The RAGE/DIAPH1 Signaling Axis & Implications for the Pathogenesis of Diabetic Complications

Regulation of the AGEs-induced inflammatory response in human periodontal ligament cells via the AMPK/NF-κB/ NLRP3 signaling pathway

The heightened prevalence and accelerated progression of periodontitis in individuals with diabetes is primarily attributed to inflammatory responses in human periodontal ligament cells (HPDLCs). This study is aimed at delineating the regulatory mechanism of nucleotide-binding oligomerization domain-like receptors (NLRs) in mediating inflammation incited by muramyl dipeptide (MDP) in HPDLCs, under the influence of advanced glycation end products (AGEs), metabolic by-products associated with diabetes. We performed RNA-seq in HPDLCs induced by AGEs treatment and delineated activation markers for the receptor of AGEs (RAGE). It showed that advanced glycation end products modulate inflammatory responses in HPDLCs by activating NLRP1 and NLRP3 inflammasomes, which are further regulated through the NF-κB signaling pathway. Furthermore, AGEs synergize with NOD2, NLRP1, and NLRP3 inflammasomes to augment MDP-induced inflammation significantly.

Emerging roles of microRNAs as diagnostics and potential therapeutic interest in type 2 diabetes mellitus

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a metabolic disease of impaired glucose utilization. Uncontrolled high sugar levels lead to advanced glycation end products (AGEs), which affects several metabolic pathways by its receptor of advanced glycation end products (RAGE) and causes diabetic complication. MiRNAs are small RNA molecules which regulate genes linked to diabetes and affect AGEs pathogenesis, and target tissues, influencing health and disease processes.

AIM

To explore miRNA roles in T2DM's metabolic pathways for potential therapeutic and diagnostic advancements in diabetes complications.

METHODS

We systematically searched the electronic database PubMed using keywords. We included free, full-length research articles that evaluate the role of miRNAs in T2DM and its complications, focusing on genetic and molecular disease mechanisms. After assessing the full-length papers of the shortlisted articles, we included 12 research articles.

RESULTS

Several types of miRNAs are linked in metabolic pathways which are affected by AGE/RAGE axis in T2DM and its complications. miR-96-5p, miR-7-5p, miR-132, has_circ_0071106, miR-143, miR-21, miR-145-5p, and more are associated with various aspects of T2DM, including disease risk, diagnostic markers, complications, and gene regulation.

CONCLUSION

Targeting the AGE/RAGE axis, with a focus on miRNA regulation, holds promise for managing T2DM and its complications. MiRNAs have therapeutic potential as they can influence the metabolic pathways affected by AGEs and RAGE, potentially reducing inflammation, oxidative stress, and vascular complications. Additionally, miRNAs may serve as early diagnostic biomarkers for T2DM. Further research in this area may lead to innovative therapeutic strategies for diabetes and its associated complications.

Cannabidiol ameliorates inflammatory response partly by AGE-RAGE pathway in diabetic mice

Cannabidiol (CBD), the most abundant nonpsychoactive constituent of Cannabis sativa plant, is a promising potential pharmacotherapy for the treatment of diabetes and associated comorbidities. Previous studies have shown the potential of CBD to prevent diabetes in mice, the precise mechanisms of action remain unclear. The purpose of this study was to explore the mechanism of CBD alleviating hyperglycemia. The results demonstrated that CBD reduced blood glucose of STZ-induced diabetic mice without causing hypoglycemia. To elucidate the possible mechanisms of CBD effect, RNA-seq analysis was performed on high glucose-induced human mesangial cells (HMCs). By cluster analysis of differential genes, the results showed that advanced glycation end products-receptor of advanced glycation endproducts (AGE-RAGE) pathway-related genes CCL2 and interleukin-1β (IL-1β) play an important role in the biological of CBD. The expression of CCL2 and IL-1β were significantly increased in HMCs. Whereas, treatment with CBD decreased the expression of CCL2 and IL-1β. In addition, CBD significantly reduced AGE-RAGE levels in high glucose-induced HMCs. Similar results were confirmed in diabetic mice. In conclusion, we discovered for the first time that CBD ameliorates hyperglycemia partly through AGE-RAGE mediated CCL2/IL-1β pathway.

RAGE/DIAPH1 and atherosclerosis through an evolving lens: Viewing the cell from the "Inside - Out"

BACKGROUND AND AIMS

In hyperglycemia, inflammation, oxidative stress and aging, Damage Associated Molecular Patterns (DAMPs) accumulate in conditions such as atherosclerosis. Binding of DAMPs to receptors such as the receptor for advanced glycation end products (RAGE) activates signal transduction cascades that contribute to cellular stress. The cytoplasmic domain (tail) of RAGE (ctRAGE) binds to the formin Diaphanous1 (DIAPH1), which is important for RAGE signaling. This Review will detail the evidence linking the RAGE/DIAPH1 signaling pathway to atherosclerosis and envisages future therapeutic opportunities from the "inside-out" point of view in affected cells.

METHODS

PubMed was searched using a variety of search terms, including "receptor for advanced glycation end products" along with various combinations including "and atherosclerosis," "soluble RAGE and atherosclerosis," "statins and RAGE," "PPAR and RAGE" and "SGLT2 inhibitor and RAGE."

RESULTS

In non-diabetic and diabetic mice, antagonism or global deletion of Ager (the gene encoding RAGE) retards progression and accelerates regression of atherosclerosis. Global deletion of Diaph1 in mice devoid of the low density lipoprotein receptor (Ldlr) significantly attenuates atherosclerosis; mice devoid of both Diaph1 and Ldlr display significantly lower plasma and liver concentrations of cholesterol and triglyceride compared to mice devoid of Ldlr. Associations between RAGE pathway and human atherosclerosis have been identified based on relationships between plasma/serum concentrations of RAGE ligands, soluble RAGEs and atherosclerosis.

CONCLUSIONS

Efforts to target RAGE/DIAPH1 signaling through a small molecule antagonist therapeutic strategy hold promise to quell accelerated atherosclerosis in diabetes and in other forms of cardiovascular disease.

Human intestine and placenta exhibit tissue-specific expression of RAGE isoforms

The receptor for advanced glycation end products (RAGE) is encoded by AGER, a gene that is subjected to tissue-specific alternative splicing. Splice variants of RAGE in intestine and placenta are unknown and contradictory data concerning RAGE protein expression in these tissues have been published. As a basis for future functional studies, we examined RAGE expression in small intestine, colon and placentas. PCR cloning revealed that full-length RAGE is the only RAGE transcript isoform expressed in placenta. In the small intestine, the major transcript isoform detected was RAGE_v1 encoding the C-terminally truncated soluble receptor. In the colon, both full-length RAGE as well as several splice variants were identified. Four antibodies were used to study protein expression by immunoblotting and were carefully validated. Appropriate controls were essential to avoid misinterpretation of bands caused by non-specific reactivity of antibodies. Only one of four antibodies tested detected full-length RAGE in placenta, whereas no RAGE-specific band was detected in intestinal tissues despite loading >30-fold more intestinal tissue than the positive control, human lung. RAGE expression levels in the placenta were 100-fold lower compared with human lung when analyzed by ELISA, and no significant differences in RAGE expression were detected between healthy placentas and placentas from women with preeclampsia, gestational diabetes mellitus, or fetal growth restriction. We conclude that healthy placental chorionic tissue expresses low levels of full-length RAGE, whereas expression of the tissue-specific intestinal isoforms is below the limit of detection. Low RAGE expression levels in combination with a lack of antibody validation may explain the conflicting published results on RAGE protein expression in intestine and placenta.

Novel insights into the nervous system affected by prolonged hyperglycemia

Multiple molecular pathways including the receptor for advanced glycation end-products-diaphanous related formin 1 (RAGE-Diaph1) signaling are known to play a role in diabetic peripheral neuropathy (DPN). Evidence suggests that neuropathological alterations in type 1 diabetic spinal cord may occur at the same time as or following peripheral nerve abnormalities. We demonstrated that DPN was associated with perturbations of RAGE-Diaph1 signaling pathway in peripheral nerve accompanied by widespread spinal cord molecular changes. More than 500 differentially expressed genes (DEGs) belonging to multiple functional pathways were identified in diabetic spinal cord and of those the most enriched was RAGE-Diaph1 related PI3K-Akt pathway. Only seven of spinal cord DEGs overlapped with DEGs from type 1 diabetic sciatic nerve and only a single gene cathepsin E (CTSE) was common for both type 1 and type 2 diabetic mice. In silico analysis suggests that molecular changes in spinal cord may act synergistically with RAGE-Diaph1 signaling axis in the peripheral nerve. KEY MESSAGES: Molecular perturbations in spinal cord may be involved in the progression of diabetic peripheral neuropathy. Diabetic peripheral neuropathy was associated with perturbations of RAGE-Diaph1 signaling pathway in peripheral nerve accompanied by widespread spinal cord molecular changes. In silico analysis revealed that PI3K-Akt signaling axis related to RAGE-Diaph1 was the most enriched biological pathway in diabetic spinal cord. Cathepsin E may be the target molecular hub for intervention against diabetic peripheral neuropathy.

Clinical Pathobiochemistry of Vitamin B12 Deficiency: Improving Our Understanding by Exploring Novel Mechanisms with a Focus on Diabetic Neuropathy

Vitamin B₁₂ (B₁₂) is an essential cofactor of two important biochemical pathways, the degradation of methylmalonic acid and the synthesis of methionine from homocysteine. Methionine is an important donor of methyl groups for numerous biochemical reactions, including DNA synthesis and gene regulation. Besides hematological abnormalities (megaloblastic anemia or even pancytopenia), a deficiency in B₁₂ may cause neurological symptoms, including symptoms resembling diabetic neuropathy. Although extensively studied, the underlining molecular mechanism for the development of diabetic peripheral neuropathy (DPN) is still unclear. Most studies have found a contribution of oxidative stress in the development of DPN. Detailed immunohistochemical investigations in sural nerve biopsies obtained from diabetic patients with DPN point to an activation of inflammatory pathways induced via elevated advanced glycation end products (AGE), ultimately resulting in increased oxidative stress. Similar results have been found in patients with B₁₂ deficiency, indicating that the observed neural changes in patients with DPN might be caused by cellular B₁₂ deficiency. Since novel results show that B₁₂ exerts intrinsic antioxidative activity in vitro and in vivo, B₁₂ may act as an intracellular, particularly as an intramitochondrial, antioxidant, independent from its classical, well-known cofactor function. These novel findings may provide a rationale for the use of B₁₂ for the treatment of DPN, even in subclinical early states.

An Introduction to the Special Issue "Protein Glycation in Food, Nutrition, Health and Disease"

On 20-24 September 2021, leading researchers in the field of glycation met online at the 14th International Symposium on the Maillard Reaction (IMARS-14), hosted by the authors of this introductory editorial, who are from Doha, Qatar [...].