Yin Chan

Normalization of obesity-associated insulin resistance through immunotherapy

Obesity and its associated metabolic syndromes represent a growing global challenge, yet mechanistic understanding of this pathology and current therapeutics are unsatisfactory. We discovered that CD4+ T lymphocytes, resident in visceral adipose tissue (VAT), control insulin resistance in mice with diet-induced obesity (DIO). Analyses of human tissue suggest that a similar process may also occur in humans. DIO VAT-associated T cells show severely biased T cell receptor Vα repertoires, suggesting antigen-specific expansion. CD4+ T lymphocyte control of glucose homeostasis is compromised in DIO progression, when VAT accumulates pathogenic interferon-γ (IFN-γ)-secreting T helper type 1 (TH1) cells, overwhelming static numbers of TH2 (CD4+GATA-binding protein-3 (GATA-3)+) and regulatory forkhead box P3 (Foxp3)+ T cells. CD4+ (but not CD8+) T cell transfer into lymphocyte-free Rag1-null DIO mice reversed weight gain and insulin resistance, predominantly through TH2 cells. In obese WT and ob/ob (leptin-deficient) mice, brief treatment with CD3-specific antibody or its F(ab′)2 fragment, reduces the predominance of TH1 cells over Foxp3+ cells, reversing insulin resistance for months, despite continuation of a high-fat diet. Our data suggest that the progression of obesity-associated metabolic abnormalities is under the pathophysiological control of CD4+ T cells. The eventual failure of this control, with expanding adiposity and pathogenic VAT T cells, can successfully be reversed by immunotherapy.

TRPV1+ Sensory Neurons Control β Cell Stress and Islet Inflammation in Autoimmune Diabetes

In type 1 diabetes, T cell-mediated death of pancreatic beta cells produces insulin deficiency. However, what attracts or restricts broadly autoreactive lymphocyte pools to the pancreas remains unclear. We report that TRPV1(+) pancreatic sensory neurons control islet inflammation and insulin resistance. Eliminating these neurons in diabetes-prone NOD mice prevents insulitis and diabetes, despite systemic persistence of pathogenic T cell pools. Insulin resistance and beta cell stress of prediabetic NOD mice are prevented when TRPV1(+) neurons are eliminated. TRPV1(NOD), localized to the Idd4.1 diabetes-risk locus, is a hypofunctional mutant, mediating depressed neurogenic inflammation. Delivering the neuropeptide substance P by intra-arterial injection into the NOD pancreas reverses abnormal insulin resistance, insulitis, and diabetes for weeks. Concordantly, insulin sensitivity is enhanced in trpv1(-/-) mice, whereas insulitis/diabetes-resistant NODxB6Idd4-congenic mice, carrying wild-type TRPV1, show restored TRPV1 function and insulin sensitivity. Our data uncover a fundamental role for insulin-responsive TRPV1(+) sensory neurons in beta cell function and diabetes pathoetiology.

Obesity predisposes to Th17 bias

Obesity is associated with numerous inflammatory conditions including atherosclerosis, autoimmune disease and cancer. Although the precise mechanisms are unknown, obesity‐associated rises in TNF‐α, IL‐6 and TGF‐β are believed to contribute. Here we demonstrate that obesity selectively promotes an expansion of the Th17 T‐cell sublineage, a subset with prominent pro‐inflammatory roles. T‐cells from diet‐induced obese mice expand Th17 cell pools and produce progressively more IL‐17 than lean littermates in an IL‐6‐dependent process. The increased Th17 bias was associated with more pronounced autoimmune disease as confirmed in two disease models, EAE and trinitrobenzene sulfonic acid colitis. In both, diet‐induced obese mice developed more severe early disease and histopathology with increased IL‐17+ T‐cell pools in target tissues. The well‐described association of obesity with inflammatory and autoimmune disease is mechanistically linked to a Th17 bias.

Targeting of Pancreatic Glia in Type 1 Diabetes

OBJECTIVE— Type 1 diabetes reflects autoimmune destruction of β-cells and peri-islet Schwann cells (pSCs), but the mechanisms of pSC death and the T-cell epitopes involved remain unclear. RESEARCH DESIGN AND METHODS— Primary pSC cultures were generated and used as targets in cytotoxic T-lymphocyte (CTL) assays in NOD mice. Cognate interaction between pSC and CD8+ T-cells was assessed by transgenic restoration of β2-microglobulin (β2m) to pSC in NOD.β2m−/− congenics. I-Ag7 and Kd epitopes in the pSC antigen glial fibrillary acidic protein (GFAP) were identified by peptide mapping or algorithms, respectively, and the latter tested by immunotherapy. RESULTS— pSC cultures did not express major histocompatibility complex (MHC) class II and were lysed by ex vivo CTLs from diabetic NOD mice. In vivo, restoration of MHC class I in GFAP-β2m transgenics significantly accelerated adoptively transferred diabetes. Target epitopes in the pSC autoantigen GFAP were mapped to residues 79–87 and 253–261 for Kd and 96–110, 116–130, and 216–230 for I-Ag7. These peptides were recognized spontaneously in NOD spleens as early as 2.5 weeks of age, with proliferative responses peaking around weaning and detectable lifelong. Several were also recognized by T-cells from new-onset type 1 diabetic patients. NOD mouse immunotherapy at 8 weeks with the CD8+ T-cell epitope, GFAP 79–87 but not 253–261, significantly inhibited type 1 diabetes and was associated with reduced γ-interferon production to whole protein GFAP. CONCLUSIONS— Collectively, these findings elucidate a role for pSC-specific CD8+ T-cells in islet inflammation and type 1 diabetes pathogenesis, further supporting neuronal involvement in β-cell demise.

Islet Glia, Neurons, and β Cells

Type 1 diabetes (T1D) is caused by autoimmune β cell destruction. The early events triggering T1D and the forces that keep diabetic autoimmunity pancreas specific have been unclear. Our discovery that autoimmune islet destruction is not β‐cell‐exclusive but includes cytotoxic T cell targeting of peri‐islet glia, evoked the possibility that T1D pathogenesis may involve neuronal elements beyond β cell/immune interactions. Recently, we have found that sensory afferent neurons are a critical component in prediabetes initiation, promoting islet inflammation through altered glucose homeostasis and progressive β cell stress. These factors orchestrate a catastrophic cascade culminating in insulin insufficiency mediated by an autoimmune‐prone host. This neuro‐immuno‐endocrinological triad explains diabetic inflammation as a consequence of local neuropeptide deficiency, leading to an innovative concept of disease pathogenesis with novel therapeutic implications.

'Sensing' the link between type 1 and type 2 diabetes.

Obesity‐associated insulin resistance is a core element of metabolic syndrome and type 2 diabetes (T2D). Notably, insulin resistance is also a feature of type 1 diabetes (T1D), where findings in the non‐obese diabetic mouse model have implicated transient receptor potential vanilloid‐1 (TRPV1+) sensory neurons in local islet inflammation and glucose metabolism. Here, we briefly review the role of TRPV1 in non‐obese diabetic (NOD) T1D pathogenesis, highlighting commonalities that suggest TRPV1 may contribute to obesity and T2D as well. With the recently discovered importance of adipose infiltrating lymphocytes in the metabolic disturbances of obesity and T2D, sensory innervation of fat may thus play an analogous role to sensory neurons in the islet—modulating neuroendocrine homeostasis and inflammation. In such a scenario, TRPV1+ sensory nerves would provide the pathoaetiological link connecting the shared metabolic and immunologic features of type 1 diabetes and T2D. Copyright