial cells, niacin inhibited the LPS-induced inflammatory response and downregulation of tight junction proteins, and these effects were eliminated by knocking down GPR109A, blocking autophagy or inhibiting Nrf2 nuclear import. These results indicate that in mastitis, GPR109A promotes autophagy and Nrf2 nuclear import through AMPK, thereby inhibiting inflammatory damage to the mammary gland and repairing the blood milk barrier. Our results suggested that GPR109A may be a potential target for the treatment of mastitis.

1α,25-Dihydroxyvitamin D3 promotes angiogenesis by alleviating AGEs-induced autophagy

Diabetes mellitus (DM) induces abnormal angiogenesis and results in multiple chronic vascular complications. Previous studies showed that advanced glycation end products (AGEs) up-regulated in diabetic patients and induced a series of cellular effects such as oxidative stress, inflammation, and autophagy. 1α,25-Dihydroxyvitamin D3 (1,25D), a hormonal form of vitamin D, proved to be beneficial for vascular diseases. However, the underlying mechanism of 1,25D in angiogenesis in DM remains unclear. Using CCK8 assay and transwell assay, we found that 1,25D could partly ameliorate impaired proliferation and migration ability of endothelial cells (ECs) induced by AGEs (200 μg/mL). Furthermore, tube formation assay, Western blot, and real-time qPCR assay were conducted to demonstrate that AGEs impaired angiogenetic ability, and that angiogenesis-related gene expression (i.e., VEGFA, VEGFB, VEGFR1, VEGFR2, TGFβ1, MMP2, MMP9) in ECs and 1,25D could promote angiogenesis and angiogenetic markers expression. By using DCFH-DA, ELISA, and Western blot assay, we also found that AGEs-induced oxidative stress impaired angiogenic ability of ECs, and 1,25D alleviated angiogenesis dysfunction by inhibiting oxidative stress. Of note, AGEs-induced excessive autophagy was found to impair angiogenesis. We elucidated that the detrimental autophagy is modulated by 1,25D and AGEs via PI3K/Akt pathway. Observed together, our findings illustrated that AGEs-induced oxidative stress and autophagy resulted in angiogenic disorder and 1,25D improved angiogenesis by restraining excessive autophagy and oxidative stress, providing a novel insight for the treatment of vascular complications in DM.

Blood-Brain Barrier Dysfunction Amplifies the Development of Neuroinflammation: Understanding of Cellular Events in Brain Microvascular Endothelial Cells for Prevention and Treatment of BBB Dysfunction

Neuroinflammation is involved in the onset or progression of various neurodegenerative diseases. Initiation of neuroinflammation is triggered by endogenous substances (damage-associated molecular patterns) and/or exogenous pathogens. Activation of glial cells (microglia and astrocytes) is widely recognized as a hallmark of neuroinflammation and triggers the release of proinflammatory cytokines, leading to neurotoxicity and neuronal dysfunction. Another feature associated with neuroinflammatory diseases is impairment of the blood-brain barrier (BBB). The BBB, which is composed of brain endothelial cells connected by tight junctions, maintains brain homeostasis and protects neurons. Impairment of this barrier allows trafficking of immune cells or plasma proteins into the brain parenchyma and subsequent inflammatory processes in the brain. Besides neurons, activated glial cells also affect BBB integrity. Therefore, BBB dysfunction can amplify neuroinflammation and act as a key process in the development of neuroinflammation. BBB integrity is determined by the integration of multiple signaling pathways within brain endothelial cells through intercellular communication between brain endothelial cells and brain perivascular cells (pericytes, astrocytes, microglia, and oligodendrocytes). For prevention of BBB disruption, both cellular components, such as signaling molecules in brain endothelial cells, and non-cellular components, such as inflammatory mediators released by perivascular cells, should be considered. Thus, understanding of intracellular signaling pathways that disrupt the BBB can provide novel treatments for neurological diseases associated with neuroinflammation. In this review, we discuss current knowledge regarding the underlying mechanisms involved in BBB impairment by inflammatory mediators released by perivascular cells.

Relative Contribution of Different Mitochondrial Oxidative Phosphorylation Components to the Retinal Pigment Epithelium Barrier Function: Implications for RPE-Related Retinal Diseases

Disruption of retinal pigment epithelial (RPE) barrier integrity is involved in the pathology of several blinding retinal diseases including age-related macular degeneration (AMD) and diabetic retinopathy (DR), but the underlying causes and pathophysiology are not completely well-defined. Mitochondria dysfunction has often been considered as a potential candidate implicated in such a process. In this study, we aimed to dissect the role of different mitochondrial components; specifically, those of oxidative phosphorylation (OxPhos), in maintaining the barrier functionality of RPE. Electric cell-substrate impedance sensing (ECIS) technology was used to collect multi-frequency electrical impedance data to assess in real-time the barrier formation of the RPE cells. For this purpose, the human retinal pigment epithelial cell line-ARPE-19-was used and treated with varying concentrations of specific mitochondrial inhibitors that target different steps in OxPhos: Rotenone for complex I (the largest protein complex in the electron transport chain (ETC)); oligomycin for ATP synthase; and carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) for uncoupling ATP synthesis from the accompanying ETC. Furthermore, data were modeled using the ECIS-Zθ software to investigate in depth the effects of these inhibitors on three separate barrier parameters: cell-cell interactions (Rb), cell-matrix interactions (α), and the cell membrane capacitance (Cm). The viability of ARPE-19 cells was determined by lactate dehydrogenase (LDH) Cytotoxicity Assay. The ECIS program's modeling demonstrated that FCCP and thus OxPhos uncoupling disrupt the barrier function in the ARPE-19 cells across all three components of the total resistance (Rb, α, and Cm) in a dose-dependent manner. On the other hand, oligomycin and thus ATP synthase inhibition mostly affects the ARPE-19 cells' attachment to their substrate evident by a significant decrease in α resistance in a dose-dependent manner, both at the end and throughout the duration of the experiment. On the contrary, rotenone and complex I inhibition mostly affect the ARPE-19 paracellular resistance Rb in a dose-dependent manner compared to basolateral resistance α or Cm. Our results clearly demonstrate differential roles for different mitochondrial components in maintaining RPE cell functionality in which uncoupling of OxPhos is a major contributing factor to the disruption barrier function. Such differences can be used in investigating gene expression as well as for screening of selective agents that improve the OxPhos coupling efficiency to be used in the therapeutic approach for treating RPE-related retinal diseases.

Relationship Between Amyloid-β Deposition and Blood-Brain Barrier Dysfunction in Alzheimer's Disease

Amyloid-β (Aβ) is the predominant pathologic protein in Alzheimer's disease (AD). The production and deposition of Aβ are important factors affecting AD progression and prognosis. The deposition of neurotoxic Aβ contributes to damage of the blood-brain barrier. However, the BBB is also crucial in maintaining the normal metabolism of Aβ, and dysfunction of the BBB aggravates Aβ deposition. This review characterizes Aβ deposition and BBB damage in AD, summarizes their interactions, and details their respective mechanisms.

Cycloastragenol inhibits Aβ1-42-induced blood-brain barrier disruption and enhances soluble Aβ efflux in vitro

This study aimed to evaluate the effect Cycloastragenol (CAG), a triterpenoid saponin isolated from the Radix astragali, on Aβ-induced BBB damage. An immortalized endothelial cell line (bEnd.3) was employed to mimic a BBB. The Western blot, TUNEL staining, Flow cytometric analysis and Enzyme-linked immunosorbent assay were performed. The present results showed that CAG (10, 50, 75 μM) can alleviate oligomer Aβ_1-42 induced bEnd.3 cell apoptosis and increase tight junction scaffold proteins expression. The result also indicated that CAG increased soluble Aβ efflux across BBB via upregulation of the P-gp and downregulation of RAGE expression.[Formula: see text].

Yi-Zhi-Fang-Dai Formula Exerts a Protective Effect on the Injury of Tight Junction Scaffold Proteins in Vitro and in Vivo by Mediating Autophagy through Regulation of the RAGE/CaMKKβ/AMPK/mTOR Pathway

Alzheimer's disease (AD) is a chronic neurodegeneration disease that is closely related to the abnormal tight junction scaffold proteins (TJ) proteins of the blood-brain barrier (BBB). Recently, Yi-Zhi-Fang-Dai Formula (YZFDF) had exerted a neuronal protective effect against amyloid peptide (Aβ) toxicity. Still, the therapeutic mechanism of YZFDF in restoring Aβ-induced injury of TJ proteins (ZO-1, Occludin, and Claudin-5) remains unclear. This study aimed to explore the underlying mechanism of YZFDF in alleviating the injury of TJ proteins. We examined the impacts of YZFDF on autophagy-related proteins and the histopathology of Aβ in the APP/PS1 double-transgenic male mice. We then performed the free intracellular calcium levels [Ca²⁺]i analysis and the cognitive behavior test of the AD model. Our results showed that YZFDF ameliorated the injury of TJ proteins by reducing the mRNA transcription and expression of the receptor for advanced glycation end-products (RAGE), the levels of [Ca²⁺]i, calmodulin-dependent protein kinase β (CaMKKβ), phosphorylated AMP-activated protein kinase (AMPK). Accordingly, YZFDF increased the expression of the phosphorylated mammalian targets of rapamycin (mTOR), leading to inhibition of autophagy (downregulated LC3 and upregulated P62). Moreover, the Aβ_1-42 oligomers-induced alterations of autophagy in murine mouse brain capillary (bEnd.3) cells were blocked by RAGE small interfering RNA (siRNA). These results suggest that YZFDF restored TJ proteins' injury by suppressing autophagy via RAGE signaling. Furthermore, YZFDF reduced the pathological precipitation of Aβ in the hippocampus, and improved cognitive behavior impairment of the AD model suggested that YZFDF might be a potential therapeutic candidate for treating AD through RAGE/CaMKKβ/AMPK/mTOR-regulated autophagy pathway.

Treatment of Alzheimer's Disease and Blood-Brain Barrier Drug Delivery

Despite the enormity of the societal and health burdens caused by Alzheimer's disease (AD), there have been no FDA approvals for new therapeutics for AD since 2003. This profound lack of progress in treatment of AD is due to dual problems, both related to the blood-brain barrier (BBB). First, 98% of small molecule drugs do not cross the BBB, and ~100% of biologic drugs do not cross the BBB, so BBB drug delivery technology is needed in AD drug development. Second, the pharmaceutical industry has not developed BBB drug delivery technology, which would enable industry to invent new therapeutics for AD that actually penetrate into brain parenchyma from blood. In 2020, less than 1% of all AD drug development projects use a BBB drug delivery technology. The pathogenesis of AD involves chronic neuro-inflammation, the progressive deposition of insoluble amyloid-beta or tau aggregates, and neural degeneration. New drugs that both attack these multiple sites in AD, and that have been coupled with BBB drug delivery technology, can lead to new and effective treatments of this serious disorder.

Lychee seed polyphenol protects the blood-brain barrier through inhibiting Aβ(25-35)-induced NLRP3 inflammasome activation via the AMPK/mTOR/ULK1-mediated autophagy in bEnd.3 cells and APP/PS1 mice

Blood-brain barrier (BBB) dysfunction has been implicated in Alzheimer's disease (AD) and is closely linked to the release of proinflammatory cytokines in brain capillary endothelial cells. We have previously reported that lychee seed polyphenols (LSP) exerted anti-neuroinflammatory effect. In this study, we aimed to explore the protective effect of LSP on BBB integrity. The monolayer permeability of bEnd.3 cells, and the mRNA level and protein expression of tight junction proteins (TJs), including Claudin 5, Occludin, and ZO-1, were examined. In addition, the inhibition of Aβ(25-35)-induced NLRP3 inflammasome activation, and the autophagy induced by LSP were investigated by detecting the expression of NLRP3, caspase-1, ASC, LC3, AMPK, mTOR, and ULK1. Furthermore, the cognitive function and the expression of TJs, NLRP3, caspase-1, IL-1β, and p62 were determined in APP/PS1 mice. The results showed that LSP significantly decreased the monolayer permeability and inhibited the NLRP3 inflammasome in Aβ(25-35)-induced bEnd3 cells. In addition, LSP induced autophagy via the AMPK/mTOR/ULK1 pathway in bEnd.3 cells, and improved the spatial learning and memory function, increased the TJs expression, and inhibited the expression of NLRP3, caspase-1, IL-1β, and p62 in APP/PS1 mice. Therefore, LSP protects BBB integrity in AD through inhibiting Aβ(25-35)-induced NLRP3 inflammasome activation via the AMPK/mTOR/ULK1-mediated autophagy.

Promiscuous Roles of Autophagy and Proteasome in Neurodegenerative Proteinopathies

Alterations in autophagy and the ubiquitin proteasome system (UPS) are commonly implicated in protein aggregation and toxicity which manifest in a number of neurological disorders. In fact, both UPS and autophagy alterations are bound to the aggregation, spreading and toxicity of the so-called prionoid proteins, including alpha synuclein (α-syn), amyloid-beta (Aβ), tau, huntingtin, superoxide dismutase-1 (SOD-1), TAR-DNA-binding protein of 43 kDa (TDP-43) and fused in sarcoma (FUS). Recent biochemical and morphological studies add to this scenario, focusing on the coordinated, either synergistic or compensatory, interplay that occurs between autophagy and the UPS. In fact, a number of biochemical pathways such as mammalian target of rapamycin (mTOR), transcription factor EB (TFEB), Bcl2-associated athanogene 1/3 (BAG3/1) and glycogen synthase kinase beta (GSk3β), which are widely explored as potential targets in neurodegenerative proteinopathies, operate at the crossroad between autophagy and UPS. These biochemical steps are key in orchestrating the specificity and magnitude of the two degradation systems for effective protein homeostasis, while intermingling with intracellular secretory/trafficking and inflammatory pathways. The findings discussed in the present manuscript are supposed to add novel viewpoints which may further enrich our insight on the complex interactions occurring between cell-clearing systems, protein misfolding and propagation. Discovering novel mechanisms enabling a cross-talk between the UPS and autophagy is expected to provide novel potential molecular targets in proteinopathies.

Fish oil protects the blood-brain barrier integrity in a mouse model of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is ranked as the most prevalent neurodegenerative disease. However, the exact molecular mechanisms underlying pathophysiological alterations in AD remain unclear, especially at the prodromal stage. The decreased proteolytic degradation of Aβ, blood-brain barrier (BBB) disruption, and neuroinflammation are considered to play key roles in the course of AD.

METHODS

Male APPswe/PS1dE9 C57BL/6 J double-transgenic (APP/PS1) mice in the age range from 1 month to 6 months and age-matched wild type mice were used in this study, intending to investigate the expression profiles of Aβ-degrading enzymes for Aβ degradation activities and zonula occludens-1 (zo-1) for BBB integrity at the prodromal stage.

RESULTS

Our results showed that there were no significant genotype-related alterations in mRNA expression levels of 4 well-characterized Aβ-degrading enzymes in APP/PS1 mice within the ages of 6 months. Interestingly, a significant decrease in zo-1 expression was observed in APP/PS1 mice starting from the age of 5 months, suggesting that BBB disrupt occurs at an early stage. Moreover, treatment of fish oil (FO) for 4 weeks remarkably increased zo-1 expression and significantly inhibited the glial activation and NF-κB activation in APP/PS1 mice.

CONCLUSION

The results of our study suggest that FO supplement could be a potential therapeutic early intervention for AD through protecting the BBB integrity and suppressing glial and NF-κB activation.

Alteration in the Function and Expression of SLC and ABC Transporters in the Neurovascular Unit in Alzheimer's Disease and the Clinical Significance

The neurovascular unit (NVU) plays an important role in maintaining the function of the central nervous system (CNS). Emerging evidence has indicated that the NVU changes function and molecules at the early stage of Alzheimer’s disease (AD), which initiates multiple pathways of neurodegeneration. Cell types in the NVU have become attractive targets in the interventional treatment of AD. The NVU transportation system contains a variety of proteins involved in compound transport and neurotransmission. Brain transporters can be classified as members of the solute carrier (SLC) and ATP-binding cassette (ABC) families in the NVU. Moreover, the transporters can regulate both endogenous toxins, including amyloid-beta (Aβ) and xenobiotic homeostasis, in the brains of AD patients. Genome-wide association studies (GWAS) have identified some transporter gene variants as susceptibility loci for late-onset AD. Therefore, the present study summarizes changes in blood-brain barrier (BBB) permeability in AD, identifies the location of SLC and ABC transporters in the brain and focuses on major SLC and ABC transporters that contribute to AD pathology.

Exploring the bi-directional relationship between autophagy and Alzheimer's disease

Alzheimer's disease (AD) is characterized by β-amyloid (Aβ) deposition and Tau phosphorylation, in which its pathogenesis has not been cleared so far. The metabolism of Aβ and Tau is critically affected by the autophagy. Abnormal autophagy is thought to be involved in the pathogenesis of AD, regulating autophagy may become a new strategy for AD treatment. In the early stage of AD, the presence of Aβ and Tau can induce autophagy to promote their clearance by means of mTOR-dependent and independent manners. As AD progress, the autophagy goes aberrant. As a result, Aβ and Tau generate continually, which aggravates both autophagy dysfunction and AD. Besides, several related genes and proteins of AD can also adapt autophagy to make an effect on the AD development. There seems to be a bi-directional relationship between AD pathology and autophagy. At present, this article reviews this relationship from these aspects: (a) the signaling pathways of regulating autophagy; (b) the relationships between the autophagy and the processing of Aβ; (c) Aβ and Tau cause autophagy dysfunction; (d) normal autophagy promotes the clearance of Aβ and Tau; (e) the relationships between the autophagy and both genes and proteins related to AD: TFEB, miRNAs, Beclin-1, Presenilin, and Nrf2; and (f) the small molecules regulating autophagy on AD therapy. All of the above may help to further elucidate the pathogenesis of AD and provide a theoretical basis for clinical treatment of AD.

FSP1 promotes the biofunctions of adventitial fibroblast through the crosstalk among RAGE, JAK2/STAT3 and Wnt3a/β-catenin signalling pathways

Emerging evidence indicates that fibroblast‐specific protein 1 (FSP1) provides vital effects in cell biofunctions. However, whether FSP1 influences the adventitial fibroblast (AF) and vascular remodelling remains unclear. Therefore, we investigated the potential role and action mechanism of FSP1‐mediated AF bioactivity. AFs were cultured and stimulated with FSP1 and siRNA‐FSP1 in vitro. Viability assays demonstrated that siRNA‐FSP1 counteracted AFs proliferative, migratory and adherent abilities enhanced with FSP1. Flow cytometry revealed that FSP1 increased AFs number in S phase and decreased cellular apoptosis. Contrarily, siRNA‐FSP1 displayed the contrary results. RT‐PCR, Western blotting and immunocytochemistry showed that FSP1 synchronously up‐regulated the expression of molecules in RAGE, JAK2/STAT3 and Wnt3a/β‐catenin pathways and induced a proinflammatory cytokine profile characterized by high levels of MCP‐1, ICAM‐1 and VCAM‐1. Conversely, FSP1 knockdown reduced the expression of these molecules and cytokines. The increased number of autophagosomes in FSP1‐stimulated group and fewer autophagic corpuscles in siRNA‐FSP1 group was observed by transmission electron microscope (TEM). Autophagy‐related proteins (LC3B, beclin‐1 and Apg7) were higher in FSP1 group than those in other groups. Conversely, the expression of p62 protein was shown an opposite trend of variation. Therefore, these pathways can promote AFs bioactivity, facilitate autophagy and induce the expression of the proinflammatory cytokines. Contrarily, siRNA‐FSP1 intercepts the crosstalk of these pathways, suppresses AF functions, restrains autophagy and attenuates the expression of the inflammatory factors. Our findings indicate that crosstalk among RAGE, STAT3/JAK2 and Wnt3a/β‐catenin signalling pathways may account for the mechanism of AF functions with the stimulation of FSP1.

Comprehensive Evaluation of White Matter Damage and Neuron Death and Whole-Transcriptome Analysis of Rats With Chronic Cerebral Hypoperfusion

Background/Aims

Chronic cerebral hypoperfusion (CCH) is induced by chronic deficit of brain perfusion, contributes to a persistent or progressive cognitive dysfunction, which is characterized by diverse neuropathological manifestations. There are currently no effective medications available. White matter damage (WMD) and cortical neuron death may be caused by CCH, which are related to cognitive impairment, while the underlying molecular mechanisms remain unclear. In the study, a database of the transcriptome level was built to determine potential biomarkers in cortex of CCH.

Methods

CCH was induced in male Sprague-Dawley rats by permanent occlusion of the bilateral common carotid arteries. Rats were randomly divided into three groups: Sham-operated group (n = 24), the 4th and 8th week of CCH groups (total = 56, n = 28 for each group). Cognitive function was evaluated using the Morris water maze task. WMD and neuron damage were detected using diffusion tensor imaging and histological analysis, respectively. Western blotting analysis of various markers was used to examine neuronal death. Whole-transcriptome microarray was performed to assess mRNA, circRNA, and lncRNA expression profiles at 4th and 8th weeks after CCH. Diversified bioinformatic tools were performed to analyze and predict the key biological processes and signaling pathways of differentially expressed RNAs and co-expressed potential target genes. Co-expression networks of mRNA–circRNA–miRNA and lncRNA–mRNA were constructed.

Results

Compared to the sham group, cognitive impairment, disintegration of white matter, blood-brain barrier damage and neuron death were induced by CCH. Neuron death including apoptosis and necroptosis might occur in the cortex of CCH. We constructed the regulatory networks of whole-transcriptomic including differentially expressed mRNAs, circRNAs, and lncRNAs, and related biological functions and pathways involved in neurological disease, cell death and survival, energy and metabolism, et al. Our results also indicated that Cyr61 mRNA may play a role in the CCH-related cortical neuronal death.

Conclusion

WMD and cortical neuronal death are worthy of attention in the pathogenesis of CCH. Additionally, the present results provide potential evidence at the whole-transcription level for CCH, offering candidate biomarkers and therapeutic targets.

Role of Endoplasmic Reticulum Stress-Autophagy Axis in Severe Burn-Induced Intestinal Tight Junction Barrier Dysfunction in Mice

Severe burn injury induces intestinal barrier dysfunction; however, the underlying mechanisms remain elusive. Our previous studies have shown that the intestinal epithelial tight junction (TJ) barrier dysfunction is associated with both endoplasmic reticulum (ER) stress and autophagy in severely burned mice, but the precise role of ER stress and autophagy in the burn-induced intestinal TJ barrier dysfunction needs to be determined. In this study, female C57/BL6 mice were assigned randomly to either sham burn or 30% total body surface area (TBSA) full-thickness burn. The effects of ER stress and autophagy on the intestinal epithelial TJ barrier were validated by inducing or inhibiting both ER stress and autophagy in mice treated with sham burn or burn injury. The intestinal permeability, expression, and localization of TJ proteins, ER stress, and autophagy were assessed by physiological, morphological, and biochemical analyses. The results showed that inducing ER stress with tunicamycin or thapsigargin caused the activation of autophagy, the increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins in the sham-burned mice, and aggravated the burn-induced activation of autophagy, increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins. In contrast, inhibiting ER stress with 4-phenylbutyrate alleviated the burn-induced activation of autophagy, increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins. In addition, inducing autophagy with rapamycin resulted in the increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins in the sham-burned mice, and aggravated the burn-induced increase of intestinal permeability as well as the reduction and reorganization of TJ proteins. However, inhibiting autophagy with 3-methyladenine attenuated the burn-induced increase of intestinal permeability, as well as the reduction and reorganization TJ proteins. It is suggested that the ER stress-autophagy axis contributes to the intestinal epithelial TJ barrier dysfunction after severe burn injury.

UHPLC-QTOF/MS-based metabolomics investigation for the protective mechanism of Danshen in Alzheimer's disease cell model induced by Aβ1-42

INTRODUCTION

Alzheimer's disease (AD) is a chronic neurodegenerative disorder with neither definitive pathogenesis nor effective therapy so far. Danshen, the dried root and rhizome of Salvia miltiorrhiza Bunge, is used extensively in Alzheimer's disease treatment to ameliorate the symptoms, but the underlying mechanism remains to be clarified.

OBJECTIVES

To investigate potential biomarkers for AD and elucidate the protective mechanism of Danshen on AD cell model.

METHODS

An ultra high performance liquid chromatography-quadrupole time of flight mass spectrometry (UHPLC-QTOF/MS)-based approach combined with partial least squares discriminant analysis (PLS-DA) has been developed to discriminate the metabolic modifications between human brain microvascular endothelial cell (hBMEC) and AD cell model induced by amyloid-β protein (Aβ_1-42). To further elucidate the pathophysiology of AD, related metabolic pathways have been studied.

RESULTS

Thirty-three distinct potential biomarkers were screened out and considered as potential biomarkers corresponding to AD, which were mostly improved and partially restored back to normalcy in Danshen pre-protection group. It was found that AD was closely related to disturbed arginine and proline metabolism, glutathione metabolism, alanine aspartate and glutamate metabolism, histidine metabolism, pantothenate and CoA biosynthesis, phenylalanine tyrosine and tryptophan biosynthesis, citrate cycle and glycerophospholipid metabolism, and the protective mechanism of Danshen in AD cell model may be related to partially regulating the perturbed pathways.

CONCLUSIONS

These outcomes provide valuable evidences for therapeutic mechanism investigation of Danshen in AD treatment, and such an approach could be transferred to unravel the mechanism of other traditional Chinese medicine (TCM) and diseases.