Peroxisome proliferator-activated receptor δ rescues xCT-deficient cells from ferroptosis by targeting peroxisomes

KSHV vIL-6 promotes SIRT3-induced deacetylation of SERBP1 to inhibit ferroptosis and enhance cellular transformation by inducing lipoyltransferase 2 mRNA degradation

Ferroptosis, a defensive strategy commonly employed by the host cells to restrict pathogenic infections, has been implicated in the development and therapeutic responses of various types of cancer. However, the role of ferroptosis in oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV)-induced cancers remains elusive. While a growing number of non-histone proteins have been identified as acetylation targets, the functions of these modifications have yet to be revealed. Here, we show KSHV reprogramming of host acetylation proteomics following cellular transformation of rat primary mesenchymal precursor. Among them, SERPINE1 mRNA binding protein 1 (SERBP1) deacetylation is increased and required for KSHV-induced cellular transformation. Mechanistically, KSHV-encoded viral interleukin-6 (vIL-6) promotes SIRT3 deacetylation of SERBP1, preventing its binding to and protection of lipoyltransferase 2 (Lipt2) mRNA from mRNA degradation resulting in ferroptosis. Consequently, a SIRT3-specific inhibitor, 3-TYP, suppresses KSHV-induced cellular transformation by inducing ferroptosis. Our findings unveil novel roles of vIL-6 and SERBP1 deacetylation in regulating ferroptosis and KSHV-induced cellular transformation, and establish the vIL-6-SIRT3-SERBP1-ferroptosis pathways as a potential new therapeutic target for KSHV-associated cancers.

Emerging small molecule inhibitors of Bach1 as therapeutic agents: Rationale, recent advances, and future perspectives

The transcription factor Nrf2 is the master regulator of cellular stress response, facilitating the expression of cytoprotective genes, including those responsible for drug detoxification, immunomodulation, and iron metabolism. FDA-approved Nrf2 activators, Tecfidera and Skyclarys for patients with multiple sclerosis and Friedreich's ataxia, respectively, are non-specific alkylating agents exerting side effects. Nrf2 is under feedback regulation through its target gene, transcriptional repressor Bach1. Specifically, in Parkinson's disease and other neurodegenerative diseases with Bach1 dysregulation, excessive Bach1 accumulation interferes with Nrf2 activation. Bach1 is a heme sensor protein, which, upon heme binding, is targeted for proteasomal degradation, relieving the repression of Nrf2 target genes. Ideally, a combination of Nrf2 stabilization and Bach1 inhibition is necessary to achieve the full therapeutic benefits of Nrf2 activation. Here, we discuss recent advances and future perspectives in developing small molecule inhibitors of Bach1, highlighting the significance of the Bach1/Nrf2 signaling pathway as a promising neurotherapeutic strategy.

Core clock gene BMAL1 and RNA-binding protein MEX3A collaboratively regulate Lgr5 expression in intestinal crypt cells

The intestinal epithelium is highly regenerative. Rapidly proliferating LGR5+ crypt base columnar (CBC) cells are responsible for epithelial turnover needed to maintain intestinal homeostasis. Upon tissue damage, loss of LGR5+ CBCs can be compensated by activation of quiescent +4 intestinal stem cells (ISCs) or early progenitor cells to restore intestinal regeneration. LGR5+ CBC self-renewal and ISC conversion to LGR5+ cells are regulated by external signals originating from the ISC niche. In contrast, little is known about intrinsic regulatory mechanisms critical for maintenance of LGR5+ CBC homeostasis. We found that LGR5 expression in intestinal crypt cells is controlled by the circadian core clock gene BMAL1 and the BMAL1-regulated RNA-binding protein MEX3A. BMAL1 directly activated transcription of Mex3a. MEX3A in turn bound to and stabilized Lgr5 mRNA. Bmal1 depletion reduced Mex3a and Lgr5 expression and led to increased ferroptosis, which consequently decreased LGR5+ CBC numbers and increased the number of crypt cells expressing +4 ISC marker BMI1. Together, these findings reveal a BMAL1-centered intrinsic regulatory pathway that maintains LGR5 expression in the crypt cells and suggest a potential mechanism contributing to ISC homeostasis.

Red clover (Trifolium pratense L.) extract inhibits ferroptotic cell death by modulating cellular iron homeostasis

ETHNOPHARMACOLOGICAL RELEVANCE

Red clover (Trifolium pratense L.) is a traditional Chinese medicine and use as herbal medicine which has the effects of regulating menopausal symptoms, heart problem, inflammatory disease, psoriasis and cognitive deficits. In previous reported, the studies of red clover were mainly focused on clinical practice. the pharmacological functions of red clover not fully elucidated.

AIM OF THE STUDY

To identify the molecules that regulate ferroptosis, we examined whether red clover (Trifolium pratense L.) extracts (RCE) affected ferroptosis induced by chemical treatment or cystine/glutamate antiporter (xCT) deficiency.

MATERIALS AND METHODS

Cellular models for ferroptosis were induced by erastin/Ras-selectiv lethal 3 (RSL3) treatment or xCT deficiency in mouse embryonic fibroblasts (MEFs). Intracellular iron and peroxidized lipid levels were determined using Calcein-AM and BODIPY-C₁₁ fluorescence dyes, respectively. Protein and mRNA were quantified by Western blot and real-time polymerase chain reaction, respectively. RNA sequencing analysis was performed on xCT^-/- MEFs.

RESULTS

RCE significantly suppressed ferroptosis induced by both erastin/RSL3 treatment and xCT deficiency. The anti-ferroptotic effects of RCE correlated to ferroptotic phenotypic changes such as cellular iron accumulation and lipid peroxidation in cellular ferroptosis models. Importantly, RCE affected levels of iron metabolism-related proteins including iron regulatory protein 1, ferroportin 1 (FPN1), divalent metal transporter 1, and transferrin receptor. RNA sequencing analysis of xCT^-/- MEFs identified that expression of cellular defense genes was upregulated, while expression of cell death-related genes was downregulated, by RCE.

CONCLUSION

RCE potently suppressed ferroptosis triggered both by erastin/RSL3 treatment and xCT deficiency by modulating cellular iron homeostasis. This is the first report that RCE has therapeutic potential in diseases associated with ferroptotic cell death, particularly ferroptosis induced by dysregulation of cellular iron metabolism.

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

The underlying pathological mechanism of ferroptosis in the development of cardiovascular disease

Cardiovascular diseases (CVDs) have been attracting the attention of academic society for decades. Numerous researchers contributed to figuring out the core mechanisms underlying CVDs. Among those, pathological decompensated cellular loss posed by cell death in different kinds, namely necrosis, apoptosis and necroptosis, was widely regarded to accelerate the pathological development of most heart diseases and deteriorate cardiac function. Recently, apart from programmed cell death revealed previously, ferroptosis, a brand-new cellular death identified by its ferrous-iron-dependent manner, has been demonstrated to govern the occurrence and development of different cardiovascular disorders in many types of research as well. Therefore, clarifying the regulatory function of ferroptosis is conducive to finding out strategies for cardio-protection in different conditions and improving the prognosis of CVDs. Here, molecular mechanisms concerned are summarized systematically and categorized to depict the regulatory network of ferroptosis and point out potential therapeutic targets for diverse cardiovascular disorders.

PPARα alleviates iron overload-induced ferroptosis in mouse liver

Ferroptosis is an iron‐dependent form of non‐apoptotic cell death implicated in liver, brain, kidney, and heart pathology. How ferroptosis is regulated remains poorly understood. Here, we show that PPARα suppresses ferroptosis by promoting the expression of glutathione peroxidase 4 (Gpx4) and by inhibiting the expression of the plasma iron carrier TRF. PPARα directly induces Gpx4 expression by binding to a PPRE element within intron 3. PPARα knockout mice develop more severe iron accumulation and ferroptosis in the liver when fed a high‐iron diet than wild‐type mice. Ferrous iron (Fe²⁺) triggers ferroptosis via Fenton reactions and ROS accumulation. We further find that a rhodamine‐based "turn‐on" fluorescent probe(probe1) is suitable for the in vivo detection of Fe²⁺. Probe1 displays high selectivity towards Fe²⁺, and exhibits a stable response for Fe²⁺ with a concentration of 20 μM in tissue. Our data thus show that PPARα activation alleviates iron overload‐induced ferroptosis in mouse livers through Gpx4 and TRF, suggesting that PPARα may be a promising therapeutic target for drug discovery in ferroptosis‐related tissue injuries. Moreover, we identified a fluorescent probe that specifically labels ferrous ions and can be used to monitor Fe²⁺in vivo.

The Mechanisms of Ferroptosis and the Applications in Tumor Treatment: Enemies or Friends?

Ferroptosis, as a newly discovered non-apoptotic cell death mode, is beginning to be explored in different cancer. The particularity of ferroptosis lies in the accumulation of iron dependence and lipid peroxides, and it is different from the classical cell death modes such as apoptosis and necrosis in terms of action mode, biochemical characteristics, and genetics. The mechanism of ferroptosis can be divided into many different pathways, so it is particularly important to identify the key sites of ferroptosis in the disease. Herein, based on ferroptosis, we analyze the main pathways in detail. More importantly, ferroptosis is linked to the development of different systems of the tumor, providing personalized plans for the examination, treatment, and prognosis of cancer patients. Although some mechanisms and side effects of ferroptosis still need to be studied, it is still a promising method for cancer treatment.

PPARδ Activation Mitigates 6-OHDA-Induced Neuronal Damage by Regulating Intracellular Iron Levels

Intracellular iron accumulation in dopaminergic neurons contributes to neuronal cell death in progressive neurodegenerative disorders such as Parkinson’s disease. However, the mechanisms of iron homeostasis in this context remain incompletely understood. In the present study, we assessed the role of the nuclear receptor peroxisome proliferator-activated receptor δ (PPARδ) in cellular iron homeostasis. We identified that PPARδ inhibited 6-hydroxydopamine (6-OHDA)-triggered neurotoxicity in SH-SY5Y neuroblastoma cells. PPARδ activation with GW501516, a specific PPARδ agonist, mitigated 6-OHDA-induced neuronal damage. Further, PPARδ activation also suppressed iron accumulation, which contributes to 6-OHDA-induced neuronal damage. PPARδ activation attenuated 6-OHDA-induced neuronal damage in a similar manner to that of the iron chelator deferoxamine. We further elucidated that PPARδ modulated cellular iron homeostasis by regulating expression of divalent metal transporter 1, ferroportin 1, and ferritin, but not transferrin receptor 1, through iron regulatory protein 1 in 6-OHDA-treated cells. Interestingly, PPARδ activation suppressed 6-OHDA-triggered generation of reactive oxygen species and lipid peroxides. The effects of GW501516 were abrogated by shRNA knockdown of PPARδ, indicating that the effects of GW501516 were PPARδ-dependent. Taken together, these findings suggest that PPARδ attenuates 6-OHDA-induced neurotoxicity by preventing intracellular iron accumulation, thereby suppressing iron overload-associated generation of reactive oxygen species and lipid peroxides, key mediators of ferroptotic cell death.

Superoxide Radicals in the Execution of Cell Death

Superoxide is a primary oxygen radical that is produced when an oxygen molecule receives one electron. Superoxide dismutase (SOD) plays a primary role in the cellular defense against an oxidative insult by ROS. However, the resulting hydrogen peroxide is still reactive and, in the presence of free ferrous iron, may produce hydroxyl radicals and exacerbate diseases. Polyunsaturated fatty acids are the preferred target of hydroxyl radicals. Ferroptosis, a type of necrotic cell death induced by lipid peroxides in the presence of free iron, has attracted considerable interest because of its role in the pathogenesis of many diseases. Radical electrons, namely those released from mitochondrial electron transfer complexes, and those produced by enzymatic reactions, such as lipoxygenases, appear to cause lipid peroxidation. While GPX4 is the most potent anti-ferroptotic enzyme that is known to reduce lipid peroxides to alcohols, other antioxidative enzymes are also indirectly involved in protection against ferroptosis. Moreover, several low molecular weight compounds that include α-tocopherol, ascorbate, and nitric oxide also efficiently neutralize radical electrons, thereby suppressing ferroptosis. The removal of radical electrons in the early stages is of primary importance in protecting against ferroptosis and other diseases that are related to oxidative stress.