Similarities Between Bacterial GAD and Human GAD65: Implications in Gut Mediated Autoimmune Type 1 Diabetes

Abstract A variety of islet autoantibodies (AAbs) can predict and possibly dictate eventual type 1 diabetes (T1D) diagnosis. Upwards of 75% of those with T1D are positive for AAbs against glutamic acid decarboxylase (GAD65), a producer of gamma-aminobutyric acid (GABA) in human pancreatic beta cells. Interestingly, bacterial populations within the human gut also express GAD65 and produce GABA. Evidence suggests that dysbiosis of the microbiome may correlate with T1D pathogenesis and physiology. Therefore, autoimmune linkages between the gut microbiome and islets susceptible to autoimmune attack need to be further elucidated. Utilizing silico analyses, we show here that 25 GAD sequences from different human gut bacterial sources show sequence and motif similarities to human beta cell GAD65. Our motif analyses determined that a majority of gut GAD sequences contain the pyroxical dependent decarboxylase domain of human GAD65 which is important for its enzymatic activity. Additionally, we showed overlap with known human GAD65 T-cell receptor epitopes which may implicate the immune destruction of beta cells. Thus, we propose a physiological hypothesis in which changes in the gut microbiome in those with T1D result in a release of bacterial GAD, thus causing miseducation of the host immune system. Due to the notable similarities, we found between humans and bacterial GAD, these deputized immune cells may then go on to target human beta cells leading to the development of T1D.

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Endogenous Levels of Gamma Amino-Butyric Acid Are Correlated to Glutamic-Acid Decarboxylase Antibody Levels in Type 1 Diabetes

Biomedicines ◽

10.3390/biomedicines10010091 ◽

2021 ◽

Vol 10 (1) ◽

pp. 91

Author(s):

Henrik Hill ◽

Andris Elksnis ◽

Per Lundkvist ◽

Kumari Ubhayasekera ◽

Jonas Bergquist ◽

...

Keyword(s):

Type 1 Diabetes ◽

Glutamic Acid ◽

Beta Cells ◽

Glutamic Acid Decarboxylase ◽

Pancreatic Beta Cells ◽

Drug Candidate ◽

Acid Decarboxylase ◽

Diabetes Research ◽

Gad Autoantibodies

Gamma-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the central nervous system (CNS) and outside of the CNS, found in the highest concentrations in immune cells and pancreatic beta-cells. GABA is gaining increasing interest in diabetes research due to its immune-modulatory and beta-cell stimulatory effects and is a highly interesting drug candidate for the treatment of type 1 diabetes (T1D). GABA is synthesized from glutamate by glutamic acid decarboxylase (GAD), one of the targets for autoantibodies linked to T1D. Using mass spectrometry, we have quantified the endogenous circulating levels of GABA in patients with new-onset and long-standing T1D and found that the levels are unaltered when compared to healthy controls, i.e., T1D patients do not have a deficit of systemic GABA levels. In T1D, GABA levels were negatively correlated with IL-1 beta, IL-12, and IL-15 15 and positively correlated to levels of IL-36 beta and IL-37. Interestingly, GABA levels were also correlated to the levels of GAD-autoantibodies. The unaltered levels of GABA in T1D patients suggest that the GABA secretion from beta-cells only has a minor impact on the circulating systemic levels. However, the local levels of GABA could be altered within pancreatic islets in the presence of GAD-autoantibodies.

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Replacing murine insulin 1 with human insulin protects NOD mice from diabetes

10.1101/823393 ◽

2019 ◽

Author(s):

Colleen M. Elso ◽

Nicholas A. Scott ◽

Lina Mariana ◽

Emma I. Masterman ◽

Andrew P.R. Sutherland ◽

...

Keyword(s):

Type 1 Diabetes ◽

Beta Cells ◽

Mouse Models ◽

Human Insulin ◽

Murine Model ◽

Pancreatic Beta Cells ◽

Autoimmune Diabetes ◽

Nod Mice ◽

Human Type 1 Diabetes

AbstractType 1, or autoimmune, diabetes is caused by the T-cell mediated destruction of the insulin-producing pancreatic beta cells. Non-obese diabetic (NOD) mice spontaneously develop autoimmune diabetes akin to human type 1 diabetes. For this reason, the NOD mouse has been the preeminent murine model for human type 1 diabetes research for several decades. However, humanized mouse models are highly sought after because they offer both the experimental tractability of a mouse model and the clinical relevance of human-based research. Autoimmune T-cell responses against insulin, and its precursor proinsulin, play central roles in the autoimmune responses against pancreatic beta cells in both humans and NOD mice. As a first step towards developing a murine model of the human autoimmune response against pancreatic beta cells we set out to replace the murine insulin 1 gene (Ins1) with the human insulin gene (INS) using CRISPR/Cas9. Here we describe a NOD mouse strain that expresses human insulin in place of murine insulin 1, referred to as HuPI. HuPI mice express human insulin, and C-peptide, in their serum and pancreata and have normal glucose tolerance. Compared with wild type NOD mice, the incidence of diabetes is much lower in HuPI mice. Only 15-20% of HuPI mice developed diabetes after 300 days, compared to more than 60% of unmodified NOD mice. Immune-cell infiltration into the pancreatic islets of HuPI mice was not detectable at 100 days but was clearly evident by 300 days. This work highlights the feasibility of using CRISPR/Cas9 to create mouse models of human diseases that express proteins pivotal to the human disease. Furthermore, it reveals that even subtle changes in proinsulin protect NOD mice from diabetes.

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Peroxiredoxin 6 Attenuates Alloxan-Induced Type 1 Diabetes Mellitus in Mice and Cytokine-Induced Cytotoxicity in RIN-m5F Beta Cells

Journal of Diabetes Research ◽

10.1155/2020/7523892 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Elena G. Novoselova ◽

Olga V. Glushkova ◽

Sergey M. Lunin ◽

Maxim O. Khrenov ◽

Svetlana B. Parfenyuk ◽

...

Keyword(s):

Type 1 Diabetes ◽

Beta Cells ◽

Cell Apoptosis ◽

Pancreatic Beta Cells ◽

Apoptotic Cell ◽

Main Idea ◽

Severe Form ◽

Peroxiredoxin 6 ◽

Cells Cultured

Type 1 diabetes is associated with the destruction of pancreatic beta cells, which is mediated via an autoimmune mechanism and consequent inflammatory processes. In this article, we describe a beneficial effect of peroxiredoxin 6 (PRDX6) in a type 1 diabetes mouse model. The main idea of this study was based on the well-known data that oxidative stress plays an important role in pathogenesis of diabetes and its associated complications. We hypothesised that PRDX6, which is well known for its various biological functions, including antioxidant activity, may provide an antidiabetic effect. It was shown that PRDX6 prevented hyperglycemia, lowered the mortality rate, restored the plasma cytokine profile, reversed the splenic cell apoptosis, and reduced the β cell destruction in Langerhans islets in mice with a severe form of alloxan-induced diabetes. In addition, PRDX6 protected rat insulinoma RIN-m5F β cells, cultured with TNF-α and IL-1β, against the cytokine-induced cytotoxicity and reduced the apoptotic cell death and production of ROS. Signal transduction studies showed that PRDX6 prevented the activation of NF-κB and c-Jun N-terminal kinase signaling cascades in RIN-m5F β cells cultured with cytokines. In conclusion, there is a prospect for therapeutic application of PRDX6 to delay or even prevent β cell apoptosis in type 1 diabetes.

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Nano-curcumin safely prevents streptozotocin-induced inflammation and apoptosis in pancreatic beta cells for effective management of Type 1 diabetes mellitus

British Journal of Pharmacology ◽

10.1111/bph.13816 ◽

2017 ◽

Vol 174 (13) ◽

pp. 2074-2084 ◽

Cited By ~ 29

Author(s):

Raghu Ganugula ◽

Meenakshi Arora ◽

Patcharawalai Jaisamut ◽

Ruedeekorn Wiwattanapatapee ◽

Heather G Jørgensen ◽

...

Keyword(s):

Diabetes Mellitus ◽

Type 1 Diabetes ◽

Type 1 Diabetes Mellitus ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Effective Management

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Membrane anchoring of the autoantigen GAD65 to microvesicles in pancreatic beta-cells by palmitoylation in the NH2-terminal domain.

The Journal of Cell Biology ◽

10.1083/jcb.118.2.309 ◽

1992 ◽

Vol 118 (2) ◽

pp. 309-320 ◽

Cited By ~ 121

Author(s):

S Christgau ◽

H J Aanstoot ◽

H Schierbeck ◽

K Begley ◽

S Tullin ◽

...

Keyword(s):

Beta Cells ◽

Pancreatic Beta Cells ◽

Immunogold Electron Microscopy ◽

Acid Decarboxylase ◽

Gamma Aminobutyric Acid ◽

Beta Cell Destruction ◽

Terminal Domain ◽

Membrane Anchoring ◽

Major Target ◽

Hydrophilic Molecule

Pancreatic beta-cells and gamma-aminobutyric acid (GABA)-secreting neurons both express the enzyme glutamic acid decarboxylase (GAD) which is a major target of autoantibodies associated with beta-cell destruction and impairment of GABA-ergic neurotransmitter pathways. The predominant form of GAD in pancreatic beta-cells, GAD65, is synthesized as a soluble hydrophilic molecule, which is modified to become firmly membrane anchored. Here we show by immunogold electron microscopy that GAD65 is localized to the membrane of small vesicles which are identical in size to small synaptic-like microvesicles in pancreatic beta-cells. The NH2-terminal domain of GAD65 is the site of a two-step modification, the last of which results in a firm membrane anchoring that involves posttranslational hydroxylamine sensitive palmitoylation. GAD65 can be released from the membrane by an apparent enzyme activity in islets, suggesting that the membrane anchoring step is reversible and potentially regulated. The hydrophobic modifications and consequent membrane anchoring of GAD65 to microvesicles that store its product GABA may be of functional importance and, moreover, significant for its selective role as an autoantigen.

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Beta Cell Autophagy in the Pathogenesis of Type 1 Diabetes

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00151.2021 ◽

2021 ◽

Author(s):

Charanya Muralidharan ◽

Amelia K Linnemann

Keyword(s):

Type 1 Diabetes ◽

Beta Cell ◽

Beta Cells ◽

Pancreatic Beta Cells ◽

Potential Role ◽

Cell Dysfunction ◽

Unconventional Secretion ◽

Insulin Dependent

Type 1 diabetes is an insulin-dependent, autoimmune disease where the pancreatic beta cells are destroyed resulting in hyperglycemia. This multi-factorial disease involves multiple environmental and genetic factors, and has no clear etiology. Accumulating evidence suggests that early signaling defects within the beta cells may promote a change in the local immune mileu, contributing to autoimmunity. Therefore, many studies have been focused on intrinsic beta cell mechanisms that aid in restoration of cellular homeostasis under environmental conditions that cause dysfunction. One of these intrinsic mechanisms to promote homeostasis is autophagy, defects in which are clearly linked with beta cell dysfunction in the context of type 2 diabetes. Recent studies have now also pointed towards beta cell autophagy defects in the context of type 1 diabetes. In this perspectives review, we will discuss the evidence supporting a role for beta cell autophagy in the pathogenesis of type 1 diabetes, including a potential role for unconventional secretion of autophagosomes/lysosomes in the changing dialogue between the beta cell and immune cells.

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The intermediate proteasome is constitutively expressed in pancreatic beta cells and upregulated by stimulatory, non-toxic concentrations of interleukin 1 β

10.1101/753061 ◽

2019 ◽

Author(s):

Muhammad Saad Khilji ◽

Danielle Verstappen ◽

Tina Dahlby ◽

Michala Cecilie Burstein Prause ◽

Celina Pihl ◽

...

Keyword(s):

Type 1 Diabetes ◽

Mhc Class I ◽

Pancreatic Beta Cells ◽

Interleukin 1 ◽

Class I ◽

Β Cells ◽

Autoimmune Attack ◽

Active Intermediate ◽

Toxic Concentrations

AbstractA central and still open question regarding the pathogenesis of autoimmune diseases, such as type 1 diabetes, concerns the processes that underlie the generation of MHC-presented autoantigenic epitopes that become targets of autoimmune attack. Proteasomal degradation is a key step in processing of proteins for MHC class I presentation. Different types of proteasomes can be expressed in cells dictating the repertoire of peptides presented by the MHC class I complex. Of particular interest for type 1 diabetes is the proteasomal configuration of pancreatic β cells, as this might facilitate autoantigen presentation by β cells and thereby their T-cell mediated destruction. Here we investigated whether so-called inducible subunits of the proteasome are constitutively expressed in β cells, regulated by inflammatory signals and participate in the formation of active intermediate or immuno-proteasomes.We show that inducible proteasomal subunits are constitutively expressed in human and rodent islets and an insulin-secreting cell-line. Moreover, the β5i subunit is incorporated into active intermediate proteasomes that are bound to 19S or 11S regulatory particles. Finally, inducible subunit expression along with increase in total proteasome activities are further upregulated by non-toxic concentrations of IL-1β stimulating proinsulin biosynthesis. These findings suggest that the β cell proteasomal repertoire is more diverse than assumed previously and may be highly responsive to a local inflammatory islet environment.

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BET Proteins Are Required for Transcriptional Activation of the Senescent Islet Cell Secretome in Type 1 Diabetes

International Journal of Molecular Sciences ◽

10.3390/ijms20194776 ◽

2019 ◽

Vol 20 (19) ◽

pp. 4776 ◽

Cited By ~ 4

Author(s):

Peter J. Thompson ◽

Ajit Shah ◽

Hara Apostolopolou ◽

Anil Bhushan

Keyword(s):

Type 1 Diabetes ◽

Beta Cells ◽

Transcriptional Activation ◽

Pancreatic Beta Cells ◽

Islet Cells ◽

Disease Onset ◽

Protein Inhibition ◽

Bet Protein

Type 1 diabetes (T1D) results from the progressive loss of pancreatic beta cells as a result of autoimmune destruction. We recently reported that during the natural history of T1D in humans and the female nonobese diabetic (NOD) mouse model, beta cells acquire a senescence-associated secretory phenotype (SASP) that is a major driver of disease onset and progression, but the mechanisms that activate SASP in beta cells were not explored. Here, we show that the SASP in islet cells is transcriptionally controlled by Bromodomain ExtraTerminal (BET) proteins, including Bromodomain containing protein 4 (BRD4). A chromatin analysis of key beta cell SASP genes in NOD islets revealed binding of BRD4 at active regulatory regions. BET protein inhibition in NOD islets diminished not only the transcriptional activation and secretion of SASP factors, but also the non-cell autonomous activity. BET protein inhibition also decreased the extent of SASP induction in human islets exposed to DNA damage. The BET protein inhibitor iBET-762 prevented diabetes in NOD mice and also attenuated SASP in islet cells in vivo. Taken together, our findings support a crucial role for BET proteins in the activation of the SASP transcriptional program in islet cells. These studies suggest avenues for preventing T1D by transcriptional inhibition of SASP.

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