Paraoxonase 2 protects against the CML mediated mitochondrial dysfunction through modulating JNK pathway in human retinal cells

Investigation of the Molecular Mechanisms of Paraoxonase-2 Mediated Radiotherapy and Chemotherapy Resistance in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is a common form of cancer, with 390,000 new cases estimated for 2022. OSCC has a poor prognosis, largely due to a high recurrence rate and resistance to therapy. Cancer cells develop resistance to standard therapy owing to various factors, such as genetic predispositions, alterations in the apoptotic pathway coupled with DNA repair pathways, drug efflux, and drug detoxification. This review is aimed at exploring the crucial role of paraoxonase 2 (PON2) in conferring resistance to chemotherapy and radiotherapy in OSCC cells. PON2, an antioxidant enzyme, protects cancer cells from the oxidative stress caused by these treatments. By influencing apoptotic pathways and DNA repair mechanisms, PON2 can reduce the effectiveness of therapy. This review is an attempt to explore the complex molecular mechanisms modulated by PON2, such as the mitigation of oxidative stress, enhancement of DNA repair, apoptosis regulation, drug efflux modulation, and drug detoxification, which decrease treatment efficacy.

PON-1 and PON-2 Polymorphisms and PON-1 Paraoxonase Activity in People Living with HIV-1

Antiretroviral therapy (ART) has significantly improved the life expectancy of people living with HIV-1 (PLWH). However, prolonged ART use is linked to metabolic alterations and oxidative stress. The paraoxonase (PON) enzymes, especially PON-1 and PON-2, are critical in maintaining antioxidant balance. Their activity can be influenced by polymorphisms such as Q192R and L55M in PON-1 and A148G and S311C in PON-2. This study examines the impact of these polymorphisms on paraoxonase activity, lipid metabolism, and infection markers in PLWH under various ART regimens. This is a case-control study with 525 participants, 175 healthy controls (HC) and 350 PLWH divided into subgroups: T0 (ART-naïve, n = 48), T1 (ART with reverse transcriptase inhibitors, n = 159), and T2 (ART with protease inhibitors, n = 143). Paraoxonase activity was higher in PLWH (123.0; IQR: 62.0-168.0) compared to HC (91.0; IQR: 48.0-136.0, p < 0.001) but similar between HC and T0 (p = 0.594). T1 (125.0; IQR: 65.5-166.0) and T2 (123.0; IQR: 61.0-182.0) showed higher activity than HC (p = 0.002 and 0.003). Among 61 complete genotypes, 13 were unique to PLWH and 6 to HC (p < 0.001). L55L was more frequent in HC (49.7% vs. 36.9% in PLWH), while M55M was higher in PLWH (p = 0.004). The S311C genotype was more frequent in HC (39.2%) than PLWH (24.9%) (p = 0.003). The L55L genotype conferred 59.9% protection against HIV-1 (OR: 0.401; 95% CI: 0.228-0.704), while the M allele increased susceptibility by ~69% (OR: 1.694; 95% CI: 1.173-2.446). The M55M genotype and/or M allele may be linked to HIV-1 susceptibility. Prolonged ART use elevates PON-1 activity in PLWH.

Retinal light damage: From mechanisms to protective strategies

Visible light serves as a crucial medium for vision formation.;however, prolonged or excessive exposure to light is recognized as a significant etiological factor contributing to retinal degenerative diseases. The retina, with its unique structure and adaptability, relies on the homeostasis of cellular functions to maintain visual health. Under normal conditions, the retina can mount adaptive responses to various insults, including light-induced damage. Unfortunately, exposure to intense and excessive light triggers a cascade of pathological alterations in retinal photoreceptor cells, pigment epithelial cells, ganglion cells, and glial cells. These alterations encompass disruption of intracellular REDOX and Ca²⁺ homeostasis, pyroptosis, endoplasmic reticulum stress, autophagy, and the release of inflammatory cytokines, culminating in irreversible retinal damage. We first delineate the mechanisms of retinal light damage through 4 main avenues: mitochondria function, endoplasmic reticulum stress, cell autophagy, and inflammation. Subsequently, we discuss protective strategies against retinal light damage, aiming to guide research toward the prevention and treatment of light-induced retinal conditions.

Unveiling the therapeutic potential of a mutated paraoxonase 2 in diabetic retinopathy: Defying glycation, mitigating oxidative stress, ER stress and inflammation

Paraoxonase 2 (PON2) is an intracellular anti-oxidant protein ubiquitously expressed in all cells and reduces reactive oxygen species, endoplasmic reticulum (ER) stress, further improves mitochondrial function and thereby shows anti-apoptotic function. In diabetes and its complications this PON gets glycated and becomes in effective. The PON activity is reported to be reduced in diabetic retinopathy and we have earlier showed Carboxy methyl lysine (AGE) decreased PON2 expression and activity in Human retinal endothelial cells (HREC) . In this study, we have designed and developed a mutated PON2 by in silico and in vitro approach which can resist glycation. Where in glycation-prone residues in PON2 was predicted using in silico analyses and a mutated PON2 was developed using in vitro site directed mutagenesis (SDM) assay mPON2 (mutant PON2-PON2-K70A) and its efficacy was compared with wPON2 (wild type PON2). CML glycated wPON2 and reduced its activity when compared with mPON2 in HREC confirmed by immunoprecipitation and in vitro experiments. Additionally, mPON2 interaction efficiency with its substrates was higher than wPON2 by insilico assay and demonstrated enhanced inhibition against CML-induced oxidative stress, ER stress, pro-inflammation, and mitochondrial fission than wPON2 by invitro assay. Further mPON2 showed increased inhibition of phosphorylation of NFĸB induced by CML. Our investigation establishes that the over expression of mPON2 in HREC can defy glycation and therefore mitigate ER stress and inflammation against CML than endogenous wPON2. These findings imply that mPON2 can be a beneficial therapeutic target against diabetic retinopathy.

Intermittent fasting promotes adipocyte mitochondrial fusion through Sirt3-mediated deacetylation of Mdh2

Fat deposition and lipid metabolism are closely related to the morphology, structure and function of mitochondria. The morphology of mitochondria between fusion and fission processes is mainly regulated by protein posttranslational modification. Intermittent fasting (IF) promotes high expression of Sirtuin 3 (Sirt3) and induces mitochondrial fusion in high-fat diet (HFD)-fed mice. However, the mechanism by which Sirt3 participates in mitochondrial protein acetylation during IF to regulate mitochondrial fusion and fission dynamics remains unclear. This article demonstrates that IF promotes mitochondrial fusion and improves mitochondrial function in HFD mouse inguinal white adipose tissue. Proteomic sequencing revealed that IF increased protein deacetylation levels in HFD mice and significantly increased Sirt3 mRNA and protein expression. After transfecting with Sirt3 overexpression or interference vectors into adipocytes, we found that Sirt3 promoted adipocyte mitochondrial fusion and improved mitochondrial function. Furthermore, Sirt3 regulates the JNK-FIS1 pathway by deacetylating malate dehydrogenase 2 (MDH2) to promote mitochondrial fusion. In summary, our study indicates that IF promotes mitochondrial fusion and improves mitochondrial function by upregulating the high expression of Sirt3 in HFD mice, promoting deacetylation of MDH2 and inhibiting the JNK-FIS1 pathway. This research provides theoretical support for studies related to energy limitation and animal lipid metabolism.

Paraoxonase 2 Deficiency Causes Mitochondrial Dysfunction in Retinal Pigment Epithelial Cells and Retinal Degeneration in Mice

Although AMD is a complex disease, oxidative stress is a crucial contributor to its development, especially in view of the higher oxygen demand of the retina. Paraoxonase 2 (PON2) is a ubiquitously and constitutively expressed antioxidant protein that is found intracellularly associated with mitochondrial membranes and modulates mitochondrial ROS production and function. The contribution of PON2 to AMD has not been studied to date. In this study, we examined the role of PON2 in AMD utilizing both in vitro and in vivo models of AMD with emphasis on mitochondrial function. Mitochondrial localization and regulation of PON2 following oxidative stress were determined in human primary cultured retinal pigment epithelium (hRPE) cells. PON2 was knocked down in RPE cells using siRNA and mitochondrial bioenergetics were measured. To investigate the function of PON2 in the retina, WT and PON2-deficient mice were administered NaIO3 (20 mg/kg) intravenously; fundus imaging, optical coherence tomography (OCT), electroretinography (ERG) were conducted; and retinal thickness and cell death were measured and quantified. In hRPE, mitochondrial localization of PON2 increased markedly with stress. Moreover, a time-dependent regulation of PON2 was observed following oxidative stress, with an initial significant increase in expression followed by a significant decrease. Mitochondrial bioenergetic parameters (basal respiration, ATP production, spare respiratory capacity, and maximal respiration) showed a significant decrease with oxidative stress, which was further exacerbated in the absence of PON2. NaIO3 treatment caused significant retinal degeneration, retinal thinning, and reduced rod and cone function in PON2-deficient mice when compared to WT mice. The apoptotic cells and active caspase 3 significantly increased in PON2-deficient mice treated with NaIO3, when compared to WT mice. Our investigation demonstrates that deficiency of PON2 results in RPE mitochondrial dysfunction and a decline in retinal function. These findings imply that PON2 may have a beneficial role in retinal pathophysiology and is worthy of further investigation.

Effects of Antioxidant Gene Overexpression on Stress Resistance and Malignization In Vitro and In Vivo: A Review

Reactive oxygen species (ROS) are normal products of a number of biochemical reactions and are important signaling molecules. However, at the same time, they are toxic to cells and have to be strictly regulated by their antioxidant systems. The etiology and pathogenesis of many diseases are associated with increased ROS levels, and many external stress factors directly or indirectly cause oxidative stress in cells. Within this context, the overexpression of genes encoding the proteins in antioxidant systems seems to have become a viable approach to decrease the oxidative stress caused by pathological conditions and to increase cellular stress resistance. However, such manipulations unavoidably lead to side effects, the most dangerous of which is an increased probability of healthy tissue malignization or increased tumor aggression. The aims of the present review were to collect and systematize the results of studies devoted to the effects resulting from the overexpression of antioxidant system genes on stress resistance and carcinogenesis in vitro and in vivo. In most cases, the overexpression of these genes was shown to increase cell and organism resistances to factors that induce oxidative and genotoxic stress but to also have different effects on cancer initiation and promotion. The last fact greatly limits perspectives of such manipulations in practice. The overexpression of GPX3 and SOD3 encoding secreted proteins seems to be the "safest" among the genes that can increase cell resistance to oxidative stress. High efficiency and safety potential can also be found for SOD2 overexpression in combinations with GPX1 or CAT and for similar combinations that lead to no significant changes in H₂O₂ levels. Accumulation, systematization, and the integral analysis of data on antioxidant gene overexpression effects can help to develop approaches for practical uses in biomedical and agricultural areas. Additionally, a number of factors such as genetic and functional context, cell and tissue type, differences in the function of transcripts of one and the same gene, regulatory interactions, and additional functions should be taken into account.