Acceleration of diabetes in young NOD mice with peritoneal macrophages

Lipid mediators and biomarkers associated with type 1 diabetes development

Type 1 diabetes (T1D) is a consequence of autoimmune β cell destruction, but the role of lipids in this process is unknown. We previously reported that activation of Ca2+-independent phospholipase A2β (iPLA2β) modulates polarization of macrophages (MΦ). Hydrolysis of the sn-2 substituent of glycerophospholipids by iPLA2β can lead to the generation of oxidized lipids (eicosanoids), pro- and antiinflammatory, which can initiate and amplify immune responses triggering β cell death. As MΦ are early triggers of immune responses in islets, we examined the impact of iPLA2β-derived lipids (iDLs) in spontaneous-T1D prone nonobese diabetic mice (NOD), in the context of MΦ production and plasma abundances of eicosanoids and sphingolipids. We find that (a) MΦNOD exhibit a proinflammatory lipid landscape during the prediabetic phase; (b) early inhibition or genetic reduction of iPLA2β reduces production of select proinflammatory lipids, promotes antiinflammatory MΦ phenotype, and reduces T1D incidence; (c) such lipid changes are reflected in NOD plasma during the prediabetic phase and at T1D onset; and (d) importantly, similar lipid signatures are evidenced in plasma of human subjects at high risk for developing T1D. These findings suggest that iDLs contribute to T1D onset and identify select lipids that could be targeted for therapeutics and, in conjunction with autoantibodies, serve as early biomarkers of pre-T1D.

A parasite-derived 68-mer peptide ameliorates autoimmune disease in murine models of Type 1 diabetes and multiple sclerosis

Helminth parasites secrete molecules that potently modulate the immune responses of their hosts and, therefore, have potential for the treatment of immune-mediated human diseases. FhHDM-1, a 68-mer peptide secreted by the helminth parasite Fasciola hepatica, ameliorated disease in two different murine models of autoimmunity, type 1 diabetes and relapsing-remitting immune-mediated demyelination. Unexpectedly, FhHDM-1 treatment did not affect the proliferation of auto-antigen specific T cells or their production of cytokines. However, in both conditions, the reduction in clinical symptoms was associated with the absence of immune cell infiltrates in the target organ (islets and the brain tissue). Furthermore, after parenteral administration, the FhHDM-1 peptide interacted with macrophages and reduced their capacity to secrete pro-inflammatory cytokines, such as TNF and IL-6. We propose this inhibition of innate pro-inflammatory immune responses, which are central to the initiation of autoimmunity in both diseases, prevented the trafficking of autoreactive lymphocytes from the periphery to the site of autoimmunity (as opposed to directly modulating their function per se), and thus prevented tissue destruction. The ability of FhHDM-1 to modulate macrophage function, combined with its efficacy in disease prevention in multiple models, suggests that FhHDM-1 has considerable potential as a treatment for autoimmune diseases.

A quantitative comparison of rates of phagocytosis and digestion of apoptotic cells by macrophages from normal (BALB/c) and diabetes-prone (NOD) mice

Macrophages play an important role in clearing apoptotic debris from tissue. Defective or reduced clearance, seen, for instance, in non-obese diabetic (NOD) mice, has been correlated with initiation of autoimmune (Type 1) diabetes (T1D) (O'Brien BA, Huang Y, Geng X, Dutz JP, Finegood DT. Diabetes 51: 2481-2488, 2002). To validate such a link, it is essential to quantify the reduced clearance (for example, by comparison to BALB/c control mice) and to determine which elements of that clearance are impaired. Recently, we fit data for the time course of in vitro macrophage feeding experiments to basic models of macrophage clearance dynamics, thus quantifying kinetics of uptake and digestion of apoptotic cells in both mouse strains (Marée AFM, Komba M, Dyck C, Łabeçki M, Finegood DT, Edelstein-Keshet L. J Theor Biol 233: 533-551, 2005). In the cycle of modeling and experimental investigation, we identified the importance of 1) measuring short-, intermediate-, and long-time data (to increase the accuracy of parameter fits), and 2) designing experiments with distinct observable regimes, including engulfment-only and digestion-only phases. Here, we report on new results from experiments so designed. In comparing macrophages from the two strains, we find that NOD macrophage engulfment of apoptotic cells is 5.5 times slower than BALB/c controls. Significantly, our new data demonstrate that digestion is at least two times slower in NOD, in contrast with previous conclusions. Moreover, new data enable us to detect an acceleration in engulfment (after the first engulfment) in both strains, but much smaller in NOD macrophages.

Protective role for cytosolic phospholipase A2alpha in autoimmune diabetes of mice

Cytosolic phospholipase A(2)alpha (cPLA(2)alpha) plays an important role in arachidonate pathway. To investigate the contribution of cPLA(2)alpha to autoimmune diabetes, we established non-obese diabetic (NOD) mouse, an excellent model for human type 1 diabetes, deficient in cPLA(2)alpha. These mice showed severe insulitis and a higher incidence of diabetes. In their macrophages, decreased prostaglandin E(2) (PGE(2)) induced by cPLA(2)alpha deficiency, and the increase in production of tumor necrosis factor (TNF)-alpha were observed. These results suggested that cPLA(2)alpha plays a protective role in progression of insulitis and development of autoimmune diabetes by suppression of TNF-alpha production from macrophages.

Quantifying macrophage defects in type 1 diabetes

Macrophages from animals prone to autoimmune (type 1) diabetes differ from those of diabetes-resistant animals in processing and clearing apoptotic cells. Using in vitro time-course assays of the number of engulfed apoptotic cells observed within macrophages, we quantified these differences in non-obese diabetic (NOD) versus Balb/c mice. Simple models lead to several elementary parameter estimation techniques. We used these to compute approximate rates of macrophage engulfment and digestion of apoptotic cells from basic features of the data (such as initial rise-times, phagocytic index and percent phagocytosis). Combining these estimates with full fitting of a sequence of model variants to the data, we find that macrophages from normal (Balb/c) mice engulf apoptotic cells up to four times faster than macrophages from the diabetes-prone (NOD) mice. Further, Balb/c macrophages appear to undergo an activation step before achieving their high engulfment rate. In NOD macrophages, we did not see evidence for this activation step. Rates of digestion of engulfed apoptotic cells by macrophages are similar in both types. Since macrophage clearance is an important mechanism of disposal of self-antigen, these macrophage defects could potentially be a factor in predisposition to type 1 diabetes.

Polymorphisms of chemokine and chemokine receptor genes in Type 1 diabetes mellitus and its complications

Cytokines and chemokines have been implicated in the pathogenesis of Type 1 diabetes mellitus (T1DM) and its microvascular complications. Recently, genetic variants of monocyte chemotactic protein-1 (MCP-1), CC-chemokine receptor 2 (CCR2), CC-chemokine receptor 5 (CCR5) genes have been identified. The aim was to investigate whether genetic variants of the MCP-1 G(-2518)A, CCR2B 64I, CCR5 G(59029)A, and CCR5 Delta32 are associated with T1DM and its microvascular complications. Two hundred and sixty patients with T1DM with and without diabetic microvascular complications, and 104 normal controls were recruited for this study. Genotypes of the MCP-1 G(-2518)A, CCR2B 64I, CCR5 G(59029)A, and CCR5 delta32 were performed by polymerase chain reaction followed by digestion with appropriate restriction endonucleases. Frequencies of the MCP-1 A(-2518) allele (74.6% vs. 63.5%, p < 0.003) and A/A genotype (54.5% vs. 34.6%, p < 0.001, Pc = 0.002) were significantly higher in patients with T1DM compared with normal controls. CCR5 G(59029) was slightly increased in the patients with microvascular complications compared with the uncomplicated (21.4% vs. 10%, p < 0.03, Pc = ns). The frequency of haplotype G/G/W was slightly increased in the patients with diabetic complications compared to the uncomplicated (39.6% vs. 28.8%, p < 0.02, Pc = ns). These results suggest that polymorphisms of the MCP-1, CCR2 and CCR5 genes may be associated with T1DM and its complications.

Human pancreatic islets produce and secrete MCP-1/CCL2: relevance in human islet transplantation

We investigated the capacity of human islets to produce monocyte chemoattractant protein-1 (MCP-1). Primary cultures of pancreatic islets expressed and secreted MCP-1, as determined by Northern blot, immunohistochemistry, in situ hybridization, and enzyme-linked immunosorbent assay. The produced MCP-1 was biologically active as it attracted monocytes in chemotaxis assay, and chemotactic activity was almost abrogated by a neutralizing anti-MCP-1 monoclonal antibody. Expression of MCP-1 was increased by primary inflammatory cytokines (interleukin-1 beta, tumor necrosis factor-alpha) and lipopolysaccharide at both the mRNA and protein levels but not by glucose. However, MCP-1 did not modulate insulin secretion. MCP-1 secreted by pancreatic islets plays a relevant role in the clinical outcome of islet transplant in patients with type 1 diabetes. In fact, low MCP-1 secretion resulted as the most relevant factor for long-lasting insulin independence. This finding opens new approaches in the management of human islet transplantation. Finally, the finding that MCP-1 appears constitutively present in normal human islet beta-cells (immunohistochemistry and in situ hybridization), in the absence of an inflammatory infiltrate, suggests that this chemokine could have functions other than monocyte recruitment and opens a new link between the endocrine and immune systems.

The APC1 concept of type I diabetes

Type I diabetes appears to be a T cell dependent disease. T cell reactivity is regulated by antigen presenting cells (APCs). In animal models of type I diabetes, abnormal reactivity of APCs, in particular of macrophages, probably is responsible for the progression of islet inflammation from T helper type 2 dependent benign periinsulitis to T helper type I dependent destructive intrainsulitis. The functional state of APCs during preferential stimulation of Th1 reactivities (APC1 state) is characterized by the release of TNFalpha, IL-12 and/or IL-18. The bias towards APC1 reactivity has been found due to defective inhibition via IL-10 and PGE2.