The role of PARP-1 and PARP-2 enzymes in metabolic regulation and disease

PAR level mediates the link between ROS and inflammatory response in patients with type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is characterized by disrupted glucose homeostasis and metabolic abnormalities, with oxidative stress and inflammation playing pivotal roles in its pathophysiology. Poly(ADP-ribosyl)ation (PARylation) is a post-translational process involving the addition of ADP-ribose polymers (PAR) to target proteins. While preclinical studies have implicated PARylation in the interplay between oxidative stress and inflammation in T2DM, direct clinical evidence in humans remains limited. This study investigates the relationship between oxidative stress, PARylation, and inflammatory response in T2DM patients.

METHODS

This cross-sectional investigation involved 61 T2DM patients and 48 controls. PAR levels were determined in peripheral blood cells (PBMC) by ELISA-based methodologies. Oxidative stress was assessed in plasma and PBMC. In plasma, we monitored reactive oxygen metabolites (d-ROMs) and ferric-reducing antioxidant power. In PBMC, we measured the expression of antioxidant enzymes SOD1, GPX1 and CAT by qPCR. Further, we evaluated the expression of inflammatory mediators such as IL6, TNF-α, CD68 and MCP1 by qPCR in PBMC.

RESULTS

T2DM patients exhibited elevated PAR levels in PBMC and increased d-ROMs in plasma. Positive associations were found between PAR levels and d-ROMs, suggesting a link between oxidative stress and altered PAR metabolism. Mediation analysis revealed that d-ROMs mediate the association between HbA1c levels and PAR, indicating oxidative stress as a potential driver of increased PARylation in T2DM. Furthermore, elevated PAR levels were found to be associated with increased expression of pro-inflammatory cytokines IL6 and TNF-α in the PBMC of T2DM patients.

CONCLUSIONS

This study highlights that hyperactivation of PARylation is associated with poor glycemic control and the resultant oxidative stress in T2DM. The increase of PAR levels is correlated with the upregulation of key mediators of the inflammatory response. Further research is warranted to validate these findings and explore their clinical implications.

NAD+ metabolism and therapeutic strategies in cardiovascular diseases

Nicotinamide adenine dinucleotide (NAD+) is a central and pleiotropic metabolite involved in cellular energy metabolism, cell signaling, DNA repair, and protein modifications. Cardiovascular diseases (CVDs) are the leading cause of death worldwide. Metabolic stress and aging directly affect the cardiovascular system. Compelling data suggest that NAD + levels decrease with age, obesity, and hypertension, which are all notable risk factors for CVD. In addition, the therapeutic elevation of NAD + levels reduces chronic low-grade inflammation, reactivates autophagy and mitochondrial biogenesis, and enhances oxidative metabolism in vascular cells of humans and rodents with vascular disorders. In preclinical models, NAD + boosting can also expand the health span, prevent metabolic syndrome, and decrease blood pressure. Moreover, NAD + storage by genetic, pharmacological, or natural dietary NAD + -increasing strategies has recently been shown to be effective in improving the pathophysiology of cardiac and vascular health in different animal models, and human health. Here, we review and discuss NAD + -related mechanisms pivotal for vascular health and summarize recent experimental evidence in NAD + research directly related to vascular disease, including atherosclerosis, and coronary artery disease. Finally, we comparatively assess distinct NAD + precursors for their clinical efficacy and the efficiency of NAD + elevation in the treatment of major CVD. These findings may provide ideas for new therapeutic strategies to prevent and treat CVD in the clinic.

Ferroptosis: mechanism, immunotherapy and role in ovarian cancer

Ovarian cancer is currently the second most common malignant tumor among gynecological cancers worldwide, primarily due to challenges in early diagnosis, high recurrence rates, and resistance to existing treatments. Current therapeutic options are inadequate for addressing the needs of ovarian cancer patients. Ferroptosis, a novel form of regulated cell death with demonstrated tumor-suppressive properties, has gained increasing attention in ovarian malignancy research. A growing body of evidence suggests that ferroptosis plays a significant role in the onset, progression, and incidence of ovarian cancer. Additionally, it has been found that immunotherapy, an emerging frontier in tumor treatment, synergizes with ferroptosis in the context of ovarian cancer. Consequently, ferroptosis is likely to become a critical target in the treatment of ovarian cancer.

Functional deterioration of vascular mitochondrial and glycolytic capacity in the aortic rings of aged mice

Vascular ageing is associated with increased arterial stiffness and cardiovascular mortality that might be linked to altered vascular energy metabolism. The aim of this study was to establish a Seahorse XFe96 Analyzer-based methodology for the reliable, functional assessment of mitochondrial respiration and glycolysis in single murine aortic rings and to validate this functional assay by characterising alterations in vascular energy metabolism in aged mice. Healthy young and old C57BL/6 mice were used for the analyses. An optimised setup consisting of the Seahorse XFe96 Analyzer and Seahorse Spheroid Microplates was applied for the mitochondrial stress test and the glycolysis stress test on the isolated murine aortic rings, supplemented with analysis of NAD content in the aorta. To confirm the age-dependent stiffness of the vasculature, pulse wave velocity was measured in vivo. In addition, the activity of vascular nitric oxide synthase and vascular wall morphology were analysed ex vivo. The vascular ageing phenotype in old mice was confirmed by increased aortic stiffness, vascular wall remodelling, and nitric oxide synthase activity impairment. The rings of the aorta taken from old mice showed changes in vascular energy metabolism, including impaired spare respiratory capacity, maximal respiration, glycolysis, and glycolytic capacity, as well as a fall in the NAD pool. In conclusion, optimised Seahorse XFe96-based analysis to study energy metabolism in single aortic rings of murine aorta revealed a robust impairment of functional vascular respiratory and glycolytic capacity in old mice linked to NAD deficiency that coincided with age-related aortic wall remodelling and stiffness.

Acute nicotinamide riboside supplementation increases human cerebral NAD+ levels in vivo

PURPOSE

The purpose of this study was to determine the effect of acute nicotinamide riboside (NR) supplementation on cerebral nicotinamide adenine dinucleotide (NAD+) levels in the human brain in vivo by means of downfield proton MRS (DF 1H MRS).

METHODS

DF 1H MRS was performed on 10 healthy volunteers in a 7.0 T MRI scanner with spectrally selective excitation and spatially selective localization to determine cerebral NAD+ levels on two back-to-back days: once after an overnight fast (baseline) and once 4 h after oral ingestion of nicotinamide riboside (900 mg). Additionally, two more baseline scans were performed following the same paradigm to assess test-retest reliability of the NAD+ levels in the absence of NR.

RESULTS

NR supplementation increased mean NAD+ concentration compared to the baseline (0.458 ± 0.053 vs. 0.392 ± 0.058 mM; p < 0.001). The additional two baseline scans demonstrated no differences in mean NAD+ concentrations (0.425 ± 0.118 vs. 0.405 ± 0.082 mM; p = 0.45), and no difference from the first baseline scan (F(2, 16) = 0.907; p = 0.424).

CONCLUSION

These preliminary results confirm that acute NR supplementation increases cerebral NAD+ levels in healthy human volunteers and shows the promise of DF 1H MRS utility for robust detection of NAD+ in humans in vivo.

PARP inhibition leads to synthetic lethality with key splicing-factor mutations in myelodysplastic syndromes

BACKGROUND

Splicing factors are frequently mutated in patients with myelodysplastic syndromes and acute myeloid leukaemia. Recent studies have revealed convergent molecular defects caused by splicing factor mutations, among which R-loop dysregulation and resultant genome instability are suggested as contributing factors to disease progression. On the other hand, understanding how mutant cells survive upon aberrant R-loop formation and genome instability is essential for developing novel therapeutics.

METHODS

The immunoprecipitation was performed to identify R-loops in association with PARP1/poly-ADP-ribosylation. The western blot, immunofluorescence, and flow cytometry assays were used to test the cell viability, cell cycle arrest, apoptosis, and ATM activation in mutant cells following the treatment of the PARP inhibitor. The Srsf2(P95H) knock-in murine hematopoietic cells and MLL-AF9 transformed leukaemia model were generated to investigate the potential of the PARP inhibitor as a therapy for haematological malignancies.

RESULTS

The disease-causing mutations in SRSF2 activate PARP and elevate the overall poly-ADP-ribosylation levels of proteins in response to R-loop dysregulation. In accordance, mutant cells are more vulnerable to the PARP inhibitors in comparison to the wild-type counterpart. Notably, the synthetic lethality was further validated in the Srsf2(P95H) knock-in murine hematopoietic cell and MLL-AF9 leukaemia model.

CONCLUSIONS

Our findings suggest that mutant cells antagonise the genome threat caused by R-loop disruption by PARP activation, thus making PARP targeting a promising therapeutic strategy for myeloid cancers with mutations in SRSF2.

NAD(P)H-quinone oxidoreductase 1 induces complicated effects on mitochondrial dysfunction and ferroptosis in an expression level-dependent manner

NAD(P)H-quinone oxidoreductase 1 (NQO1) is an essential redox enzyme responsible for redox balance and energy metabolism. Despite of its importance, the brain contains high capacity of polyunsaturated fatty acids and maintains low levels of NQO1 expression. In this study, we examined how levels of NQO1 expression affects cell survival in response to toxic insults causing mitochondrial dysfunction and ferroptosis, and whether NQO1 has a potential as a biomarker in different stressed conditions. Following treatment with rotenone, overexpressed NQO1 in SH-SY5Y cells improved cell survival by reducing mitochondrial reductive stress via increased NAD+ supply without mitochondrial biogenesis. However, NQO1 overexpression boosted lipid peroxidation following treatment with RSL3 and erastin. A lipid droplet staining assay showed increased lipid droplets in cells overexpressing NQO1. In contrast, NQO1 knockdown protected cells against ferroptosis by increasing GPX4, xCT, and the GSH/GSSG system. Also, NQO1 knockdown showed lower iron contents and lipid droplets than non-transfectants and cells overexpressing NQO1, even though it could not attenuate cell death when exposed to rotenone. In summary, our study suggests that different NQO1 levels may have advantages and disadvantages depending on the surrounding environments. Thus, regulating NQO1 expression could be a potential supplementary tool when treating neuronal diseases.

Discovery of Potent Isoindolinone Inhibitors that Target an Active Conformation of PARP1 Using DNA-Encoded Libraries

Inhibition of poly (ADP-ribose) polymerase-1 (PARP1), a DNA repair enzyme, has proven to be a successful strategy for the treatment of various cancers. With the appropriate selection conditions and protein design, DNA-encoded library (DEL) technology provides a powerful avenue to identify small molecules with the desired mechanism of action towards a target of interest. However, DNA-binding proteins, such as PARP1, can be challenging targets for DEL screening due to non-specific protein-DNA interactions. To overcome this, we designed and screened a PARP1 catalytic domain construct without the autoinhibitory helical domain. This allowed us to interrogate an active, functionally-relevant form of the protein resulting in the discovery of novel isoindolinone PARP1 inhibitors with single-digit nanomolar potency. These inhibitors also demonstrated little to no PARP1-DNA trapping, a property that could be advantageous in the clinic.

Beyond monotherapy: An era ushering in combinations of PARP inhibitors with immune checkpoint inhibitors for solid tumors

The introduction of PARP inhibitors (PARPis) and immune checkpoint inhibitors (ICIs) has marked a significant shift in the treatment landscape for solid tumors. Emerging preclinical evidence and initial clinical trials have indicated that the synergistic application of PARPis and ICIs may enhance treatment efficacy and potentially improve long-term patient outcomes. Nonetheless, how to identify specific tumor types and molecular subgroups most likely to benefit from this combination remains an area of ongoing research. This review thoroughly examines current studies on the co-administration of PARPis and ICIs across various solid tumors. It explores the underlying mechanisms of action, evaluates clinical efficacy, identifies potential responder populations, and delineates common adverse events alongside strategic management approaches. The aim is to offer a detailed understanding of this combination therapy, potentially guiding future therapeutic strategies for solid tumors.

Molecular mechanisms of aging and anti-aging strategies

Aging is a complex and multifaceted process involving a variety of interrelated molecular mechanisms and cellular systems. Phenotypically, the biological aging process is accompanied by a gradual loss of cellular function and the systemic deterioration of multiple tissues, resulting in susceptibility to aging-related diseases. Emerging evidence suggests that aging is closely associated with telomere attrition, DNA damage, mitochondrial dysfunction, loss of nicotinamide adenine dinucleotide levels, impaired macro-autophagy, stem cell exhaustion, inflammation, loss of protein balance, deregulated nutrient sensing, altered intercellular communication, and dysbiosis. These age-related changes may be alleviated by intervention strategies, such as calorie restriction, improved sleep quality, enhanced physical activity, and targeted longevity genes. In this review, we summarise the key historical progress in the exploration of important causes of aging and anti-aging strategies in recent decades, which provides a basis for further understanding of the reversibility of aging phenotypes, the application prospect of synthetic biotechnology in anti-aging therapy is also prospected.

Specific and shared biological functions of PARP2 - is PARP2 really a lil' brother of PARP1?

PARP2, that belongs to the family of ADP-ribosyl transferase enzymes (ART), is a discovery of the millennium, as it was identified in 1999. Although PARP2 was described initially as a DNA repair factor, it is now evident that PARP2 partakes in the regulation or execution of multiple biological processes as inflammation, carcinogenesis and cancer progression, metabolism or oxidative stress-related diseases. Hereby, we review the involvement of PARP2 in these processes with the aim of understanding which processes are specific for PARP2, but not for other members of the ART family. A better understanding of the specific functions of PARP2 in all of these biological processes is crucial for the development of new PARP-centred selective therapies.

A Molecular Perspective and Role of NAD+ in Ovarian Aging

The decline in female fecundity is linked to advancing chronological age. The ovarian reserve diminishes in quantity and quality as women age, impacting reproductive efficiency and the aging process in the rest of the body. NAD+ is an essential coenzyme in cellular energy production, metabolism, cell signaling, and survival. It is involved in aging and is linked to various age-related conditions. Hallmarks associated with aging, diseases, and metabolic dysfunctions can significantly affect fertility by disturbing the delicate relationship between energy metabolism and female reproduction. Enzymes such as sirtuins, PARPs, and CD38 play essential roles in NAD+ biology, which actively consume NAD+ in their enzymatic activities. In recent years, NAD+ has gained much attention for its role in aging and age-related diseases like cancer, Alzheimer's, cardiovascular diseases, and neurodegenerative disorders, highlighting its involvement in various pathophysiological processes. However, its impact on female reproduction is not well understood. This review aims to bridge this knowledge gap by comprehensively exploring the complex interplay between NAD+ biology and female reproductive aging and providing valuable information that could help develop plans to improve women's reproductive health and prevent fertility issues.

Poly(ADP-Ribose) Polymerases-Inhibitor Talazoparib Inhibits Muscle Atrophy and Fatty Infiltration in a Tendon Release Infraspinatus Sheep Model: A Pilot Study

Structural muscle changes, including muscle atrophy and fatty infiltration, follow rotator cuff tendon tear and are associated with a high repair failure rate. Despite extensive research efforts, no pharmacological therapy is available to successfully prevent both muscle atrophy and fatty infiltration after tenotomy of tendomuscular unit without surgical repair. Poly(ADP-ribose) polymerases (PARPs) are identified as a key transcription factors involved in the maintenance of cellular homeostasis. PARP inhibitors have been shown to influence muscle degeneration, including mitochondrial hemostasis, oxidative stress, inflammation and metabolic activity, and reduced degenerative changes in a knockout mouse model. Tenotomized infraspinatus were assessed for muscle degeneration for 16 weeks using a Swiss Alpine sheep model (n = 6). All sheep received daily oral administration of 0.5 mg Talazoparib. Due to animal ethics, the treatment group was compared with three different controls from prior studies of our institution. To mitigate potential batch heterogeneity, PARP-I was evaluated in comparison with three distinct control groups (n = 6 per control group) using the same protocol without treatment. The control sheep were treated with an identical study protocol without Talazoparib treatment. Muscle atrophy and fatty infiltration were evaluated at 0, 6 and 16 weeks post-tenotomy using DIXON-MRI. The controls and PARP-I showed a significant (control p < 0.001, PARP-I p = 0.01) decrease in muscle volume after 6 weeks. However, significantly less (p = 0.01) atrophy was observed in PARP-I after 6 weeks (control 1: 76.6 ± 8.7%; control 2: 80.3 ± 9.3%, control 3: 73.8 ± 6.7% vs. PARP-I: 90.8 ± 5.1% of the original volume) and 16 weeks (control 1: 75.7 ± 9.9; control 2: 74.2 ± 5.6%; control 3: 75.3 ± 7.4% vs. PARP-I 93.3 ± 10.6% of the original volume). All experimental groups exhibited a statistically significant (p < 0.001) augmentation in fatty infiltration following a 16-week period when compared to the initial timepoint. However, the PARP-I showed significantly less fatty infiltration (p < 0.003) compared to all controls (control 1: 55.6 ± 6.7%, control 2: 53.4 ± 9.4%, control 3: 52.0 ± 12.8% vs. PARP-I: 33.5 ± 8.4%). Finally, a significantly (p < 0.04) higher proportion and size of fast myosin heavy chain-II fiber type was observed in the treatment group. This study shows that PARP-inhibition with Talazoparib inhibits the progression of both muscle atrophy and fatty infiltration over 16 weeks in retracted sheep musculotendinous units.

Rational Design of PARP1/c-Met Dual Inhibitors for Overcoming PARP1 Inhibitor Resistance Induced by c-Met Overexpression

The emergence of resistance to PARP1 inhibitors poses a current therapeutic challenge, necessitating the development of novel strategies to overcome this obstacle. The present study describes the design and synthesis of a series of small molecules that target both PARP1 and c-Met. Among them, compound 16 is identified as a highly potent dual inhibitor, exhibiting excellent inhibitory activities against PARP1 (IC50 = 3.3 nM) and c-Met (IC50 = 32.2 nM), as well as demonstrating good antiproliferative effects on HR-proficient cancer cell lines and those resistant to PARP1 inhibitors. Importantly, compound 16 demonstrates superior antitumor potency compared to the PARP1 inhibitor Olaparib and the c-Met inhibitor Crizotinib, either alone or in combination, in MDA-MB-231 and HCT116OR xenograft models. These findings highlight the potential of PARP1/c-Met dual inhibitors for expanding the indications of PARP1 inhibitors and overcoming tumor cells' resistance to them.

Exposure to fluoride exacerbates the cognitive deficit of diabetic patients living in areas with endemic fluorosis, as well as of rats with type 2 diabetes induced by streptozotocin via a mechanism that may involve excessive activation of the poly(ADP ribose) polymerase-1/P53 pathway

Epidemiology has shown that fluoride exposure is associated with the occurrence of diabetes. However, whether fluoride affects diabetic encephalopathy is unclear. Elderly diabetic patients in areas with endemic (n = 169) or no fluorosis (108) and controls (85) underwent Montreal Cognitive Assessment. Sprague-Dawley rats receiving streptozotocin and/or different fluoride doses were examined for spatial learning and memory, brain morphology, blood-brain barrier, fasting blood glucose and insulin. Cultured SH-SY5Y cells were treated with 50 mM glucose and/or low- or high-dose fluoride, and P53-knockdown or poly-ADP-ribose polymerase-1 (PARP-1) inhibition. The levels of PARP-1, P53, poly-ADP-ribose (PAR), apoptosis-inducing factor (AIF), and phosphorylated-histone H2A.X (ser139) were measured by Western blotting. Reactive oxygen species (ROS), 8-hydroxydeguanosine (8-OHdG), PARP-1 activity, acetyl-P53, nicotinamide adenine dinucleotide (NAD+), activities of mitochondrial hexokinase1 (HK1) and citrate synthase (CS), mitochondrial membrane potential and apoptosis were assessed biochemically. Cognition of diabetic patients in endemic fluorosis areas was poorer than in other regions. In diabetic rats, fasting blood glucose, insulin resistance and blood-brain barrier permeability were elevated, while spatial learning and memory and Nissl body numbers in neurons declined. In these animals, expression and activity of P53 and PARP-1 and levels of NAD+, PAR, ROS, 8-OHdG, p-histone H2A.X (ser139), AIF and apoptosis content increased; whereas mitochondrial HK1 and CS activities and membrane potential decreased. SH-SY5Y cells exposed to glucose exhibited changes identical to diabetic rats. The changes in diabetic rats and cells treated with glucose were aggravated by fluoride. P53-knockout or PARP-1 inhibition mitigated the effects of glucose with/without low-dose fluoride. Elevation of diabetic encephalopathy was induced by exposure to fluoride and the underlying mechanism may involve overactivation of the PARP-1/P53 pathway.

Anemonin ameliorates human diploid fibroblasts 2BS and IMR90 cell senescence by PARP1-NAD+-SIRT1 signaling pathway

OBJECTIVE

Aging becomes the most predominant risk factor for all age-associated pathological conditions with the increase of life expectancy and the aggravation of social aging. Slowing down the speed of aging is considered an effective way to improve health, but so far, effective anti-aging methods are relatively lacking.

METHODS

Anemonin (ANE) was screened from eight existing small-molecule compounds by cell viability assay. The function of ANE was determined by the analysis of cell proliferation, β -galactosidase (SA-β -Gal) activity, cell cycle, SASP secretion, NAD+/NADH ratio, and other aging-related indicators. The targets of ANE were predicted by Drug Target Prediction System (DTPS) and Swiss Targe Prediction System. The effect of ANE on PARP-1-NAD+-SIRT1 signaling pathway was assessed by quantitative reverse-transcription polymerase chain reaction (RT-PCR), Western blot, PARP1, NAD+ and SIRT1 activity detection.

RESULTS

ANE can delay cell senescence; PARP1 is one of the targets of ANE and plays a crucial role in ANE anti-aging; ANE release more NAD+ by inhibiting PARP1 activity, thereby conversely promoting the function of SIRT1 and delay cell senescence.

CONCLUSIONS

Our study indicates that ANE can delay cellular senescence through the PARP1-NAD+-SIRT1 signaling pathway, which may be considered as an effective anti-aging strategy.

Impact of NAD+ metabolism on ovarian aging

Nicotinamide adenine dinucleotide (NAD+), a crucial coenzyme in cellular redox reactions, is closely associated with age-related functional degeneration and metabolic diseases. NAD exerts direct and indirect influences on many crucial cellular functions, including metabolic pathways, DNA repair, chromatin remodeling, cellular senescence, and immune cell functionality. These cellular processes and functions are essential for maintaining tissue and metabolic homeostasis, as well as healthy aging. Causality has been elucidated between a decline in NAD levels and multiple age-related diseases, which has been confirmed by various strategies aimed at increasing NAD levels in the preclinical setting. Ovarian aging is recognized as a natural process characterized by a decline in follicle number and function, resulting in decreased estrogen production and menopause. In this regard, it is necessary to address the many factors involved in this complicated procedure, which could improve fertility in women of advanced maternal age. Concerning the decrease in NAD+ levels as ovarian aging progresses, promising and exciting results are presented for strategies using NAD+ precursors to promote NAD+ biosynthesis, which could substantially improve oocyte quality and alleviate ovarian aging. Hence, to acquire further insights into NAD+ metabolism and biology, this review aims to probe the factors affecting ovarian aging, the characteristics of NAD+ precursors, and the current research status of NAD+ supplementation in ovarian aging. Specifically, by gaining a comprehensive understanding of these aspects, we are optimistic about the prominent progress that will be made in both research and therapy related to ovarian aging.

Combinatorial Treatment with PARP and MAPK Inhibitors Overcomes Phenotype Switch-Driven Drug Resistance in Advanced Melanoma

Metastatic melanoma is either intrinsically resistant or rapidly acquires resistance to targeted therapy treatments, such as MAPK inhibitors (MAPKi). A leading cause of resistance to targeted therapy is a dynamic transition of melanoma cells from a proliferative to a highly invasive state, a phenomenon called phenotype switching. Mechanisms regulating phenotype switching represent potential targets for improving treatment of patients with melanoma. Using a drug screen targeting chromatin regulators in patient-derived three-dimensional MAPKi-resistant melanoma cell cultures, we discovered that PARP inhibitors (PARPi) restore sensitivity to MAPKis, independent of DNA damage repair pathways. Integrated transcriptomic, proteomic, and epigenomic analyses demonstrated that PARPis induce lysosomal autophagic cell death, accompanied by enhanced mitochondrial lipid metabolism that ultimately increases antigen presentation and sensitivity to T-cell cytotoxicity. Moreover, transcriptomic and epigenetic rearrangements induced by PARP inhibition reversed epithelial-mesenchymal transition-like phenotype switching, which redirected melanoma cells toward a proliferative and MAPKi-sensitive state. The combination of PARP and MAPKis synergistically induced cancer cell death both in vitro and in vivo in patient-derived xenograft models. Therefore, this study provides a scientific rationale for treating patients with melanoma with PARPis in combination with MAPKis to abrogate acquired therapy resistance.

SIGNIFICANCE

PARP inhibitors can overcome resistance to MAPK inhibitors by activating autophagic cell death and reversing phenotype switching, suggesting that this synergistic combination could help improve the prognosis of patients with melanoma.

Liquid-liquid phase separation in DNA double-strand breaks repair

DNA double-strand breaks (DSBs) are the fatal type of DNA damage mostly induced by exposure genome to ionizing radiation or genotoxic chemicals. DSBs are mainly repaired by homologous recombination (HR) and nonhomologous end joining (NHEJ). To repair DSBs, a large amount of DNA repair factors was observed to be concentrated at the end of DSBs in a specific spatiotemporal manner to form a repair center. Recently, this repair center was characterized as a condensate derived from liquid-liquid phase separation (LLPS) of key DSBs repair factors. LLPS has been found to be the mechanism of membraneless organelles formation and plays key roles in a variety of biological processes. In this review, the recent advances and mechanisms of LLPS in the formation of DSBs repair-related condensates are summarized.

Combination Treatment Strategies to Overcome PARP Inhibitor Resistance

Poly(ADP-ribose) polymerase (PARP) enzymes have been shown to be essential for DNA repair pathways, including homologous recombination repair (HRR). Cancers with HRR defects (e.g., BRCA1 and BRCA2 mutations) are targets for PARP inhibitors (PARPis) based on the exploitation of "synthetic lethality". As a result, PARPis offer a promising treatment option for advanced ovarian and breast cancers with deficiencies in HRR. However, acquired resistance to PARPis has been reported for most tumors, and not all patients with BRCA1/2 mutations respond to PARPis. Therefore, the formulation of effective treatment strategies to overcome resistance to PARPis is urgently necessary. This review summarizes the molecular mechanism of therapeutic action and resistance to PARPis, in addition to emerging combination treatment options involving PARPis.

Discovery of a First-in-Class CD38 Inhibitor for the Treatment of Mitochondrial Myopathy

CD38 is a crucial NADase in mammalian tissues that degrades NAD+ and thus regulates cellular NAD+ levels. Abnormal CD38 expression is linked to mitochondrial dysfunction under several pathological conditions. We present a novel CD38 inhibitor, compound 1, with high potency for CD38 (IC50 of 11 nM) and minimal activity against other targets. In a Pus1 knockout (Pus1-/-) mouse model of mitochondrial myopathy, compound 1 treatment rescued the decline in running endurance in a dose-dependent manner, associated with an elevated NAD+ level in muscle tissue, increased expression of Nrf2, which is known to promote mitochondrial biogenesis, and reduced lactate production. RNA sequencing data indicated that compound 1 has a great effect on mitochondrial function, metabolic processes, muscle contraction/development, and actin filament organization via regulating the expression of relevant genes. Compound 1 is a promising candidate for its excellent in vivo efficacy, favorable pharmacokinetics, and attractive safety profile.

A new wave of innovations within the DNA damage response

Genome instability has been identified as one of the enabling hallmarks in cancer. DNA damage response (DDR) network is responsible for maintenance of genome integrity in cells. As cancer cells frequently carry DDR gene deficiencies or suffer from replicative stress, targeting DDR processes could induce excessive DNA damages (or unrepaired DNA) that eventually lead to cell death. Poly (ADP-ribose) polymerase (PARP) inhibitors have brought impressive benefit to patients with breast cancer gene (BRCA) mutation or homologous recombination deficiency (HRD), which proves the concept of synthetic lethality in cancer treatment. Moreover, the other two scenarios of DDR inhibitor application, replication stress and combination with chemo- or radio- therapy, are under active clinical exploration. In this review, we revisited the progress of DDR targeting therapy beyond the launched first-generation PARP inhibitors. Next generation PARP1 selective inhibitors, which could maintain the efficacy while mitigating side effects, may diversify the application scenarios of PARP inhibitor in clinic. Albeit with unavoidable on-mechanism toxicities, several small molecules targeting DNA damage checkpoints (gatekeepers) have shown great promise in preliminary clinical results, which may warrant further evaluations. In addition, inhibitors for other DNA repair pathways (caretakers) are also under active preclinical or clinical development. With these progresses and efforts, we envision that a new wave of innovations within DDR has come of age.

Increased SIRT3 combined with PARP inhibition rescues motor function of SBMA mice

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease with substantial mitochondrial and metabolic dysfunctions. SBMA is caused by polyglutamine (polyQ) expansion in the androgen receptor (AR). Activating or increasing the NAD+-dependent deacetylase, SIRT3, reduced oxidative stress and death of cells modeling SBMA. However, increasing diminished SIRT3 in AR100Q mice failed to reduce acetylation of the SIRT3 target/antioxidant, SOD2, and had no effect on increased total acetylated peptides in quadriceps. Yet, overexpressing SIRT3 resulted in a trend of motor recovery, and corrected TCA cycle activity by decreasing acetylation of SIRT3 target proteins. We sought to boost blunted SIRT3 activity by replenishing diminished NAD+ with PARP inhibition. Although NAD+ was not affected, overexpressing SIRT3 with PARP inhibition fully restored hexokinase activity, correcting the glycolytic pathway in AR100Q quadriceps, and rescued motor endurance of SBMA mice. These data demonstrate that targeting metabolic anomalies can restore motor function downstream of polyQ-expanded AR.

How ligands regulate the binding of PARP1 with DNA: Deciphering the mechanism at the molecular level

The catalytic (CAT) domain is a key region of poly (ADP-ribose) polymerase 1 (PARP1), which has crucial interactions with inhibitors, DNA, and other domains of PARP1. To facilitate the development of potential inhibitors of PARP1, it is of great significance to clarify the differences in structural dynamics and key residues between CAT/inhibitors and DNA/PARP1/inhibitors through structure-based computational design. In this paper, conformational changes in PAPR1 and differences in key residue interactions induced by inhibitors were revealed at the molecular level by comparative molecular dynamics (MD) simulations and energy decomposition. On one hand, PARP1 inhibitors indirectly change some residues of the CAT domain which interact with DNA and other domains. Furthermore, the interaction between ligands and catalytic binding sites can be transferred to the DNA recognition domain of PARP1 by a strong negative correlation movement among multi-domains of PARP1. On the other hand, it is not reliable to use the binding energy of CAT/ligand as a measure of ligand activity, because it may in some cases differs greatly from the that of PARP1/DNA/ligand. For PARP1/DNA/ligand, the stronger the binding stability between the ligand and PARP1, the stronger the binding stability between PARP1 and DNA. The findings of this work can guide further novel inhibitor design and the structural modification of PARP1 through structure-based computational design.

PARP2 poly(ADP-ribosyl)ates nuclear factor erythroid 2-related factor 2 (NRF2) affecting NRF2 subcellular localization

PARP2 is a member of the PARP enzyme family. Although, PARP2 plays role in DNA repair, it has regulatory roles in mitochondrial and lipid metabolism, it has pivotal role in bringing about the adverse effects of pharmacological PARP inhibitors. Previously, we showed that the ablation of PARP2 induces oxidative stress and, consequently, mitochondrial fragmentation. In attempt to identify the source of the reactive species we assessed the possible role of a central regulator of cellular antioxidant defense, nuclear factor erythroid 2-related factor 2 (NRF2). The silencing of PARP2 did not alter either the mRNA or the protein expression of NRF2, but changed its subcellular localization, decreasing the proportion of nuclear, active fraction of NRF2. Pharmacological inhibition of PARP2 partially restored the normal localization pattern of NRF2 and in line with that, we showed that NRF2 is PARylated that is absent in the cells in which PARP2 was silenced. Apparently, the PARylation of NRF2 by PARP2 has pivotal role in regulating the subcellular (nuclear) localization of NRF2. The silencing of PARP2 rearranged the expression of genes encoding proteins with antioxidant function, among these a subset of NRF2-dependent genes.

NAD+ metabolism-based immunoregulation and therapeutic potential

Nicotinamide adenine dinucleotide (NAD⁺) is a critical metabolite that acts as a cofactor in energy metabolism, and serves as a cosubstrate for non-redox NAD⁺-dependent enzymes, including sirtuins, CD38 and poly(ADP-ribose) polymerases. NAD⁺ metabolism can regulate functionality attributes of innate and adaptive immune cells and contribute to inflammatory responses. Thus, the manipulation of NAD⁺ bioavailability can reshape the courses of immunological diseases. Here, we review the basics of NAD⁺ biochemistry and its roles in the immune response, and discuss current challenges and the future translational potential of NAD⁺ research in the development of therapeutics for inflammatory diseases, such as COVID-19.

Nicotinamide Mononucleotide Alleviates Angiotensin II-Induced Human Aortic Smooth Muscle Cell Senescence in a Microphysiological Model

ABSTRACT

The occurrence and development of aortic aneurysms are accompanied by senescence of human aortic smooth muscle cells (HASMCs). Because the mechanism of HASMC senescence has not been fully elucidated, the efficacy of various antisenescence treatments varies. Decreased nicotinamide adenine dinucleotide (NAD + ) levels are one of the mechanisms of cell senescence, and there is a lack of evidence on whether increasing NAD + levels could alleviate HASMC senescence and further retard the progression of aortic aneurysms.We constructed an HASMC-based organ-on-a-chip microphysiological model. RNA sequencing was performed on cell samples from the vehicle control and angiotensin II groups to explore biological differences. We detected cellular senescence markers and NAD + levels in HASMC-based organ-on-a-chip. Subsequently, we pretreated HASMC using the synthetic precursor of NAD + , nicotinamide mononucleotide, and angiotensin II treatment, and used rhythmic stretching to investigate whether nicotinamide mononucleotide could delay HASMC senescence.The HASMC-based organ-on-a-chip model can simulate the biomechanical microenvironment of HASMCs in vivo, and the use of angiotensin II in the model replicated senescence in HASMCs. The senescence of HASMCs was accompanied by downregulation of the expression level of nicotinamide phosphoribosyltransferase and NAD + . Pretreatment with nicotinamide mononucleotide significantly increased the NAD + level and alleviated the senescence of HASMCs, but did not change the expression level of nicotinamide phosphoribosyltransferase.Our study provides a complementary research platform between traditional cell culture and animal experiments to explore HASMC senescence in aortic aneurysms. Furthermore, it provides evidence for NAD + boosting therapy in the clinical treatment of aortic aneurysms.

Emerging roles of TFE3 in metabolic regulation

TFE3 is a member of the MiT family of the bHLH-leucine zipper transcription factor. We previously focused on the role of TFE3 in autophagy and cancer. Recently, an increasing number of studies have revealed that TFE3 plays an important role in metabolic regulation. TFE3 participates in the metabolism of energy in the body by regulating pathways such as glucose and lipid metabolism, mitochondrial metabolism, and autophagy. This review summarizes and discusses the specific regulatory mechanisms of TFE3 in metabolism. We determined both the direct regulation of TFE3 on metabolically active cells, such as hepatocytes and skeletal muscle cells, and the indirect regulation of TFE3 through mitochondrial quality control and the autophagy-lysosome pathway. The role of TFE3 in tumor cell metabolism is also summarized in this review. Understanding the diverse roles of TFE3 in metabolic processes can provide new avenues for the treatment of some metabolism-related disorders.

Fer and FerT: A New Regulatory Link between Sperm and Cancer Cells

Fer and its sperm and cancer specific variant, FerT, are non-receptor tyrosine kinases which play roles in cancer progression and metastasis. Recent studies have shed light on the regulatory role of these kinases in ensuring proper sperm function. Comparison of the regulatory cascades in which Fer and FerT are engaged in sperm and cancer cells presents an interesting picture, in which similar regulatory interactions of these enzymes are integrated in a similar or different regulatory context in the two cell types. These diverse compositions extend from the involvement of Fer in modulation of actin cytoskeleton integrity and function, to the unique regulatory interactions of Fer with PARP-1 and the PP1 phosphatase. Furthermore, recent findings link the metabolic regulatory roles of Fer and FerT in sperm and cancer cells. In the current review, we discuss the above detailed aspects, which portray Fer and FerT as new regulatory links between sperm and malignant cells. This perspective view can endow us with new analytical and research tools that will deepen our understanding of the regulatory trajectories and networks that govern these two multi-layered systems.

Expression profile of key genes involved in DNA repair mechanisms in bovine cumulus cells cultured with bovine serum albumin or fetal calf serum

Cumulus cells from cumulus-oocyte complexes (COC) matured in vitro in serum-free medium show high incidence of apoptosis and DNA double-strand breaks (DSB). This study aimed to characterize the transcript expression profile of selected genes involved in DNA repair mechanisms in bovine cumulus cells cultured with bovine serum albumin (BSA) or fetal calf serum (FCS). Briefly, bovine cumulus-oocyte complexes were in vitro matured with either, 0.4% BSA or 10% FCS for 3, 6, 12 or 24 h. The total RNA of cumulus cells was used for real-time PCR analysis. Transcript abundance of XRCC6, XRCC5, DNAPK, GAAD45B, TP53BP1, RAD50, RAD52, ATM and BRCA2 target genes changed as the IVM proceeded (P < 0.05). However, an interaction between protein source (FCS or BSA) and time was not detected (P ≥ 0.05). Cumulus cells from COCs matured with BSA presented higher mRNA expression of two genes compared to FCS group: TP53BP1 at 6 h and BRCA1 at 3, 6, 12 and 24 h (P < 0.05). In summary, our results showed for the first time the expression profile of the key genes involved in DSB repair mechanisms in cumulus cells obtained from bovine COCs matured with FCS or BSA. The higher mRNA expression of BRCA1 and TP53BP1 and lower mRNA expression of TNFAIP6 suggests an increase in apoptosis rate and DNA damage in cumulus cells cultured in BSA-supplemented medium and may explain, at least to some extent, the reduced developmental potential of bovine oocytes matured in serum-free medium.

NAD+ Homeostasis and NAD+-Consuming Enzymes: Implications for Vascular Health

Nicotinamide adenine dinucleotide (NAD⁺) is a ubiquitous metabolite that takes part in many key redox reactions. NAD⁺ biosynthesis and NAD⁺-consuming enzymes have been attracting markedly increasing interest since they have been demonstrated to be involved in several crucial biological pathways, impacting genes transcription, cellular signaling, and cell cycle regulation. As a consequence, many pathological conditions are associated with an impairment of intracellular NAD⁺ levels, directly or indirectly, which include cardiovascular diseases, obesity, neurodegenerative diseases, cancer, and aging. In this review, we describe the general pathways involved in the NAD⁺ biosynthesis starting from the different precursors, analyzing the actual state-of-art of the administration of NAD⁺ precursors or blocking NAD⁺-dependent enzymes as strategies to increase the intracellular NAD⁺ levels or to counteract the decline in NAD⁺ levels associated with ageing. Subsequently, we focus on the disease-related and age-related alterations of NAD⁺ homeostasis and NAD⁺-dependent enzymes in endothelium and the consequent vascular dysfunction, which significantly contributes to a wide group of pathological disorders.

The Central Role of the NAD+ Molecule in the Development of Aging and the Prevention of Chronic Age-Related Diseases: Strategies for NAD+ Modulation

The molecule NAD+ is a coenzyme for enzymes catalyzing cellular redox reactions in several metabolic pathways, encompassing glycolysis, TCA cycle, and oxidative phosphorylation, and is a substrate for NAD+-dependent enzymes. In addition to a hydride and electron transfer in redox reactions, NAD+ is a substrate for sirtuins and poly(adenosine diphosphate-ribose) polymerases and even moderate decreases in its cellular concentrations modify signaling of NAD+-consuming enzymes. Age-related reduction in cellular NAD+ concentrations results in metabolic and aging-associated disorders, while the consequences of increased NAD+ production or decreased degradation seem beneficial. This article reviews the NAD+ molecule in the development of aging and the prevention of chronic age-related diseases and discusses the strategies of NAD+ modulation for healthy aging and longevity.

Human PARP1 substrates and regulators of its catalytic activity: An updated overview

Poly (ADP-ribose) polymerase 1 (PARP1) is a key DNA damage sensor that is recruited to damaged sites after DNA strand breaks to initiate DNA repair. This is achieved by catalyzing attachment of ADP-ribose moieties, which are donated from NAD⁺, on the amino acid residues of itself or other acceptor proteins. PARP inhibitors (PARPi) that inhibit PARP catalytic activity and induce PARP trapping are commonly used for treating BRCA1/2-deficient breast and ovarian cancers through synergistic lethality. Unfortunately, resistance to PARPi frequently occurs. In this review, we present the novel substrates and regulators of the PARP1-catalyzed poly (ADP-ribosyl)ation (PARylatison) that have been identified in the last 3 years. The overall aim is the presentation of protein interactions of potential therapeutic intervention for overcoming the resistance to PARPi.

NAD+ Metabolism and Interventions in Premature Renal Aging and Chronic Kidney Disease

Premature aging causes morphological and functional changes in the kidney, leading to chronic kidney disease (CKD). CKD is a global public health issue with far-reaching consequences, including cardio-vascular complications, increased frailty, shortened lifespan and a heightened risk of kidney failure. Dialysis or transplantation are lifesaving therapies, but they can also be debilitating. Currently, no cure is available for CKD, despite ongoing efforts to identify clinical biomarkers of premature renal aging and molecular pathways of disease progression. Kidney proximal tubular epithelial cells (PTECs) have high energy demand, and disruption of their energy homeostasis has been linked to the progression of kidney disease. Consequently, metabolic reprogramming of PTECs is gaining interest as a therapeutic tool. Preclinical and clinical evidence is emerging that NAD⁺ homeostasis, crucial for PTECs' oxidative metabolism, is impaired in CKD, and administration of dietary NAD⁺ precursors could have a prophylactic role against age-related kidney disease. This review describes the biology of NAD⁺ in the kidney, including its precursors and cellular roles, and discusses the importance of NAD⁺ homeostasis for renal health. Furthermore, we provide a comprehensive summary of preclinical and clinical studies aimed at increasing NAD⁺ levels in premature renal aging and CKD.

SIRT1 activation and its effect on intercalated disc proteins as a way to reduce doxorubicin cardiotoxicity

According to the World Health Organization, the neoplasm is one of the main reasons for morbidity and mortality worldwide. At the same time, application of cytostatic drugs like an independent type of cancer treatment and in combination with surgical methods, is often associated with the development of cardiovascular complications both in the early and in the delayed period of treatment. Doxorubicin (DOX) is the most commonly used cytotoxic anthracycline antibiotic. DOX can cause both acute and delayed side effects. The problem is still not solved, as evidenced by the continued activity of researchers in terms of developing approaches for the prevention and treatment of cardiovascular complications. It is known, the heart muscle consists of cardiomyocytes connected by intercalated discs (ID), which ensure the structural, electrical, metabolic unity of the heart. Various defects in the ID proteins can lead to the development of cardiovascular diseases of various etiologies, including DOX-induced cardiomyopathy. The search for ways to influence the functioning of ID proteins of the cardiac muscle can become the basis for the creation of new therapeutic approaches to the treatment and prevention of cardiac pathologies. SIRT1 may be an interesting cardioprotective variant due to its wide functional significance. SIRT1 activation triggers nuclear transcription programs that increase the efficiency of cellular, mitochondrial metabolism, increases resistance to oxidative stress, and promotes cell survival. It can be assumed that SIRT1 can not only provide a protective effect at the cardiomyocytes level, leading to an improvement in mitochondrial and metabolic functions, reducing the effects of oxidative stress and inflammatory processes, but also have a protective effect on the functioning of IDs structures of the cardiac muscle.

Depletion of PARP10 inhibits the growth and metastatic potential of oral squamous cell carcinoma

Background: Although poly (ADP-ribose) polymerase family member 10 (PARP10) has been implicated in the progression of multiple cancer types, its role in oral squamous cell carcinoma (OSCC) remains unknown. This study aimed to examine the function of PARP10 in OSCC and investigate the underlying mechanisms.

Methods: The expression of PARP10 in OSCC was investigated in OSCC patient cohorts. Kaplan-Meier curve analysis was performed to assess the association between PARP10 and prognosis in OSCC. Correlation between PARP10 expression and the related variables was analyzed by χ² test. CKK-8, transwell assay, western blot, immunohistochemistry, immunofluorescence, and bioinformatic analysis, were applied to clarify the role of PARP10 in OSCC.

Results: PARP10 was found to be markedly elevated in OSCC tissues. The upregulation of PARP10 predicted shorter overall survival and disease-specific survival and was significantly correlated with several malignant features. Moreover, depletion of PARP10 markedly inhibited the proliferation, migration, and invasion of OSCC cells, and promoted OSCC cell apoptosis, and resulted in alterations of relevant proteins. Furthermore, a positive correlation was observed between the expression of PARP10 and Ki67, PARP1, MMP2, and VEGF. In addition, depletion of PARP10 impaired the PI3K-AKT and MAPK signaling pathways.

Conclusion: PARP10 is involved in the progression of OSCC via regulation of PI3K-AKT and MAPK signaling pathways.

Long-Term Activation of Glucagon-like peptide-1 receptor by Dulaglutide Prevents Diabetic Heart Failure and Metabolic Remodeling in Type 2 Diabetes

Background Mechanistic insights of glucagon-like peptide-1 receptor agonists remain incompletely identified, despite the efficacy in heart failure observed in clinical trials. Here, we evaluated the effects of dulaglutide on heart complications and illuminated its underlying mechanism. Methods and Results We used mice with high-fat diet (HFD)/streptozotocin-induced type 2 diabetes to investigate the effects of dulaglutide upon diabetic cardiac dysfunction. After the onset of diabetes, control and diabetic mice were injected subcutaneously with either dulaglutide (type 2 diabetes-dulaglutide and control-dulaglutide groups) or vehicle (type 2 diabetes-vehicle and control-vehicle groups) for 8 weeks. Subsequently, heart characteristics, cardiometabolic profile and mitochondrial morphology and function were evaluated. Also, we analyzed the effects of dulaglutide on neonatal rat ventricular myocytes treated with high glucose plus palmitic acid. In addition, wild type and AMP-activated protein kinase α2 mutant mice were used to evaluate the underlying mechanism. In type 2 diabetes mouse model, dulaglutide ameliorated insulin resistance, improved glucose tolerance, reduced hyperlipidemia, and promoted fatty acid use in the myocardium. Dulaglutide treatment functionally attenuated cardiac remodeling and dysfunction and promoted metabolic reprogramming in diabetic mice. Furthermore, dulaglutide improved mitochondria fragmentation in myocytes, and simultaneously reinstated mitochondrial morphology and function in diabetic hearts. We also found that dulaglutide preserved AMP-activated protein kinase α2-dependent mitochondrial homeostasis, and the protective effects of dulaglutide on diabetic heart was almost abated by AMP-activated protein kinase α2 knockout. Conclusions Dulaglutide prevents diabetic heart failure and favorably affects myocardial metabolic remodeling by impeding mitochondria fragmentation, and we suggest a potential strategy to develop a long-term activation of glucagon-like peptide-1 receptor-based therapy to treat diabetes associated cardiovascular complications.

A Double-Edged Sword: The Two Faces of PARylation

Poly ADP-ribosylation (PARylation) is a post-translational modification process. Following the discovery of PARP-1, numerous studies have demonstrated the role of PARylation in the DNA damage and repair responses for cellular stress and DNA damage. Originally, studies on PARylation were confined to PARP-1 activation in the DNA repair pathway. However, the interplay between PARylation and DNA repair suggests that PARylation is important for the efficiency and accuracy of DNA repair. PARylation has contradicting roles; however, recent evidence implicates its importance in inflammation, metabolism, and cell death. These differences might be dependent on specific cellular conditions or experimental models used, and suggest that PARylation may play two opposing roles in cellular homeostasis. Understanding the role of PARylation in cellular function is not only important for identifying novel therapeutic approaches; it is also essential for gaining insight into the mechanisms of unexplored diseases. In this review, we discuss recent reports on the role of PARylation in mediating diverse cellular functions and homeostasis, such as DNA repair, inflammation, metabolism, and cell death.

Nicotinamide adenine dinucleotide attenuates acetaminophen-induced acute liver injury via activation of PARP1, Sirt1, and Nrf2 in mice

The aim of this study was to investigate the protective effect of nicotinamide adenine dinucleotide (NAD⁺) against acute liver injury (ALI) induced by acetaminophen (APAP) overdose in mice. First, serum transaminases were used to assess the protective effect of NAD⁺, and the data revealed that NAD⁺ mitigated the APAP-induced ALI in a dose-dependent manner. Then, we performed hematoxylin-eosin staining of liver tissues and found that NAD⁺ alleviated the abnormalities of histopathology. Meanwhile, increase in the malondialdehyde content and decrease in glutathione, superoxide dismutase (SOD), and glutathione peroxidase were identified in the APAP group, which were partially prevented by the NAD⁺ pretreatment. Moreover, compared with the mice treated with APAP only, the expression of poly ADP-ribose polymerase 1 (PARP1), Sirtuin1 (Sirt1), SOD2, nuclear factor erythroid 2-related factor 2 (Nrf2), and hemoxygenase-1 was upregulated, while Kelch-like ECH-associated protein 1 and histone H2AX phosphorylated on Ser-139 were downregulated by NAD⁺ in NAD⁺ + APAP group. Conversely, NAD⁺ could not correct the elevated expression of phospho-Jun N-terminal kinase and phospho-extracellular signal-regulated kinase induced by APAP. Taken together, these findings suggest that NAD⁺ confers an anti-ALI effect to enhance the expression of PARP1 and Sirt1, and to simultaneously stimulate the Nrf2 anti-oxidant signaling pathway.

NAD+ Kinase Enzymes Are Reversible, and NAD+ Product Inhibition Is Responsible for the Observed Irreversibility of the Human Enzyme

The NAD⁺ kinase (NADK) is the only known enzyme capable of phosphorylating NAD(H) to NADP(H) and therefore it plays a crucial role in maintaining NAD(P)(H) homeostasis. All domains of life contain at least one NADK gene, and the commonly investigated isoforms have been measured, or assumed, to be functionally irreversible. In 1977, the kinetics of native pigeon liver NADK were thoroughly investigated, and it was reported to exhibit reversible activity, such that ATP and NAD⁺ can be formed from ADP and NADP⁺. We hypothesized that the reverse activity of the pigeon enzyme may enable compensation of the high picolinic acid carboxylase (PC) activity present in pigeon livers, which inhibits NAD⁺ biosynthesis from dietary tryptophan. Here, we report the characterization of four recombinantly expressed NADKs and explore their reversible activities. Duck and cat livers have higher PC activity than pigeon livers, and the recombinant duck and cat NADKs exhibit high activity in the reverse direction. The human NADK has an affinity for NAD⁺ that is ∼600 times higher than the pigeon, duck, and cat isoforms, and we conclude that NAD⁺ serves as a potent product inhibitor for the reverse activity of the human NADK, which accounts for the observed irreversible behavior. These results demonstrate that while all four NADKs are reversible, the reverse activity of the human enzyme alone is impeded via product inhibition. This mechanism─the conversion of a reversible to a unidirectional reaction by product inhibition─may be valuable in future metabolic engineering applications.

Balancing NAD+ deficits with nicotinamide riboside: therapeutic possibilities and limitations

Alterations in cellular nicotinamide adenine dinucleotide (NAD+) levels have been observed in multiple lifestyle and age-related medical conditions. This has led to the hypothesis that dietary supplementation with NAD+ precursors, or vitamin B3s, could exert health benefits. Among the different molecules that can act as NAD+ precursors, Nicotinamide Riboside (NR) has gained most attention due to its success in alleviating and treating disease conditions at the pre-clinical level. However, the clinical outcomes for NR supplementation strategies have not yet met the expectations generated in mouse models. In this review we aim to provide a comprehensive view on NAD+ biology, what causes NAD+ deficits and the journey of NR from its discovery to its clinical development. We also discuss what are the current limitations in NR-based therapies and potential ways to overcome them. Overall, this review will not only provide tools to understand NAD+ biology and assess its changes in disease situations, but also to decide which NAD+ precursor could have the best therapeutic potential.

Novel therapeutic combinations with PARP inhibitors for small cell lung cancer: A bench-to-bedside review

Small cell lung cancer (SCLC) is treated as a monolithic disease despite the evident intra- and intertumoral heterogeneity. Non-specific DNA-damaging agents have remained the first-line treatment for decades. Recently, emerging transcriptomic and genomic profiling of SCLC tumors identified distinct SCLC subtypes and vulnerabilities towards targeted therapeutics, including inhibitors of the nuclear enzyme poly (ADP-ribose) polymerase (PARPi). SCLC cell lines and tumors exhibited an elevated level of PARP1 protein and mRNA compared to healthy lung tissues and other subtypes of lung tumors. Notable responses to PARPi were also observed in preclinical SCLC models. Clinically, PARPi monotherapy exerted variable benefits for SCLC patients. To date, research is being vigorously conducted to examine predictive biomarkers of PARPi response and various PARPi combination strategies to maximize the clinical utility of PARPi. This narrative review summarizes existing preclinical evidence supporting PARPi monotherapy, combination therapy, and respective translation to the clinic. Specifically, we covered the combination of PARPi with DNA-damaging chemotherapy (cisplatin, etoposide, temozolomide), thoracic radiotherapy, immunotherapy (immune checkpoint inhibitors), and many other novel therapeutic agents that target DNA damage response, tumor microenvironment, epigenetic modulation, angiogenesis, the ubiquitin-proteasome system, or autophagy. Putative biomarkers, such as SLFN11 expression, MGMT methylation, E2F1 expression, and platinum sensitivity, which may be predictive of response to distinct therapeutic combinations, were also discussed. The future of SCLC treatment is undergoing rapid change with a focus on tailored and personalized treatment strategies. Further development of cancer therapy with PARPi will immensely benefit at least a subset of biomarker-defined SCLC patients.

A Cytological Atlas of the Human Liver Proteome from PROTEOMESKY-LIVERHu 2.0, a Publicly Available Database

The liver plays a unique role as a metabolic center of the body, and also performs other important functions such as detoxification and immune response. Here, we establish a cell type-resolved healthy human liver proteome including hepatocytes (HCs), hepatic stellate cells (HSCs), Kupffer cells (KCs), and liver sinusoidal endothelial cells (LSECs) by high-resolution mass spectrometry. Overall, we quantify total 8354 proteins for four cell types and over 6000 proteins for each cell type. Analysis of this data set and regulatory pathway reveals the cellular labor division in the human liver follows the pattern that parenchymal cells make the main components of pathways, but nonparenchymal cells trigger these pathways. Human liver cells show some novel molecular features: HCs maintain KCs and LSECs homeostasis by producing cholesterol and ketone bodies; HSCs participate in xenobiotics metabolism as an agent deliverer; KCs and LSECs mediate immune response through MHC class II-TLRs and MHC class I-TGFβ cascade, respectively; and KCs play a central role in diurnal rhythms regulation through sensing diurnal IGF and temperature flux. Together, this work expands our understandings of liver physiology and provides a useful resource for future analyses of normal and diseased livers.

NAD+ Precursors: A Questionable Redundancy

The last decade has seen a strong proliferation of therapeutic strategies for the treatment of metabolic and age-related diseases based on increasing cellular NAD⁺ bioavailability. Among them, the dietary supplementation with NAD⁺ precursors—classically known as vitamin B3—has received most of the attention. Multiple molecules can act as NAD⁺ precursors through independent biosynthetic routes. Interestingly, eukaryote organisms have conserved a remarkable ability to utilize all of these different molecules, even if some of them are scarcely found in nature. Here, we discuss the possibility that the conservation of all of these biosynthetic pathways through evolution occurred because the different NAD⁺ precursors might serve specialized purposes.

Methods of PARP-1 Determination and its Importance in Living Organisms

Abstract:

PARP-1 is one of the 18 PARP enzymes that are involved in important processes at the cellular level. The most important tasks of PARP-1 are to detect and repair DNA damage and to prevent processes of apoptosis. By finding and using new strategies for marking and detecting the activity of this protein, it is possible to identify more and more tasks in which it participates. In pathological states, PARP-1 activity increases significantly. Since the 1980s, scientists have been searching for and discussing substances that may inhibit PARP-1 activity and disrupt DNA damage response pathways. In this way, unwanted cells could be destroyed. The paper presents a short description of the methods used in the determination of PARP-1 by various research groups. A critical approach to each of them was also made by pointing to the advantages and disadvantages of the described analytical methods. The literature review contains information on methods useful for PARP-1 determination, such as SPR, QCM, CL and FL, DPV, SDS-PAGE with MS, MALDI MS, Western Blot, ELISA and ATR-FTIR spectroscopy. It also includes analysis of the results of research on inhibitors that may be effective in the diagnosis and treatment of cancer and other diseases.

Modification Effect of PARP4 and ERCC1 Gene Polymorphisms on the Relationship between Particulate Matter Exposure and Fasting Glucose Level

Particulate matter (PM) has been linked to adverse health outcomes, including insulin resistance (IR). To evaluate the relationships between exposures to PM₁₀, PM_2.5–10, and PM_2.5; the serum level of fasting glucose, a key IR indicator; and effects of polymorphisms of two repair genes (PARP4 and ERCC1) on these relations, PMs exposure data and blood samples for glucose measurement and genotyping were collected from 527 Korean elders. Daily average levels of PMs during 8 days, from 7 days before examination to the health examination day (from lag day 7 to lag day 0), were used for association analyses, and mean concentrations of PM₁₀, PM_2.5–10, and PM_2.5 during the study period were 43.4 µg/m³, 19.9 µg/m³, and 23.6 µg/m³, respectively. All three PMs on lag day 4 (mean, 44.5 µg/m³ for PM₁₀, 19.9 µg/m³ for PM_2.5–10, and 24.3 µg/m³ for PM_2.5) were most strongly associated with an increase in glucose level (percent change by inter-quartile range-change of PM: (β) = 1.4 and p = 0.0023 for PM₁₀; β = 3.0 and p = 0.0010 for PM_2.5–10; and β = 2.0 and p = 0.0134 for PM_2.5). In particular, elders with PARP4 G-C-G or ERCC1 T-C haplotype were susceptible to PMs exposure in relation to glucose levels (PARP4 G-C-G: β = 2.6 and p = 0.0006 for PM₁₀, β = 3.5 and p = 0.0009 for PM_2.5–10, and β = 1.6 and p = 0.0020 for PM_2.5; ERCC1 T-C: β = 2.2 and p = 0.0016 for PM₁₀, β = 3.5 and p = 0.0003 for PM_2.5–10, and β = 1.2 and p = 0.0158 for PM_2.5). Our results indicated that genetic polymorphisms of PARP4 and ERCC1 could modify the relationship between PMs exposure and fasting glucose level in the elderly.

Harnessing NAD+ Metabolism as Therapy for Cardiometabolic Diseases

PURPOSE OF THE REVIEW

This review summarizes current understanding on the roles of nicotinamide adenine dinucleotide (NAD⁺) metabolism in the pathogeneses and treatment development of metabolic and cardiac diseases.

RECENT FINDINGS

NAD⁺ was identified as a redox cofactor in metabolism and a co-substrate for a wide range of NAD⁺-dependent enzymes. NAD⁺ redox imbalance and depletion are associated with many pathologies where metabolism plays a key role, for example cardiometabolic diseases. This review is to delineate the current knowledge about harnessing NAD⁺ metabolism as potential therapy for cardiometabolic diseases. The review has summarized how NAD⁺ redox imbalance and depletion contribute to the pathogeneses of cardiometabolic diseases. Therapeutic evidence involving activation of NAD⁺ synthesis in pre-clinical and clinical studies was discussed. While activation of NAD⁺ synthesis shows great promise for therapy, the field of NAD⁺ metabolism is rapidly evolving. Therefore, it is expected that new mechanisms will be discovered as therapeutic targets for cardiometabolic diseases.