Characterization of Host-Pathogen-Device Interactions in Pseudomonas aeruginosa Infection of Breast Implants.

BACKGROUND: Pseudomonas aeruginosa accounts for 7 to 22 percent of breast implant-associated infections, which can result in reconstructive failures and explantation. Investigating host-pathogen-device interactions in mice and patient samples will improve the understanding of colonization mechanisms, for targeted treatments and clinical guidelines. METHODS: Mice with and without implants were infected with PAO1 laboratory strain or BIP2 or BIP16 clinical strains and killed at 1 day or 7 days after infection to evaluate for colonization of implants and underlying tissues by means of colony-forming unit enumeration. Immunostaining was performed on mouse implants, human tissue expanders colonized by BIP2, and acellular dermal matrix colonized by BIP16. RESULTS: Colonization of tissues and smooth implants by P. aeruginosa was strain-dependent: at 1 day after infection, all strains acutely infected tissues with and without implants with colonization levels reflecting growth rates of individual strains. At 7 days after infection, PAO1 caused colonization of approximately 10 5 colony-forming units/100 mg of tissue but required implant presence, whereas in mice infected with BIP2/BIP16, colony-forming units were below the limit of detection with or without implants. Immunofluorescence staining of mouse implants, however, demonstrated continued presence of BIP2 and BIP16. Staining showed co-localization of all strains with fibrinogen, collagen I, and collagen III on mouse and human samples. CONCLUSIONS: The trajectory of P. aeruginosa in breast implant-associated infections was strain-dependent, and strains could exhibit acute symptomatic or chronic asymptomatic colonization. With strains causing clinical symptoms, the presence of an implant significantly worsened infection. For asymptomatic colonizers, further studies investigating their long-term impacts, especially during periods of immunosuppression in hosts, are needed.

Mucosal infection rewires TNFɑ signaling dynamics to skew susceptibility to recurrence.

A mucosal infectious disease episode can render the host either more or less susceptible to recurrent infection, but the specific mechanisms that tip the balance remain unclear. We investigated this question in a mouse model of recurrent urinary tract infection and found that a prior bladder infection resulted in an earlier onset of tumor necrosis factor-alpha (TNFɑ)-mediated bladder inflammation upon subsequent bacterial challenge, relative to age-matched naive mice. However, the duration of TNFɑ signaling activation differed according to whether the first infection was chronic (Sensitized) or self-limiting (Resolved). TNFɑ depletion studies revealed that transient early-phase TNFɑ signaling in Resolved mice promoted clearance of bladder-colonizing bacteria via rapid recruitment of neutrophils and subsequent exfoliation of infected bladder cells. In contrast, sustained TNFɑ signaling in Sensitized mice prolonged damaging inflammation, worsening infection. This work reveals how TNFɑ signaling dynamics can be rewired by a prior infection to shape diverse susceptibilities to future mucosal infections.

Host restriction of Escherichia coli recurrent urinary tract infection occurs in a bacterial strain-specific manner.

Urinary tract infections (UTI) are extremely common and can be highly recurrent, with 1-2% of women suffering from six or more recurrent episodes per year. The high incidence of recurrent UTI, including recurrent infections caused by the same bacterial strain that caused the first infection, suggests that at least some women do not mount a protective adaptive immune response to UTI. Here we observed in a mouse model of cystitis (bladder infection) that infection with two different clinical uropathogenic Escherichia coli (UPEC) isolates, UTI89 or CFT073, resulted in different kinetics of bacterial clearance and different susceptibility to same-strain recurrent infection. UTI89 and CFT073 both caused infections that persisted for at least two weeks in similar proportions of mice, but whereas UTI89 infections could persist indefinitely, CFT073 infections began to clear two weeks after inoculation and were uniformly cleared within eight weeks. Mice with a history of CFT073 cystitis lasting four weeks were protected against recurrent CFT073 infection after antibiotic therapy, but were not protected against challenge with UTI89. In contrast, mice with a history of UTI89 cystitis lasting four weeks were highly susceptible to challenge infection with either strain after antibiotic treatment. We found that depletion of CD4+ and CD8+ T cell subsets impaired the ability of the host to clear CFT073 infections and rendered mice with a history of CFT073 cystitis lasting four weeks susceptible to recurrent CFT073 cystitis upon challenge. Our findings demonstrate the complex interplay between the broad genetic diversity of UPEC and the host innate and adaptive immune responses during UTI. A better understanding of these host-pathogen interactions is urgently needed for effective drug and vaccine development in the era of increasing antibiotic resistance.

A complement-microglial axis drives synapse loss during virus-induced memory impairment.

Over 50% of patients who survive neuroinvasive infection with West Nile virus (WNV) exhibit chronic cognitive sequelae. Although thousands of cases of WNV-mediated memory dysfunction accrue annually, the mechanisms responsible for these impairments are unknown. The classical complement cascade, a key component of innate immune pathogen defence, mediates synaptic pruning by microglia during early postnatal development. Here we show that viral infection of adult hippocampal neurons induces complement-mediated elimination of presynaptic terminals in a murine WNV neuroinvasive disease model. Inoculation of WNV-NS5-E218A, a WNV with a mutant NS5(E218A) protein leads to survival rates and cognitive dysfunction that mirror human WNV neuroinvasive disease. WNV-NS5-E218A-recovered mice (recovery defined as survival after acute infection) display impaired spatial learning and persistence of phagocytic microglia without loss of hippocampal neurons or volume. Hippocampi from WNV-NS5-E218A-recovered mice with poor spatial learning show increased expression of genes that drive synaptic remodelling by microglia via complement. C1QA was upregulated and localized to microglia, infected neurons and presynaptic terminals during WNV neuroinvasive disease. Murine and human WNV neuroinvasive disease post-mortem samples exhibit loss of hippocampal CA3 presynaptic terminals, and murine studies revealed microglial engulfment of presynaptic terminals during acute infection and after recovery. Mice with fewer microglia (Il34(-/-) mice with a deficiency in IL-34 production) or deficiency in complement C3 or C3a receptor were protected from WNV-induced synaptic terminal loss. Our study provides a new murine model of WNV-induced spatial memory impairment, and identifies a potential mechanism underlying neurocognitive impairment in patients recovering from WNV neuroinvasive disease.

CCR5 limits cortical viral loads during West Nile virus infection of the central nervous system.

BACKGROUND: Cell-mediated immunity is critical for clearance of central nervous system (CNS) infection with the encephalitic flavivirus, West Nile virus (WNV). Prior studies from our laboratory have shown that WNV-infected neurons express chemoattractants that mediate recruitment of antiviral leukocytes into the CNS. Although the chemokine receptor, CCR5, has been shown to play an important role in CNS host defense during WNV infection, regional effects of its activity within the infected brain have not been defined. METHODS: We used CCR5-deficient mice and an established murine model of WNV encephalitis to determine whether CCR5 activity impacts on WNV levels within the CNS in a region-specific fashion. Statistical comparisons between groups were made with one- or two-way analysis of variance; Bonferroni's post hoc test was subsequently used to compare individual means. Survival was analyzed by the log-rank test. Analyses were conducted using Prism software (GraphPad Prism). All data were expressed as means ± SEM. Differences were considered significant if P ≤ 0.05. RESULTS: As previously shown, lack of CCR5 activity led to increased symptomatic disease and mortality in mice after subcutaneous infection with WNV. Evaluation of viral burden in the footpad, draining lymph nodes, spleen, olfactory bulb, and cerebellum derived from WNV-infected wild-type, and CCR5(-/-) mice showed no differences between the genotypes. In contrast, WNV-infected, CCR5(-/-) mice exhibited significantly increased viral burden in cortical tissues, including the hippocampus, at day 8 post-infection. CNS regional studies of chemokine expression via luminex analysis revealed significantly increased expression of CCR5 ligands, CCL4 and CCL5, within the cortices of WNV-infected, CCR5(-/-) mice compared with those of similarly infected WT animals. Cortical elevations in viral loads and CCR5 ligands in WNV-infected, CCR5(-/-) mice, however, were associated with decreased numbers of infiltrating mononuclear cells and increased permeability of the blood-brain barrier. CONCLUSIONS: These data indicate that regional differences in chemokine expression occur in response to WNV infection of the CNS, and that cortical neurons require CCR5 activity to limit viral burden in this brain region.

Enhanced sphingosine-1-phosphate receptor 2 expression underlies female CNS autoimmunity susceptibility.

Multiple sclerosis (MS) is an inflammatory disease of the CNS that is characterized by BBB dysfunction and has a much higher incidence in females. Compared with other strains of mice, EAE in the SJL mouse strain models multiple features of MS, including an enhanced sensitivity of female mice to disease; however, the molecular mechanisms that underlie the sex- and strain-dependent differences in disease susceptibility have not been described. We identified sphingosine-1-phosphate receptor 2 (S1PR2) as a sex- and strain-specific, disease-modifying molecule that regulates BBB permeability by destabilizing adherens junctions. S1PR2 expression was increased in disease-susceptible regions of the CNS of both female SJL EAE mice and female patients with MS compared with their male counterparts. Pharmacological blockade or lack of S1PR2 signaling decreased EAE disease severity as the result of enhanced endothelial barrier function. Enhanced S1PR2 signaling in an in vitro BBB model altered adherens junction formation via activation of Rho/ROCK, CDC42, and caveolin endocytosis-dependent pathways, resulting in loss of apicobasal polarity and relocation of abluminal CXCL12 to vessel lumina. Furthermore, S1PR2-dependent BBB disruption and CXCL12 relocation were observed in vivo. These results identify a link between S1PR2 signaling and BBB polarity and implicate S1PR2 in sex-specific patterns of disease during CNS autoimmunity.

CXCR7 antagonism prevents axonal injury during experimental autoimmune encephalomyelitis as revealed by in vivo axial diffusivity.

BACKGROUND: Multiple Sclerosis (MS) is characterized by the pathological trafficking of leukocytes into the central nervous system (CNS). Using the murine MS model, experimental autoimmune encephalomyelitis (EAE), we previously demonstrated that antagonism of the chemokine receptor CXCR7 blocks endothelial cell sequestration of CXCL12, thereby enhancing the abluminal localization of CXCR4-expressing leukocytes. CXCR7 antagonism led to decreased parenchymal entry of leukocytes and amelioration of ongoing disease during EAE. Of note, animals that received high doses of CXCR7 antagonist recovered to baseline function, as assessed by standard clinical scoring. Because functional recovery reflects axonal integrity, we utilized diffusion tensor imaging (DTI) to evaluate axonal injury in CXCR7 antagonist- versus vehicle-treated mice after recovery from EAE. METHODS: C57BL6/J mice underwent adoptive transfer of MOG-reactive Th1 cells and were treated daily with either CXCR7 antagonist or vehicle for 28 days; and then evaluated by DTI to assess for axonal injury. After imaging, spinal cords underwent histological analysis of myelin and oligodendrocytes via staining with luxol fast blue (LFB), and immunofluorescence for myelin basic protein (MBP) and glutathione S-transferase-π (GST-π). Detection of non-phosphorylated neurofilament H (NH-F) was also performed to detect injured axons. Statistical analysis for EAE scores, DTI parameters and non-phosphorylated NH-F immunofluorescence were done by ANOVA followed by Bonferroni post-hoc test. For all statistical analysis a p < 0.05 was considered significant. RESULTS: In vivo DTI maps of spinal cord ventrolateral white matter (VLWM) axial diffusivities of naïve and CXCR7 antagonist-treated mice were indistinguishable, while vehicle-treated animals exhibited decreased axial diffusivities. Quantitative differences in injured axons, as assessed via detection of non-phosphorylated NH-F, were consistent with axial diffusivity measurements. Overall, qualitative myelin content and presence of oligodendrocytes were similar in all treatment groups, as expected by their radial diffusivity values. Quantitative assessment of persistent inflammatory infiltrates revealed significant decreases within the parenchyma of CXCR7 antagonist-treated mice versus controls. CONCLUSIONS: These data suggest that CXCR7 antagonism not only prevents persistent inflammation but also preserves axonal integrity. Thus, targeting CXCR7 modifies both disease severity and recovery during EAE, suggesting a role for this molecule in both phases of disease.

CXCR7 influences leukocyte entry into the CNS parenchyma by controlling abluminal CXCL12 abundance during autoimmunity.

Loss of CXCL12, a leukocyte localizing cue, from abluminal surfaces of the blood-brain barrier occurs in multiple sclerosis (MS) lesions. However, the mechanisms and consequences of reduced abluminal CXCL12 abundance remain unclear. Here, we show that activation of CXCR7, which scavenges CXCL12, is essential for leukocyte entry via endothelial barriers into the central nervous system (CNS) parenchyma during experimental autoimmune encephalomyelitis (EAE), a model for MS. CXCR7 expression on endothelial barriers increased during EAE at sites of inflammatory infiltration. Treatment with a CXCR7 antagonist ameliorated EAE, reduced leukocyte infiltration into the CNS parenchyma and parenchymal VCAM-1 expression, and increased abluminal levels of CXCL12. Interleukin 17 and interleukin 1ß increased, whereas interferon-γ decreased, CXCR7 expression on and CXCL12 internalization in primary brain endothelial cells in vitro. These findings identify molecular requirements for the transvascular entry of leukocytes into the CNS and suggest that CXCR7 blockade may have therapeutic utility for the treatment of MS.

CXCR4 promotes differentiation of oligodendrocyte progenitors and remyelination.

Multiple sclerosis is a neurodegenerative disease characterized by episodes of autoimmune attack of oligodendrocytes leading to demyelination and progressive functional deficits. Because many patients exhibit functional recovery in between demyelinating episodes, understanding mechanisms responsible for repair of damaged myelin is critical for developing therapies that promote remyelination and prevent disease progression. The chemokine CXCL12 is a developmental molecule known to orchestrate the migration, proliferation, and differentiation of neuronal precursor cells within the developing CNS. Although studies suggest a role for CXCL12 in oligodendroglia ontogeny in vitro, no studies have investigated the role of CXCL12 in remyelination in vivo in the adult CNS. Using an experimental murine model of demyelination mediated by the copper chelator cuprizone, we evaluated the expression of CXCL12 and its receptor, CXCR4, within the demyelinating and remyelinating corpus callosum (CC). CXCL12 was significantly up-regulated within activated astrocytes and microglia in the CC during demyelination, as were numbers of CXCR4+NG2+ oligodendrocyte precursor cells (OPCs). Loss of CXCR4 signaling via either pharmacological blockade or in vivo RNA silencing led to decreased OPCs maturation and failure to remyelinate. These data indicate that CXCR4 activation, by promoting the differentiation of OPCs into oligodendrocytes, is critical for remyelination of the injured adult CNS.

IL-1R signaling within the central nervous system regulates CXCL12 expression at the blood-brain barrier and disease severity during experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is an autoimmune disease of the CNS characterized by disruption of the blood-brain barrier (BBB). This breach in CNS immune privilege allows undeterred trafficking of myelin-specific lymphocytes into the CNS where they induce demyelination. Although the mechanism of BBB compromise is not known, the chemokine CXCL12 has been implicated as a molecular component of the BBB whose pattern of expression is specifically altered during MS and which correlates with disease severity. The inflammatory cytokine IL-1beta has recently been shown to contribute not only to BBB permeability but also to the development of IL-17-driven autoimmune responses. Using experimental autoimmune encephalomyelitis, the rodent model of MS, we demonstrate that IL-1beta mediates pathologic relocation of CXCL12 during the induction phase of the disease, before the development of BBB disruption. We also show that CD4, CD8, and, surprisingly gammadelta T cells are all sources of IL-1beta. In addition, gammadelta T cells are also targets of this cytokine, contributing to IL-1beta-mediated production of IL-17. Finally, we show that the level of CNS IL-1R determines the clinical severity of experimental autoimmune encephalomyelitis. These data suggest that T cell-derived IL-1beta contributes to loss of immune privilege during CNS autoimmunity via pathologic alteration in the expression of CXCL12 at the BBB.

Regional CNS responses to IFN-gamma determine lesion localization patterns during EAE pathogenesis.

The localization of inflammatory foci within the cerebellum is correlated to severe clinical outcomes in multiple sclerosis (MS). Previous studies of experimental autoimmune encephalomyelitis (EAE), a model of MS, revealed distinct clinical outcomes correlated with the capacity of the animal to produce IFN-gamma. Outcomes were linked to localization of inflammatory cells in either the spinal cord (wild type [WT]) or the cerebellum and brain stem (IFN-gamma deficient). We demonstrate, using an adoptive transfer system, that the ability of the central nervous system (CNS) to sense pathogenic T cell-produced IFN-gamma during EAE initiation determines the sites of CNS pathogenesis. Transfer of WT Th1 cells into IFN-gamma receptor-deficient mice results in pathogenic invasion of the brain stem and cerebellum with attendant clinical symptoms, which are identical to the disease observed after transfer of IFN-gamma-deficient T cells to WT hosts. Inflammation of the spinal cord associated with classical EAE is abrogated in both IFN-gamma-deficient systems. Cotransfer of CNS antigen-specific WT Th1 cells with IFN-gamma-deficient T cells is sufficient to restore spinal cord invasion and block cerebellar and brain stem invasion. These data demonstrate that interaction between IFN-gamma and host CNS cells during the initiation of EAE can selectively promote or suppress neuroinflammation and pathogenesis.

Erythropoietin and its carbamylated derivative prevent the development of experimental diabetic autonomic neuropathy in STZ-induced diabetic NOD-SCID mice.

Autonomic neuropathy is a significant diabetic complication resulting in increased morbidity and mortality. Studies of autopsied diabetic patients and several rodent models demonstrate that the neuropathologic hallmark of diabetic sympathetic autonomic neuropathy in prevertebral ganglia is the occurrence of synaptic pathology resulting in distinctive dystrophic neurites ("neuritic dystrophy"). Our prior studies show that neuritic dystrophy is reversed by exogenous IGF-I administration without altering the metabolic severity of diabetes, i.e. functioning as a neurotrophic substance. The description of erythropoietin (EPO) synergy with IGF-I function and the recent discovery of EPO's multifaceted neuroprotective role suggested it might substitute for IGF-I in treatment of diabetic autonomic neuropathy. Our current studies demonstrate EPO receptor (EPO-R) mRNA in a cDNA set prepared from NGF-maintained rat sympathetic neuron cultures which decreased with NGF deprivation, a result which demonstrates clearly that sympathetic neurons express EPO-R, a result confirmed by immunohistochemistry. Treatment of STZ-diabetic NOD-SCID mice have demonstrated a dramatic preventative effect of EPO and carbamylated EPO (CEPO, which is neuroprotective but not hematopoietic) on the development of neuritic dystrophy. Neither EPO nor CEPO had a demonstrable effect on the metabolic severity of diabetes. Our results coupled with reported salutary effects of EPO on postural hypotension in a few clinical studies of EPO-treated anemic diabetic and non-diabetic patients may reflect a primary neurotrophic effect of EPO on the sympathetic autonomic nervous system, rather than a primary hematopoietic effect. These findings may represent a major clinical advance since EPO has been widely and safely used in anemic patients due to a variety of clinical conditions.

Sympathetic neuroaxonal dystrophy in the aged rat pineal gland.

Dysfunction of circadian melatonin production by the pineal gland in aged humans and rats is thought to reflect the functional loss of its sympathetic innervation. Our ultrastructural neuropathologic studies of the sympathetic innervation of the pineal gland of aged (24 months old) Fischer-344 and Sprague-Dawley rats showed loss of nerve terminals as well as the development of neuroaxonal dystrophy (NAD), an ultrastructurally distinctive distal axonopathy, far in excess of that in young control rats. Immunolocalization of tyrosine hydroxylase confirmed the age-related loss of normal noradrenergic innervation and development of NAD. NAD was more frequent in aged female rats compared to males and was particularly severe in aged female Sprague-Dawley rats compared to Fischer-344 rats. Pineal NGF content was significantly increased or unchanged in female and male aged Fischer-344 rats, respectively, compared to young controls. The rat pineal is a sensitive experimental model for the quantitative ultrastructural examination of age-related neuropathological changes in nerve terminals of postganglionic noradrenergic sympathetic axons, changes which may reflect similar changes in the diffusely distributed sympathetic innervation of other targeted endorgans.

A potent sorbitol dehydrogenase inhibitor exacerbates sympathetic autonomic neuropathy in rats with streptozotocin-induced diabetes.

We have developed an animal model of diabetic sympathetic autonomic neuropathy which is characterized by neuroaxonal dystrophy (NAD), an ultrastructurally distinctive axonopathy, in chronic streptozotocin (STZ)-diabetic rats. Diabetes-induced alterations in the sorbitol pathway occur in sympathetic ganglia and therapeutic agents which inhibit aldose reductase or sorbitol dehydrogenase improve or exacerbate, respectively, diabetes-induced NAD. The sorbitol dehydrogenase inhibitor SDI-711 (CP-470711, Pfizer) is approximately 50-fold more potent than the structurally related compound SDI-158 (CP 166,572) used in our earlier studies. Treatment with SDI-711 (5 mg/kg/day) for 3 months increased ganglionic sorbitol (26-40 fold) and decreased fructose content (20-75%) in control and diabetic rats compared to untreated animals. SDI-711 treatment of diabetic rats produced a 2.5- and 4-5-fold increase in NAD in the SMG and ileal mesenteric nerves, respectively, in comparison to untreated diabetics. Although SDI-711 treatment of non-diabetic control rat ganglia increased ganglionic sorbitol 40-fold (a value 8-fold higher than untreated diabetics), the frequency of NAD remained at control levels. Levels of ganglionic sorbitol pathway intermediates in STZ-treated rats (a model of type 1 diabetes) and Zucker Diabetic Fatty rats (ZDF, a genetic model of type 2 diabetes) were comparable, although STZ-diabetic rats develop NAD and ZDF-diabetic rats do not. SDI failed to increase diabetes-related ganglionic NGF above levels seen in untreated diabetics. Initiation of Sorbinil treatment for the last 4 months of a 9 month course of diabetes, substantially reversed the frequency of established NAD in the diabetic rat SMG without affecting the metabolic severity of diabetes. These findings indicate that sorbitol pathway-linked metabolic alterations play an important role in the development of NAD, but sorbitol pathway activity, not absolute levels of sorbitol or fructose per se, may be most critical to its pathogenesis.

Ganglion-specific patterns of diabetes-modulated gene expression are established in prevertebral and paravertebral sympathetic ganglia prior to the development of neuroaxonal dystrophy.

In both humans and animal models, diabetic sympathetic autonomic neuropathy is associated with the selective development of markedly enlarged distal axons and nerve terminals (neuroaxonal dystrophy, NAD). NAD occurs in the prevertebral superior mesenteric and celiac ganglia (SMG-CG), but not in the paravertebral superior cervical ganglion (SCG). To identify molecular differences between these ganglia that may explain their selective vulnerability to NAD, we have examined global gene expression patterns in control and diabetic rat sympathetic ganglia before and after the onset of structural evidence of NAD. As predicted, major differences in transcriptional profiles exist between SCG and SMG-CG in normal young adult animals including, but not limited to, known differences in neurotransmitter-related gene expression. Gene expression patterns of diabetic SMG-CG and SCG, prior to the development of NAD lesions, also differ from their age-matched non-diabetic counterparts. However, diabetes has ganglion-specific effects on gene expression; of approximately 110 transcripts that were differentially expressed between diabetic and control sympathetic ganglia, only 5 were differentially expressed as a result of diabetes in both SCG and SMG-CG. Genes involving synapse and mitochondrial structure and function, oxidative stress, and glycolysis were highly represented in the differentially expressed gene set. Differences in the number of synapse-related gene alterations in diabetic SMG-CG (18 genes) versus SCG (2 genes) prior to the onset of NAD may also well explain the selective development of NAD in the SMG-CG. These results provide support for the specificity of diabetes-modulated gene expression for selected neuronal subpopulations of sympathetic noradrenergic neurons.

Experimental rat models of types 1 and 2 diabetes differ in sympathetic neuroaxonal dystrophy.

Dysfunction of the autonomic nervous system is a recognized complication of diabetes, ranging in severity from relatively minor sweating and pupillomotor abnormality to debilitating interference with cardiovascular, genitourinary, and alimentary dysfunction. Neuroaxonal dystrophy (NAD), a distinctive distal axonopathy involving terminal axons and synapses, represents the neuropathologic hallmark of diabetic sympathetic autonomic neuropathy in man and several insulinopenic experimental rodent models. Although the pathogenesis of diabetic sympathetic NAD is unknown, recent studies have suggested that loss of the neurotrophic effects of insulin and/or insulin-like growth factor-I (IGF-I) on sympathetic neurons rather than hyperglycemia per se, may be critical to its development. Therefore, in our current investigation we have compared the sympathetic neuropathology developing after 8 months of diabetes in the streptozotocin (STZ)-induced diabetic rat and BB/ Wor rat, both models of hypoinsulinemic type 1 diabetes, with the BBZDR/Wor rat, a hyperglycemic and hyperinsulinemic type 2 diabetes model. Both STZ- and BB/Wor-diabetic rats reproducibly developed NAD in nerve terminals in the prevertebral superior mesenteric sympathetic ganglia (SMG) and ileal mesenteric nerves. The BBZDR/Wor-diabetic rat, in comparison, failed to develop superior mesenteric ganglionic NAD in excess of that of age-matched controls. Similarly, NAD which developed in axons of ileal mesenteric nerves of BBZDR/Wor rats was substantially less frequent than in BB/Wor- and STZ-rats. These data, considered in the light of the results of previous experiments, argue that hyperglycemia alone is not sufficient to produce sympathetic ganglionic NAD, but rather that it may be the diabetes-induced superimposed loss of trophic support, likely of IGF-I, insulin, or C-peptide, that ultimately causes NAD.

Non-obese diabetic mice rapidly develop dramatic sympathetic neuritic dystrophy: a new experimental model of diabetic autonomic neuropathy.

To address the pathogenesis of diabetic autonomic neuropathy, we have examined the sympathetic nervous system in non-obese diabetic (NOD) and streptozotocin (STZ)-induced diabetic mice, two models of type 1 diabetes, and the db/db mouse, a model of type 2 diabetes. After only 3 to 5 weeks of diabetes, NOD mice developed markedly swollen axons and dendrites ("neuritic dystrophy") in the prevertebral superior mesenteric and celiac ganglia (SMG-CG), similar to the pathology described in diabetic STZ- and BBW-rat and man. Comparable changes failed to develop in the superior cervical ganglia of the NOD mouse or in the SMG-CG of non-diabetic NOD siblings. STZ-induced diabetic mice develop identical changes, although at a much slower pace and to a lesser degree than NOD mice. NOD-SCID mice, which are genetically identical to NOD mice except for the absence of T and B cells, do not develop diabetes or neuropathology comparable to diabetic NOD mice. However, STZ-treated NOD-SCID mice develop severe neuritic dystrophy, evidence against an exclusively autoimmune pathogenesis for autonomic neuropathy in this model. Chronically diabetic type 2 db/db mice fail to develop neuritic dystrophy, suggesting that hyperglycemia alone may not be the critical and sufficient element. The NOD mouse appears to be a valuable model of diabetic sympathetic autonomic neuropathy with unambiguous, rapidly developing neuropathology which corresponds closely to the characteristic pathology of other rodent models and man.

Analysis of the Zucker Diabetic Fatty (ZDF) type 2 diabetic rat model suggests a neurotrophic role for insulin/IGF-I in diabetic autonomic neuropathy.

Dysfunction of the autonomic nervous system is a recognized complication of diabetes. Neuroaxonal dystrophy (NAD), a distinctive axonopathy involving distal axons and synapses, represents the neuropathologic hallmark of diabetic sympathetic autonomic neuropathy in human and several insulinopenic experimental rodent models. Recent studies have suggested that loss of the neurotrophic effects of insulin and/or IGF-I on sympathetic neurons and not hyperglycemia per se, may underlie the development of sympathetic NAD. The streptozotocin (STZ)-diabetic and BB/W rat, the most commonly used experimental rodent models, develop marked hyperglycemia and concomitant deficiency in both circulating insulin and IGF-I. These animals reproducibly develop NAD in nerve terminals in the prevertebral sympathetic ganglia and the distal portions of noradrenergic ileal mesenteric nerves. The Zucker Diabetic Fatty (ZDF) rat, an animal model of type 2 diabetes, also develops severe hyperglycemia comparable to that in the STZ- and BB/W-diabetic rat models, although in the presence of hyperinsulinemia. In our study, ZDF rats maintained for 6 to 7 months in a severely diabetic state, as assessed by plasma glucose and glycated hemoglobin levels, maintained significant hyperinsulinemia and normal levels of plasma IGF-I at sacrifice. NAD did not develop in diabetic ZDF rat sympathetic ganglia and ileal mesenteric nerves as assessed by quantitative ultrastructural techniques, which is in dramatic contrast to neuropathologic findings in comparably hyperglycemic 6-month STZ-diabetic insulinopenic rats. These data combined with our previous results argue very strongly that hyperglycemia is not the critical and sufficient element in the pathogenesis of diabetes-induced NAD, rather that it is the loss of trophic support, most likely of IGF-I or insulin, that causes NAD.