Alessandra Antonucci

Aims: Aim of this study was to investigate in type 2 diabetes whether expression level of GALNT2, a positive modulator of insulin sensitivity, is associated with a metabolic signature. Methods: Five different metabolite families, including acylcarnitines, aminoacids, biogenic amines, phospholipids and sphingolipids were investigated in fasting serum of 70 patients with type 2 diabetes, by targeted metabolomics. GALNT2 expression levels were measured in peripheral white blood cells by RT-PCR. The association between GALNT2 expression and serum metabolites was assessed using false discovery rate followed by stepwise selection and, finally, multivariate model including several clinical parameters as confounders. The association between GALNT2 expression and the same clinical parameters was also investigated. Results: GALNT2 expression was independently correlated with HbA1c levels (P value = 0.0052), a finding that is the likely consequence of the role of GALNT2 on insulin sensitivity. GALNT2 expression was also independently associated with serum levels of the aminoacid glycine (P value = 0.014) and two biogenic amines phenylethylamine (P value = 0.0065) and taurine (P value = 0.0011). The association of GALNT2 expression with HbA1c was not mediated by these three metabolites. Conclusions: Our data indicate that in type 2 diabetes the expression of GALNT2 is associated with several serum metabolites. This association needs to be further investigated to understand in depth its role in mediating the effect of GALNT2 on insulin sensitivity, glucose control and other clinical features in people with diabetes.

Several studies have shown that downregulation of GALNT2 (Polypeptide N‐Acetylgalactosaminyltransferase 2), encoding polypeptide N‐acetylgalactosaminyltransferase 2, decreases high‐density lipoprotein cholesterol (HDL‐C) and increases triglycerides levels by glycosylating key enzymes of lipid metabolism, such as angiopoietin like 3, apolipoprotein C‐III, and phospholipid transfer protein. GALNT2 is also a positive modulator of insulin signaling and action, associated with in vivo insulin sensitivity and during adipogenesis strongly upregulates adiponectin. Thus, the hypothesis that GALNT2 affects HDL‐C and triglycerides levels also through insulin sensitivity and/or circulating adiponectin, is tested. In 881 normoglycemic individuals the G allele of rs4846914 SNP at the GALNT2 locus, known to associate with GALNT2 downregulation, is associated with low HDL‐C and high values of triglycerides, triglycerides/HDL‐C ratio, and theHomeostatic Model Assessment of insulin resistance HOMA_IR (p‐values = 0.01, 0.027, 0.002, and 0.016, respectively). Conversely, no association is observed with serum adiponectin levels (p = 0.091). Importantly, HOMA_IR significantly mediates a proportion of the genetic association with HDL‐C (21%, 95% CI: 7–35%, p = 0.004) and triglyceride levels (32%, 95% CI: 4–59%, p = 0.023). The results are compatible with the hypothesis that, besides the effect on key lipid metabolism enzymes, GALNT2 alters HDL‐C and triglyceride levels also indirectly through a positive effect on insulin sensitivity.

O-linked glycosylation, the greatest form of post-translational modifications, plays a key role in regulating the majority of physiological processes. It is, therefore, not surprising that abnormal O-linked glycosylation has been related to several human diseases. Recently, GALNT2, which encodes the GalNAc-transferase 2 involved in the first step of O-linked glycosylation, has attracted great attention as a possible player in many highly prevalent human metabolic diseases, including atherogenic dyslipidemia, type 2 diabetes and obesity, all clustered on the common ground of insulin resistance. Data available both in human and animal models point to GALNT2 as a molecule that shapes the risk of the aforementioned abnormalities affecting diverse protein functions, which eventually cause clinically distinct phenotypes (a typical example of pleiotropism). Pathways linking GALNT2 to dyslipidemia and insulin resistance have been partly identified, while those for type 2 diabetes and obesity are yet to be understood. Here, we will provide a brief overview on the present knowledge on GALNT2 function and dysfunction and propose novel insights on the complex pathogenesis of the aforementioned metabolic diseases, which all impose a heavy burden for patients, their families and the entire society.

Context Type 2 diabetes (T2D) shows a high mortality rate, partly mediated by atherosclerotic plaque instability. Discovering novel biomarkers may help identify high-risk patients who would benefit from more aggressive and specific managements. We recently described a serum resistin and multicytokine inflammatory pathway (REMAP), including resistin, interleukin (IL)-1β, IL-6, IL-8, and TNF-α, that is associated with cardiovascular disease. Objective We investigated whether REMAP is associated with and improves the prediction of mortality in T2D. Methods A REMAP score was investigated in 3 cohorts comprising 1528 patients with T2D (409 incident deaths) and in 59 patients who underwent carotid endarterectomy (CEA; 24 deaths). Plaques were classified as unstable/stable according to the modified American Heart Association atherosclerosis classification. Results REMAP was associated with all-cause mortality in each cohort and in all 1528 individuals (fully adjusted hazard ratio [HR] for 1 SD increase = 1.34, P < .001). In CEA patients, REMAP was associated with mortality (HR = 1.64, P = .04) and a modest change was observed when plaque stability was taken into account (HR = 1.58; P = .07). REMAP improved discrimination and reclassification measures of both Estimation of Mortality Risk in Type 2 Diabetic Patients and Risk Equations for Complications of Type 2 Diabetes, well-established prediction models of mortality in T2D (P < .05-< .001). Conclusion REMAP is independently associated with and improves predict all-cause mortality in T2D; it can therefore be used to identify high-risk individuals to be targeted with more aggressive management. Whether REMAP can also identify patients who are more responsive to IL-6 and IL-1β monoclonal antibodies that reduce cardiovascular burden and total mortality is an intriguing possibility to be tested.

3T3L1 mouse pre-adipocytes develop into adipocytes differently in response to GALNT2 overexpression or to stimulation with rosiglitazone, a reference inducer of adipogenesis. To investigate the biology of alternative pathways of adipogenesis, we studied lipid droplets (LD) morphology, chromatin organization, and gene expression in GALNT2- versus rosiglitazone-induced 3T3L1 adipogenesis. 3T3L1 overexpressing either GALNT2 (GALNT2) or GFP and treated with rosiglitazone (GFPR) were differentiated into adipocytes. LD and nuclei were profiled measuring their morphological features. The expression of adipogenesis-related genes was measured by RT-PCR. As compared to GFPR, GALNT2 showed smaller and more clustered LD, more nuclei with condensed chromatin and several gene expression changes (P < 0.001 for all). As compared to those stimulated by rosiglitazone, GALNT2 overexpressing cells show differences in the most established readouts of adipogenesis. Characterizing alternative pathways of adipogenesis may help tackle those diseases which are secondary to increased dysfunctional mass of adipose tissue.

The near-infrared emissions of single-walled carbon nanotubes (SWCNTs) falls within the optical transparency window of biological tissue, allowing deep-tissue, in vivo and in vitro imaging. However, the relatively low photoluminescence quantum yield of SWCNTs, which typically lies in the range of 0.1 - 1.5%, limits the penetration depth and sensitivity of these fluorophores when used as imaging agents and optical sensors. In the present work, we enhance the fluorescence emission of SWCNTs up to 10-fold by employing different localized surface plasmon resonance (LSPR) nanostructures. We observe a chirality-dependent enhancement that varies with the nanostructure geometry and material. The proposed mechanism is based on changes in the charge density following nanoparticle conjugation with the SWCNT. In agreement with this mechanism, the enhancement and quenching effects show a strong correlation with the distance between the SWCNTs and the nanostructures. Finally, we demonstrate the applicability of this technology in a single-molecule imaging SWCNT application.

The distinctive properties of single-walled carbon nanotubes (SWCNTs) have inspired the development of innovative applications in the field of cell nanobiotechnology. Most studies to date have focused on eukaryotic cells capable of internalizing SWCNTs functionalized with a variety of non-covalent wrappings. However, the effect of SWCNT functionalization on transport across the thick cell wall of prokaryotes remains unexplored. In this study, we explore the uptake of SWCNTs in Gram-negative cyanobacteria and demonstrate selective internalization of SWCNTs decorated with charged protein wrappings. The functionalized SWCNTs are shown to traverse the outer cell wall of both filamentous and unicellular strains of cyanobacteria, independent of whether the strain is naturally competent for DNA uptake, with adsorption and internalization rate constants of k_ads = (9.08 ± 0.16) x 10^-8 s^-1 and k_in = (1.466 ± 0.011) x 10^-4 s^-1, respectively. A custom-built, spinning disc confocal microscope was used for the first time to directly image near-infrared (NIR) SWCNT fluorescence within cells, revealing a highly inhomogeneous distribution of SWCNTs that is otherwise overlooked using conventional NIR widefield imaging. The nanobionic cells show sustained photosynthetic activity and growth, offering a powerful avenue for engineering photosynthetic organisms with augmented and even inherited nanobionic capabilities.

A better understanding of adipose tissue biology is crucial to tackle insulin resistance and eventually coronary heart disease and diabetes, leading causes of morbidity and mortality worldwide. GALNT2, a GalNAc-transferase, positively modulates insulin signaling in human liver cells by down-regulating ENPP1, an insulin signaling inhibitor. GALNT2 expression is increased in adipose tissue of obese as compared to that of non-obese individuals. Whether this association is secondary to a GALNT2-insulin sensitizing effect exerted also in adipocytes is unknown. We then investigated in mouse 3T3-L1 adipocytes the GALNT2 effect on adipogenesis, insulin signaling and expression levels of both Enpp1 and 72 adipogenesis-related genes. Stable over-expressing GALNT2 and GFP preadipocytes (T₀) were generated. Adipogenesis was induced with (R+) or without (R−) rosiglitazone and investigated after 15 days (T₁₅). Lipid accumulation (by Oil Red-O staining) and intracellular triglycerides (by fluorimetric assay) were measured. Lipid droplets (LD) measures were analyzed at confocal microscope. Gene expression was assessed by RT-PCR and insulin-induced insulin receptor (IR), IRS1, JNK and AKT phosphorylation by Western blot. Lipid accumulation, triglycerides and LD measures progressively increased from T₀ to T₁₅R- and furthermore to T₁₅R+. Such increases were significantly higher in GALNT2 than in GFP cells so that, as compared to T₁₅R+GFP, T₁₅R- GALNT2 cells showed similar (intracellular lipid and triglycerides accumulation) or even higher (LD measures, p < 0.01) values. In GALNT2 preadipocytes, insulin-induced IR, IRS1 and AKT activation was higher than that in GFP cells. GALNT2 effect was totally abolished during adipocyte maturation and completely reversed at late stage maturation. Such GALNT2 effect trajectory was paralleled by coordinated changes in the expression of Enpp1 and adipocyte-maturation key genes. GALNT2 is a novel modulator of adipogenesis and related cellular phenotypes, thus becoming a potential target for tackling the obesity epidemics and its devastating sequelae.