Increased cellular protein modification by methylglyoxal activates endoplasmic reticulum-based sensors of the unfolded protein response

The Hepatic Axis Fructose-Methylglyoxal-AMPK: Starring or Secondary Role in Chronic Metabolic Disease?

Biochemical alterations linked to metabolic syndrome (MetS), type 2 diabetes (T2DM), and metabolic dysfunction-associated steatotic liver disease (MASLD) may be brought on by the Western diet. Based on research conducted over the past decade, fructose is one of the main culprits. Over 80% of ingested fructose is metabolized by the liver at first pass, where it stimulates de novo lipogenesis (DNL) to drive hepatic triglyceride (TG) synthesis, which contributes to MASLD, hepatic insulin resistance (IR), and dyslipidemia. Fructose reduction produces quick and significant amelioration in these metabolic disturbances. We hereby propose potential overarching processes that can link these pathways to signaling disruption by the critical metabolic sensor AMP-activated protein kinase (AMPK). We proffer that when large amounts of fructose and glucose enter the liver, triose fluxes may be sufficient to produce transient increases in methylglyoxal (MG), allowing steady-state concentrations between its production and catabolism by glyoxalases to be high enough to modify AMPK-sensitive functional amino acid residues. These reactions would transiently interfere with AMPK activation by both AMP and aldolase. Such a sequence of events would boost the well-documented lipogenic impact of fructose. Given that MG adducts are irreversible, modified AMPK molecules would be less effective in metabolite sensing until they were replaced by synthesis. If proven, this mechanism provides another avenue of possibilities to tackle the problem of fructose in our diet. We additionally discuss potential multimodal treatments and future research avenues for this apparent hepatic AMPK malfunction.

Exploring Glyoxalase Strategies for Managing Sugar-Induced Chronic Diseases

The liver's crucial role in methylglyoxal (MG) metabolism is frequently overlooked in the literature. We present a perspective that enhances the current understanding of the role of methylglyoxal (MG) and the glyoxalase cycle in the pathogenesis of insulin resistance and obesity, ultimately leading to type 2 diabetes mellitus (DM) and cardiovascular disease (CVD). Fructose may be a significant substrate contributing, particularly in contemporary times, to the flux of trioses in the liver, accounting for a substantial portion of MG production. The steady-state concentration of MG-and the subsequent modification of proteins-would then be determined by the flux of trioses, their utilization in lipogenesis, and their decomposition into MG, which is further converted into D-lactate by glyoxalase enzymes GLO1 and GLO2. Consequently, enhancing the activity and/or expression of GLO1 could potentially mitigate the adverse effects of fructose in the liver. Additional research and validation are required to confirm these biological pathways. These arguments are in favor of further research into safe and efficient ways to activate the glyoxalase pathway to lessen the negative effects of fructose metabolism that lead to insulin resistance (IR) and its related repercussions.

SEC24D depletion induces osteogenic differentiation deficiency by inactivating the ATF6/TGF-β/Runx2 regulatory loop

Protein coat complexes strongly influence intracellular cargo trafficking. Coatopathies represent a wide range of genetic conditions caused by mutations in protein coat components. The SEC24D gene, which encodes a Sec24 isoform that constitutes a cargo-specific capturer in the COPII coat, is responsible for a rare type of autosomal recessive osteogenesis imperfecta. We report an OI patient. Clinical and imaging findings suggested that the patient had OI. Genetic detection by whole-exome sequencing (WES) identified a compound heterozygous SEC24D variants, including c.2609_2610delGA (p. R870fs*10) and c.938G>A (p. R313H). In silico analysis suggested that the missense R313H mutation most likely affects protein stability and secondary structure. In vitro studies showed that knockdown or mutation of SEC24D affected the osteogenic differentiation of mesenchymal stem cells (MSCs) and inducted ER stress. Transcriptomic sequencing suggested that the TGF-β pathway mediated the destructive effect of SEC24D depletion on osteogenic differentiation. Further experiments confirmed that ATF6 participated in regulating the TGF-β pathway and osteogenic biomarkers by SEC24D. This study identified a SEC24D variation causing OI, which expanded the mutation spectrum of this gene. Further studies on the mechanism of action showed that SEC24D defects may induce osteogenic differentiation deficiency by inactivating the ATF6/TGF-β/Runx2 regulatory loop.

Dual roles of methylglyoxal in cancer

Cancer treatment currently includes a variety of approaches. Chemotherapy, targeted therapy, and immunotherapy are combined based on cancer characteristics to develop personalized treatment plans. However, drug resistance can hinder the progress of treatment over time. Methylglyoxal (MG) is a metabolite with hormesis, exhibiting both pro-tumor and anti-tumor actions depending on its concentration during cancer progression. The MG-related metabolic pathway is being explored in the development of anti-cancer drugs, focusing on reducing MG stress or exploiting its cytotoxic effects to inhibit cancer progression. This article investigates the dual role of MG in cancer, emphasizing its effects on cell metabolism and tumor progression. It proposes MG capture therapy for the pre-cancerous stage and MG toxicity therapy for the cancer stage, contributing to the development of precise and individualized cancer treatments.

Methylglyoxal Formation-Metabolic Routes and Consequences

Methylglyoxal (MGO), a by-product of glycolysis, plays a significant role in cellular metabolism, particularly under stress conditions. However, MGO is a potent glycotoxin, and its accumulation has been linked to the development of several pathological conditions due to oxidative stress, including diabetes mellitus and neurodegenerative diseases. This paper focuses on the biochemical mechanisms by which MGO contributes to oxidative stress, particularly through the formation of advanced glycation end products (AGEs), its interactions with antioxidant systems, and its involvement in chronic diseases like diabetes, neurodegeneration, and cardiovascular disorders. MGO exerts its effects through multiple signaling pathways, including NF-κB, MAPK, and Nrf2, which induce oxidative stress. Additionally, MGO triggers apoptosis primarily via intrinsic and extrinsic pathways, while endoplasmic reticulum (ER) stress is mediated through PERK-eIF2α and IRE1-JNK signaling. Moreover, the activation of inflammatory pathways, particularly through RAGE and NF-κB, plays a crucial role in the pathogenesis of these conditions. This study points out the connection between oxidative and carbonyl stress due to increased MGO formation, and it should be an incentive to search for a marker that could have prognostic significance or could be a targeted therapeutic intervention in various diseases.

T-2 Toxin Nephrotoxicity: Toxic Effects, Mechanisms, Mitigations, and Future Perspectives

T-2 toxin is a highly toxic fungal toxin that threatens humans and animals' health. As a major detoxifying and metabolic organ, the kidney is also a target of T-2 toxin. This article reviews T-2 toxin nephrotoxicity research progress, covering renal structure and function damage, nephrotoxicity mechanisms, and detoxification methods to future research directions. T-2 toxin damages kidney structure, causing renal dysfunction. The nephrotoxicity mechanism of T-2 toxin involves multiple factors including oxidative stress, endoplasmic reticulum stress, mitophagy, inflammatory responses, and apoptosis, which are intertwined and interdependent. Current detoxification strategies mainly involve reducing T-2 toxin in feedstuff and using antioxidant substances, but both have limits. Future research should focus on renal cells sensitivity to T-2 toxin, exploring key molecules in T-2 toxin's nephrotoxicity, renal injury's impact on other organs, and better detoxification methods. This review aims to guide future research and underpin T-2 toxin-induced nephrotoxicity prevention and treatment.

Polysulfide and persulfide-mediated activation of the PERK-eIF2α-ATF4 pathway increases Sestrin2 expression and reduces methylglyoxal toxicity

Unfolded protein response (UPR) is activated in cells under endoplasmic reticulum (ER) stress. One sensor protein involved in this response is PERK, which is activated through its redox-dependent oligomerization. Prolonged UPR activation is associated with the development and progression of various diseases, making it essential to understanding the redox regulation of PERK. Sulfane sulfur, such as polysulfides and persulfides, can modify the cysteine residues and regulate the function of various proteins. However, the regulatory mechanism and physiological effects of sulfane sulfur on the PERK-eIF2α-ATF4 pathway remain poorly understood. This study focuses on the persulfidation of PERK to elucidate the effects of polysulfides on the PERK-eIF2α-ATF4 pathway and investigate its cytoprotective mechanism. Here, we demonstrated that polysulfide treatment promoted the oligomerization of PERK and PTP1B in neuronal cells using western blotting under nonreducing conditions. We also observed that l-cysteine, a biological source of sulfane sulfur, promoted the oligomerization of PERK and the knockdown of CBS and 3-MST, two sulfane sulfur-producing enzymes, and reduced PERK oligomerization induced by l-cysteine treatment. Furthermore, the band shift assay and LC-MS/MS studies revealed that polysulfides and persulfides induce PTP1B and PERK persulfidation. Additionally, polysulfides promoted eIF2α phosphorylation and ATF4 accumulation in the nucleus, suggesting that polysulfides activate the PERK-eIF2α-ATF4 pathway in neuronal cells. Moreover, polysulfides protected neuronal cells from methylglyoxal-induced toxicity, and this protective effect was reduced when the expression of Sestrin2, regulated by ATF4 activity, was suppressed. This study identified a novel mechanism for the activation of the PERK-eIF2α-ATF4 pathway through persulfidation by polysulfides and persulfides. Interestingly, activation of this pathway overcame the toxicity of methylglyoxal in dependence on Sestrin2 expression. These findings deepen our understanding of neuronal diseases involving ER stress and UPR disturbance and may inspire new therapeutic strategies.

Unraveling the impaired incretin effect in obesity and type 2 diabetes: Key role of hyperglycemia-induced unscheduled glycolysis and glycolytic overload

Glucagon-like peptide-1 (GLP-1) agonists and GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) co-agonists are major treatment options for subjects with obesity and patients with type 2 diabetes mellitus (T2DM). They counter without addressing the mechanistic cause of the impaired incretin effect associated with obesity and T2DM. Incretin effect impairment is characterized by decreased secretion of incretins from enteroendocrine cells and incretin resistance of pancreatic β-cells. It is linked to hyperglycemia. We present evidence that subversion of the gating of glucose entry into glycolysis, mainly by glucokinase (hexokinase-4), during persistent hyperglycemia in enteroendocrine cells, pancreatic β- and α-cells and appetite-regulating neurons contributes to the biochemical mechanism of the impaired incretin effect. Unscheduled glycolysis and glycolytic overload thereby produced decreases cell signalling of incretin secretion to glucose and other secretion stimuli and incretin receptor responses. This mechanism provides a guide for development of alternative therapies targeting recovery of the impaired incretin effect.