Heparan Sulfate Proteoglycans in Diabetes

Identification of potential shared gene signatures between gastric cancer and type 2 diabetes: a data-driven analysis

Background

Gastric cancer (GC) and type 2 diabetes (T2D) contribute to each other, but the interaction mechanisms remain undiscovered. The goal of this research was to explore shared genes as well as crosstalk mechanisms between GC and T2D.

Methods

The Gene Expression Omnibus (GEO) database served as the source of the GC and T2D datasets. The differentially expressed genes (DEGs) and weighted gene co-expression network analysis (WGCNA) were utilized to identify representative genes. In addition, overlapping genes between the representative genes of the two diseases were used for functional enrichment analysis and protein-protein interaction (PPI) network. Next, hub genes were filtered through two machine learning algorithms. Finally, external validation was undertaken with data from the Cancer Genome Atlas (TCGA) database.

Results

A total of 292 and 541 DEGs were obtained from the GC (GSE29272) and T2D (GSE164416) datasets, respectively. In addition, 2,704 and 336 module genes were identified in GC and T2D. Following their intersection, 104 crosstalk genes were identified. Enrichment analysis indicated that "ECM-receptor interaction," "AGE-RAGE signaling pathway in diabetic complications," "aging," and "cellular response to copper ion" were mutual pathways. Through the PPI network, 10 genes were identified as candidate hub genes. Machine learning further selected BGN, VCAN, FN1, FBLN1, COL4A5, COL1A1, and COL6A3 as hub genes.

Conclusion

"ECM-receptor interaction," "AGE-RAGE signaling pathway in diabetic complications," "aging," and "cellular response to copper ion" were revealed as possible crosstalk mechanisms. BGN, VCAN, FN1, FBLN1, COL4A5, COL1A1, and COL6A3 were identified as shared genes and potential therapeutic targets for people suffering from GC and T2D.

The effect of hormones insulin and glucagon on ubiquitin modifications elucidated by proteomics in liver cells

AIMS

Insulin action is intertwined with changing levels of glucose and counter-regulatory hormone glucagon. While insulin lowers blood sugar level, glucagon raises it by promoting the breakdown of the stored glycogen in liver and releases glucose into the bloodstream. The hormones insulin and glucagon are key in the pathogenesis of type 2 diabetes (T2D). Insulin resistance is a primary predisposing factor for diabetes. Phosphorylation of insulin signaling molecules is altered in the insulin-resistant state. However, ubiquitin (Ub) modifications in insulin-resistant state are relatively understudied. To dissect the underlying mechanisms, we performed a proteomics study on hepatoma cells to study the regulation of ubiquitination by insulin and glucagon.

MATERIALS AND METHODS

We performed western blotting, immunoprecipitations, and affinity pull down using tandem Ub binding entities (TUBE) reagents on hepatoma cells treated with insulin or glucagon. Next, we performed MS/MS analysis on Ub-linkage specific affinity pull down samples. Gene ontology analysis and protein-protein interaction network analysis was performed using DAVID GO and STRING db, respectively.

KEY FINDINGS

The ubiquitination pattern of total Ub, K48-linked Ub, and K63-linked Ub was altered with the treatment of hormones insulin and glucagon. Ubiquitination in immunoprecipitated samples showed enrichment with total Ub and K48-linked Ub but not with K63-linked Ub. Ubiquitination by treatment with hormones mainly enriched key signaling pathways MAPK, Akt, oxidative stress etc. SIGNIFICANCE: Our study identified key altered proteins and signal transduction pathways which aids in understanding the mechanisms of hormonal action on ubiquitination and identify new therapeutic targets for T2D.

The potential role of human islet amyloid polypeptide in type 2 diabetes mellitus and Alzheimer's diseases

Human Islet amyloid polypeptide (hIAPP) from pancreatic β cells in the islet of Langerhans has different physiological functions including inhibiting the release of insulin and glucagon. Type 2 diabetes mellitus (T2DM) is an endocrine disorder due to relative insulin insufficiency and insulin resistance (IR) is associated with increased circulating hIAPP. Remarkably, hIAPP has structural similarity with amyloid beta (Aβ) and can engage in the pathogenesis of T2DM and Alzheimer's disease (AD). Therefore, the present review aimed to elucidate how hIAPP acts as a link between T2DM and AD. IR, aging and low β cell mass increase expression of hIAPP which binds cell membrane leading to the aberrant release of Ca²⁺ and activation of the proteolytic enzymes leading to a series of events causing loss of β cells. Peripheral hIAPP plays a major role in the pathogenesis of AD, and high circulating hIAPP level increase AD risk in T2DM patients. However, there is no hard evidence for the role of brain-derived hIAPP in the pathogenesis of AD. Nevertheless, oxidative stress, mitochondrial dysfunction, chaperon-mediated autophagy, heparan sulfate proteoglycan (HSPG), immune response, and zinc homeostasis in T2DM could be the possible mechanisms for the induction of the aggregation of hIAPP which increase AD risk. In conclusion, increasing hIAPP circulating levels in T2DM patients predispose them to the development and progression of AD. Dipeptidyl peptidase 4 (DPP4) inhibitors and glucagon-like peptide-1 (GLP-1) agonists attenuate AD in T2DM by inhibiting expression and deposition of hIAP.

Pathogenic Roles of Heparan Sulfate and Its Use as a Biomarker in Mucopolysaccharidoses

Heparan sulfate (HS) is an essential glycosaminoglycan (GAG) as a component of proteoglycans, which are present on the cell surface and in the extracellular matrix. HS-containing proteoglycans not only function as structural constituents of the basal lamina but also play versatile roles in various physiological processes, including cell signaling and organ development. Thus, inherited mutations of genes associated with the biosynthesis or degradation of HS can cause various diseases, particularly those involving the bones and central nervous system (CNS). Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders involving GAG accumulation throughout the body caused by a deficiency of GAG-degrading enzymes. GAGs are stored differently in different types of MPSs. Particularly, HS deposition is observed in patients with MPS types I, II, III, and VII, all which involve progressive neuropathy with multiple CNS system symptoms. While therapies are available for certain symptoms in some types of MPSs, significant unmet medical needs remain, such as neurocognitive impairment. This review presents recent knowledge on the pathophysiological roles of HS focusing on the pathogenesis of MPSs. We also discuss the possible use and significance of HS as a biomarker for disease severity and therapeutic response in MPSs.

Heparan Sulfate: A Regulator of White Adipocyte Differentiation and of Vascular/Adipocyte Interactions

White adipose tissues are major endocrine organs that release factors, termed adipokines, which affect other major organ systems. The development and functions of adipose tissues depend largely upon the glycosaminoglycan heparan sulfate. Heparan sulfate proteoglycans (HSPGs) surround both adipocytes and vascular structures and facilitate the communication between these two components. This communication mediates the continued export of adipokines from adipose tissues. Heparan sulfates regulate cellular physiology and communication through a sulfation code that ionically interacts with heparan-binding regions on a select set of proteins. Many of these proteins are growth factors and chemokines that regulate tissue function and inflammation. Cells regulate heparan sulfate sulfation through the release of heparanases and sulfatases. It is now possible to tissue engineer vascularized adipose tissues that express heparan sulfate proteoglycans. This makes it possible to use these tissue constructs to study the role of heparan sulfates in the regulation of adipokine production and release. It is possible to regulate the production of heparanases and sulfatases in order to fine-tune experimental studies.