Triplet repeat in the Repin1 3'-untranslated region on rat chromosome 4 correlates with facets of the metabolic syndrome

Lipid droplet deposition in the regenerating liver: A promoter, inhibitor, or bystander?

Liver regeneration (LR) is a complex process involving intricate networks of cellular connections, cytokines, and growth factors. During the early stages of LR, hepatocytes accumulate lipids, primarily triacylglycerol, and cholesterol esters, in the lipid droplets. Although it is widely accepted that this phenomenon contributes to LR, the impact of lipid droplet deposition on LR remains a matter of debate. Some studies have suggested that lipid droplet deposition has no effect or may even be detrimental to LR. This review article focuses on transient regeneration-associated steatosis and its relationship with the liver regenerative response.

REPIN1 regulates iron metabolism and osteoblast apoptosis in osteoporosis

Osteoporosis is not well treated due to the difficulty of finding commonalities between the various types of it. Iron homeostasis is a vital component in supporting biochemical functions, and iron overload is recognized as a common risk factor for osteoporosis. In this research, we found that there is indeed evidence of iron accumulation in the bone tissue of patients with osteoporosis and REPIN1, as an origin specific DNA binding protein, may play a key role in this process. We revealed that sh-Repin1 therapy can rescue bone loss in an iron-overload-induced osteoporosis mouse model. Knockdown of Repin1 can inhibit apoptosis and enhance the resistance of osteoblasts to iron overload toxicity. REPIN1 promoted apoptosis by regulating iron metabolism in osteoblasts. Mechanistically, knockdown of Repin1 decreased the expression of Lcn2, which ameliorated the toxic effects of intracellular iron overload. The anti-iron effect of lentivirus sh-Repin1 was partially reversed or replicated by changing LCN2 expression level via si-RNA or plasmid, which indirectly verified the key regulatory role of LCN2 as a downstream target. Furthermore, the levels of BCL2 and BAX, which play a key role in the mitochondrial apoptosis pathway, were affected. In summary, based on the results of clinical specimens, animal models and in vitro experiments, for the first time, we proved the key role of REPIN1 in iron metabolism-related osteoporosis.

Ramipril Reduces Acylcarnitines and Distinctly Increases Angiotensin-Converting Enzyme 2 Expression in Lungs of Rats

The angiotensin-converting enzyme 2 (ACE2) receptor has been identified as the entry receptor for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that is abundantly expressed in many organs. With respect to the role of circulating ACE2 and its receptor expression in the pathogenesis of the SARS-CoV-2 infection, it is still debated whether diseases such as hypertension or pharmacotherapies, including ACE inhibitors and angiotensin receptor blockers that affect ACE2 receptor expression, may modulate the severity and outcome of the coronavirus disease 2019 (COVID-19). We therefore tested the hypothesis that treatment with the ACE inhibitor Ramipril affects organ-specific ACE2 receptor mRNA and protein expression as well as the serum metabolome in BioBreeding (BB) rats. Twelve male BioBreeding rats were randomly divided into a Ramipril (10 mg/kg body weight) treatment group or a control group (N = 12; n = 6 per group) over a period of seven days. Ramipril treatment resulted in the reduction of acylcarnitines (C3–C6) out of 64 metabolites. Among the different organs studied, only in the lungs did Ramipril treatment significantly increase both Ace2 mRNA and ACE2 receptor membrane protein levels. Increased ACE2 receptor lung expression after Ramipril treatment was not associated with differences in ACE2 serum concentrations between experimental groups. Our data provide experimental in vivo evidence that the ACE inhibitor Ramipril selectively increases pulmonary ACE2 receptor mRNA and protein levels and reduces acylcarnitines.

Super-Enhancer Associated Five-Gene Risk Score Model Predicts Overall Survival in Multiple Myeloma Patients

Multiple myeloma (MM) is a malignant plasma cell tumor with high heterogeneity, characterized by anemia, hypercalcemia, renal failure, and lytic bone lesions. Although various powerful prognostic factors and models have been exploited, the development of more accurate prognosis and treatment for MM patients is still facing many challenges. Given the essential roles of super-enhancer (SE) associated genes in the tumorigenesis of MM, we tried to initially screen and identify the significant prognostic factors from SE associated genes in MM by the least absolute shrinkage and selection operator (Lasso) penalized Cox regression, univariate and multivariate Cox regression analysis using GSE24080 and GSE9782 datasets. Risk score model of five genes including CSGALNACT1, FAM53B, TAPBPL, REPIN1, and DDX11, was further constructed and the Kaplan-Meier (K-M) curves showed that the low-risk group seems to have better clinical outcome of survival compared to the high-risk group. Time-dependent receiver operating characteristic (ROC) curves presented the favorable performance of the model. An interactive nomogram consisting of the five-gene risk group and eleven clinical traits was established and identified by calibration curves. Therefore, the risk score model of SE associated five genes developed here could be used to predict the prognosis of MM patients, which may assist the clinical treatment of MM patients in the future.

Repin1 deficiency in liver tissue alleviates NAFLD progression in mice

There is an increasing prevalence of obesity and metabolic syndrome, which promote the development of non-alcoholic fatty liver disease (NAFLD), a disease that can evolve into cirrhosis and hepatocellular carcinoma. Repin1 loss was previously shown to have beneficial effects on lipid and glucose metabolism and obesity regulation. Herein, we characterized NAFLD in mice with hepatic deletion of Repin1 (LRep1-/-). For this purpose, liver disease was analysed in male LRep1-/- and wild-type mice treated with streptozotocin/high fat diet or a control diet over a period of 20 wks. Streptozotocin/high fat diet treated LRep1-/- mice showed a significant decrease in systemic and hepatic lipid accumulation, accompanied by diminished chronic inflammation and a subsequent reduction in liver injury. Remarkably, Repin1-deficient mice exhibited a lower tumour prevalence and tumour frequency, as well as a reduced liver weight/body weight index. A therapeutic approach using Repin1 siRNA in the early phase of NAFLD verified the observed beneficial effects of Repin1 deficiency. This study provides evidence that loss of Repin1 in the liver attenuates NAFLD progression, most likely by reducing fat accumulation and alleviating chronic tissue inflammation. Thus, modulating Repin1 expression may become a novel strategy and potential tool to inhibit NAFLD progression.

Rat Models of Metabolic Syndrome

Metabolic syndrome is a complex disorder that comprises several other complex disorders, including obesity, hypertension, dyslipidemia, and diabetes. There are several rat models that encompass component features of MetS. Some models are inbred strains selected for one or more traits underlying MetS; others are population models with genetic risk for MetS traits, are induced by environmental stressors such as diet, are spontaneous monogenic mutant models, or are congenic strains derived from a combination of these models. Together they can be studied to identify the genetic and physiological underpinnings of MetS to identify candidate genes or mechanisms for study in human MetS subjects.

Liver-specific Repin1 deficiency impairs transient hepatic steatosis in liver regeneration

Transient hepatic steatosis upon liver resection supposes functional relationships between lipid metabolism and liver regeneration. Repin1 has been suggested as candidate gene for obesity and dyslipidemia by regulating key genes of lipid metabolism and lipid storage. Herein, we characterized the regenerative potential of mice with a hepatic deletion of Repin1 (LRep1−/−) after partial hepatectomy (PH) in order to determine the functional significance of Repin1 in liver regeneration. Lipid dynamics and the regenerative response were analyzed at various time points after PH. Hepatic Repin1 deficiency causes a significantly decreased transient hepatic lipid accumulation. Defects in lipid uptake, as analyzed by decreased expression of the fatty acid transporter Cd36 and Fatp5, may contribute to attenuated and shifted lipid accumulation, accompanied by altered extent and chronological sequence of liver cell proliferation in LRep1−/− mice. In vitro steatosis experiments with primary hepatocytes also revealed attenuated lipid accumulation and occurrence of smaller lipid droplets in Repin1-deficient cells, while no direct effect on proliferation in HepG2 cells was observed. Based on these results, we propose that hepatocellular Repin1 might be of functional significance for early accumulation of lipids in hepatocytes after PH, facilitating efficient progression of liver regeneration.

Metabolic effects of genetic variation in the human REPIN1 gene

BACKGROUND

Replication initiator 1 (Repin1) is a zinc finger protein highly expressed in liver and adipose tissue. The Repin1 resides within a quantitative trait locus (QTL) for body weight and triglyceride levels in the rat, and its hepatic deletion in mice results in improved insulin sensitivity and lower body weight. Here, we analyzed whether genetic variation within the Repin1 affects parameters of glucose and lipid metabolism.

METHODS

We sequenced REPIN1 in 48 non-related Caucasian subjects. We discovered a 12 base pair deletion (12 bp del; rs3832490), which was subsequently genotyped in two well-characterized cohorts (N = 3013) to test for associations with metabolic traits. Functional consequences of the variant were investigated in HepG2 cells in vitro.

RESULTS

In human cohorts, we show that the 12 bp del associates with improved glucose metabolism (lower fasting plasma glucose, fasting plasma insulin, and HOMA IR). Cells transfected with the plasmid carrying the 12 bp del variant are characterized by increased GLUT2 and fatty acid translocase CD36 expression and more lipid droplets.

CONCLUSION

Our data suggest that genetic variation in human REPIN1 plays a role in glucose and lipid metabolism by differentially affecting the expression of REPIN1 target genes including glucose and fatty acid transporters.

Liver-restricted Repin1 deficiency improves whole-body insulin sensitivity, alters lipid metabolism, and causes secondary changes in adipose tissue in mice

Replication initiator 1 (Repin1) is a zinc finger protein highly expressed in liver and adipose tissue and maps within a quantitative trait locus (QTL) for body weight and triglyceride (TG) levels in the rat. The QTL has further been supported as a susceptibility locus for dyslipidemia and related metabolic disorders in congenic and subcongenic rat strains. Here, we elucidated the role of Repin1 in lipid metabolism in vivo. We generated a liver-specific Repin1 knockout mouse (LRep1(-/-)) and systematically characterized the consequences of Repin1 deficiency in the liver on body weight, glucose and lipid metabolism, liver lipid patterns, and protein/mRNA expression. Hyperinsulinemic-euglycemic clamp studies revealed significantly improved whole-body insulin sensitivity in LRep1(-/-) mice, which may be due to significantly lower TG content in the liver. Repin1 deficiency causes significant changes in potential downstream target molecules including Cd36, Pparγ, Glut2 protein, Akt phosphorylation, and lipocalin2, Vamp4, and Snap23 mRNA expression. Mice with hepatic deletion of Repin1 display secondary changes in adipose tissue function, which may be mediated by altered hepatic expression of lipocalin2 or chemerin. Our findings indicate that Repin1 plays a role in insulin sensitivity and lipid metabolism by regulating key genes of glucose and lipid metabolism.

Low-anxiety rat phenotypes can be further reduced through genetic intervention

BACKGROUND

A previous study using an intercross between the inbred rat strains Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) identified a locus on chromosome 4, named Anxrr16, influencing an experimental index of anxiety and showing a transgressive effect, with alleles from the LEW strain (more anxious) decreasing rather than increasing anxiety.

OBJECTIVE

To confirm the location and isolate the effect of a rat genome region named Anxrr16 through a planned genomic recombination strategy, where the target locus in SHR rats was replaced with LEW genetic material.

METHODS

A new congenic strain, named SHR.LEW-Anxrr16 (SLA16), was developed from a cross between LEW (donor) and SHR (receptor) rats and then evaluated in several anxiety-related tests. The activity and attention levels of the new strain were also evaluated, since hyperactivity was observed during its construction and because SHR is a model of attention deficit hyperactivity disorder.

RESULTS

Significant effects of Anxrr16 were found for open field central locomotion, as well as for other indices of anxiety from the light/dark box, triple test and T-maze. In all cases, the low-anxiety levels of SHR rats were further reduced by the insertion of LEW alleles. Differences in locomotor activity were found only in unfamiliar (hence stressful) environments and no genetic effects were observed in indices of attention.

CONCLUSION

The SLA16 strain can help in the identification of the molecular pathways involved in experimental anxiety and it demonstrates how apparently extreme phenotypes sometimes hide major opposite-acting genes.

Replication initiator 1 in adipose tissue function and human obesity

Replication initiator 1 (Repin1) was discovered as the replication initiation-region protein 60kDa (RIP60) and characterized as a zinc finger protein involved in DNA binding and bending during initiation of DNA replication. As with many members of the zinc finger family, physiological functions and regulations of Repin1 as well as the underlying molecular mechanisms have remained elusive since its discovery in 1990. However, recent results have revealed interesting new insights into Repin1 function. Repin1 is highly expressed in liver and adipose tissue and it has been suggested as a candidate gene for obesity and related metabolic disorders in congenic and subcongenic rat strains. Repin1 seems to participate in the regulation of genes involved in adipogenesis, lipid droplet formation and fusion, as well as glucose and fatty acid transport in adipocytes. Given the observation that Repin1 expression in human adipose tissue significantly correlates with total body fat mass and adipocyte size, therapeutic strategies to reduce Repin1 action in adipose tissue may be a potential approach to tackle adipose tissue dysfunction in obesity. Thus, human and in vitro data suggest a role of Repin1 in adipocyte function and could therefore emerge as an interesting therapeutic target in human obesity.

Gene expression profiling supports the role of Repin1 in the pathophysiology of metabolic syndrome

Congenic BB rat strains carrying a SHR segment (D4Got41-Tacr1; 60.5-122.8 Mb; BB.4S) or a WOKW segment (D4Got41-Fabp1; 60.5-104.6 Mb; BB.4W) of chromosome 4 within the BB/OK background develop facets of the metabolic syndrome when compared with their parental BB/OK rats. To narrow down potential genes involved in the pathophysiology of metabolic syndrome, gene expression studies in adipose tissues of BB/OK, BB.4S, and BB.4W rats were initiated. Total RNA of subcutaneous and epididymal adipose tissue of BB/OK (n=10), congenic BB.4S (n=8), and BB.4W (n=9) males at an age of 4 weeks was isolated. The mRNA expression of 92 genes involved in obesity, insulin resistance and other metabolic traits was measured by RT-PCR. Significant differences in gene expression were only found in Repin1 in both adipose tissues. Congenic BB.4W showed significantly lower gene expression than did BB.4S and BB/OK. Our findings and newly published findings of Repin1 in 3T3-L1 adipocytes support the hypothesis that Repin1 may affect the development of facets of the metabolic syndrome.

High-fat diet protects BB/OK rats from developing type 1 diabetes

BACKGROUND

It is well known that lipid metabolism plays an important role in the early stages of type 1 diabetes (T1D). For that reason, we examined factors that influence lipid metabolism of BioBreeding/Ottawa Kalsburg (BB/OK) rats that spontaneously develop an insulin-dependent T1D.

METHODS

BB/OK female rats were fed a high-fat diet during pregnancy (Ssniff R-Z + 10% tallow) and their progeny were also given this diet up to an age of 30 weeks (n = 55) or 4 weeks (n = 14) to study gene expression of Pparg, Fasn, Lep, Adipoq, Repin1, Rarres 2, and Glut4 in adipose tissue. Forty-two BB/OK rats fed the normal diet (Ssniff R-Z) during pregnancy and the observation period served as controls.

RESULTS

The high-fat diet significantly decreased diabetes frequency in BB/OK rats when compared with control rats (71 versus 95%, p = 0.002). Although this difference was also reflected in the male rats (68 versus 100%, p = 0.003), no significant variation was observed in female rats (73 versus 90%, p = 0.23). The high-fat diet resulted in significantly reduced mRNA expression of examined genes in subcutaneous adipose tissue, but not in visceral adipose tissue, except for Fasn and Repin1 expression.

CONCLUSIONS

A high-fat diet seems to protect BB/OK rats from T1D in a sex-specific manner. The data suggest that a high-fat diet might influence fat accumulation and/or fat metabolism and prevent T1D development in male rats, which is supported by changes in adipose tissue gene expression.

Repin1 maybe involved in the regulation of cell size and glucose transport in adipocytes

Replication initiator 1 (Repin1) is highly expressed in liver and adipose tissue and has been suggested as candidate gene for obesity and its related metabolic disorders in congenic and subcongenic rat strains. The cellular localization and function of Repin1 has remained elusive since its discovery in 1990. To characterize the role of Repin1 in adipocyte biology, we used siRNA knockdown technology to reduce the expression of Repin1 by electroporation of semiconfluent 3T3-L1 preadipocytes. Glucose transport, palmitate uptake as well as triglyceride content were measured. In paired samples of human visceral and subcutaneous adipose tissue, we investigated whether Repin1 mRNA expression is related to measures of fat accumulation and adipocyte size. We demonstrate that Repin1 increases during adipogenesis. RNA interference based Repin1 downregulation in mature adipocytes significantly reduces adipocyte size and causes reduced basal, but enhanced insulin stimulated glucose uptake into 3T3-L1 cells. Additionally, knockdown of Repin1 resulted in reduced palmitate uptake and significantly changed the mRNA expression of genes involved lipid droplet formation, adipogenesis, glucose and fatty acid transport. Furthermore, we found significant correlations between Repin1 mRNA expression in human paired visceral and subcutaneous adipose tissue and total body fat mass as well as adipocyte size. We have identified a potential role for Repin1 in the regulation of adipocyte size and expression of glucose transporters GLUT1 and GLUT4 in adipocytes.

Genetic dissection reveals diabetes loci proximal to the gimap5 lymphopenia gene

Congenic DRF.(f/f) rats are protected from type 1 diabetes (T1D) by 34 Mb of F344 DNA introgressed proximal to the gimap5 lymphopenia gene. To dissect the genetic factor(s) that confer protection from T1D in the DRF.(f/f) rat line, DRF.(f/f) rats were crossed to inbred BBDR or DR.(lyp/lyp) rats to generate congenic sublines that were genotyped and monitored for T1D, and positional candidate genes were sequenced. All (100%) DR.(lyp/lyp) rats developed T1D by 83 days of age. Reduction of the DRF.(f/f) F344 DNA fragment by 26 Mb (42.52-68.51 Mb) retained complete T1D protection. Further dissection revealed that a 2 Mb interval of F344 DNA (67.41-70.17 Mb) (region 1) resulted in 47% protection and significantly delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Retaining <1 Mb of F344 DNA at the distal end (76.49-76.83 Mb) (region 2) resulted in 28% protection and also delayed onset (P < 0.001 compared with DR.(lyp/lyp)). Comparative analysis of diabetes frequency in the DRF.(f/f) congenic sublines further refined the RNO4 region 1 interval to approximately 670 kb and region 2 to the 340 kb proximal to gimap5. All congenic DRF.(f/f) sublines were prone to low-grade pancreatic mononuclear cell infiltration around ducts and vessels, but <20% of islets in nondiabetic rats showed islet infiltration. Coding sequence analysis revealed TCR Vbeta 8E, 12, and 13 as candidate genes in region 1 and znf467 and atp6v0e2 as candidate genes in region 2. Our results show that spontaneous T1D is controlled by at least two genetic loci 7 Mb apart on rat chromosome 4.

Nociceptin/orphanin FQ-induced food intake and cocaine amphetamine regulated transcript gene expression in strains derived from rats prone (WOKW) and resistant (Dark Agouti) to metabolic syndrome

In previous work, we observed that N/OFQ-induced hyperphagia is greater in DA rats, animals resistant to metabolic syndrome, than in WOKW animals, which are prone to this disease. We attributed this difference to the fact that these two strains have different Cart gene sequences and expression. As a preliminary approach to pursue this hypothesis, the present work focused on Cart gene expression by developing from DA and WOKW rats various congenic animals with exchanges of metabolic syndrome-related QTL's of different chromosomes (3, 5, 10 and 16), and analyzing their N/OFQ-induced (2.1, 4.2, and 8.4nmol/rat) food intake in terms of their CART gene expression and N/OFQ hypothalamic immunostaining. Two groupings emerged, the first, with strains 3a, 3b, and 5a with elevated N/OFQ-induced feeding similar to that of the DA rats, and the second, with strains 16 and 10, with lower feeding, like the WOKW rats. There was a perfect correlation between Cart gene expression and N/OFQ-induced feeding data at 30min for the strains DA, 3a, 3b, 5 in the first group, and 16 and WOKW for the second, but not for strain 10. As expected, the strains with low content of Cart gene expression had elevated N/OFQ-induced feeding, but contrary to expectations, strain 10, with the lowest Cart gene expression, exhibited low N/OFQ-induced feeding, on the order of that of the WOKW rats. A comparable trend was observed with N/OFQ hypothalamic immunostaining. This anomaly may be due to other satiety-related factors involved in N/OFQ-induced feeding.

Genes and pathways differentially expressed in the brains of Fxr2 knockout mice

Fragile X syndrome is a common inherited form of mental retardation and originates from the absence of expression of the FMR1 gene. This gene and its two homologues, FXR1 and FXR2, encode for a family of fragile X related (FXR) proteins with similar tissue distribution, together with sequence and functional homology. Based on these characteristics, it has been suggested that these proteins might partly complement one another. To unravel the function of Fxr2 protein, the expression pattern of 12,588 genes was studied in the brains of wild-type and Fxr2 knockout mice, an animal model which shows behavioral abnormalities partly similar to those observed in Fmr1-knockout mice. By genome expression profiling and stringent significance tests we identify genes and gene groups de-regulated in the brains of Fxr2 knockout mice. Differential expression of candidate genes was validated by real-time PCR, in situ hybridization, immunohistochemistry and western blot analysis. A number of differentially expressed genes associated with the Fxr2 phenotype have been previously involved in other memory or cognitive disorders.