Crossroads between membrane trafficking machinery and copper homeostasis in the nerve system

Sleep fragmentation exacerbates myocardial ischemia‒reperfusion injury by promoting copper overload in cardiomyocytes

Sleep disorders increase the risk and mortality of heart disease, but the brain-heart interaction has not yet been fully elucidated. Cuproptosis is a copper-dependent type of cell death activated by the excessive accumulation of intracellular copper. Here, we showed that 16 weeks of sleep fragmentation (SF) resulted in elevated copper levels in the male mouse heart and exacerbated myocardial ischemia-reperfusion injury with increased myocardial cuproptosis and apoptosis. Mechanistically, we found that SF promotes sympathetic overactivity, increases the germination of myocardial sympathetic nerve terminals, and increases the level of norepinephrine in cardiac tissue, thereby inhibits VPS35 expression and leads to impaired ATP7A related copper transport and copper overload in cardiomyocytes. Copper overload further leads to exacerbated cuproptosis and apoptosis, and these effects can be rescued by excision of the sympathetic nerve or administration of copper chelating agent. Our study elucidates one of the molecular mechanisms by which sleep disorders aggravate myocardial injury and suggests possible targets for intervention.

Lead aggravates Alzheimer's disease pathology via mitochondrial copper accumulation regulated by COX17

Alzheimer's disease (AD) is a common neurodegenerative disease that is associated with multiple environmental risk factors, including heavy metals. Lead (Pb) is a heavy metal contaminant, which is closely related to the incidence of AD. However, the research on the role of microglia in Pb-induced AD-like pathology is limited. To determine the mechanism by which Pb exposure aggravates AD progression and the role of microglial activation, we exposed APP/PS1 mice and Aβ1-42-treated BV-2 cells to Pb. Our results suggested that chronic Pb exposure exacerbated learning and memory impairments in APP/PS1 mice. Pb exposure increased the activation of microglia in the hippocampus of APP/PS1 mice, which was associated with increased deposition of Aβ1-42, and induced hippocampal neuron damage. Pb exposure upregulated copper transporter 1 (CTR1) and downregulated copper P-type ATPase transporter (ATP7A) in the hippocampus of APP/PS1 mice and Aβ1-42-treated BV-2 cells. Moreover, Pb enhanced mitochondrial translocation of the mitochondrial copper transporter COX17, leading to an increase in mitochondrial copper concentration and mitochondrial damage. This could be reversed by copper-chelating agents or by inhibiting the mitochondrial translocation of COX17. The increased mitochondrial copper concentration caused by increased mitochondrial translocation of COX17 after Pb exposure may be related to the enhanced mitochondrial import pathway of AIF/CHCHD4. These results indicate that Pb induces the activation of microglia by increasing the concentration of copper in the mitochondria of microglia, and microglia release inflammatory factors to promote neuroinflammation, thus aggravating the pathology of AD. The present study provides new ideas for the prevention of Pb-induced AD.

The interplay between copper metabolism and microbes: in perspective of host copper-dependent ATPases ATP7A/B

Copper, a vital element in various physiological processes, is transported from the gastrointestinal tract to tissues and cells through diverse copper transporters. Among these transporters, ATP7A and ATP7B play significant roles in regulating systemic copper metabolism and exhibit precise regulation in their intracellular trafficking. These transporters undergo dynamic shuttling between the trans-Golgi network (TGN) and the plasma membrane via the endocytic recycling mechanism, which involves the retromer and other associated factors. Interestingly, the antimicrobial attribute of copper implies a potential connection between microbial infection and copper metabolism. Several microbes, including Salmonella enterica, Cryptococcus, Influenza A virus (IAV) and Zika virus (ZIKV) have been observed to impact the regulatory mechanisms of ATP7A/B, either directly or indirectly, as a means of survival. This review summarizes the key features and trafficking mechanisms of the copper transporters ATP7A/B, and examines the intricate interplay between microbes and copper metabolism. Ultimately, it highlights how microbes can perturb copper homeostasis through interactions with host factors, offering valuable insights into the mechanistic aspects of host-microbe interactions.

[Lead exposure aggravates Aβ1-42-induced microglial activation and copper ion accumulation in microglial cells]

OBJECTIVE

To investigate the effect of lead (Pb) exposure on Aβ1-42-induced microglial activation and copper ion accumulation in microglial cells and explore the regulatory mechanism of Pb-induced aggravation of Alzheimer's disease (AD)-like pathology.

METHODS

Cultured microglial BV2 cells were treated with different concentrations of Aβ1-42, lead acetate or their combination for 12 h, and the changes in cell viability and morphology were evaluated. Immunofluorescence assay was performed to detect iNOS and oxidative stress level in the treated cells, and the release of inflammatory factors was detected using ELISA. Western blotting and inductively coupled plasma-mass spectrometry (ICP-MS) were used to detect the expressions of CTR1 and ATP7A proteins and copper content in the cells.

RESULTS

Treatment with 15 and 20 μmol/L Aβ1-42 for 12 h significantly lowered the viability of BV2 cells. Treatment with Aβ1-42 at 10 μmol/L for 12 h obviously increased the release of iNOS, TNF-α and IL-6 in the cells (P<0.05), and its combination with 15 or 20 μmol/L lead acetate more strongly lowered BV2 cell viability (P<0.05). Compared with 10 μmol/L Aβ1-42 treatment alone, 10 μmol/L Aβ1-42 combined with 10 μmol/L lead acetate for 12 h caused more obvious microglial activation, as manifested by enlarged cell bodies, increased cell protrusions and elongation, enhanced release of iNOS, TNF-α, IL-6, IL-1β and ROS, and increased intracellular copper ion accumulation and expression of copper transporter CTR1 (P<0.05). Compared with the conditioned medium from activated BV2 cells, which caused obvious injuries in hippocampal neuron HT22 cells (P<0.001), the medium from BV2 cells treated with NAC and the copper ion chelating agent TM caused milder injuries in HT22 cells (P<0.05).

CONCLUSION

Lead exposure aggravates neuronal damage caused by Aβ1-42-treated microglial cells by increasing copper ion accumulation, oxidative stress, and inflammatory factor release to trigger microglial activation.

SNAP-tagging live cells via chelation-assisted copper-catalyzed azide-alkyne cycloaddition

SNAP-tag is a single-turnover enzyme that has become a powerful tool, hence a popular choice, of targeted cellular protein labeling. Three SNAP-tag substrates that carry the copper-chelating 2-picolyl azide moiety are prepared, one of which has an unconventional 5-pyridylmethyl-substituted guanine structure, rather than the usual benzylguanine that is optimized to be accepted by SNAP-tag. All three substrates are effective in transferring a 2-picolyl azide moiety to SNAP-tag in live cells under conventional labeling conditions (30-minute incubation of cells with labeling reagents at 37 °C under 5% CO2). Live cells that are decorated with chelating azido groups on the extracellular side of membranes undergo copper-catalyzed azide-alkyne cycloaddition (CuAAC) with an ethynyl-functionalized fluorophore to accomplish membrane protein labeling by a fluorescent dye. The chelation-assisted CuAAC labeling step is rapid (<1 minute) with a relatively low dose of the copper catalyst (20 μM), and consequently exerts no ill effect on the labeled cells. A SNAP-tag substrate that carries a non-chelating azide moiety, on the other hand, fails to produce satisfactory labeling under the same constraints. The rapid, live cell-compatible SNAP-tag/chelation-assisted CuAAC two-step method expands the utility of SNAP-tag in protein labeling applications.

Excessive copper impairs intrahepatocyte trafficking and secretion of selenoprotein P

Selenium homeostasis depends on hepatic biosynthesis of selenoprotein P (SELENOP) and SELENOP-mediated transport from the liver to e.g. the brain. In addition, the liver maintains copper homeostasis. Selenium and copper metabolism are inversely regulated, as increasing copper and decreasing selenium levels are observed in blood during aging and inflammation. Here we show that copper treatment increased intracellular selenium and SELENOP in hepatocytes and decreased extracellular SELENOP levels. Hepatic accumulation of copper is a characteristic of Wilson's disease. Accordingly, SELENOP levels were low in serum of Wilson's disease patients and Wilson's rats. Mechanistically, drugs targeting protein transport in the Golgi complex mimicked some of the effects observed, indicating a disrupting effect of excessive copper on intracellular SELENOP transport resulting in its accumulation in the late Golgi. Our data suggest that hepatic copper levels determine SELENOP release from the liver and may affect selenium transport to peripheral organs such as the brain.

Subcellular redox responses reveal different Cu-dependent antioxidant defenses between mitochondria and cytosol

Excess intracellular Cu perturbs cellular redox balance and thus causes diseases. However, the relationship between cellular redox status and Cu homeostasis and how such an interplay is coordinated within cellular compartments has not yet been well established. Using combined approaches of organelle-specific redox sensor Grx1-roGFP2 and non-targeted proteomics, we investigate the real-time Cu-dependent antioxidant defenses of mitochondria and cytosol in live HEK293 cells. The Cu-dependent real-time imaging experiments show that CuCl2 treatment results in increased oxidative stress in both cytosol and mitochondria. In contrast, subsequent excess Cu removal by bathocuproine sulfonate, a Cu chelating reagent, lowers oxidative stress in mitochondria but causes even higher oxidative stress in the cytosol. The proteomic data reveal that several mitochondrial proteins, but not cytosolic ones, undergo significant abundance change under Cu treatments. The proteomic analysis also shows that proteins with significant changes are related to mitochondrial oxidative phosphorylation and glutathione synthesis. The differences in redox behaviors and protein profiles in different cellular compartments reveal distinct mitochondrial and cytosolic response mechanisms upon Cu-induced oxidative stress. These findings provide insights into how redox and Cu homeostasis interplay by modulating specific protein expressions at the subcellular levels, shedding light on understanding the effects of Cu-induced redox misregulation on the diseases.

Copper Modulates Adult Neurogenesis in Brain Subventricular Zone

The subventricular zone (SVZ) in lateral ventricles is the largest neurogenic region in adult brain containing high amounts of copper (Cu). This study aims to define the role of Cu in adult neurogenesis by chelating labile Cu ions using a well-established Cu chelator D-Penicillamine (D-Pen). A neurosphere model derived from adult mouse SVZ tissues was established and characterized for its functionality with regards to neural stem/progenitor cells (NSPCs). Applying D-Pen in cultured neurospheres significantly reduced intracellular Cu levels and reversed the Cu-induced suppression of NSPC’s differentiation and migration. An in vivo intracerebroventricular (ICV) infusion model was subsequently established to infuse D-Pen directly into the lateral ventricle. Metal analyses revealed a selective reduction of Cu in SVZ by 13.1% (p = 0.19) and 21.4% (p < 0.05) following D-Pen infusions at low (0.075 μg/h) and high (0.75 μg/h) doses for 28 days, respectively, compared to saline-infused controls. Immunohistochemical studies revealed that the 7-day, low-dose D-Pen infusion significantly increased Ki67(+)/Nestin(+) cell counts in SVZ by 28% (p < 0.05). Quantification of BrdU(+)/doublecortin (DCX)(+) newborn neuroblasts in the rostral migration stream (RMS) and olfactory bulb (OB) further revealed that the short-term, low-dose D-Pen infusion, as compared with saline-infused controls, resulted in more newborn neuroblasts in OB, while the high-dose D-Pen infusion showed fewer newborn neuroblasts in OB but with more arrested in the RMS. Long-term (28-day) infusion revealed similar outcomes. The qPCR data from neurosphere experiments revealed altered expressions of mRNAs encoding key proteins known to regulate SVZ adult neurogenesis, including, but not limited to, Shh, Dlx2, and Slit1, in response to the changed Cu level in neurospheres. Further immunohistochemical data indicated that Cu chelation also altered the expression of high-affinity copper uptake protein 1 (CTR1) and metallothionein-3 (MT3) in the SVZ as well as CTR1 in the choroid plexus, a tissue regulating brain Cu homeostasis. Taken together, this study provides first-hand evidence that a high Cu level in SVZ appears likely to maintain the stability of adult neurogenesis in this neurogenic zone.