Angiotensin II type 1 receptor-associated protein deletion combined with angiotensin II stimulation accelerates the development of diabetic kidney disease in mice on a C57BL/6 strain.

The progress in the research field of diabetic kidney disease (DKD) has been disturbed by the lack of reliable animal models. Angiotensin II (Ang II) type 1 receptor (AT1R)-associated protein (ATRAP) promotes internalization of AT1R and selectively inhibits pathological AT1R signaling. In this study, we investigated whether overactivation of the renin-angiotensin system (RAS) through a combination of ATRAP deletion with Ang II stimulation developed a progressive DKD model in C57BL/6 mice, which are resistant to the development of kidney injury. Eight-week-old male systemic ATRAP-knockout mice on the C57BL/6 strain (KO) and their littermate wild-type mice (Ctrl) were divided into five groups: 1) Ctrl, 2) Ctrl-streptozotocin (STZ), 3) KO-STZ, 4) Ctrl-STZ-Ang II, and 5) KO-STZ-Ang II. Ang II was administered for 6 weeks from 4 weeks after STZ administration. At 10 weeks after STZ administration, mice were euthanized to evaluate kidney injuries. Neither ATRAP deletion alone nor Ang II stimulation alone developed a progressive DKD model in STZ-induced diabetic C57BL/6 mice. However, a combination of ATRAP deletion with Ang II stimulation accelerated the development of DKD as manifested by overt albuminuria, glomerular hypertrophy, podocyte loss, mesangial expansion, kidney interstitial fibrosis and functional insufficiency, concomitant with increased angiotensinogen and AT1R expression in the kidneys. In STZ-induced diabetic C57BL/6 mice that are resistant to the development of kidney injury, the combination of ATRAP deletion and Ang II stimulation accelerates the development of DKD, which may be associated with intrarenal RAS overactivation.

Combination of sacubitril/valsartan and blockade of the PI3K pathway enhanced kidney protection in a mouse model of cardiorenal syndrome.

Aims: Angiotensin receptor-neprilysin inhibitor (ARNI) is an established treatment for heart failure. However, whether ARNI has renoprotective effects beyond renin-angiotensin system inhibitors alone in cardiorenal syndrome (CRS) has not been fully elucidated. Here, we examined the effects of ARNI on the heart and kidneys of CRS model mice with overt albuminuria and identified the mechanisms underlying ARNI-induced kidney protection. Methods and results: C57BL6 mice were subjected to chronic angiotensin II infusion, nephrectomy, and salt loading (ANS); they developed CRS phenotypes and were divided into the vehicle treatment (ANS-vehicle), sacubitril/valsartan treatment (ANS-ARNI), and two different doses of valsartan treatment (ANS-VAL M, ANS-VAL H) groups. Four weeks after treatment, the hearts and kidneys of each group were evaluated. The ANS-vehicle group showed cardiac fibrosis, cardiac dysfunction, overt albuminuria, and kidney fibrosis. The ANS-ARNI group showed a reduction in cardiac fibrosis and cardiac dysfunction compared with the valsartan treatment groups. However, regarding the renoprotective effects characterized by albuminuria and fibrosis, ARNI was less effective than valsartan. Kidney transcriptomic analysis showed that the ANS-ARNI group exhibited a significant enhancement in the phosphoinositide 3-kinase (PI3K)-AKT signalling pathway compared with the ANS-VAL M group. Adding PI3K inhibitor treatment to ARNI ameliorated kidney injury to levels comparable with those of ANS-VAL M while preserving the superior cardioprotective effect of ARNI. Conclusion: PI3K pathway activation has been identified as a key mechanism affecting remnant kidney injury under ARNI treatment in CRS pathology, and blockading the PI3K pathway with simultaneous ARNI treatment is a potential therapeutic strategy for treating CRS with overt albuminuria.

miR-125a-5p/miR-125b-5p contributes to pathological activation of angiotensin II-AT1R in mouse distal convoluted tubule cells by the suppression of Atrap.

The renin-angiotensin system plays a crucial role in the regulation of blood pressure. Activation of the angiotensin II (Ang II)-Ang II type 1 receptor (AT1R) signaling pathway contributes to the pathogenesis of hypertension and subsequent organ damage. AT1R-associated protein (ATRAP) has been identified as an endogenous inhibitory protein of the AT1R pathological activation. We have shown that mouse Atrap (Atrap) represses various Ang II-AT1R-mediated pathologies, including hypertension in mice. The expression of human ATRAP (ATRAP)/Atrap can be altered in various pathological states in humans and mice, such as Ang II stimulation and serum starvation. However, the regulatory mechanisms of ATRAP/Atrap are not yet fully elucidated. miRNAs are 21 to 23 nucleotides of small RNAs that post-transcriptionally repress gene expression. Single miRNA can act on hundreds of target mRNAs, and numerous miRNAs have been identified as the Ang II-AT1R signaling-associated disease phenotype modulator, but nothing is known about the regulation of ATRAP/Atrap. In the present study, we identified miR-125a-5p/miR-125b-5p as the evolutionarily conserved miRNAs that potentially act on ATRAP/Atrap mRNA. Further analysis revealed that miR-125a-5p/miR-125b-5p can directly repress both ATRAP and Atrap. In addition, the inhibition of miR-125a-5p/miR-125b-5p resulted in the suppression of the Ang II-AT1R signaling in mouse distal convoluted tubule cells. Taken together, miR-125a-5p/miR-125b-5p activates Ang II-AT1R signaling by the suppression of ATRAP/Atrap. Our results provide new insights into the potential approaches for achieving the organ-protective effects by the repression of the miR-125 family associated with the enhancement of ATRAP/Atrap expression.

Angiotensin II type 1 receptor-associated protein in immune cells: a possible key factor in the pathogenesis of visceral obesity.

BACKGROUND AND AIM: Dysregulation of angiotensin II type 1 receptor-associated protein (ATRAP) expression in cardiovascular, kidney, and adipose tissues is involved in the pathology of hypertension, cardiac hypertrophy, atherosclerosis, kidney injury, and metabolic disorders. Furthermore, ATRAP is highly expressed in bone marrow-derived immune cells; however, the functional role of immune cell ATRAP in obesity-related pathology remains unclear. Thus, we sought to identify the pathophysiological significance of immune cell ATRAP in the development of visceral obesity and obesity-related metabolic disorders using a mouse model of diet-induced obesity. METHODS: Initially, we examined the effect of high-fat diet (HFD)-induced obesity on the expression of immune cell ATRAP in wild-type mice. Subsequently, we conducted bone marrow transplantation to generate two types of chimeric mice: bone marrow wild-type chimeric (BM-WT) and bone marrow ATRAP knockout chimeric (BM-KO) mice. These chimeric mice were provided an HFD to induce visceral obesity, and then the effects of immune cell ATRAP deficiency on physiological parameters and adipose tissue in the chimeric mice were investigated. RESULTS: In wild-type mice, body weight increase by HFD was associated with increased expression of immune cell ATRAP. In the bone marrow transplantation experiments, BM-KO mice exhibited amelioration of HFD-induced weight gain and visceral fat expansion with small adipocytes compared BM-WT mice. In addition, BM-KO mice on the HFD showed significant improvements in white adipose tissue metabolism, inflammation, glucose tolerance, and insulin resistance, compared with BM-WT mice on the HFD. Detailed analysis of white adipose tissue revealed significant suppression of HFD-induced activation of transforming growth factor-beta signaling, a key contributor to visceral obesity, via amelioration of CD206+ macrophage accumulation in the adipose tissue of BM-KO mice. This finding suggests a relevant mechanism for the anti-obesity phenotype in BM-KO mice on the HFD. Finally, transcriptome analysis of monocytes indicated the possibility of genetic changes, such as the enhancement of interferon-γ response at the monocyte level, affecting macrophage differentiation in BM-KO mice. CONCLUSION: Collectively, our results indicate that ATRAP in bone marrow-derived immune cells plays a role in the pathogenesis of visceral obesity. The regulation of ATRAP expression in immune cells may be a key factor against visceral adipose obesity with metabolic disorders.

Effects of a High-Protein Diet on Kidney Injury under Conditions of Non-CKD or CKD in Mice.

Considering the prevalence of obesity and global aging, the consumption of a high-protein diet (HPD) may be advantageous. However, an HPD aggravates kidney dysfunction in patients with chronic kidney disease (CKD). Moreover, the effects of an HPD on kidney function in healthy individuals are controversial. In this study, we employed a remnant kidney mouse model as a CKD model and aimed to evaluate the effects of an HPD on kidney injury under conditions of non-CKD and CKD. Mice were divided into four groups: a sham surgery (sham) + normal diet (ND) group, a sham + HPD group, a 5/6 nephrectomy (Nx) + ND group and a 5/6 Nx + HPD group. Blood pressure, kidney function and kidney tissue injury were compared after 12 weeks of diet loading among the four groups. The 5/6 Nx groups displayed blood pressure elevation, kidney function decline, glomerular injury and tubular injury compared with the sham groups. Furthermore, an HPD exacerbated glomerular injury only in the 5/6 Nx group; however, an HPD did not cause kidney injury in the sham group. Clinical application of these results suggests that patients with CKD should follow a protein-restricted diet to prevent the exacerbation of kidney injury, while healthy individuals can maintain an HPD without worrying about the adverse effects.

Angiotensin II type-1 receptor-associated protein interacts with transferrin receptor-1 and promotes its internalization.

Kidney fibrosis is a common pathway that leads to chronic kidney disease. Angiotensin II type-1 receptor (AT1R)-associated protein (ATRAP) was originally identified as an AT1R-binding protein. Previously, we reported that systemic knockout of ATRAP exacerbates kidney fibrosis in aged mice. Although these effects of ATRAP appeared to be AT1R-independent actions, the molecular mechanism remains poorly understood. To elucidate the molecular mechanism of ATRAP independent of AT1R, we explored novel ATRAP-interacting proteins. Mass spectrometric analysis of the immunoprecipitants of a Flag-tagged ATRAP complex revealed 376 candidate proteins that potentially interact with ATRAP. Gene ontology analysis revealed that proteins related to vesicle trafficking, membrane transport, and many membrane proteins, including transferrin receptor 1 (TfR1), were enriched. Because TfR1 promotes cellular iron uptake and iron is a key factor involved in kidney fibrosis, we focused on TfR1 and confirmed that it interacts with ATRAP. In addition, our findings revealed that enhanced ATRAP expression decreased cell-surface TfR1 expression without altering the overall cellular TfR1 expression levels. Furthermore, enhanced ATRAP expression attenuated cellular iron levels. Together, our results highlight the role of ATRAP as a suppressor of TfR1 that functions by facilitating TfR1 internalization, which affects iron metabolism and oxidative stress signaling.

Expression of Transferrin Protein and Messenger RNA in Neural Cells from Mouse and Human Brain Tissue.

Iron is an essential nutrient in the body. However, iron generates oxidative stress and hence needs to be bound to carrier proteins such as the glycoprotein transferrin (Tf) in body fluids. We previously reported that cerebrospinal fluid contains Tf glycan-isoforms that are derived from the brain, but their origins at the cellular level in the brain have not yet been elucidated. In the present report, we described the localization of Tf protein and mRNA in mouse and human brain tissue. In situ hybridization of mouse brain tissue revealed that Tf mRNA is expressed by different cell types such as epithelial cells in the choroid plexus, oligodendrocyte-like cells in the medulla, and neurons in the cortex, hippocampus, and basal ganglia. In contrast, Tf protein was barely detected by immunohistochemistry in hippocampal and some cortical neurons, but it was detected in other types of cells such as oligodendrocyte-like cells and choroid plexus epithelial cells. The results showed that Tf mRNA is expressed by neural cells, while Tf protein is expressed in different brain regions, though at very low levels in hippocampal neurons. Low Tf level in the hippocampus may increases susceptibility to iron-induced oxidative stress, and account for neuron death in neurodegenerative diseases.

Effects of tumor necrosis factor-α inhibition on kidney fibrosis and inflammation in a mouse model of aristolochic acid nephropathy.

Tumor necrosis factor (TNF)-α is a potent mediator of inflammation and is involved in the pathophysiology of chronic kidney disease (CKD). However, the effects of TNF-α inhibition on the progression of kidney fibrosis have not been fully elucidated. We examined the effects of TNF-α inhibition by etanercept (ETN) on kidney inflammation and fibrosis in mice with aristolochic acid (AA) nephropathy as a model of kidney fibrosis. C57BL/6 J mice were administered AA for 4 weeks, followed by a 4-week remodeling period. The mice exhibited kidney fibrosis, functional decline, and albuminuria concomitant with increases in renal mRNA expression of inflammation- and fibrosis-related genes. The 8-week ETN treatment partially but significantly attenuated kidney fibrosis and ameliorated albuminuria without affecting kidney function. These findings were accompanied by significant suppression of interleukin (IL)-1ß, IL-6, and collagen types I and III mRNA expression. Moreover, ETN tended to reduce the AA-induced increase in interstitial TUNEL-positive cells with a significant reduction in Bax mRNA expression. Renal phosphorylated p38 MAPK was significantly upregulated by AA but was normalized by ETN. These findings indicate a substantial role for the TNF-α pathway in the pathogenesis of kidney fibrosis and suggest that TNF-α inhibition could become an adjunct therapeutic strategy for CKD with fibrosis.

Aristolochic Acid Induces Renal Fibrosis and Senescence in Mice.

The kidney is one of the most susceptible organs to age-related impairments. Generally, renal aging is accompanied by renal fibrosis, which is the final common pathway of chronic kidney diseases. Aristolochic acid (AA), a nephrotoxic agent, causes AA nephropathy (AAN), which is characterized by progressive renal fibrosis and functional decline. Although renal fibrosis is associated with renal aging, whether AA induces renal aging remains unclear. The aim of the present study is to investigate the potential use of AAN as a model of renal aging. Here, we examined senescence-related factors in AAN models by chronically administering AA to C57BL/6 mice. Compared with controls, the AA group demonstrated aging kidney phenotypes, such as renal atrophy, renal functional decline, and tubulointerstitial fibrosis. Additionally, AA promoted cellular senescence specifically in the kidneys, and increased renal p16 mRNA expression and senescence-associated ß-galactosidase activity. Furthermore, AA-treated mice exhibited proximal tubular mitochondrial abnormalities, as well as reactive oxygen species accumulation. Klotho, an antiaging gene, was also significantly decreased in the kidneys of AA-treated mice. Collectively, the results of the present study indicate that AA alters senescence-related factors, and that renal fibrosis is closely related to renal aging.

Transferrin Biosynthesized in the Brain Is a Novel Biomarker for Alzheimer's Disease.

Glycosylation is a cell type-specific post-translational modification that can be used for biomarker identification in various diseases. Aim of this study is to explore glycan-biomarkers on transferrin (Tf) for Alzheimer's disease (AD) in cerebrospinal fluid (CSF). Glycan structures of CSF Tf were analyzed by ultra-performance liquid chromatography followed by mass spectrometry. We found that a unique mannosylated-glycan is carried by a Tf isoform in CSF (Man-Tf). The cerebral cortex contained Man-Tf as a major isofom, suggesting that CSF Man-Tf is, at least partly, derived from the cortex. Man-Tf levels were analyzed in CSF of patients with neurological diseases. Concentrations of Man-Tf were significantly increased in AD and mild cognitive impairment (MCI) comparing with other neurological diseases, and the levels correlated well with those of phosphorylated-tau (p-tau), a representative AD marker. Consistent with the observation, p-tau and Tf were co-expressed in hippocampal neurons of AD, leading to the notion that a combined p-tau and Man-Tf measure could be a biomarker for AD. Indeed, levels of p-tau x Man-Tf showed high diagnostic accuracy for MCI and AD; 84% sensitivities and 90% specificities for MCI and 94% sensitivities and 89% specificities for AD. Thus Man-Tf could be a new biomarker for AD.

Tissue-specific expression of the SARS-CoV-2 receptor, angiotensin-converting enzyme 2, in mouse models of chronic kidney disease.

Elevated angiotensin-converting enzyme 2 (ACE2) expression in organs that are potential targets of severe acute respiratory syndrome coronavirus 2 may increase the risk of coronavirus disease 2019 (COVID-19) infection. Previous reports show that ACE2 alter its tissue-specific expression patterns under various pathological conditions, including renal diseases. Here, we examined changes in pulmonary ACE2 expression in two mouse chronic kidney disease (CKD) models: adenine-induced (adenine mice) and aristolochic acid-induced (AA mice). We also investigated changes in pulmonary ACE2 expression due to renin-angiotensin system (RAS) blocker (olmesartan) treatment in these mice. Adenine mice showed significant renal functional decline and elevated blood pressure, compared with controls. AA mice also showed significant renal functional decline, compared with vehicles; blood pressure did not differ between groups. Renal ACE2 expression was significantly reduced in adenine mice and AA mice; pulmonary expression was unaffected. Olmesartan attenuated urinary albumin excretion in adenine mice, but did not affect renal or pulmonary ACE2 expression levels. The results suggest that the risk of COVID-19 infection may not be elevated in patients with CKD because of their stable pulmonary ACE2 expression. Moreover, RAS blockers can be used safely in treatment of COVID-19 patients with CKD.

Tissue xanthine oxidoreductase activity in a mouse model of aristolochic acid nephropathy.

Xanthine oxidoreductase (XOR) is a critical enzyme in purine metabolism and uric acid production, and its levels are reported to increase during stress, thereby promoting organ damage. Herein, we investigated the activity of XOR in a mouse model of aristolochic acid I (AA)-induced nephropathy, a type of nephrotoxic chronic kidney disease (CKD). A persistent decrease in renal function was observed in mice up to 4 weeks after 4 weeks of AA (2.5 mg kg-1 ) administration. Renal histology revealed an increase in tubular interstitial fibrosis over time. Although AA administration did not change XOR activity in the plasma, heart, liver, or muscle, XOR activity was persistently increased in renal tissue. Our results suggest that the renal tissue-specific increase in XOR activity is involved in the progression of tubulo-interstitial disorders, specifically fibrosis.

Cardiovascular and renal outcomes with SGLT-2 inhibitors versus GLP-1 receptor agonists in patients with type 2 diabetes mellitus and chronic kidney disease: a systematic review and network meta-analysis.

BACKGROUND: Emerging evidence suggests that sodium-glucose cotransporter-2 (SGLT-2) inhibitors and glucagon-like peptide-1 receptor agonists (GLP-1 RAs) are associated with decreased risk of cardiovascular and renal events in type 2 diabetes mellitus (DM) patients. However, no study to date has compared the effect of SGLT-2 inhibitors with that of GLP-1 RAs in type 2 DM patients with chronic kidney disease (CKD). We herein investigated the benefits of SGLT-2 inhibitors and GLP-1 RAs in CKD patients. METHODS: We performed a systematic literature search through November 2020. We selected randomized control trials that compared the risk of major adverse cardiovascular events (MACE) and a composite of renal outcomes. We performed a network meta-analysis to compare SGLT-2 inhibitors with GLP-1 RAs indirectly. Risk ratios (RRs) with corresponding 95% confidence intervals (CI) were synthesized. RESULTS: Thirteen studies were selected with a total of 32,949 patients. SGLT-2 inhibitors led to a risk reduction in MACE and renal events (RR [95% CI]; 0.85 [0.75-0.96] and 0.68 [0.59-0.78], respectively). However, GLP-1 RAs did not reduce the risk of cardiovascular or renal adverse events (RR 0.91 [0.80-1.04] and 0.86 [0.72-1.03], respectively). Compared to GLP-1 RAs, SGLT-2 inhibitors did not demonstrate a significant difference in MACE (RR 0.94 [0.78-1.12]), while SGLT-2 inhibitors were associated with a lower risk of renal events compared to GLP-1 RAs (RR 0.79 [0.63-0.99]). A sensitivity analysis revealed that GLP-1 analogues significantly decreased MACE when compared to placebo treatment (RR 0.81 [0.69-0.95]), while exendin-4 analogues did not (RR 1.03 [0.88-1.20]). CONCLUSIONS: In patients with type 2 DM and CKD, SGLT-2 inhibitors were associated with a decreased risk of cardiovascular and renal events, but GLP-1 RAs were not. SGLT-2 inhibitors significantly decreased the risk of renal events compared to GLP-1 RAs. Among GLP-1 RAs, GLP-1 analogues showed a positive impact on cardiovascular and renal outcomes, while exendin-4 analogues did not.

Effect of renin-angiotensin system blockers on contrast-induced acute kidney injury in patients with normal or mild-to-moderate reduced kidney function undergoing coronary angiography: A systematic review and meta-analysis.

INTRODUCTION: Contrast-induced acute kidney injury (CI-AKI) is a major complication after coronary angiography (CAG) or percutaneous coronary intervention (PCI) and is associated with increased morbidity and mortality. It remains controversial whether renin-angiotensin system (RAS) blockers increase or decrease CI-AKI. In this meta-analysis, we investigated the association between RAS blockers and CI-AKI in patients with normal kidney function or mild-to-moderate chronic kidney disease (CKD). MATERIALS AND METHODS: We performed a systematic search of PubMed, EMBASE, clinicaltrials.gov, and the Cochrane Library up to December 2019 for studies that assessed the association between RAS blockers and CI-AKI events after CAG/PCI. The primary outcome was the development of CI-AKI. Odds ratios (ORs) with corresponding 95% confidence interval (CI) were synthesized. RESULTS: Five randomized controlled trials (RCTs) and five observational studies were included, accounting for a total of 7,420 patients. Unstratified, RAS blocker administration was significantly associated with an increased risk of CI-AKI (pooled OR = 1.63, 95% CI 1.19 - 2.25, p = 0.003). However, the effect was not observed in RCTs (pooled OR = 1.22, 95% CI 0.54 - 2.74, p = 0.63). Sensitivity analysis in observational studies showed significant association (pooled OR = 1.77, 95% CI 1.22 - 2.55, p = 0.003) with high heterogeneity and evidence of publication bias. CONCLUSION: In patients with relatively-preserved renal function, the association of RAS blockers with an increased risk of CI-AKI after contrast media exposure was inconclusive, as sensitivity analysis showed conflicting results and bias. Although this study did not demonstrate significant evidence, it indicated that clinicians need to be vigilant in assessing the potential risk for RAS blockers to cause CI-AKI in low-risk patients.

Systematic Review of the Association Between Worsening Renal Function and Mortality in Patients With Acute Decompensated Heart Failure.

INTRODUCTION: Outcomes in acute decompensated heart failure (ADHF) have remained poor. Worsening renal function (WRF) is common among patients with ADHF. However, the impact of WRF on the prognosis is controversial. We hypothesized that in patients with ADHF, the achievement of concomitant decongestion would diminish the signal for harm associated with WRF. METHODS: We performed a systematic search of PubMed, EMBASE, and the Cochrane Library up to December 2019 for studies that assessed signs of decongestion in patients with WRF during ADHF admission. The primary outcome was all-cause mortality and heart transplantation. RESULTS: Thirteen studies were selected with a pooled population of 8138 patients. During the follow-up period of 60-450 days, 19.2% of patients died. Unstratified, patients with WRF versus no WRF had a higher risk for mortality (odds ratio [OR], 1.71 [95% confidence interval {CI}, 1.45-2.01]; P < 0.0001). However, patients who achieved decongestion had a similar prognosis (OR, 1.15 [95% CI, 0.89-1.49]; P = 0.30). Moreover, patients with WRF who achieved decongestion had a better prognosis compared with those without WRF or decongestion (OR, 0.63 [95% CI, 0.46-0.86]; P = 0.004). This tendency persisted for the sensitivity analyses. CONCLUSIONS: Decongestion is a powerful effect modifier that attenuates harmful associations of WRF with mortality. Future studies should not assess WRF as an endpoint without concomitant assessment of achieved volume status.

Angiotensin II type 1 receptor-associated protein deficiency attenuates sirtuin1 expression in an immortalised human renal proximal tubule cell line.

The proximal tubule is a particularly important site for ageing-related kidney damage. Sirtuin 1 (SIRT1), an NAD+ (nicotinamide adenine dinucleotide)-dependent deacetylase in the proximal tubule, may be involved in renal injury associated with ageing. However, the mechanisms of SIRT1 regulation remain to be elucidated. We recently reported that angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP)-deficient mice displayed age-associated renal function decline and tubulointerstitial fibrosis. Our data showed that SIRT1 protein expression was reduced in ATRAP-deficient mice, although the relationship between ATRAP deficiency and age-associated renal fibrosis is still not fully understood. It is, therefore, necessary to investigate how ATRAP affects SIRT1 protein expression to resolve ageing-associated kidney dysfunction. Here, since ageing studies are inherently lengthy, we used an ex vivo model of the proximal tubule to determine the role of ATRAP in SIRT1 protein expression. We first generated a clonal immortalised human renal proximal tubule epithelial cell line (ciRPTEC) expressing AT1R and ATRAP. Using this cell line, we demonstrated that ATRAP knockdown reduced SIRT1 protein expression in the ciRPTEC but did not alter SIRT1 mRNA expression. Thus, ATRAP likely mediates SIRT1 protein abundance in ciRPTEC.

The glycerol-3-phosphate acyltransferase PLAT2 functions in the generation of DHA-rich glycerolipids in Aurantiochytrium limacinum F26-b.

Thraustochytrids possess docosahexaenoic acid (DHA, 22:6n-3) as acyl chain(s) of triacylglycerol (TG) and phosphatidylcholine (PC), some of which contain multiple DHAs. However, little is known about how these DHA-rich glycerolipids are produced in thraustochytrids. In this study, we identified PLAT2 in Aurantiochytrium limacinum F26-b as a glycerol-3-phosphate (G3P) acyltransferase (GPAT) by heterologous expression of the gene in budding yeast. Subsequently, we found that GPAT activity was reduced by disruption of the PLAT2 gene in A. limacinum, resulting in a decrease in DHA-containing lysophosphatidic acid (LPA 22:6). Conversely, overexpression of PLAT2 increased both GPAT activity and LPA 22:6. These results indicate that PLAT2 is a GPAT that transfers DHA to G3P in vivo as well as in vitro. Overexpression of the PLAT2 gene increased the production of a two DHA-containing diacylglycerol (DG 44:12), followed by an increase in the three DHA-containing TG (TG 66:18), two-DHA-containing TG (TG 60:12), and two DHA-containing PC (PC 44:12). However, overexpression of PLAT2 did not increase DHA-free DG (DG32:0), which was preferentially converted to three 16:0-containing TG (TG 48:0) but not two 16:0-containing PC (PC 32:0). Collectively, we revealed that DHA-rich glycerolipids are produced from a precursor, LPA 22:6, which is generated by incorporating DHA to G3P by PLAT2 in the A. limacinum.

Enhancement of Fixed-bed Flow Reactions under Microwave Irradiation by Local Heating at the Vicinal Contact Points of Catalyst Particles.

The formation of local high temperature regions, or so-called "hot spots", in heterogeneous reaction systems has been suggested as a critical factor in the enhancement of chemical reactions using microwave heating. In this paper, we report the generation of local high temperature regions between catalyst particles under microwave heating. First, we demonstrated that reaction rate of the dehydrogenation of 2-propanol over a magnetite catalyst was enhanced 17- (250 °C) to 38- (200 °C) fold when heated with microwave irradiation rather than an electrical furnace. Subsequently, the existence of microwave-generated specific local heating was demonstrated using a coupled simulation of the electromagnetic fields and heat transfer as well as in situ emission spectroscopy. Specific high-temperature regions were generated at the vicinal contact points of the catalyst particles due to the concentrated microwave electric field. We also directly observed local high temperature regions at the contact points of the particles during microwave heating of a model silicon carbide spherical material using in situ emission spectroscopy. We conclude that the generation of local heating at the contact points between the catalyst particles is a key factor for enhancing fixed-bed flow reactions under microwave irradiation.

Correction: Novel Lysophospholipid Acyltransferase PLAT1 of Aurantiochytrium limacinum F26-b Responsible for Generation of Palmitate-Docosahexaenoate-Phosphatidylcholine and Phosphatidylethanolamine.

[This corrects the article DOI: 10.1371/journal.pone.0102377.].