Cadmium favors F-actin depolymerization in rat renal mesangial cells by site-specific, disulfide-based dimerization of the CAP1 protein

Cadmium Highlights Common and Specific Responses of Two Freshwater Sentinel Species, Dreissena polymorpha and Dreissena rostriformis bugensis

Zebra mussel (ZM), Dreissena polymorpha, commonly used as a sentinel species in freshwater biomonitoring, is now in competition for habitat with quagga mussel (QM), Dreissena rostriformis bugensis. This raises the question of the quagga mussel's use in environmental survey. To better characterise QM response to stress compared with ZM, both species were exposed to cadmium (100 µg·L-1), a classic pollutant, for 7 days under controlled conditions. The gill proteomes were analysed using two-dimensional electrophoresis coupled with mass spectrometry. For ZM, 81 out of 88 proteoforms of variable abundance were identified using mass spectrometry, and for QM, 105 out of 134. Interestingly, the proteomic response amplitude varied drastically, with 5.6% of proteoforms of variable abundance (DAPs) in ZM versus 9.4% in QM. QM also exhibited greater cadmium accumulation. Only 12 common DAPs were observed. Several short proteoforms were detected, suggesting proteolysis. Functional analysis is consistent with the pleiotropic effects of the toxic metal ion cadmium, with alterations in sulphur and glutathione metabolisms, cellular calcium signalling, cytoskeletal dynamics, energy production, chaperone activation, and membrane events with numerous proteins involved in trafficking and endocytosis/exocytosis processes. Beyond common responses, the sister species display distinct reactions, with cellular response to stress being the main category involved in ZM as opposed to calcium and cytoskeleton alterations in QM. Moreover, QM exhibited greater evidence of proteolysis and cell death. Overall, these results suggest that QM has a weaker stress response capacity than ZM.

Recent advances in mass spectrometry-based methods to investigate reversible cysteine oxidation

The post-translational modification of cysteine to diverse oxidative states is understood as a critical cellular mechanism to combat oxidative stress. To study the role of cysteine oxidation, cysteine enrichments and subsequent analysis via mass spectrometry are necessary. As such, technologies and methods are rapidly developing for sensitive and efficient enrichments of cysteines to further explore its role in signaling pathways. In this review, we analyze recent developments in methods to miniaturize cysteine enrichments, analyze the underexplored disulfide bound redoxome, and quantify site-specific cysteine oxidation. We predict that further development of these methods will improve cysteine coverage across more diverse organisms than those previously studied and elicit novel roles cysteines play in stress response.

Knockout of cyclase-associated protein CAP1 confers tolerance towards salt and osmotic stress in Arabidopsis

As a regulator of actin filament turnover, Arabidopsis thaliana CAP1 plays an important role in plant growth and development. Here, we analyzed the phenotypes of two Arabidopsis cap1 mutants: cap1-1 (a T-DNA insertion mutant) and Cas9-CAP1 (generated by CRISPR-Cas9 gene editing). Phenotypic analysis demonstrated that loss of CAP1 results in defects in seed germination and seedling morphology, with some seedlings exhibiting one or three cotyledons. The cap1-1 mutant took longer than the wild type to complete its life cycle, but its flowering time was normal, indicating that loss of CAP1 prolongs reproductive but not vegetative growth. Moreover, loss of CAP1 severely reduces seed production in self-pollinated plants, due to disruption of pollen tube elongation. RNA-seq and qRT-PCR analyses demonstrated that CAP1 may be involved in osmotic stress responses. Indeed, the cap1-1 mutant showed increased tolerance of salt and mannitol treatment, indicating that CAP1 plays a negative role in osmotic stress tolerance in Arabidopsis. Taken together, our results demonstrate that CAP1 functions not only in plant growth and development, but also in Arabidopsis responses to osmotic stress.

Red CdSe/ZnS QDs' Intracellular Trafficking and Its Impact on Yeast Polarization and Actin Filament

Quantum dots are nanoparticles (2-10 nm) that emit strong and tunable fluorescence. Quantum dots have been heavily used in high-demand commercialized products, research, and for medical purposes. Emerging concerns have demonstrated the negative impact of quantum dots on living cells; however, the intracellular trafficking of QDs in yeast cells and the effect of this interaction remains unclear. The primary goal of our research is to investigate the trafficking path of red cadmium selenide zinc sulfide quantum dots (CdSe/ZnS QDs) in Saccharomyces cerevisiae and the impact QDs have on yeast cellular dynamics. Using cells with GFP-tagged reference organelle markers and confocal microscopy, we were able to track the internalization of QDs. We found that QDs initially aggregate at the exterior of yeast cells, enter the cell using clathrin-receptor-mediated endocytosis, and distribute at the late Golgi/trans-Golgi network. We also found that the treatment of red CdSe/ZnS QDs resulted in growth rate reduction and loss of polarized growth in yeast cells. Our RNA sequence analysis revealed many altered genes. Particularly, we found an upregulation of DID2, which has previously been associated with cell cycle arrest when overexpressed, and a downregulation of APS2, a gene that codes for a subunit of AP2 protein important for the recruitment of proteins to clathrin-mediated endocytosis vesicle. Furthermore, CdSe/ZnS QDs treatment resulted in a slightly delayed endocytosis and altered the actin dynamics in yeast cells. We found that QDs caused an increased level of F-actin and a significant reduction in profilin protein expression. In addition, there was a significant elevation in the amount of coronin protein expressed, while the level of cofilin was unchanged. Altogether, this suggests that QDs favor the assembly of actin filaments. Overall, this study provides a novel toxicity mechanism of red CdSe/ZnS QDs on yeast actin dynamics and cellular processes, including endocytosis.

CORO1A regulates lipoprotein uptake in Leydig cells exposed to cadmium

Cadmium (Cd) is one of the most common environmental pollutants, which has a long biological half-life. Maternal Cd-exposure in the natural environment causes steroidogenesis defects resulting in spermatogenesis disorder in male offspring. For better understanding its underlying mechanism, we have employed iTRAQ to screen the differentially expressed protein and found that the expression of CORO1A and Cofilin 1 was up-regulated approximately 2 fold in Leydig cells of maternal Cd-exposure offspring. As the major source of steroid hormone, cholesterol is transported to cells via receptor-mediated endocytosis which relies on the remodel of cytoskeleton, then stores in lipid droplets (LDs). However, few studies have focused on the role of cytoskeleton in abnormal steroidogenesis. This study was performed to explore the role of CORO1A in androgen deficiency caused by Cd exposure and its involvement of low-density lipoprotein (LDL) uptake and effects on LDs. We found that Cd resulted in the up-regulation of CORO1A and Cofilin 1, and down-regulation of Profilin 1 in the testis of male offspring with maternal exposure. The structure of filamentous actin was broken, disordered and even crumpled up in Cd-treated R2C cells. F-actin disassembly led to a low uptake of LDL with a reduced number of LDs, followed by decreased total cholesterol and low progesterone production. When CORO1A was silenced, the expression of Cofilin 1 was down-regulated and Profilin 1 was up-regulated in Cd-treated R2C cells. The filamentous actin was rescued and the integrated cytoskeleton prompted LDL uptake, which resulted in the increased total cholesterol and high progesterone production. These findings highlight the crucial role of CORO1A as a cytoskeleton regulatory protein in steroidogenesis, which may help to better understand Cd-induced steroid hormone deficiency in children.

CAPt'n of Actin Dynamics: Recent Advances in the Molecular, Developmental and Physiological Functions of Cyclase-Associated Protein (CAP)

Cyclase-associated protein (CAP) has been discovered three decades ago in budding yeast as a protein that associates with the cyclic adenosine monophosphate (cAMP)-producing adenylyl cyclase and that suppresses a hyperactive RAS2 variant. Since that time, CAP has been identified in all eukaryotic species examined and it became evident that the activity in RAS-cAMP signaling is restricted to a limited number of species. Instead, its actin binding activity is conserved among eukaryotes and actin cytoskeleton regulation emerged as its primary function. However, for many years, the molecular functions as well as the developmental and physiological relevance of CAP remained unknown. In the present article, we will compile important recent progress on its molecular functions that identified CAP as a novel key regulator of actin dynamics, i.e., the spatiotemporally controlled assembly and disassembly of actin filaments (F-actin). These studies unraveled a cooperation with ADF/Cofilin and Twinfilin in F-actin disassembly, a nucleotide exchange activity on globular actin monomers (G-actin) that is required for F-actin assembly and an inhibitory function towards the F-actin assembly factor INF2. Moreover, by focusing on selected model organisms, we will review current literature on its developmental and physiological functions, and we will present studies implicating CAP in human pathologies. Together, this review article summarizes and discusses recent achievements in understanding the molecular, developmental and physiological functions of CAP, which led this protein emerge as a novel CAPt'n of actin dynamics.

Cyclase-associated protein 2 dimerization regulates cofilin in synaptic plasticity and Alzheimer's disease

Regulation of actin cytoskeleton dynamics in dendritic spines is crucial for learning and memory formation. Hence, defects in the actin cytoskeleton pathways are a biological trait of several brain diseases, including Alzheimer's disease. Here, we describe a novel synaptic mechanism governed by the cyclase-associated protein 2, which is required for structural plasticity phenomena and completely disrupted in Alzheimer's disease. We report that the formation of cyclase-associated protein 2 dimers through its Cys³² is important for cyclase-associated protein 2 binding to cofilin and for actin turnover. The Cys³²-dependent cyclase-associated protein 2 homodimerization and association to cofilin are triggered by long-term potentiation and are required for long-term potentiation-induced cofilin translocation into spines, spine remodelling and the potentiation of synaptic transmission. This mechanism is specifically affected in the hippocampus, but not in the superior frontal gyrus, of both Alzheimer's disease patients and APP/PS1 mice, where cyclase-associated protein 2 is down-regulated and cyclase-associated protein 2 dimer synaptic levels are reduced. Notably, cyclase-associated protein 2 levels in the cerebrospinal fluid are significantly increased in Alzheimer's disease patients but not in subjects affected by frontotemporal dementia. In Alzheimer's disease hippocampi, cofilin association to cyclase-associated protein 2 dimer/monomer is altered and cofilin is aberrantly localized in spines. Taken together, these results provide novel insights into structural plasticity mechanisms that are defective in Alzheimer's disease.

Cadmium induces mitophagy via AMP-activated protein kinases activation in a PINK1/Parkin-dependent manner in PC12 cells

Objectives

Cadmium (Cd) induces mitophagy in neuronal cells, but the underlying mechanisms remain unknown. In this study, we aimed to investigate these mechanisms.

Materials and methods

The effects of Cd on the mitophagy in rat pheochromocytoma PC12 cells were detected, and the role of PINK1/Parkin pathway in Cd‐induced mitophagy was also analysed by using PINK1 siRNA. In order to explore the relationship between AMPK and PINK1/Parkin in Cd‐induced mitophagy in PC12 cells, the CRISPR‐Cas9 system was used to knock down AMPK expression.

Results

The results showed that Cd treatment triggered a significant increase in mitophagosome formation and the colocalization of mitochondria and lysosomes, which was further proved by the colocalization of LC3 puncta and its receptors NDP52 or P62 with mitochondria in PC12 cells. Moreover, an accumulation of PINK1 and Parkin was found in mitochondria. Additionally, upon PINK1 knock‐down using PINK1 siRNA, Cd‐induced mitophagy was efficiently suppressed. Interestingly, chemical or genetic reversal of AMPK activation: (a) significantly inhibited the activation of mitophagy and (b) promoted NLRP3 activation by inhibiting PINK/Parkin translocation.

Conclusions

These results suggest that Cd induces mitophagy via the PINK/Parkin pathway following AMPK activation in PC12 cells. Targeting the balanced activity of AMPK/PINK1/Parkin‐mediated mitophagy signalling may be a potential therapeutic approach to treat Cd‐induced neurotoxicity.

Cell organelles as targets of mammalian cadmium toxicity

Ever increasing environmental presence of cadmium as a consequence of industrial activities is considered a health hazard and is closely linked to deteriorating global health status. General animal and human cadmium exposure ranges from ingestion of foodstuffs sourced from heavily polluted hotspots and cigarette smoke to widespread contamination of air and water, including cadmium-containing microplastics found in household water. Cadmium is promiscuous in its effects and exerts numerous cellular perturbations based on direct interactions with macromolecules and its capacity to mimic or displace essential physiological ions, such as iron and zinc. Cell organelles use lipid membranes to form complex tightly-regulated, compartmentalized networks with specialized functions, which are fundamental to life. Interorganellar communication is crucial for orchestrating correct cell behavior, such as adaptive stress responses, and can be mediated by the release of signaling molecules, exchange of organelle contents, mechanical force generated through organelle shape changes or direct membrane contact sites. In this review, cadmium effects on organellar structure and function will be critically discussed with particular consideration to disruption of organelle physiology in vertebrates.

Cadmium Exposure of Female Mice Impairs the Meiotic Maturation of Oocytes and Subsequent Embryonic Development

Cadmium is one major pollutant that is highly toxic to animals and humans. The mechanism of cadmium toxicity on the female reproductive system, particularly oocyte maturation and fertility, remains to be clarified. In this study, we used a mouse model to investigate the effects of cadmium in the drinking water on the meiotic maturation of oocytes and subsequent embryonic development, and the underlying mechanisms associated with the impairment of oocyte maturation such as mitochondrial distribution and histone modifications. Our results show that cadmium exposure decreased the number of ovulated oocytes and impaired oocyte meiotic maturation rate both in vivo and in vitro. The embryonic development after fertilization was also impaired even when the potential hazards of cadmium on the spermatozoa or the genital tract have been excluded by fertilization and embryonic development in culture. Cadmium exposure disrupted meiotic spindle morphology and actin filament, which are responsible for successful chromosome segregation and the polar body extrusion during oocyte maturation and fertilization. ATP contents, which are required for proper meiotic spindle assembly in the oocyte, were decreased, consistent with altered mitochondrial distribution after cadmium exposure. Finally, cadmium exposure affected the levels of H3K9me2 and H4K12ac in the oocyte, which are closely associated with the acquisition of oocyte developmental competence and subsequent embryonic development. In conclusion, cadmium exposure in female mice impaired meiotic maturation of oocytes and subsequent embryonic development by affecting the cytoskeletal organization, mitochondrial function, and histone modifications.

Effects of sub-chronic, low-dose cadmium exposure on kidney damage and potential mechanisms

Background

The present study was to investigate the potential mechanisms underlying the sub-chronic low-dose cadmium (Cd) exposure induced renal injury in rats.

Methods

Totally 40 male adult SD rats were randomly divided into four groups: control group, low-dose Cd group (1 mg/kg CdCl₂), moderate-dose Cd group (2.5 mg/kg) and high-dose Cd group (5 mg/kg).

Results

From the 3^rd week, the body weight of rats in moderate-dose and high-dose declined significantly as compared to the control group (P<0.05); the liver to body weight ratio increased, the volumes of 24-hour urine and drinking-water decreased markedly (P<0.05), the BUN, SCr and β₂-MG increased significantly, but the Fe²⁺ concentration decreased markedly as compared to the control group (P<0.05); the serum MDA and SOD₁ content contents increased, but the serum SOD₂ and CAT contents decreased significantly in Cd-treated groups (P<0.05); Renal injury deteriorated with the increase in Cd dose; swelling glomeruli showed stenotic renal-tubules, and epithelial-cell-necrosis, shedding and accumulation in the lumen, massive infiltrated inflammatory cells and interstitial hyperaemia were observed; The mitochondria in renal-tubular-epithelial-cells displayed swelling, deformation and vacuolation; the renal ROS content increased in Cd-exposure-groups; the renal SOD₁ expression increased but the expression of SOD₂ and CAT decreased (P<0.05). The Bcl-2 expression decreased, but Bax expression and Bax/Bcl-2 ratio increased significantly in a Cd-dose dependent manner.

Conclusions

Cd may cause renal injury in a dose dependent manner, which may be ascribed to the disordered Fe²⁺ absorption, redox imbalance and apoptosis in the kidney.

Potential mechanisms of cellular injury following exposure to a physiologically relevant species of inorganic mercury

Mercury is a toxic metal that is found ubiquitously in the environment. Humans are exposed to different forms of mercury via ingestion, inhalation, and/or dermal absorption. Following exposure, mercuric ions may gain access to target cells and subsequently lead to cellular intoxication. The mechanisms by which mercury accumulation leads to cellular injury and death are not understood fully. Therefore, purpose of this study was to identify the specific intracellular mechanisms that are altered by exposure to inorganic mercury (Hg²⁺). Normal rat kidney (NRK) cells were exposed to a physiologically relevant form of Hg²⁺, as a conjugate of cysteine (10 μM or 50 μM). Alterations in oxidative stress were estimated by measuring lipid peroxidation and mitochondrial oxidative stress. Alterations in actin and tubulin were measured using specific fluorescent dyes. Calcium levels were measured using Fluo-3 AM Calcium Indicator while autophagy was identified with Premo^™ Autophagy Sensor LC3B-GFP. The current findings show that exposure to Hg²⁺ leads to enhanced oxidative stress, alterations in cytoskeletal structure, increases in intracellular calcium, and enhanced autophagy. We have established a more complete understanding of intoxication and cellular injury induced by a relevant form of Hg²⁺ in proximal tubule cells.

Mapping disulfide bonds from sub-micrograms of purified proteins or micrograms of complex protein mixtures

Disulfide bonds are vital for protein functions, but locating the linkage sites has been a challenge in protein chemistry, especially when the quantity of a sample is small or the complexity is high. In 2015, our laboratory developed a sensitive and efficient method for mapping protein disulfide bonds from simple or complex samples (Lu et al. in Nat Methods 12:329, 2015). This method is based on liquid chromatography–mass spectrometry (LC–MS) and a powerful data analysis software tool named pLink. To facilitate application of this method, we present step-by-step disulfide mapping protocols for three types of samples—purified proteins in solution, proteins in SDS-PAGE gels, and complex protein mixtures in solution. The minimum amount of protein required for this method can be as low as several hundred nanograms for purified proteins, or tens of micrograms for a mixture of hundreds of proteins. The entire workflow—from sample preparation to LC–MS and data analysis—is described in great detail. We believe that this protocol can be easily implemented in any laboratory with access to a fast-scanning, high-resolution, and accurate-mass LC–MS system.