Heavy-Metals-Mediated Phospholipids Scrambling by Human Phospholipid Scramblase 3: A Probable Role in Mitochondrial Apoptosis

The Rpf107 gene, a homolog of LOR, is required for the symbiotic nodulation of Robinia pseudoacacia

MAIN CONCLUSION

Rpf107 is involved in the infection process of rhizobia and the maintenance of symbiotic nitrogen fixation in black locust root nodules. The LURP-one related (LOR) protein family plays a pivotal role in mediating plant defense responses against both biotic and abiotic stresses. However, our understanding of its function in the symbiotic interaction between legumes and rhizobia remains limited. Here, Rpf107, a homolog of LOR, was identified in Robinia pseudoacacia (black locust). The subcellular localization of Rpf107 was analyzed, and its function was investigated using RNA interference (RNAi) and overexpression techniques. The subcellular localization assay revealed that Rpf107 was mainly distributed in the plasma membrane and nucleus. Rpf107 silencing prevented rhizobial infection and hampered plant growth. The number of infected cells in the nitrogen fixation zone of the Rpf107-RNAi nodules was also noticeably lower than that in the control nodules. Notably, Rpf107 silencing resulted in bacteroid degradation and the premature aging of nodules. In contrast, the overexpression of Rpf107 delayed the senescence of nodules and prolonged the nitrogen-fixing ability of nodules. These results demonstrate that Rpf107 was involved in the infection of rhizobia and the maintenance of symbiotic nitrogen fixation in black locust root nodules. The findings reveal that a member of the LOR protein family plays a role in leguminous root nodule symbiosis, which is helpful to clarify the functions of plant LOR protein family and fully understand the molecular mechanisms underlying legume-rhizobium symbiosis.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Phospholipid scramblase 3: a latent mediator connecting mitochondria and heavy metal apoptosis

Lead and mercury are the ubiquitous heavy metals triggering toxicity and initiating apoptosis in cells. Though the toxic effects of heavy metals on various organs are known, there is a paucity of information on the mechanisms that instigate the current study. A plausible role of phospholipid scramblase 3 (PLSCR3) in Pb2+ and Hg2+ induced apoptosis was investigated with human embryonic kidney (HEK 293) cells. After 12 h of exposure, ~30-40% of the cells were in the early stage of apoptosis with increased reactive oxygen species (ROS), decreased mitochondrial membrane potential, and increased intracellular calcium levels. Also, ~20% of the cardiolipin localized within the inner mitochondrial membrane was translocated to the outer mitochondrial membrane along with the mobilization of truncated Bid (t-Bid) to the mitochondria and cytochrome c from the mitochondria. The endogenous expression levels of PLSCR3, caspase 8, and caspase 3 were upregulated in Pb2+ and Hg2+ induced apoptosis. The activation and upregulation of PLSCR3 mediate CL translocation playing a potential role in initiating the heavy metal-induced apoptosis. Therefore, PLSCR3 could be the linker between mitochondria and heavy metal apoptosis.

Design, synthesis and pharmacological characterization of aminopyrimidine derivatives as BTK/FLT3 dual-target inhibitors against acute myeloid leukemia

A novel class of aminopyrimidine-based Bruton's tyrosine kinase (BTK) and FMS-like tyrosine kinase 3 (FLT3) dual-target inhibitors based on the BTK inhibitor spebrutinib was designed for the treatment of acute myeloid leukemia. Representative compounds 14d, 14g, 14j and 14m effectively inhibited BTK, FLT3, and FLT3(D835Y) mutant activities with low nanomolar IC₅₀'s. These compounds displayed potent antiproliferative activities against leukemia cells with IC₅₀'s of 0.29-950 nM. In particular, 14m had IC₅₀ values 101-1045 times lower than those of spebrutinib against all cancer cell lines tested. Compound 14m effectively induced autophagy and apoptosis in MV-4-11 cells through regulating related proteins in a dose-dependent manner. Finally, intraperitoneal administration of 14m at 20 mg/kg significantly repressed the growth of MV-4-11 cells with a TGI value of 95.68% with no apparent toxicity. These BTK/FLT3 dual-target inhibitors represent promising leads for further structural optimization and antitumor mechanism studies.

Di-(2-Ethylhexyl) Phthalate and Microplastics Induced Neuronal Apoptosis through the PI3K/AKT Pathway and Mitochondrial Dysfunction

Di-(2-Ethylhexyl) phthalate (DEHP) and microplastics (MPs) have released widespread residues to the environment and possess the ability to cause damage to humans and animals. However, there are still gaps in the study of damage to neurons caused by DEHP and MPs in mice cerebra and whether they have combined toxic effects. To investigate the underlying mechanism of action, mice were fed 200 mg/kg DEHP and 10 mg/L MPs in vivo. In vitro, NS20Y (CBNumber: CB15474825) cells were treated with 25 μM DEHP and 775 mg/L MPs. Next, qRT-PCR and western blot analysis were performed to evaluate PI3K/AKT pathway genes, mitochondrial dynamics-related genes, apoptosis-related genes, and GSK-3β and its associated genes, mRNA, and protein expression. To determine pathological changes in the mice cerebra, hematoxylin and eosin (H&E) staining, transmission electron microscopy, and TUNEL staining were employed. To determine the levels of reactive oxygen species (ROS) and apoptosis cells in vitro, ROS staining, acridine orange/ethidium bromide (AO/EB) staining, and flow cytometry were performed. Our results demonstrated that DEHP and MPs caused changes in mitochondrial function, and GSK-3β and its associated gene expression in mice through the PI3K/AKT pathway, which eventually led to apoptosis of neurons. Moreover, our findings showed that DEHP and MPs have a combined toxic effect on mice cerebra. Our findings facilitate the understanding of the neurotoxic effects of DEHP and MPs on neurons in the cerebra of mice and help identify the important role of maintaining normal mitochondrial function in protecting cerebrum health.

Are cysteine residues of human phospholipid scramblase 1 essential for Pb2+ and Hg2+ binding-induced scrambling of phospholipids?

Lead and mercury being common environmental pollutants are often associated with erythrocytes, where phosphatidylserine (PS) exposure-mediated procoagulant activation is induced. Human phospholipid scramblase 1 (hPLSCR1) identified in the erythrocyte membrane is a type II transmembrane protein involved in Ca²⁺-dependent bidirectional scrambling of phospholipids (PL) during blood coagulation, cell activation, and apoptosis. The prominent role of hPLSCR1 in Pb²⁺ and Hg²⁺ poisoning was demonstrated by a biochemical assay, where recombinant hPLSCR1 induced PL scrambling across bilayer with a higher binding affinity (K_d) towards Hg²⁺ (4.1 µM) and Pb²⁺ (5.8 µM) than Ca²⁺ (25.6 mM). The increased affinity could be the outcome of heavy metals interacting at auxiliary sites other than the calcium-binding motif of hPLSCR1. Similar to other metal-binding proteins, cysteine-based metal-binding motifs could be the potential additional binding sites in hPLSCR1. To explore the hypothesis, the cysteines were chemically modified, which significantly reduced only the Hg²⁺- and Pb²⁺-induced scrambling activity leaving Ca²⁺-induced activity unaltered. Recombinant constructs with deletion of prominent cysteine residues and point mutation in the calcium-binding motif including Δ100-hPLSCR1, Δ160-hPLSCR1, and D275A-hPLSCR1 were generated, purified, and assayed for scramblase activity. The cysteine-deleted constructs of hPLSCR1 showed reduced binding affinity (K_d) for Hg²⁺ and Pb²⁺ without altering the Ca²⁺-binding affinity whereas the point mutant had completely lost its affinity for Ca²⁺ and reduced affinities for Hg²⁺ and Pb²⁺. The results accentuated the significance of cysteine residues as additional binding sites for heavy metal ions in hPLSCR1.

Cognitive Impairment Induced by Lead Exposure during Lifespan: Mechanisms of Lead Neurotoxicity

Lead (Pb) is considered a strong environmental toxin with human health repercussions. Due to its widespread use and the number of people potentially exposed to different sources of this heavy metal, Pb intoxication is recognized as a public health problem in many countries. Exposure to Pb can occur through ingestion, inhalation, dermal, and transplacental routes. The magnitude of its effects depends on several toxicity conditions: lead speciation, doses, time, and age of exposure, among others. It has been demonstrated that Pb exposure induces stronger effects during early life. The central nervous system is especially vulnerable to Pb toxicity; Pb exposure is linked to cognitive impairment, executive function alterations, abnormal social behavior, and fine motor control perturbations. This review aims to provide a general view of the cognitive consequences associated with Pb exposure during early life as well as during adulthood. Additionally, it describes the neurotoxic mechanisms associated with cognitive impairment induced by Pb, which include neurochemical, molecular, and morphological changes that jointly could have a synergic effect on the cognitive performance.