Knockout of the urate oxidase gene provides a stable mouse model of hyperuricemia associated with metabolic disorders

The urate oxidase (Uox) gene encodes uricase that in the rodent liver degrades uric acid into allantoin, forming an obstacle for establishing stable mouse models of hyperuricemia. The loss of uricase in humans during primate evolution causes their vulnerability to hyperuricemia. Thus, we generated a Uox-knockout mouse model on a pure C57BL/6J background using the transcription activator-like effector nuclease (TALEN) technique. These Uox-knockout mice spontaneously developed hyperuricemia (over 420 μmol/l) with about 40% survival up to 62 weeks. Renal dysfunction (elevated serum creatinine and blood urea nitrogen) and glomerular/tubular lesions were observed in these Uox-knockout mice. Male Uox-knockout mice developed glycol-metabolic disorders associated with compromised insulin secretion and elevated vulnerability to streptozotocin-induced diabetes, whereas female mice developed hypertension accompanied by aberrant lipo-metabolism. Urate-lowering drugs reduced serum uric acid and improved hyperuricemia-induced disorders. Thus, uricase knockout provides a suitable mouse model to investigate hyperuricemia and associated disorders mimicking the human condition, suggesting that hyperuricemia has a causal role in the development of metabolic disorders and hypertension. The urate oxidase (Uox) gene encodes uricase that in the rodent liver degrades uric acid into allantoin, forming an obstacle for establishing stable mouse models of hyperuricemia. The loss of uricase in humans during primate evolution causes their vulnerability to hyperuricemia. Thus, we generated a Uox-knockout mouse model on a pure C57BL/6J background using the transcription activator-like effector nuclease (TALEN) technique. These Uox-knockout mice spontaneously developed hyperuricemia (over 420 μmol/l) with about 40% survival up to 62 weeks. Renal dysfunction (elevated serum creatinine and blood urea nitrogen) and glomerular/tubular lesions were observed in these Uox-knockout mice. Male Uox-knockout mice developed glycol-metabolic disorders associated with compromised insulin secretion and elevated vulnerability to streptozotocin-induced diabetes, whereas female mice developed hypertension accompanied by aberrant lipo-metabolism. Urate-lowering drugs reduced serum uric acid and improved hyperuricemia-induced disorders. Thus, uricase knockout provides a suitable mouse model to investigate hyperuricemia and associated disorders mimicking the human condition, suggesting that hyperuricemia has a causal role in the development of metabolic disorders and hypertension. Uric acid (UA) is the end product of purine metabolism in humans. Due to the evolutionary disruption of the Uox gene encoding urate oxidase (Uox) or uricase, humans are vulnerable to hyperuricemia (HUA).1Alvarez-Lario B. Macarron-Vicente J. Uric acid and evolution.Rheumatology. 2010; 49: 2010-2015Crossref PubMed Scopus (211) Google Scholar HUA, a metabolic disorder of purine, contributes to the development of gout and renal disease, and also relates to multiple complications including hyperlipidemia, hypertension, and diabetes.2Merriman T.R. Dalbeth N. The genetic basis of hyperuricaemia and gout.Joint Bone Spine. 2011; 78: 35-40Crossref PubMed Scopus (124) Google Scholar, 3Li C. Hsieh M.C. Chang S.J. Metabolic syndrome, diabetes, and hyperuricemia.Curr Opin Rheumatol. 2013; 25: 210-216Crossref PubMed Scopus (251) Google Scholar, 4Bonakdaran S. Kharaqani B. Association of serum uric acid and metabolic syndrome in type 2 diabetes.Curr Diabetes Rev. 2014; 10: 113-117Crossref PubMed Scopus (44) Google Scholar The prevalence of HUA has reached 21.4% (21.1% in men and 21.6% in women) in US adults according to the National Health and Nutrition Examination Survey (NHANES) 2007–2008.5Zhu Y. Pandya B.J. Choi H.K. Comorbidities of gout and hyperuricemia in the US general population: NHANES 2007-2008.Am J Med. 2012; 125: 679-687 e1Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar In a systematic meta-analysis, the prevalence of hyperuricemia in mainland China was estimated to be 13.3% (19.4% in men and 7.9% in women).6Liu R. Han C. Wu D. et al.Prevalence of hyperuricemia and gout in mainland China from 2000 to 2014: a systematic review and meta-analysis.Biomed Res Int. 2015; 2015: 762820Crossref PubMed Scopus (380) Google Scholar Elevated serum UA (SUA) can lead to the formation of monosodium urate crystals in connective tissues, causing the pathogenesis of gout. Approximately 10% of HUA eventually develop into gout. HUA has also been identified to be an independent risk factor of cardiovascular diseases.7Feig D.I. Madero M. Jalal D.I. et al.Uric acid and the origins of hypertension.J Pediatr. 2013; 162: 896-902Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar, 8Mangge H. Pilz S. Haj-Yahya S. et al.Uric acid indicates a high cardiovascular risk profile but is not closely associated with insulin resistance in obese adolescents.Diabetes Care. 2008; 31: e21Crossref PubMed Scopus (6) Google Scholar Uricase expressed in the liver of rodents can further degrade UA into allantoin,1Alvarez-Lario B. Macarron-Vicente J. Uric acid and evolution.Rheumatology. 2010; 49: 2010-2015Crossref PubMed Scopus (211) Google Scholar which has hindered the establishment of suitable rodent models for HUA. Currently, the mechanisms underlying the pernicious effects of HUA remain poorly understood, and the development of effective medications for HUA remains largely halted, partially due to the lack of an efficient and stable animal model of HUA. So far, drug induction using purine synthesis promoters (e.g., adenine) and/or uricase inhibitors (e.g., potassium oxonate) and injection of UA remain the primary strategies for establishing HUA mouse models.9Morisaki T. [Animal models for abnormal purine metabolism].Nihon Rinsho. 2003; 61 Suppl 1: 482-486PubMed Google Scholar However, UA levels often fluctuate by large margins in drug-induced HUA animals.9Morisaki T. [Animal models for abnormal purine metabolism].Nihon Rinsho. 2003; 61 Suppl 1: 482-486PubMed Google Scholar Alternatively, gene targeting in embryonic stem cells has been employed to generate Uox-deficient mice.10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar However, UA levels often reach lethal ranges in these mice, so few of them survive to maturity.10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar In order to establish a stable HUA mouse model for long-term studies, we herein generated a Uox-knockout (KO) mouse on a pure C57BL/6J genetic background using the transcription activator-like effector nuclease (TALEN) technology, and examined the phenotypes of these mice in terms of SUA, survival rate, renal function, glucose and lipid metabolism, cardiovascular function and dimensions, and response to multiple urate-lowering drugs (ULDs). This study characterized HUA-related phenotypes comprehensively for the first time. The successful generation of this Uox-KO mouse model with spontaneous HUA provides a suitable tool for HUA-related research. The knockout scheme was described in Methods (Figure 1a). Both uricase mRNA and protein dramatically decreased in the Uox-KO mouse liver compared to wild-type (WT) mice as determined by quantitative reverse-transcription polymerase chain reaction (RT-PCR) and Western blot (Figure 1b and c). Kaplan-Meier analysis of survival rate over a 62-week observation period showed that roughly 40% of the Uox-KO mice deceased within 5 weeks after birth, and the survival rate stabilized at approximately 40% from 10 weeks after birth (Figure 1d). Genotyping at 3 to 4 weeks after birth showed that the distribution of homogeneous, heterogeneous Uox-KO mice and WT mice had a different plot from the Mendelian inheritance law, at 15.94% (55 of 345), 51.60% (178 of 345), and 32.46% (112 of 345), respectively, suggesting loss of the Uox gene might lead to embryonic or neonatal death. Uox-KO mice had significantly higher SUA levels compared with WT mice (Figure 1e). Notably, male Uox-KO mice had higher SUA levels than did females (Figure 1e), displaying a pattern similar to that of humans.5Zhu Y. Pandya B.J. Choi H.K. Comorbidities of gout and hyperuricemia in the US general population: NHANES 2007-2008.Am J Med. 2012; 125: 679-687 e1Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar The SUA stabilized at elevated levels (> 420 μmol/l) in the Uox-KO mice from 4 to 30 weeks of age (Figure 1f). To examine the effects of HUA on the kidney, renal function and kidney histology were determined in the Uox-KO mice. Compared with WT controls, serum creatinine and blood urea nitrogen (BUN) were significantly elevated in both male and female Uox-KO mice (Figure 2a), suggesting that glomerular filtration was compromised. Kidney histology was examined from 2 to 8 weeks of age (Supplementary Figure S1). Lesions in kidney tissues initially occurred at 6 weeks of age in the Uox-KO mice. Histological impairments in the kidneys of 8-week-old Uox-KO mice included dilated Bowman's spaces and tubules, collapsed and necrotic nephrons, and focal tubulointerstitial fibrosis (Figure 2b and c). Severe nonspecific chronic corticomedullar inflammation was observed as manifested by substantial lymphocyte (CD3+) and macrophage (CD68+) infiltration (Figure 2d and e). Urate crystals were detected in kidney interstices under polarized light (Figure 2f). In addition, mRNA expression of inflammatory cytokines F4/80 and interleukin-1β (IL-1β) were significantly elevated in the kidneys of Uox-KO mice compared with WT mice (Figure 2g and h). To examine the effects of HUA on the cardiovascular system, blood pressure (BP) and cardiac function were determined by sphygmomanometer and echocardiography. Notably, 8-week-old female Uox-KO mice developed significantly higher systolic BP (SBP) and diastolic BP (DBP) than WT controls, while male Uox-KO showed no differences from their WT counterparts (Figure 3). Echocardiography was performed on 26-week-old Uox-KO mice to examine the effects of long-term HUA on cardiac dimensions and function. Neither dimensional (i.e., mass, volume, inner diameter, and wall thickness of the left ventricle) nor functional parameters (i.e., cardiac output, stroke volume, fractional shortening, and ejection fraction) were significantly altered in the Uox-KO mice compared with WT controls (Supplementary Table S1). Analysis of lipid profiles revealed that, compared with WT counterparts, total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol were significantly elevated in female Uox-KO mice, whereas TG was significantly lower in male Uox-KO mice (Table 1).Table 1Biochemical parameters of lipid metabolismParametersMaleFemaleWT (n = 10)KO (n = 7)WT (n = 10)KO (n = 8)Total cholesterol (mmol/l)2.68 ± 0.062.61 ± 0.142.44 ± 0.102.99 ± 0.09P < 0.05, **P < 0.01.Triglycerides (mmol/l)1.34 ± 0.051.09 ± 0.03P < 0.05, **P < 0.01.1.12 ± 0.041.25 ± 0.05∗P < 0.05, **P < 0.01.HDL cholesterol (mmol/l)0.84 ± 0.030.81 ± 0.080.68 ± 0.040.82 ± 0.06LDL cholesterol (mmol/l)1.01 ± 0.041.00 ± 0.091.08 ± 0.061.26 ± 0.02∗P < 0.05, **P < 0.01.HDL, high-density lipoprotein; KO, knockout; LDL, low-density lipoprotein; WT, wild-type.Data were compared between WT and Uox-KO mice of the same gender.∗ P < 0.05, **P < 0.01. Open table in a new tab HDL, high-density lipoprotein; KO, knockout; LDL, low-density lipoprotein; WT, wild-type. Data were compared between WT and Uox-KO mice of the same gender. Neither fasting insulin nor fasting glucose was significantly changed in the Uox-KO mice compared with WT controls (Figure 4a and b). No apparent histological lesions were detected in the pancreatic islets of the Uox-KO mice either (Supplementary Figure S2). However, upon i.p. glucose tolerance test (IPGTT), blood glucose at 15 and 30 minutes after initiation was significantly higher in male Uox-KO mice than in male WT controls (Figure 4c, left panel). Consistently, calculation of the area under the curve (AUC) showed it was significantly larger for male Uox-KO mice than male WT mice (Figure 4c, right panel). Upon insulin tolerance test (ITT), both sexes of Uox-KO mice displayed a similar pattern to WT controls (Figure 4d), suggesting that insulin resistance was unlikely to contribute to the aberrant glycometabolism in the Uox-KO mice. Islet function was determined by glucose-stimulated insulin secretion (GSIS) performed in vitro and in vivo. Although isolated islets derived from 8-week-old male Uox-KO mice secreted a similar amount of insulin to WT islets at baseline glucose concentration (3.3 mmol/l), insulin secretion was decreased by 20.56% in Uox-KO islets at an elevated glucose concentration (16.7 mmol/l), as shown in Figure 4e. Furthermore, after a glucose injection (2 g/kg), 8-week-old male Uox-KO mice secreted a significantly lower amount of insulin at 15 and 30 minutes (Figure 4f), consistent with the IPGTT results above. By induction with multiple injections of low-dose streptozotocin (STZ; 40 mg/kg/d, consecutively for 5 days), 87.5% of male and 80.0% of female Uox-KO mice developed diabetes at day 20 after the end of STZ treatment, at significantly higher rates than among their WT counterparts (Figure 5a). It was noted that the onset of diabetes in male Uox-KO mice was much earlier than in females (Figure 5a), suggesting that male Uox-KO mice were more sensitive than females to islet impairment. Histological examination of the pancreas from STZ-treated male Uox-KO mice revealed many atrophic islets associated with reduced number of insulin-positive β cells (Figure 5b). In addition, the β-cell mass of male Uox-KO mice was significantly lower than that of male WT mice (Figure 5c). Terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay of pancreatic sections showed that the TUNEL-positive β-cell ratio was significantly higher for STZ-treated male Uox-KO mice than STZ-treated male WT mice (Figure 5d), suggesting that HUA in the Uox-KO mice might have promoted STZ-induced islet β-cell impairments by aggravating apoptosis. The effects of 3 common ULDs, allopurinol (40 mg/kg), benzbromarone (10 mg/kg), and febuxostat (8 mg/kg), were assessed in male Uox-KO mice. SUA was reduced significantly by ULDs from the end of the second week onward (Figure 6a). Administration with a higher dosage of allopurinol (100 mg/kg) for 2 weeks lowered SUA to approximately 220 μmol/l, similar to the SUA level of WT mice (Figure 6b). Serum creatinine and BUN of the Uox-KO mice were significantly decreased by administration of allopurinol, and a dose-dependent pattern was present (Figure 6c). Tubulointerstitial fibrosis (Figure 6d) did not change, whereas lymphocyte infiltration (Figure 6e) and macrophage infiltration (Figure 6f) in the kidney of Uox-KO mice were markedly alleviated by allopurinol (100 mg/kg) treatment. Consistently, the expression of α-smooth muscle actin, a fibrosis indicator, did not change after allopurinol treatment in the kidney of Uox-KO mice, whereas the expression of F4/80 and IL-1β were markedly decreased, suggesting that renal inflammation was attenuated without significant changes in fibrosis (Figure 6g–i). Both SBP and DBP of female Uox-KO mice were significantly decreased to normal range by treatment with 100 mg/kg allopurinol for 2 weeks (Figure 6j). In addition, islet function of male Uox-KO mice was improved after allopurinol treatment as manifested by GSIS results (Figure 6k). The prevalence of HUA has been increased in recent years.5Zhu Y. Pandya B.J. Choi H.K. Comorbidities of gout and hyperuricemia in the US general population: NHANES 2007-2008.Am J Med. 2012; 125: 679-687 e1Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar A mouse model with stable HUA and long lifespan is essential for further research on HUA and related diseases. However, the presence of hepatic uricase has hindered the establishment of suitable mouse models of HUA. The present study has generated a new mouse model of HUA by knocking out Uox on a pure C57BL/6J background, characterized by stably elevated UA levels. In addition, HUA-related disorders and the efficacy of ULDs were characterized comprehensively for the first time. The Uox-KO mice in this study had stable elevated SUA levels at 420 to 520 μmol/l, 2- to 3-fold higher than in WT mice and mimicking the SUA level of HUA patients. In previous studies using other Uox-KO mice,10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar, 11Chen X. Burdett T.C. Desjardins C.A. et al.Disrupted and transgenic urate oxidase alter urate and dopaminergic neurodegeneration.Proc Natl Acad Sci U S A. 2013; 110: 300-305Crossref PubMed Scopus (94) Google Scholar, 12Watanabe T. Tomioka N.H. Watanabe S. et al.The mechanism of false in vitro elevation of uric acid level in mouse blood.Biol Pharm Bull. 2016; 39: 1081-1084Crossref PubMed Scopus (7) Google Scholar SUA levels varied between 200 and 660 μmol/l. In a Glut9-KO mouse model,13Preitner F. Pimentel A. Metref S. et al.No development of hypertension in the hyperuricemic liver-Glut9 knockout mouse.Kidney Int. 2015; 87: 940-947Abstract Full Text Full Text PDF PubMed Scopus (23) Google Scholar SUA was elevated to 120 μmol/l, making it necessary to supplement inosine so that SUA could be further increased to human pathological levels. The additional exogenous intervention would interfere with the effects of HUA per se. It is noted that approximately 40% of our homozygous HUA mice deceased within 5 weeks after birth, a much lower mortality rate than that reported by Wu et al., with 65% of homozygous HUA mice dead by 4 weeks of age.10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar Although the Uox-KO mice were generated on a pure C57BL/6J background, the phenotypic heterogeneity regarding survival might result from some unknown factors, which made the survivors capable of coping with HUA. Nonetheless, the surviving Uox-KO mice maintained stably elevated SUA levels up to 62 weeks, making them suitable for long-term studies. HUA is a potential risk factor for adverse renal outcomes.14Li L. Yang C. Zhao Y. et al.Is hyperuricemia an independent risk factor for new-onset chronic kidney disease?: A systematic review and meta-analysis based on observational cohort studies.BMC Nephrol. 2014; 15: 122Crossref PubMed Scopus (224) Google Scholar, 15Sheikhbahaei S. Fotouhi A. Hafezi-Nejad N. et al.Serum uric acid, the metabolic syndrome, and the risk of chronic kidney disease in patients with type 2 diabetes.Metab Syndr Relat Disord. 2014; 12: 102-109Crossref PubMed Scopus (24) Google Scholar Serum creatinine and BUN significantly increased in our Uox-KO mice, indicating compromised glomerular filtration function. Consistent with previous studies,10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar kidney histologies showed the presence of glomerular and tubular malformation. The presence of CD3+ lymphocyte and CD68+ macrophage infiltration and increased F4/80 and IL-1β mRNA indicated inflammation, likely mediated by the activation of the NLRP3 inflammasome–IL-1β pathway by UA.16Cullen S.P. Kearney C.J. Clancy D.M. et al.Diverse activators of the NLRP3 inflammasome promote IL-1beta secretion by triggering necrosis.Cell Rep. 2015; 11: 1535-1548Abstract Full Text Full Text PDF PubMed Scopus (159) Google Scholar The pathological alterations in the kidneys of our Uox-KO mice started to occur from 6 weeks after birth, but their UA remained at a stable level for more than 30 weeks, suggesting that the renal excretion of UA was unaffected over the whole observation time. Epidemiological studies have detected an association between HUA and hypertension, although the causal relationship has not been fully established.7Feig D.I. Madero M. Jalal D.I. et al.Uric acid and the origins of hypertension.J Pediatr. 2013; 162: 896-902Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar, 17Bobulescu I.A. Moe O.W. Renal transport of uric acid: evolving concepts and uncertainties.Adv Chronic Kidney Dis. 2012; 19: 358-371Abstract Full Text Full Text PDF PubMed Scopus (241) Google Scholar In the present study, SBP and DBP increased significantly in female Uox-KO mice, and ULT reduced the BP of female Uox-KO mice to normal levels, providing evidence supporting a causal role of HUA in hypertension. These results concur with clinical data showing that a significant association between HUA and cardiovascular events was stronger in women than in men.18Ndrepepa G. Cassese S. Braun S. et al.A gender-specific analysis of association between hyperuricaemia and cardiovascular events in patients with coronary artery disease.Nutr Metab Cardiovasc Dis. 2013; 23: 1195-1201Abstract Full Text Full Text PDF PubMed Scopus (33) Google Scholar However, the mechanisms underlying this sexual dimorphism remain evasive. Our Uox-KO mice have offered a useful model for studying HUA-associated vascular disorders. While some studies have reported an association between HUA and diabetes,19Kodama S. Saito K. Yachi Y. et al.Association between serum uric acid and development of type 2 diabetes.Diabetes Care. 2009; 32: 1737-1742Crossref PubMed Scopus (349) Google Scholar, 20Sluijs I. Holmes M.V. van der Schouw Y.T. et al.A Mendelian randomization study of circulating uric acid and type 2 diabetes.Diabetes. 2015; 64: 3028-3036Crossref PubMed Scopus (79) Google Scholar other studies failed to detect a link between UA and diabetes.21Pfister R. Barnes D. Luben R. et al.No evidence for a causal link between uric acid and type 2 diabetes: a Mendelian randomisation approach.Diabetologia. 2011; 54: 2561-2569Crossref PubMed Scopus (77) Google Scholar At present, a causal relationship between UA and diabetes remains controversial.22Johnson R.J. Merriman T. Lanaspa M.A. Causal or noncausal relationship of uric acid with diabetes.Diabetes. 2015; 64: 2720-2722Crossref PubMed Scopus (32) Google Scholar The abnormal IPGTT and GSIS results of our male Uox-KO mice indicated islet function was compromised, which was also supported by the higher vulnerability of these mice to STZ-induced diabetes. Administration with allopurinol improved islet performance of the Uox-KO mice upon GSIS assay. These data suggest that HUA was probably a causal factor of islet dysfunction. ITT results eliminated the involvement of insulin resistance in the aberrant glycometabolism in these mice. Upon low-dose STZ induction, the Uox-KO mice were more prone to develop diabetes than were WT controls (e.g., 87.5% vs. 23.1% in males). Pancreatic histology and islet TUNEL assay of STZ-induced mice revealed that islet atrophy and β-cell apoptosis were more severe in the Uox-KO mice, although no apparent β-cell apoptosis was detected in untreated Uox-KO mice (data not shown). These results suggest that the Uox-KO mice were more susceptible to STZ-induced β-cell impairments, and that HUA might promote STZ-induced β-cell apoptosis, while HUA might not be sufficient to induce β-cell apoptosis on its own. Indeed, the presence of islet dysfunction and aberrant glycometabolism in untreated Uox-KO mice indicates that islet β cells were already compromised in these mice. Actually, Jia et al.23Jia L. Xing J. Ding Y. et al.Hyperuricemia causes pancreatic beta-cell death and dysfunction through NF-kappaB signaling pathway.PloS One. 2013; 8: e78284Crossref PubMed Scopus (66) Google Scholar reported that UA could directly cause β-cell apoptosis and dysfunction by activation of the NF-κB-iNOS-NO signal axis. Nonetheless, our understanding of the molecular mechanisms of HUA-induced islet dysfunction remains rather limited. Allopurinol, benzbromarone, and febuxostat are 3 common ULDs with different pharmacological mechanisms. All 3 ULDs reduced SUA within the first week of treatment, and the xanthine oxidase inhibitors (allopurinol and febuxostat) produced significant decreases in SUA from the end of the second week. While it has been reported that SUA can be reduced to levels similar to those observed in WT mice, those studies were predominantly performed in drug-induced HUA models,9Morisaki T. [Animal models for abnormal purine metabolism].Nihon Rinsho. 2003; 61 Suppl 1: 482-486PubMed Google Scholar which are prone to large fluctuations in SUA. We have noticed that, in a similar Uox-KO mouse model generated by ES targeting strategy on a 129Sv background,10Wu X. Wakamiya M. Vaishnav S. et al.Hyperuricemia and urate nephropathy in urate oxidase-deficient mice.Proc Natl Acad Sci U S A. 1994; 91: 742-746Crossref PubMed Scopus (230) Google Scholar SUA was decreased by 50% (from 11 mg/dl or 660 μmol/l) in 3-week-old Uox-KO mice after administration of 150 mg/l allopurinol in drinking water for 2 weeks, approximately 75 mg/kg assuming water consumption at 5 ml per day and body weight at 10 g. The SUA in our spontaneous HUA mouse model decreased by 26% after lavaging with allopurinol at 40 mg/kg, and by 61.5% at 100 mg/kg to 220 μmol/l (close to the SUA level of WT controls). These results are consistent with Wu et al.'s study in terms of a dose-effect relationship. Moreover, renal function (creatinine and BUN), kidney inflammation cell infiltration, BP, and GSIS were all improved after ULT. These results demonstrate the sensitivity of our HUA model to classic ULDs and consolidate the causal role of HUA in kidney impairments and metabolic disorders. Previous studies have observed that HUA is usually accompanied by elevated TC and TG levels.24Teng F. Zhu R. Zou C. et al.Interaction between serum uric acid and triglycerides in relation to blood pressure.J Hum Hypertens. 2011; 25: 686-691Crossref PubMed Scopus (33) Google Scholar A correlation between UA and TC or TG was also present in an HUA mouse model generated by knocking out xanthine oxidoreductase.25Ohtsubo T. Matsumura K. Sakagami K. et al.Xanthine oxidoreductase depletion induces renal interstitial fibrosis through aberrant lipid and purine accumulation in renal tubules.Hypertension. 2009; 54: 868-876Crossref PubMed Scopus (53) Google Scholar Regarding lipid profiles of our HUA mouse model, TC, TG, and low-density lipoprotein cholesterol levels were significantly elevated in female Uox-KO mice versus female WT mice, whereas only TG was significantly lower in male Uox-KO mice versus male WT mice. These observations might result from HUA-related alterations in sex hormone levels. It has been reported that gout is associated with lowered testosterone and estradiol levels.26Mukhin I.V. Ignatenko G.A. Nikolenko V.Y. Dyshormonal disorders in gout: experimental and clinical studies.Bull Exp Biol Med. 2002; 133: 491-493Crossref PubMed Scopus (13) Google Scholar In rodents, testosterone deficiency leads to decreased serum TG by compromising lipid assembly and secretion,27Senmaru T. Fukui M. Okada H. et al.Testosterone deficiency induces markedly decreased serum triglycerides, increased small dense LDL, and hepatic steatosis mediated by dysregulation of lipid assembly and secretion in mice fed a high-fat diet.Metabolism. 2013; 62: 851-860Abstract Full Text Full Text PDF PubMed Scopus (50) Google Scholar while reduced estradiol promotes hepatic TG production.28Zhu L. Brown W.C. Cai Q. et al.Estrogen treatment after ovariectomy protects against fatty liver and may improve pathway-selective insulin resistance.Diabetes. 2013; 62: 424-434Crossref PubMed Scopus (214) Google Scholar Sex hormone results also supported the lipid profiles in our Uox-KO and WT mice (data not shown). The mechanisms underlying the distinct sexual difference in the incidence of metabolic disorders (i.e., glycometabolism disorder in males and lipometabolism disorder in females) remain unclear. In humans, women are more susceptible than men to dyslipidemia.29Alamgir M.A. Javid R.A. Hameed A. et al.Gender difference in components of metabolic syndrome among patients of type 2 diabetes.Pak J Med Sci. 2015; 31: 886-890PubMed Google Scholar Estrogen, a potential contributor to this sexual difference, is involved in adipocyte biology, and glucose and lipid metabolism.30Faulds M.H. Zhao C. Dahlman-Wright K. et al.The diversity of sex steroid action: regulation of metabolism by estrogen signaling.J Endocrinol. 2012; 212: 3-12Crossref PubMed Scopus (159) Google Scholar Imbalance in the ERα-ERβ ratio has been reported to contribute to the development of metabolic syndrome.31Barros R.P. Gustafsson J.A. Estrogen receptors and the metabolic network.Cell Metab. 2011; 14: 289-299Abstract Full Text Full Text PDF PubMed Scopus (298) Google Scholar Other factors such as body fat distribution, adipocyte size and function may also enhance the susceptibility of women to metabolic syndrome, as demonstrated in premenopausal women.32Pradhan A.D. Sex differences in the metabolic syndrome: implications for cardiovascular health in women.Clin Chem. 2014; 60: 44-52Crossref PubMed Scopus (163) Google Scholar In summary, we have generated a new mouse model of HUA by knocking out Uox on a pure C57BL/6J background, characterized by stably elevated SUA over a long time, compromised renal function, aberrant glycometabolism and lipometabolism, and sensitivity to ULDs. By comprehensively characterizing the HUA mouse mo