The Histone Deacetylases Hst1 and Rpd3 Integrate De Novo NAD+ Metabolism with Phosphate Sensing in Saccharomyces cerevisiae.

Nicotinamide adenine dinucleotide (NAD+) is a critical cofactor essential for various cellular processes. Abnormalities in NAD+ metabolism have also been associated with a number of metabolic disorders. The regulation and interconnection of NAD+ metabolic pathways are not yet completely understood. By employing an NAD+ intermediate-specific genetic system established in the model organism S. cerevisiae, we show that histone deacetylases (HDACs) Hst1 and Rpd3 link the regulation of the de novo NAD+ metabolism-mediating BNA genes with certain aspects of the phosphate (Pi)-sensing PHO pathway. Our genetic and gene expression studies suggest that the Bas1-Pho2 and Pho2-Pho4 transcription activator complexes play a role in this co-regulation. Our results suggest a model in which competition for Pho2 usage between the BNA-activating Bas1-Pho2 complex and the PHO-activating Pho2-Pho4 complex helps balance de novo activity with PHO activity in response to NAD+ or phosphate depletion. Interestingly, both the Bas1-Pho2 and Pho2-Pho4 complexes appear to also regulate the expression of the salvage-mediating PNC1 gene negatively. These results suggest a mechanism for the inverse regulation between the NAD+ salvage pathways and the de novo pathway observed in our genetic models. Our findings help provide a molecular basis for the complex interplay of two different aspects of cellular metabolism.

The histone deacetylases Rpd3 and Hst1 antagonistically regulate de novo NAD+ metabolism in the budding yeast Saccharomyces cerevisiae.

NAD+ is a cellular redox cofactor involved in many essential processes. The regulation of NAD+ metabolism and the signaling networks reciprocally interacting with NAD+-producing metabolic pathways are not yet fully understood. The NAD+-dependent histone deacetylase (HDAC) Hst1 has been shown to inhibit de novo NAD+ synthesis by repressing biosynthesis of nicotinic acid (BNA) gene expression. Here, we alternatively identify HDAC Rpd3 as a positive regulator of de novo NAD+ metabolism in the budding yeast Saccharomyces cerevisiae. We reveal that deletion of RPD3 causes marked decreases in the production of de novo pathway metabolites, in direct contrast to deletion of HST1. We determined the BNA expression profiles of rpd3Δ and hst1Δ cells to be similarly opposed, suggesting the two HDACs may regulate the BNA genes in an antagonistic fashion. Our chromatin immunoprecipitation analysis revealed that Rpd3 and Hst1 mutually influence each other's binding distribution at the BNA2 promoter. We demonstrate Hst1 to be the main deacetylase active at the BNA2 promoter, with hst1Δ cells displaying increased acetylation of the N-terminal tail lysine residues of histone H4, H4K5, and H4K12. Conversely, we show that deletion of RPD3 reduces the acetylation of these residues in an Hst1-dependent manner. This suggests that Rpd3 may function to oppose spreading of Hst1-dependent heterochromatin and represents a unique form of antagonism between HDACs in regulating gene expression. Moreover, we found that Rpd3 and Hst1 also coregulate additional targets involved in other branches of NAD+ metabolism. These findings help elucidate the complex interconnections involved in effecting the regulation of NAD+ metabolism.

Timing of the first cannulation and survival of arteriovenous grafts in hemodialysis patients: a multicenter retrospective cohort study.

Arteriovenous graft (AVG) is an important vascular access route in hemodialysis patients. The optimal waiting time between AVG creation and the first cannulation is still undetermined, therefore the current study investigated the association between ideal timing for cannulation and AVG survival. This retrospective cohort study used data from the Taiwan National Health Insurance Database, which included 6,493 hemodialysis patients with AVGs between July 1st 2008 and June 30th 2012. The waiting cannulation time was defined as the time from the date of shunt creation to the first successful cannulation. Patients were categorized according to the waiting cannulation time of their AVGs as follows: ≤30 days, between 31 and 90 days, between 91 and 180 days, and >180 days. The primary outcome was functional cumulative survival, measured as the time from the first cannulation to shunt abandonment. The AVGs which were cannulated between 31 and 90 days (reference group) after construction had significantly superior functional cumulative survival compared with those cannulated ≤30 days (adjusted HR = 1.651 with 95% CI 1.482-1.839; p < 0.0001) and >180 days (adjusted HR = 1.197 with 95% CI 1.012-1.417; p = 0.0363) after construction. An analysis of the hazard ratios in patients with different demographic characteristics, revealed that the functional cumulative survival of AVGs in most groups was better when they received cannulation >30 days after construction. Consequently, in order to achieve the best long-term survival, AVGs should be cannulated at least 1 month after construction, but you should avoid waiting for >3 months.

Effect of chronic kidney disease on outcomes following proximal humerus fragility fracture surgery in diabetic patients: A nationwide population-based cohort study.

BACKGROUND: The proximal humerus fracture (PHF) is the third most common fragility fracture. Diabetes mellitus (DM) and chronic kidney disease (CKD) are both risks for fragility fractures; however, the interplay of DM and CKD makes treatment outcomes unpredictable. This study aimed to investigate and compare early and late outcomes following proximal humerus fracture fixation surgery in diabetic patients with different renal function conditions. METHODS: DM patients receiving PHF fixation surgery during 1998-2013 were recruited from Taiwan's National Health Insurance Research Database. According to their renal function, patients were divided into three study groups: non-chronic kidney disease (CKD), non-dialysis CKD, and dialysis. Outcomes of interest were early and late perioperative outcomes. Early outcomes included in-hospital newly-onset morbidities. Late outcomes included infection, revision, readmission, and all-cause mortality. RESULTS: This study included a total of 10,850 diabetic patients: 2152 had CKD (non-dialysis CKD group), 196 underwent permanent dialysis (dialysis group), and the remaining 8502 did not have CKD (non-CKD group). During a mean follow-up of 5.56 years, the dialysis group showed the highest risk of overall infection, all-cause revision, readmission, and mortality compared to the non-dialysis CKD group and non-CKD group. Furthermore, subgroup analysis showed that CKD patients had a higher risk of surgical infection following PHF surgery than non-CKD patients in cases with a traffic accident or fewer comorbidities (Charlson Comorbidity Index, CCI <3) (P for interaction: 0.086 and 0.096, respectively). Also, CKD patients had an even higher mortality risk after PHF surgery than non-CKD patients, in females, those living in higher urbanization areas, or with more comorbidities (CCI ≥3) (P for interaction: 0.011, 0.057, and 0.069, respectively). CONCLUSION: CKD was associated with elevated risks for infection, revision, readmission, and mortality after PHF fixation surgery in diabetic patients. These findings should be taken into consideration when caring for diabetic patients.

Chronic Kidney Disease Is Associated with High Mortality Risk in Patients with Diabetes after Primary Shoulder Arthroplasty: A Nationwide Population-Based Cohort Study.

The number of diabetic patients with chronic kidney disease (CKD) undergoing shoulder arthroplasty is growing. This study aims to compare perioperative outcomes of shoulder arthroplasty in diabetic patients at different renal function stages. Between 1998 and 2013, a total of 4443 diabetic patients with shoulder arthroplasty were enrolled: 1174 (26%) had CKD without dialysis (CKD group), 427 (9%) underwent dialysis (dialysis group), and 3042 (68%) had no CKD (non-CKD group). Compared with the non-CKD group, the CKD (odds ratio [OR], 4.69; 95% confidence interval [CI], 2.02-10.89) and dialysis (OR, 6.71; 95% CI, 1.63-27.73) groups had a high risk of in-hospital death. The dialysis group had a high risk of infection after shoulder arthroplasty compared with the CKD (subdistribution hazard ratio [SHR], 1.69; 95% CI, 1.07-2.69) and non-CKD (SHR, 1.76; 95% CI, 1.14-2.73) groups. The dialysis group showed higher risks of all-cause readmission and mortality than the CKD and non-CKD groups after a 3-month follow-up. In conclusion, CKD was associated with worse outcomes after shoulder arthroplasty. Compared with those without CKD, CKD patients had significantly increased readmission and mortality risks but did not have an increased risk of surgical complications, including superficial infection or implant removal.

NAD+ Metabolism, Metabolic Stress, and Infection.

Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite with wide-ranging and significant roles in the cell. Defects in NAD+ metabolism have been associated with many human disorders; it is therefore an emerging therapeutic target. Moreover, NAD+ metabolism is perturbed during colonization by a variety of pathogens, either due to the molecular mechanisms employed by these infectious agents or by the host immune response they trigger. Three main biosynthetic pathways, including the de novo and salvage pathways, contribute to the production of NAD+ with a high degree of conservation from bacteria to humans. De novo biosynthesis, which begins with l-tryptophan in eukaryotes, is also known as the kynurenine pathway. Intermediates of this pathway have various beneficial and deleterious effects on cellular health in different contexts. For example, dysregulation of this pathway is linked to neurotoxicity and oxidative stress. Activation of the de novo pathway is also implicated in various infections and inflammatory signaling. Given the dynamic flexibility and multiple roles of NAD+ intermediates, it is important to understand the interconnections and cross-regulations of NAD+ precursors and associated signaling pathways to understand how cells regulate NAD+ homeostasis in response to various growth conditions. Although regulation of NAD+ homeostasis remains incompletely understood, studies in the genetically tractable budding yeast Saccharomyces cerevisiae may help provide some molecular basis for how NAD+ homeostasis factors contribute to the maintenance and regulation of cellular function and how they are regulated by various nutritional and stress signals. Here we present a brief overview of recent insights and discoveries made with respect to the relationship between NAD+ metabolism and selected human disorders and infections, with a particular focus on the de novo pathway. We also discuss how studies in budding yeast may help elucidate the regulation of NAD+ homeostasis.

Direct oral anticoagulants and the risk of osteoporotic fractures in patients with non-valvular atrial fibrillation.

BACKGROUND: The incidence of osteoporotic fracture increases with age, particularly in elderly populations with atrial fibrillation (AF). However, direct oral anticoagulants (DOACs) have less effect on osteoporotic fracture than vitamin K antagonists, it is unclear whether the risk of osteoporotic fracture is affected by different types and doses of DOACs in AF patients. METHODS: This nationwide population-based cohort study included AF patients prescribed DOACs between 2011 and 2016 taken from the Taiwan National Health Insurance database. Adjusted hazard ratios (aHRs) for the risk of osteoporotic, hip, and spine fractures between DOAC users were compared using the Fine and Gray subdistribution hazard model to adjust for possible confounders. RESULTS: A total of 56,795 patients who were prescribed DOACs were included in the present study. Among them, 24,597 patients received dabigatran, 26,968 received rivaroxaban, and 5230 received apixaban. After 2 years' follow up, there was no significant difference in the incidence of osteoporotic, spine, or hip fracture among those receiving dabigatran, rivaroxaban, or apixaban. Subgroup analysis showed that patients taking dabigatran had a higher incidence of osteoporotic and hip fracture than those taking rivaroxaban and apixaban in cases with concomitant peripheral artery disease (PAD) or a history of hip fracture (p for interaction: 0.004 and 0.030, respectively). However, dabigatran users had a lower incidence of osteoporotic fracture and spine fracture in those receiving standard-dose DOACs compared with rivaroxaban and apixaban; whereas, they had a higher incidence of hip fractures when administered at low dose. CONCLUSION: AF patients with different DOACs did not have different risks of osteoporotic fracture overall. However, additional concomitant morbidities, such as PAD or a history of hip fracture, and standard/low doses might be associated with different risks for different DOACs. These findings should be taken into consideration in the clinic when the DOAC is being chosen. PLAIN LANGUAGE SUMMARY: Different direct oral anticoagulants had different impact on osteoporotic fracture Anticoagulation therapy is an essential therapy in atrial fibrillation (AF) patients, but osteoporotic fracture is another important issue in these patients prescribed with anticoagulants. However, no study has been conducted to evaluate the impact of different DOACs on different types of osteoporotic fractures. In our findings, although different DOACs had no significantly different impact on osteoporotic fractures, dabigatran users had a slightly higher incidence of osteoporotic and hip fractures among different DOACs, particularly in those have simultaneously had peripheral artery disease, a history of hip fracture. In addition, when AF patients taking low-dose DOACs, dabigatran users also have higher incidence of hip fracture than those taking other DOACs.

N-terminal protein acetylation by NatB modulates the levels of Nmnats, the NAD+ biosynthetic enzymes in Saccharomyces cerevisiae.

NAD+ is an essential metabolite participating in cellular biochemical processes and signaling. The regulation and interconnection among multiple NAD+ biosynthesis pathways are incompletely understood. Yeast (Saccharomyces cerevisiae) cells lacking the N-terminal (Nt) protein acetyltransferase complex NatB exhibit an approximate 50% reduction in NAD+ levels and aberrant metabolism of NAD+ precursors, changes that are associated with a decrease in nicotinamide mononucleotide adenylyltransferase (Nmnat) protein levels. Here, we show that this decrease in NAD+ and Nmnat protein levels is specifically due to the absence of Nt-acetylation of Nmnat (Nma1 and Nma2) proteins and not of other NatB substrates. Nt-acetylation critically regulates protein degradation by the N-end rule pathways, suggesting that the absence of Nt-acetylation may alter Nmnat protein stability. Interestingly, the rate of protein turnover (t½) of non-Nt-acetylated Nmnats did not significantly differ from those of Nt-acetylated Nmnats. Accordingly, deletion or depletion of the N-end rule pathway ubiquitin E3 ligases in NatB mutants did not restore NAD+ levels. Next, we examined whether the status of Nt-acetylation would affect the translation of Nmnats, finding that the absence of Nt-acetylation does not significantly alter the polysome formation rate on Nmnat mRNAs. However, we observed that NatB mutants have significantly reduced Nmnat protein maturation. Our findings indicate that the reduced Nmnat levels in NatB mutants are mainly due to inefficient protein maturation. Nmnat activities are essential for all NAD+ biosynthesis routes, and understanding the regulation of Nmnat protein homeostasis may improve our understanding of the molecular basis and regulation of NAD+ metabolism.

NAD+ Metabolism and Regulation: Lessons From Yeast.

Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite involved in various cellular processes. The cellular NAD+ pool is maintained by three biosynthesis pathways, which are largely conserved from bacteria to human. NAD+ metabolism is an emerging therapeutic target for several human disorders including diabetes, cancer, and neuron degeneration. Factors regulating NAD+ homeostasis have remained incompletely understood due to the dynamic nature and complexity of NAD+ metabolism. Recent studies using the genetically tractable budding yeast Saccharomyces cerevisiae have identified novel NAD+ homeostasis factors. These findings help provide a molecular basis for how may NAD+ and NAD+ homeostasis factors contribute to the maintenance and regulation of cellular function. Here we summarize major NAD+ biosynthesis pathways, selected cellular processes that closely connect with and contribute to NAD+ homeostasis, and regulation of NAD+ metabolism by nutrient-sensing signaling pathways. We also extend the discussions to include possible implications of NAD+ homeostasis factors in human disorders. Understanding the cross-regulation and interconnections of NAD+ precursors and associated cellular pathways will help elucidate the mechanisms of the complex regulation of NAD+ homeostasis. These studies may also contribute to the development of effective NAD+-based therapeutic strategies specific for different types of NAD+ deficiency related disorders.

Effects of Chronic Kidney Disease on Hemiarthroplasty Outcomes for Fragility Hip Fracture in Diabetic Patients: A Nationwide Population-Based Observational Study.

BACKGROUND: The aim of this study is to compare perioperative outcomes, readmission, and mortality after hemiarthroplasty for hip fractures in diabetic patients with different renal function statuses. METHODS: In this retrospective population-based cohort study, diabetic patients who received primary hemiarthroplasty for hip fracture between January 1997 and December 2013 were identified from the Taiwan National Health Insurance Research Database. Primary outcomes were perioperative outcomes including infection and revision. Secondary outcomes were all-cause readmission and mortality. RESULTS: A total of 29,535 diabetic patients were included: 8270 patients had chronic kidney disease (CKD group), 1311 patients underwent permanent dialysis (dialysis group), and 19,954 patients did not have CKD (non-CKD group). During a mean follow-up of 4.5 years, these 3 groups had comparable risks of any infection, including superficial and deep infection. Dialysis patients had a significantly higher risk of revision than did CKD and non-CKD patients (subdistribution hazard ratio 1.65, 95% confidence interval 1.16-2.36; subdistribution hazard ratio 1.57, 95% confidence interval 1.10-2.24, respectively). Compared with the non-CKD group, the dialysis group had significantly higher risks of readmission and mortality at all time points, namely 3 months after surgery, 1 year after surgery, and the final follow-up. The CKD group also had higher risks of readmission and mortality than did the non-CKD group at all time points. CONCLUSION: CKD is associated with poor outcomes following hemiarthroplasty for fragility hip fracture. CKD patients may have higher risks of surgical complications including revision than non-CKD patients, and they have significantly elevated risks of readmission and mortality.

Cross-talk in NAD+ metabolism: insights from Saccharomyces cerevisiae.

NAD+ (nicotinamide adenine dinucleotide) is an essential metabolite involved in a myriad of cellular processes. The NAD+ pool is maintained by three biosynthesis pathways, which are largely conserved from bacteria to human with some species-specific differences. Studying the regulation of NAD+ metabolism has been difficult due to the dynamic flexibility of NAD+ intermediates, the redundancy of biosynthesis pathways, and the complex interconnections among them. The budding yeast Saccharomyces cerevisiae provides an efficient genetic model for the isolation and study of factors that regulate specific NAD+ biosynthesis pathways. A recent study has uncovered a putative cross-regulation between the de novo NAD+ biosynthesis and copper homeostasis mediated by a copper-sensing transcription factor Mac1. Mac1 appears to work with the Hst1-Sum1-Rfm1 complex to repress the expression of de novo NAD+ biosynthesis genes. Here, we extend the discussions to include additional nutrient- and stress-sensing pathways that have been associated with the regulation of NAD+ homeostasis. NAD+ metabolism is an emerging therapeutic target for several human diseases. NAD+ preservation also helps ameliorate age-associated metabolic disorders. Recent findings in yeast contribute to the understanding of the molecular basis underlying the cross-regulation of NAD+ metabolism and other signaling pathways.

The copper-sensing transcription factor Mac1, the histone deacetylase Hst1, and nicotinic acid regulate de novo NAD+ biosynthesis in budding yeast.

NADH (NAD+) is an essential metabolite involved in various cellular biochemical processes. The regulation of NAD+ metabolism is incompletely understood. Here, using budding yeast (Saccharomyces cerevisiae), we established an NAD+ intermediate-specific genetic system to identify factors that regulate the de novo branch of NAD+ biosynthesis. We found that a mutant strain (mac1Δ) lacking Mac1, a copper-sensing transcription factor that activates copper transport genes during copper deprivation, exhibits increases in quinolinic acid (QA) production and NAD+ levels. Similar phenotypes were also observed in the hst1Δ strain, deficient in the NAD+-dependent histone deacetylase Hst1, which inhibits de novo NAD+ synthesis by repressing BNA gene expression when NAD+ is abundant. Interestingly, the mac1Δ and hst1Δ mutants shared a similar NAD+ metabolism-related gene expression profile, and deleting either MAC1 or HST1 de-repressed the BNA genes. ChIP experiments with the BNA2 promoter indicated that Mac1 works with Hst1-containing repressor complexes to silence BNA expression. The connection of Mac1 and BNA expression suggested that copper stress affects de novo NAD+ synthesis, and we show that copper stress induces both BNA expression and QA production. Moreover, nicotinic acid inhibited de novo NAD+ synthesis through Hst1-mediated BNA repression, hindered the reuptake of extracellular QA, and thereby reduced de novo NAD+ synthesis. In summary, we have identified and characterized novel NAD+ homeostasis factors. These findings will expand our understanding of the molecular basis and regulation of NAD+ metabolism.

The Prognostic Significance of Puncture Timing to Survival of Arteriovenous Fistulas in Hemodialysis Patients: A Multicenter Retrospective Cohort Study.

(1) Background: A functional shunt is critical to hemodialysis, but the ideal timing of shunt cannulation is still not established. In this study, we assessed the association between ideal puncture timing and shunt survival. (2) Methods: This retrospective cohort study using data from the Taiwan Health and Welfare database, which included 26885 hemodialysis patients with arteriovenous fistulas from 1 July 2008 to 30 June 2012. Fistulas were categorized by functional maturation time, defined as the time from the date of shunt construction to the first successful cannulation. Functional cumulative survival, measured as the duration from the first puncture to shunt abandonment, was mainly regarded. (3) Results: The fistulas created between 91 and 180 days prior to the first cannulation had significantly greater cumulative functional survival (HR 0.883; 95% CI 0.792⁻0.984), and there was no more benefit on their survival from waiting more than 180 days (HR 0.957; 95% CI 0.853⁻1.073) for shunt maturity. (4) Conclusions: Our results showed that to achieve better long-term shunt survivals, fistulas should be constructed at least 90 days before starting hemodialysis. Notably, there was no additional benefit on waiting more than 180 days prior to cannulation.

Chronic Kidney Disease Worsens Health Outcomes in Diabetic Patients After Hip Fracture Surgery: An Asian Nationwide Population-Based Cohort Study.

There is an increased tendency for hip fractures in patients with chronic kidney disease (CKD). Although surgery is the mainstay of treatment for hip fractures, there is scant information on outcomes after hip fracture surgery in diabetic patients at different stages of CKD. In this population-based cohort study, we compared the surgical outcome, readmission, and mortality rates after osteosynthesis of hip fractures in diabetic patients with different stages of renal function. Diabetic patients who received primary osteosynthesis for hip fracture between January 1997 and December 2013 were enrolled. The primary outcomes were surgical outcomes, including infection and revision surgery. The secondary outcomes were all-cause readmission and mortality. This study included 44,065 patients; 11,954 had CKD (diabetic CKD group), 1662 patients were receiving dialysis (diabetic dialysis group), and 30,449 patients had no CKD (diabetic non-CKD group). We found that the diabetic dialysis group had a significantly higher risk of infection and revision surgery compared with diabetic non-CKD patients (HR = 1.52, 95% CI, 1.24 to 1.87; HR = 1.62, 95% CI, 1.33 to 1.97, respectively, both P < 0.001) and diabetic CKD patients (HR = 1.62, 95% CI, 1.32 to 1.99; HR = 1.48, 95% CI, 1.22 to 1.80, respectively, both P < 0.001). Diabetic CKD patients had a comparable risk of surgical complications including infection and revision as diabetic non-CKD patients. For readmission and mortality, the diabetic dialysis group had the highest risk among the three groups at all time-points (3 months after surgery, 1 year, and the last follow-up, all P < 0.001). Compared with the diabetic non-CKD group, the diabetic CKD group had an elevated risk of readmission and mortality at all time-points (all P < 0.001). In conclusion, CKD was associated with worse outcomes after hip fracture fixation surgery. Although at significantly higher risk of readmission and mortality, CKD patients still had a comparable risk of infection and revision to non-CKD patients. © 2019 American Society for Bone and Mineral Research.

A functional link between NAD+ homeostasis and N-terminal protein acetylation in Saccharomyces cerevisiae.

Nicotinamide adenine dinucleotide (NAD+) is an essential metabolite participating in cellular redox chemistry and signaling, and the complex regulation of NAD+ metabolism is not yet fully understood. To investigate this, we established a NAD+-intermediate specific reporter system to identify factors required for salvage of metabolically linked nicotinamide (NAM) and nicotinic acid (NA). Mutants lacking components of the NatB complex, NAT3 and MDM20, appeared as hits in this screen. NatB is an Nα-terminal acetyltransferase responsible for acetylation of the N terminus of specific Met-retained peptides. In NatB mutants, increased NA/NAM levels were concomitant with decreased NAD+ We identified the vacuolar pool of nicotinamide riboside (NR) as the source of this increased NA/NAM. This NR pool is increased by nitrogen starvation, suggesting NAD+ and related metabolites may be trafficked to the vacuole for recycling. Supporting this, increased NA/NAM release in NatB mutants was abolished by deleting the autophagy protein ATG14 We next examined Tpm1 (tropomyosin), whose function is regulated by NatB-mediated acetylation, and Tpm1 overexpression (TPM1-oe) was shown to restore some NatB mutant defects. Interestingly, although TPM1-oe largely suppressed NA/NAM release in NatB mutants, it did not restore NAD+ levels. We showed that decreased nicotinamide mononucleotide adenylyltransferase (Nma1/Nma2) levels probably caused the NAD+ defects, and NMA1-oe was sufficient to restore NAD+ NatB-mediated N-terminal acetylation of Nma1 and Nma2 appears essential for maintaining NAD+ levels. In summary, our results support a connection between NatB-mediated protein acetylation and NAD+ homeostasis. Our findings may contribute to understanding the molecular basis and regulation of NAD+ metabolism.

Chronic kidney disease is associated with a risk of higher mortality following total knee arthroplasty in diabetic patients: a nationwide population-based study.

Diabetes and chronic kidney disease (CKD) are associated with a higher rate of complications in patients undergoing total knee arthroplasty (TKA). The purpose of this study was to determine the effects of CKD and diabetes in patients after TKA. Diabetic patients who received unilateral primary TKA between January 2008 and December 2011 were enrolled. The follow-up period was more than 6 months. The primary outcome was a TKA-related infection and the secondary outcome was all-cause mortality. The study cohort included 13844 patients who were followed for a mean period of 2 years, of whom 1459 (10.5%) had CKD. The patients with CKD were older than those without CKD (71.6 versus 70.3 years, P<0.0001) and had higher rates of hypertension, gouty arthritis, ischemic heart disease, chronic pulmonary obstructive disease, pulmonary embolism and deep vein thrombosis (all P<0.0001). After adjustment of comorbidities, the CKD group had a higher incidence of urinary tract infections (OR: 1.61, 95% CI: 1.19-2.17). There were no significant differences in wound infections, pneumonia, pulmonary embolism or in-hospital death between the two groups. After adjustment of confounders, the CKD group had higher rates of myocardial infarction (HR: 2.06, 95% CI: 1.26-3.39) and mortality (HR: 1.99, 95% CI: 1.59-2.48). The risk of TKA-related infection during follow-up was comparable between the two groups (HR: 1.31, 95% CI: 0.94-1.82). In conclusion, CKD is associated with increased risks of urinary tract infections, myocardial infarction and all-cause mortality after TKA. Surgeons should be aware of this when evaluating TKA patients with renal disease.

Reduced Ssy1-Ptr3-Ssy5 (SPS) signaling extends replicative life span by enhancing NAD+ homeostasis in Saccharomyces cerevisiae.

Attenuated nutrient signaling extends the life span in yeast and higher eukaryotes; however, the mechanisms are not completely understood. Here we identify the Ssy1-Ptr3-Ssy5 (SPS) amino acid sensing pathway as a novel longevity factor. A null mutation of SSY5 (ssy5Δ) increases replicative life span (RLS) by ∼50%. Our results demonstrate that several NAD(+) homeostasis factors play key roles in this life span extension. First, expression of the putative malate-pyruvate NADH shuttle increases in ssy5Δ cells, and deleting components of this shuttle, MAE1 and OAC1, largely abolishes RLS extension. Next, we show that Stp1, a transcription factor of the SPS pathway, directly binds to the promoter of MAE1 and OAC1 to regulate their expression. Additionally, deletion of SSY5 increases nicotinamide riboside (NR) levels and phosphate-responsive (PHO) signaling activity, suggesting that ssy5Δ increases NR salvaging. This increase contributes to NAD(+) homeostasis, partially ameliorating the NAD(+) deficiency and rescuing the short life span of the npt1Δ mutant. Moreover, we observed that vacuolar phosphatase, Pho8, is partially required for ssy5Δ-mediated NR increase and RLS extension. Together, our studies present evidence that supports SPS signaling is a novel NAD(+) homeostasis factor and ssy5Δ-mediated life span extension is likely due to concomitantly increased mitochondrial and vacuolar function. Our findings may contribute to understanding the molecular basis of NAD(+) metabolism, cellular life span, and diseases associated with NAD(+) deficiency and aging.

Less is more: Nutrient limitation induces cross-talk of nutrient sensing pathways with NAD+ homeostasis and contributes to longevity.

Nutrient sensing pathways and their regulation grant cells control over their metabolism and growth in response to changing nutrients. Factors that regulate nutrient sensing can also modulate longevity. Reduced activity of nutrient sensing pathways such as glucose-sensing PKA, nitrogen-sensing TOR and S6 kinase homolog Sch9 have been linked to increased life span in the yeast, Saccharomyces cerevisiae, and higher eukaryotes. Recently, reduced activity of amino acid sensing SPS pathway was also shown to increase yeast life span. Life span extension by reduced SPS activity requires enhanced NAD+ (nicotinamide adenine dinucleotide, oxidized form) and nicotinamide riboside (NR, a NAD+ precursor) homeostasis. Maintaining adequate NAD+ pools has been shown to play key roles in life span extension, but factors regulating NAD+ metabolism and homeostasis are not completely understood. Recently, NAD+ metabolism was also linked to the phosphate (Pi)-sensing PHO pathway in yeast. Canonical PHO activation requires Pi-starvation. Interestingly, NAD+ depletion without Pi-starvation was sufficient to induce PHO activation, increasing NR production and mobilization. Moreover, SPS signaling appears to function in parallel with PHO signaling components to regulate NR/NAD+ homeostasis. These studies suggest that NAD+ metabolism is likely controlled by and/or coordinated with multiple nutrient sensing pathways. Indeed, cross-regulation of PHO, PKA, TOR and Sch9 pathways was reported to potentially affect NAD+ metabolism; though detailed mechanisms remain unclear. This review discusses yeast longevity-related nutrient sensing pathways and possible mechanisms of life span extension, regulation of NAD+ homeostasis, and cross-talk among nutrient sensing pathways and NAD+ homeostasis.

Regulation of NAD+ metabolism, signaling and compartmentalization in the yeast Saccharomyces cerevisiae.

Pyridine nucleotides are essential coenzymes in many cellular redox reactions in all living systems. In addition to functioning as a redox carrier, NAD(+) is also a required co-substrate for the conserved sirtuin deacetylases. Sirtuins regulate transcription, genome maintenance and metabolism and function as molecular links between cells and their environment. Maintaining NAD(+) homeostasis is essential for proper cellular function and aberrant NAD(+) metabolism has been implicated in a number of metabolic- and age-associated diseases. Recently, NAD(+) metabolism has been linked to the phosphate-responsive signaling pathway (PHO pathway) in the budding yeast Saccharomyces cerevisiae. Activation of the PHO pathway is associated with the production and mobilization of the NAD(+) metabolite nicotinamide riboside (NR), which is mediated in part by PHO-regulated nucleotidases. Cross-regulation between NAD(+) metabolism and the PHO pathway has also been reported; however, detailed mechanisms remain to be elucidated. The PHO pathway also appears to modulate the activities of common downstream effectors of multiple nutrient-sensing pathways (Ras-PKA, TOR, Sch9/AKT). These signaling pathways were suggested to play a role in calorie restriction-mediated beneficial effects, which have also been linked to Sir2 function and NAD(+) metabolism. Here, we discuss the interactions of these pathways and their potential roles in regulating NAD(+) metabolism. In eukaryotic cells, intracellular compartmentalization facilitates the regulation of enzymatic functions and also concentrates or sequesters specific metabolites. Various NAD(+)-mediated cellular functions such as mitochondrial oxidative phosphorylation are compartmentalized. Therefore, we also discuss several key players functioning in mitochondrial, cytosolic and vacuolar compartmentalization of NAD(+) intermediates, and their potential roles in NAD(+) homeostasis. To date, it remains unclear how NAD(+) and NAD(+) intermediates shuttle between different cellular compartments. Together, these studies provide a molecular basis for how NAD(+) homeostasis factors and the interacting signaling pathways confer metabolic flexibility and contribute to maintaining cell fitness and genome stability.