Role of zinc finger transcription factor zfp69 in body fat storage and diabetes susceptibility of mice

Combination of blockade of endothelin signalling and compensation of IGF1 expression protects the retina from degeneration

Retinitis pigmentosa (RP) and macular dystrophy (MD) cause severe retinal dysfunction, affecting 1 in 4000 people worldwide. This disease is currently assumed to be intractable, because effective therapeutic methods have not been established, regardless of genetic or sporadic traits. Here, we examined a RP mouse model in which the Prominin-1 (Prom1) gene was deficient and investigated the molecular events occurring at the outset of retinal dysfunction. We extracted the Prom1-deficient retina subjected to light exposure for a short time, conducted single-cell expression profiling, and compared the gene expression with and without stimuli. We identified the cells and genes whose expression levels change directly in response to light stimuli. Among the genes altered by light stimulation, Igf1 was decreased in rod photoreceptor cells and astrocytes under the light-stimulated condition. Consistently, the insulin-like growth factor (IGF) signal was weakened in light-stimulated photoreceptor cells. The recovery of Igf1 expression with the adeno-associated virus (AAV) prevented photoreceptor cell death, and its treatment in combination with the endothelin receptor antagonist led to the blockade of abnormal glial activation and the promotion of glycolysis, thereby resulting in the improvement of retinal functions, as assayed by electroretinography. We additionally demonstrated that the attenuation of mammalian/mechanistic target of rapamycin (mTOR), which mediates IGF signalling, leads to complications in maintaining retinal homeostasis. Together, we propose that combinatorial manipulation of distinct mechanisms is useful for the maintenance of the retinal condition.

Bacteriocyte development is sexually differentiated in Bemesia tabaci

Some symbiotic microbes are restricted to specialized host cells called bacteriocytes. However, the molecular and cellular mechanisms underlying the development of bacteriocytes are largely obscure. We find that maternally inherited bacteriocytes proliferate in adult females but degenerate in adult males of the whitefly Bemisia tabaci. Single-cell transcriptomics and immunohistochemistry reveal that cell division only occurs in the bacteriocytes of adult females, whereas autophagy and apoptosis are induced in the bacteriocytes of adult males. A transcription factor, Adf-1, enriched in bacteriocytes, is highly expressed in female bacteriocytes relative to male bacteriocytes. Silencing Adf-1 reduces the bacteriocyte number and Portiera titer and activates autophagy and apoptosis in females. The differential dynamics of both cell division and death in bacteriocytes and distinct expression of Adf-1 in bacteriocytes between whitefly sexes underlie the sexual differentiation of bacteriocyte development. Our study reveals that insect sex affects the development of bacteriocytes by cellular and molecular remodeling.

Epigenetic landscape in blood leukocytes following ketosis and weight loss induced by a very low calorie ketogenic diet (VLCKD) in patients with obesity

BACKGROUND

The molecular mechanisms underlying the potential health benefits of a ketogenic diet are unknown and could be mediated by epigenetic mechanisms.

OBJECTIVE

To identify the changes in the obesity-related methylome that are mediated by the induced weight loss or are dependent on ketosis in subjects with obesity underwent a very-low calorie ketogenic diet (VLCKD).

METHODS

Twenty-one patients with obesity (n = 12 women, 47.9 ± 1.02 yr, 33.0 ± 0.2 kg/m²) after 6 months on a VLCKD and 12 normal weight volunteers (n = 6 women, 50.3 ± 6.2 yrs, 22.7 ± 1.5 kg/m²) were studied. Data from the Infinium MethylationEPIC BeadChip methylomes of blood leukocytes were obtained at time points of ketotic phases (basal, maximum ketosis, and out of ketosis) during VLCKD (n = 10) and at baseline in volunteers (n = 12). Results were further validated by pyrosequencing in representative cohort of patients on a VLCKD (n = 18) and correlated with gene expression.

RESULTS

After weight reduction by VLCKD, differences were found at 988 CpG sites (786 unique genes). The VLCKD altered methylation levels in patients with obesity had high resemblance with those from normal weight volunteers and was concomitant with a downregulation of DNA methyltransferases (DNMT)1, 3a and 3b. Most of the encoded genes were involved in metabolic processes, protein metabolism, and muscle, organ, and skeletal system development. Novel genes representing the top scoring associated events were identified, including ZNF331, FGFRL1 (VLCKD-induced weight loss) and CBFA2T3, C3orf38, JSRP1, and LRFN4 (VLCKD-induced ketosis). Interestingly, ZNF331 and FGFRL1 were validated in an independent cohort and inversely correlated with gene expression.

CONCLUSIONS

The beneficial effects of VLCKD therapy on obesity involve a methylome more suggestive of normal weight that could be mainly mediated by the VLCKD-induced ketosis rather than weight loss.

ZNF577 Methylation Levels in Leukocytes From Women With Breast Cancer Is Modulated by Adiposity, Menopausal State, and the Mediterranean Diet

The methylation levels of ZNF577 in breast tumors has been previously identified as a possible epigenetic mark of breast cancer associated with obesity. The aim of the current study was to investigate differences in methylation levels of ZNF577 depending on obesity, menopausal state and dietary pattern in blood leukocytes, a non-invasive sample. The methylation levels of ZNF577 of two CpG sites (CpGs) located in promoter and island previously identified as differentially methylated according to adiposity and menopausal state by 450 k array (cg10635122, cg03562414) were evaluated by pyrosequencing in DNA from the blood leukocytes of breast cancer patients [n = 90; n = 64 (71.1%) overweight/obesity and n = 26 (28.9%) normal-weight] and paired tumor tissue biopsies (n = 8 breast cancer patients with obesity; n = 3/5 premenopausal/postmenopausal women). Differences in methylation levels were evaluated at each CpGs individually and at the mean of the two evaluated CpGs. Adherence to the Mediterranean diet was evaluated using the MEDAS-validated questionnaire, and the consumption of food groups of interest was also evaluated using the recommended intakes of the Sociedad Española de Nutricion Comunitaria. The methylation levels of ZNF577 were correlated between paired leukocytes and breast tumor biopsies (r = 0.62; p = 0.001). Moreover, higher methylation was found in leukocytes from patients with obesity (p = 0.002) and postmenopausal patients (p = 0.022) than patients with normal-weight or premenopausal, respectively. After adjusting for the body mass index and age, higher levels of ZNF577 methylation were also found in women with greater adherence to the Mediterranean diet (p = 0.017) or specific foods. Relevantly, the methylation levels of ZNF577 showed a good ability for fish consumption detection [area under the ROC curve (AUC) = 0.72; p = 0.016]. In conclusion, the association between methylation of ZNF577 and adiposity, menopausal state, and adherence to the Mediterranean diet can be detected in the blood leukocytes. The results guarantee the need of performing further studies in longer longitudinal cohorts in order to elucidate the role of ZNF577 methylation in the association between breast cancer, adiposity and dietary patterns.

An Epigenetic Signature in Adipose Tissue Is Linked to Nicotinamide N-Methyltransferase Gene Expression

SCOPE

The enzyme nicotinamide N-methyltransferase (NNMT) is a major methyltransferase in adipose tissue. We hypothesized an epigenetic signature in association with NNMT gene expression in adipose tissue.

METHODS AND RESULTS

The global human methylome was analyzed in visceral adipose tissue (VAT) from morbidly obese patients using the Infinium Human Methylation 450 BeadChip array (discovery cohort: n = 11). The findings were confirmed in two additional independent cohorts (cohort 1: n = 60; BMI 20-60 kg m^-2 and cohort 2: n = 40; BMI > 40 kg m^-2 ) and validated after weight loss (using microarray data). Among the genes associated with the largest methylation fold change were genes related to metabolic processes, proliferation, inflammation, and extracellular matrix remodeling, such as COL23A1, PLEC1, FBXO21, STEAP3, RGS12, IGDCC3, FOXK2, and ORAI2. In fact, the results showed 577 differentially methylated CpG sites (DMCpGs) associated with the NNMT expression levels, with low methylation levels paralleling high NNMT expression. The expression of FBXO21 and FOXK2 was specifically modified after weight loss concomitantly with a decrease in NNMT expression and inflammation-related genes. Interestingly, the adipose tissue NNMT gene expression correlated with markers of adipose tissue inflammation.

CONCLUSIONS

The expression of NNMT in VAT is associated with a specific methylome signature involving genes linked to adipose tissue metabolic pathophysiology.

Genome-wide DNA methylation pattern in visceral adipose tissue differentiates insulin-resistant from insulin-sensitive obese subjects

Elucidating the potential mechanisms involved in the detrimental effect of excess body weight on insulin action is an important priority in counteracting obesity-associated diseases. The present study aimed to disentangle the epigenetic basis of insulin resistance by performing a genome-wide epigenetic analysis in visceral adipose tissue (VAT) from morbidly obese patients depending on the insulin sensitivity evaluated by the clamp technique. The global human methylome screening performed in VAT from 7 insulin-resistant (IR) and 5 insulin-sensitive (IS) morbidly obese patients (discovery cohort) analyzed using the Infinium HumanMethylation450 BeadChip array identified 982 CpG sites able to perfectly separate the IR and IS samples. The identified sites represented 538 unique genes, 10% of which were diabetes-associated genes. The current work identified novel IR-related genes epigenetically regulated in VAT, such as COL9A1, COL11A2, CD44, MUC4, ADAM2, IGF2BP1, GATA4, TET1, ZNF714, ADCY9, TBX5, and HDACM. The gene with the largest methylation fold-change and mapped by 5 differentially methylated CpG sites located in island/shore and promoter region was ZNF714. This gene presented lower methylation levels in IR than in IS patients in association with increased transcription levels, as further reflected in a validation cohort (n = 24; 11 IR and 13 IS). This study reveals, for the first time, a potential epigenetic regulation involved in the dysregulation of VAT that could predispose patients to insulin resistance and future type 2 diabetes in morbid obesity, providing a potential therapeutic target and biomarkers for counteracting this process.

The Transcriptional Repressive Activity of KRAB Zinc Finger Proteins Does Not Correlate with Their Ability to Recruit TRIM28

KRAB domain Zinc finger proteins are one of the most abundant families of transcriptional regulators in higher vertebrates. The prevailing view is that KRAB domain proteins function as potent transcriptional repressors by recruiting TRIM28 and promoting heterochromatin spreading. However, the extent to which all KRAB domain proteins are TRIM28-dependent transcriptional repressors is currently unclear. Our studies on mouse ZFP568 revealed that TRIM28 recruitment by KRAB domain proteins is not sufficient to warrant transcriptional repressive activity. By using luciferase reporter assays and yeast two-hybrid experiments, we tested the ability of ZFP568 and other mouse KRAB domain proteins to repress transcription and bind TRIM28. We found that some mouse KRAB domain proteins are poor transcriptional repressors despite their ability to recruit TRIM28, while others showed strong KRAB-dependent transcriptional repression, but no TRIM28 binding. Together, our results show that the transcriptional repressive activity of KRAB-ZNF proteins does not correlate with their ability to recruit TRIM28, and provide evidence that KRAB domains can regulate transcription in a TRIM28-independent fashion. Our findings challenge the current understanding of the molecular mechanisms used by KRAB domain proteins to control gene expression and highlight that a high percentage of KRAB domain proteins in the mouse genome differ from the consensus KRAB sequence at amino acid residues that are critical for TRIM28 binding and/or repressive activity.

Genetic background (DDD/Sgn versus C57BL/6J) strongly influences postnatal growth of male mice carrying the A(y) allele at the agouti locus: identification of quantitative trait loci associated with diabetes and body weight loss

Background

Mice carrying the A^y allele at the agouti locus become obese and are heavier than their non-A^y littermates. However, this does not hold true for the genetic background of the DDD mouse strain. At 22 weeks of age, DDD.Cg-A^y females are heavier than DDD females, whereas DDD.Cg-A^y males are lighter than DDD males. This study aimed to determine the possible cause and identify the genes responsible for the lower body weight of DDD.Cg-A^y males.

Results

Growth curves of DDD.Cg-A^y mice were analyzed and compared with those of B6.Cg-A^y mice from 5 to 25 weeks. In DDD.Cg-A^y males, body weight gain stopped between 16 and 17 weeks and the body weight gradually decreased; thus, the lower body weight was a consequence of body weight loss. Quantitative trait locus (QTL) mapping was performed in backcrossed (BC) males of DDD × (B6 × DDD.Cg-A^y) F₁-A^y mice. For the body weight at 25 weeks, significant QTLs were identified on chromosomes 1 and 4. The DDD allele was associated with a lower body weight at both loci. In particular, the QTL on chromosome 4 interacted with the A^y allele. Furthermore, suggestive QTLs for plasma glucose and high molecular weight adiponectin levels were coincidentally mapped to chromosome 4. The DDD allele was associated with increased glucose and decreased adiponectin levels. When the body weight at 25 weeks and plasma glucose levels were considered as dependent and independent variables, respectively, BC A^y males were classified into two groups according to statistical analysis using the partition method. Mice of one group had significantly higher glucose and lower adiponectin levels than those of the other group and exhibited body weight loss as observed with DDD-A^y males.

Conclusions

The lower body weight of DDD.Cg-A^y male mice was a consequence of body weight loss. Diabetes mellitus has been suggested to be a possible contributory factor causing body weight loss. The QTL on distal chromosome 4 contained the major responsible genes. This QTL interacted with the A^y allele, implying the reason why body weight loss occurs in DDD.Cg-A^y but not in DDD males.

Systems genetics of susceptibility to obesity-induced diabetes in mice

Inbred strains of mice are strikingly different in susceptibility to obesity-driven diabetes. For instance, deficiency in leptin receptor (db/db) leads to hyperphagia and obesity in both C57BL/6 and DBA/2 mice, but only on the DBA/2 background do the mice develop beta-cell loss leading to severe diabetes, while C57BL/6 mice are relatively resistant. To further investigate the genetic factors predisposing to diabetes, we have studied leptin receptor-deficient offspring of an F2 cross between C57BL/6J (db/+) males and DBA/2J females. The results show that the genetics of diabetes susceptibility are enormously complex and a number of quantitative trait loci (QTL) contributing to diabetes-related traits were identified, notably on chromosomes 4, 6, 7, 9, 10, 11, 12, and 19. The Chr. 4 locus is likely due to a disruption of the Zfp69 gene in C57BL/6J mice. To identify candidate genes and to model coexpression networks, we performed global expression array analysis in livers of the F2 mice. Expression QTL (eQTL) were identified and used to prioritize candidate genes at clinical trait QTL. In several cases, clusters of eQTLs colocalized with clinical trait QTLs, suggesting a common genetic basis. We constructed coexpression networks for both 5 and 12 wk old mice and identified several modules significantly associated with clinical traits. One module in 12 wk old mice was associated with several measures of hepatic fat content as well as with other lipid- and diabetes-related traits. These results add to the understanding of the complex genetic interactions contributing to obesity-induced diabetes.

Pathophysiology and genetics of obesity and diabetes in the New Zealand obese mouse: a model of the human metabolic syndrome

The New Zealand Obese (NZO) mouse is one of the most thoroughly investigated polygenic models for the human metabolic syndrome and type 2 diabetes. It presents the main characteristics of the disease complex, including early-onset obesity, insulin resistance, dyslipidemia, and hypertension. As a consequence of this syndrome, a combination of lipotoxicity and glucotoxicity produces beta-cell failure and apoptosis resulting in hypoinsulinemia and diabetic hyperglycemia. With NZO as a breeding partner, several adipogenic and diabetogenic gene variants have been identified by hypothesis-free positional cloning (Tbc1d1, Zfp69) or by combining genetic screens and candidate gene approaches (Pctp, Abcg1, Nmur2, Lepr). This chapter summarizes the present knowledge of the NZO strain and describes its pathophysiology as well as the known underlying genetic defects.