Development of standardized insulin treatment protocols for spontaneous rodent models of type 1 diabetes

Standardized protocols for maintaining near-normal glycemic levels in diabetic rodent models for testing therapeutic agents to treat disease are unavailable. We developed protocols for 2 common models of spontaneous type 1 diabetes, the BioBreeding diabetes-prone (BBDP) rat and nonobese diabetic (NOD) mouse. Insulin formulation, dose level, timing of dose administration, and delivery method were examined and adjusted so that glycemic levels remained within a normal range and fluctuation throughout feeding and resting cycles was minimized. Protamine zinc formulations provided the longest activity, regardless of the source of insulin. Glycemic control with few fluctuations was achieved in diabetic BBDP rats through twice-daily administration of protamine zinc insulin, and results were similar regardless of whether BBDP rats were acutely or chronically diabetic at initiation of treatment. In contrast, glycemic control could not be attained in NOD mice through administration of insulin twice daily. However, glycemic control was achieved in mice through daily administration of 0.25 U insulin through osmotic pumps. Whereas twice-daily injections of protamine zinc insulin provided glycemic control with only minor fluctuations in BBDP rats, mice required continuous delivery of insulin to prevent wide glycemic excursions. Use of these standard protocols likely will aid in the testing of agents to prevent or reverse diabetes.

A mucosal vaccination approach for herpes simplex virus type 2

An estimated 1 out of every 5 Americans is infected with herpes simplex virus type 2 (HSV-2). Efforts in developing a potent vaccine for HSV-2 have shown limited success. Here we describe a heterologous vaccination strategy for HSV-2 based on an intramuscular DNA prime followed by a liposome-encapsulated antigen boost delivered intranasally. Both portions of the vaccine express the immunogenic HSV-2 glycoprotein D. In female Balb/c mice, this heterologous immunisation regimen stimulated high titers of serum neutralising antibodies, a DNA priming dose dependent T helper type response, enhanced mucosal immune responses and potent protective immunity at the portal of entry for the virus: the vaginal cavity. A clear synergistic effect on immune responses and protection from infection was seen using this heterologous immunisation approach. Suboptimal DNA prime (0.5 μg) followed by the liposome boost resulted in an 80% survival rate when mice were infected 2 weeks after immunisation. A higher dose of DNA priming (5 μg) followed by the liposome boost resulted in sterilising immunity in 80% of mice. The vaccine induced durable protection in mice, demonstrated by a 60% survival rate when lethal infections were performed 20 weeks after the immunisation primed with 0.5 μg of DNA vaccine.

Infection with viruses from several families triggers autoimmune diabetes in LEW*1WR1 rats: prevention of diabetes by maternal immunization

OBJECTIVE

The contribution of antecedent viral infection to the development of type 1 diabetes in humans is controversial. Using a newer rat model of the disease, we sought to 1) identify viruses capable of modulating diabetes penetrance, 2) identify conditions that increase or decrease the diabetogenicity of infection, and 3) determine whether maternal immunization would prevent diabetes.

RESEARCH DESIGN AND METHODS

About 2% of LEW*1WR1 rats develop spontaneous autoimmune diabetes, but disease penetrance is much higher if weanling rats are exposed to environmental perturbants including Kilham rat virus (KRV). We compared KRV with other viruses for diabetogenic activity.

RESULTS

Both KRV and rat cytomegalovirus (RCMV) induced diabetes in up to 60% of LEW*1WR1 rats, whereas H-1, vaccinia, and Coxsackie B4 viruses did not. Simultaneous inoculation of KRV and RCMV induced diabetes in 100% of animals. Pretreatment of rats with an activator of innate immunity increased the diabetogenicity of KRV but not RCMV and was associated with a moderate rate of diabetes after Coxsackie B4 and vaccinia virus infection. Inoculation of LEW*1WR1 dams with both KRV and RCMV prior to pregnancy protected weanling progeny from virus-induced diabetes in a virus-specific manner.

CONCLUSIONS

Exposure to viruses can affect the penetrance of autoimmune diabetes in genetically susceptible animals. The diabetogenicity of infection is virus specific and is modified by immunomodulation prior to inoculation. Maternal immunization protects weanlings from virus-induced diabetes, suggesting that modification of immune responses to infection could provide a means of preventing islet autoimmunity.

A DNA vaccine prime followed by a liposome-encapsulated protein boost confers enhanced mucosal immune responses and protection

A variety of DNA vaccine prime and recombinant viral boost immunization strategies have been developed to enhance immune responses in humans, but inherent limitations to these strategies exist. There is still an overwhelming need to develop safe and effective approaches that raise broad humoral and T cell-mediated immune responses systemically and on mucosal surfaces. We have developed a novel mucosal immunization regimen that precludes the use of viral vectors yet induces potent T cell responses. Using hepatitis B surface Ag (HBsAg), we observed that vaccination of BALB/c mice with an i.m. HBsAg-DNA vaccine prime followed by an intranasal boost with HBsAg protein encapsulated in biologically inert liposomes enhanced humoral and T cell immune responses, particularly on mucosal surfaces. Intranasal live virus challenge with a recombinant vaccinia virus expressing HBsAg revealed a correlation between T cell immune responses and protection of immunized mice. A shortened immunization protocol was developed that was successful in both adult and neonatal mice. These results support the conclusion that this new approach is capable of generating a Th-type-1-biased, broad spectrum immune response, specifically at mucosal surfaces. The success of this design may provide a safe and effective vaccination alternative for human use.

LEW.1WR1 rats develop autoimmune diabetes spontaneously and in response to environmental perturbation

We describe a new rat model of autoimmune diabetes that arose in a major histocompatibility complex congenic LEW rat. Spontaneous diabetes in LEW.1WR1 rats (RT1(u/u/a)) occurs with a cumulative frequency of approximately 2% at a median age of 59 days. The disease is characterized by hyperglycemia, glycosuria, ketonuria, and polyuria. Both sexes are affected, and islets of acutely diabetic rats are devoid of beta-cells, whereas alpha- and delta-cell populations are spared. The peripheral lymphoid phenotype is normal, including the fraction of ART2(+) regulatory T-cells. We tested the hypothesis that the expression of diabetes would be increased by immunological perturbation of innate or adaptive immunity. Treatment of young rats with depleting anti-ART2.1 monoclonal antibody increased the frequency of diabetes to 50%. Treatment with the toll-like receptor 3 ligand polyinosinic:polycytidylic acid increased the frequency of diabetes to 100%. All diabetic rats exhibited end-stage islets. The LEW.1WR1 rat is also susceptible to collagen-induced arthritis but is free of spontaneous thyroiditis. The LEW.1WR1 rat provides a new model for studying autoimmune diabetes and arthritis in an animal with a genetic predisposition to both disorders that can be amplified by environmental perturbation.

Biochemical and functional analysis of smallpox growth factor (SPGF) and anti-SPGF monoclonal antibodies

Variola, the causative agent of smallpox, is a highly infectious double-stranded DNA virus of the orthopox genus that replicates within the cytoplasm of infected cells. For unknown reasons prominent skin manifestations, including "pox," mark the course of this systemic human disease. Here we characterized smallpox growth factor (SPGF), a protein containing an epidermal growth factor (EGF)-like domain that is conserved among orthopox viral genomes, and investigated its possible mechanistic link. We show that after recombinant expression, refolding, and purification, the EGF domain of SPGF binds exclusively to the broadly expressed cellular receptor, erb-B1 (EGF receptor), with subnanomolar affinity, stimulating the growth of primary human keratinocytes and fibroblasts. High affinity monoclonal antibodies specific for SPGF reveal in vivo immunoprotection in a murine vaccinia pneumonia model by a mechanism distinct from viral neutralization. These findings suggest that blockade of pathogenic factor actions, in general, may be advantageous to the infected host.

The BBZDR/Wor Rat Model for Investigating the Complications of Type 2 Diabetes Mellitus

Congenic and inbred strains of rats offer researchers invaluable insight into the etiopathogenesis of diabetes and associated complications. The inbred Bio-Breeding Zucker diabetic rat (BBZDR)/Wor rat strain is a relatively new and emerging model of type 2 diabetes. This strain was created by classical breeding methods used to introgress the defective leptin receptor gene (Lepr(fa)) from insulin-resistant Zucker fatty rats into the inbred BBDR/Wor strain background. The diabetic male BBZDR/Wor rat is homozygous for the fatty mutation and shares the genetic background of the original BB strain. Although lean littermates are phenotypically normal, obese juvenile BBZDR/Wor rats are hyperlipidemic and hyperleptinemic, become insulin resistant, and ultimately develop hyperglycemia. Furthermore, the BBZDR/Wor rat is immune competent and does not develop autoimmunity. Similar to patients with clinical diabetes, the BBZDR/Wor rat develops complications associated with hyperglycemia. The BBZDR/Wor rat is a model system that fully encompasses the ability to study the complications that affect human type 2 diabetic patients. In this review, recent work that has evaluated type 2 diabetic complications in BBZDR/Wor rats is discussed, including the authors' preliminary unpublished studies on cardiovascular disease.

The human cytomegalovirus US8 glycoprotein binds to major histocompatibility complex class I products

Human cytomegalovirus US8 is a type I membrane protein that partially colocalizes with cellular endosomal and lysosomal proteins. Although US8 does not have discernible effects on the processing and cell surface distribution of major histocompatibility complex (MHC) class I products, we have demonstrated that US8 binds to MHC class I heavy chains in the endoplasmic reticulum.

Human cytomegalovirus open reading frame TRL11/IRL11 encodes an immunoglobulin G Fc-binding protein

Several herpesviruses encode Fc receptors that may play a role in preventing antibody-mediated clearance of the virus in vivo. Human cytomegalovirus (HCMV) induces an Fc-binding activity in cells upon infection, but the gene that encodes this Fc-binding protein has not been identified. Here, we demonstrate that the HCMV AD169 open reading frame TRL11 and its identical copy, IRL11, encode a type I membrane glycoprotein that possesses IgG Fc-binding capabilities.

Viral immune evasion strategies and the underlying cell biology

Evasion of the immune system by viruses is a well-studied field. It remains a challenge to understand how these viral tactics affect pathogenesis and the viral lifecycle. At the same time, the study of viral proteins involved in immune evasion has helped us to better understand a number of cellular processes at the molecular level. Here we review recent data on different viral tactics for immune evasion and highlight what these viral interventions might teach us about cell biology.

The role of virion membrane protein endocytosis in the herpesvirus life cycle

Endocytosis of cellular surface membrane proteins is a well-characterized, common occurrence. Internalization of cell surface receptors, often with bound ligands, aid in global events, such as cellular metabolism, as well as in specific, directed functions, such as the induction of signal transduction cascades or immune function. Some, but not all, herpesvirus membrane proteins are internalized from the plasma membrane by a process similar to receptor-mediated endocytosis. No known functions, however, have been ascribed to endocytosis of these proteins. In this review, we consider the function of herpesvirus membrane protein endocytosis. We compare and contrast the endocytosis and intracellular trafficking of two pseudorabies virus membrane proteins, the type I glycoprotein, gE, and the type II, tail-anchored membrane protein, Us9, and discuss the possible function of their internalization during the virus life cycle.

Role of the pseudorabies virus gI cytoplasmic domain in neuroinvasion, virulence, and posttranslational N-linked glycosylation

The glycoproteins I and E of pseudorabies virus are important mediators of cell-to-cell spread and virulence in all animal models tested. Although these two proteins form a complex with one another, ascribing any function to the individual proteins has been difficult. We have shown previously, using nonsense mutations, that the N-terminal ectodomain of the gE protein is sufficient for gE-mediated transsynaptic spread whereas the cytoplasmic domain of the protein is required for full expression of virulence. These same studies demonstrated that the cytoplasmic domain of gE is also required for endocytosis of the protein. In this report, we describe the construction of viruses with nonsense mutations in gI that allowed us to determine the contributions of the gI cytoplasmic domain to protein expression as well as virus neuroinvasion and virulence after infection of the rat eye. We also constructed double mutants with nonsense mutations in both gE and gI so that the contributions of both the gE and gI cytoplasmic domains could be determined. We observed that the gI cytoplasmic domain is required for efficient posttranslational modification of the gI protein. The gE cytoplasmic domain has no effect on gE posttranslational glycosylation. In addition, we found that infection of all gE-gI-dependent anterograde circuits projecting from the rat retina requires both ectodomains and at least one of the cytoplasmic domains of the proteins. The gI cytoplasmic domain promotes transsynaptic spread of virus better than the gE cytoplasmic domain. Interestingly, both gE and gI cytoplasmic tails are required for virulence; lack of either one or both results in an attenuated infection. These data suggest that gE and gI play differential roles in mediating directional neuroinvasion of the rat; however, the gE and gI cytoplasmic domains most likely function together to promote virulence.

Retrograde, transneuronal spread of pseudorabies virus in defined neuronal circuitry of the rat brain is facilitated by gE mutations that reduce virulence

The pseudorabies virus (PRV) gE gene encodes a multifunctional membrane protein found in infected cell membranes and in the virion envelope. Deletion of the gE gene results in marked attenuation of the virus in almost every animal species tested that is permissive for PRV. A common inference is that gE mutants are less virulent because they have reduced ability to spread from cell to cell; e.g., gE mutants infect fewer cells and, accordingly, animals live longer. In this report, we demonstrate that this inference does not hold in a rat experimental model for virus invasion of the brain. We find that animals infected with gE mutants live longer despite extensive retrograde, transneuronal spread of virus in the rat brain. In this model of brain infection, virus is injected into the stomach musculature and virions spread to the brain in long axons of brain stem neurons that give rise to the tenth cranial nerve (the vagus). The infection then spreads from neuron to neuron in well-defined, and physically separated, areas of the brain involved in autonomic regulation of the viscera. We examined the progression of infection of five PRV strains in this circuitry: the wild-type PRV-Becker strain, the attenuated PRV-Bartha vaccine strain, and three gE mutants isogenic with the PRV-Becker strain. By 60 to 67 h after infection, all PRV-Becker-infected animals were dead. Analysis of Becker-infected rats killed prior to virus-induced death demonstrated that the virus had established an infection only in the primary vagal neurons connected directly to the stomach and synaptically linked neurons in the immediate vicinity of the caudal brain stem. There was little spread to other neurons in the vagus circuitry. In contrast, rats infected with PRV-Bartha or PRV-Becker gE mutants survived to at least 96 h and exhibited few overt signs of disease. Despite this long survival and the lack of symptoms, brains of animals sacrificed at this time revealed extensive transsynaptic infection not only of the brain stem but also of areas of the forebrain synaptically linked to neurons in the brain stem. This finding provides evidence that the gE protein plays a role in promoting symptoms of infection and death in animals that is independent of neuron-to-neuron spread during brain infection. When this early virulence function is not active, animals live longer, resulting in more extensive spread of virus in the brain.

Mutation of the YXXL endocytosis motif in the cytoplasmic tail of pseudorabies virus gE

The role of alphaherpesvirus membrane protein internalization during the course of viral infection remains a matter of speculation. To determine the role of internalization of the pseudorabies virus (PRV) gE and gI proteins, we constructed viral mutants encoding specific mutations in the cytoplasmic tail of the gE gene that inhibited internalization of the gE-gI complex. We used these mutants to assess the role of gE-gI endocytosis in incorporation of the proteins into the viral envelope and in gE-mediated spread or gE-promoted virulence. In addition, we report that another viral mutant, PRV 25, which encodes a gE protein defective in endocytosis, contains an additional, previously uncharacterized mutation in the gE gene. We compared PRV 25 to another viral mutant, PRV 107, that does not express the cytoplasmic tail of the gE protein. The gE protein encoded by PRV 107 is also defective in endocytosis. We conclude that efficient endocytosis of gE is not required for gE incorporation into virions, gE-mediated virulence, or spread of virus in the rat central nervous system. However, we do correlate the defect in endocytosis to a small-plaque phenotype in cultured cells.

Molecular mechanisms of neurotropic herpesvirus invasion and spread in the CNS

Pseudorabies virus (PRV) is a herpesvirus in the subfamily alphaherpesvirinae (the alpha herpesviruses). After primary infection at mucosal surfaces, PRV infects the peripheral nervous system in its natural host (swine) with occasional invasion of the central nervous system. When other hosts (including cows and rodents) are infected, the infection almost always gives rise to fatal disease in the CNS as a result of infection of peripheral neurons and subsequent spread to the brain. Part of the ability to cause fatal CNS disease can be attributed to a viral glycoprotein called gE. Viruses lacking gE are thought to be less virulent because they do not spread efficiently from cell to cell. Based on a set of gE mutations we have constructed, we suggest that these two phenotypes of cell-cell spread and virulence reflect separate functions of the gE protein. In this report, we show that viruses carrying these new gE mutations have marked reduction in virulence, yet spread efficiently in defined neural circuits in the rat brain. As such, they offer new insight and opportunities for understanding of viral disease and host response to injury, as well as in the construction of viral tracers of neuronal connections.

The C. elegans MDL-1 and MXL-1 proteins can functionally substitute for vertebrate MAD and MAX

The genes of the myc/max/mad family play an important role in controlling cell proliferation and differentiation. We have identified the first homologues of the mad and max genes in the nematode C. elegans, which we have named mdl-1 and mxl-1 respectively. Like the vertebrate MAD proteins, MDL-1 binds an E-box DNA sequence (CACGTG) when dimerized with MXL-1. However, unlike vertebrate MAX, MXL-1 can not form homodimers and bind to DNA alone. Promoter fusions to a GFP reporter suggest that these genes are coexpressed in posterior intestinal and post-mitotic neuronal cells during larval development. The coexpression in the posterior intestinal cells occurs before their final division at the end of the L1 stage and persists afterwards, demonstrating that mad and max expression can be correlated directly to the cell cycle state of an individual cell type. These data also show that mxl-1 is an obligate partner for mdl-1 in vivo and in vitro and indicate that these genes may play an important role in post-embryonic development. Finally, MDL-1 can suppress activated c-MYC/RAS-induced focus formation in a rat embryo fibroblast transformation assay. Like the vertebrate MAD protein, MDL-1 activity in suppressing transformation is dependent on a functional SIN3 interaction domain.

Role of envelope protein gE endocytosis in the pseudorabies virus life cycle

Several groups have reported that certain herpesvirus envelope proteins do not remain on the surface of cells that express them but rather are internalized by endocytosis in a recycling process. The biological function of membrane protein endocytosis in the virus life cycle remains a matter of speculation and debate. In this report, we demonstrate that some, but not all, membrane proteins encoded by the alphaherpesvirus pseudorabies virus (PRV) are internalized after reaching the plasma membrane. Glycoproteins gE and gB are internalized from the plasma membrane of cells, while gI and gC are not internalized efficiently. We show for gE that the cytoplasmic domain of the protein is required for endocytosis. While the gI protein is incapable of endocytosis on its own, it can be internalized when complexed with gE. We demonstrate that endocytosis of the gE-gI complex and gB occurs early after infection of tissue culture cells but that this process stops completely after 6 h of infection, a time that correlates with significant shutoff of host protein synthesis. We also show that gE protein internalized at 4 h postinfection is not present in virions formed at a later time. We discuss the differences in PRV gE and gI endocytosis compared to that of the varicella-zoster virus homologs and the possible roles of glycoprotein endocytosis in the virus life cycle.

Characterization of pseudorabies virus mutants expressing carboxy-terminal truncations of gE: evidence for envelope incorporation, virulence, and neurotropism domains

Glycoprotein E (gE) gene of pseudorabies virus (PRV) is conserved among diverse alphaherpesviruses and therefore is predicted to be important for virus survival. gE contributes to viral spread from cell to cell in a variety of hosts and is responsible, in part, for increased virulence or pathogenesis of the virus. Virulence and spread mediated by gE are thought to be highly correlated. We initiated this study to explore the hypothesis that these two phenotypes might reflect separate functions of the gE protein. We did so by focusing on the role of the gE carboxy terminus in neuronal spread. Viruses harboring nonsense mutations affecting the expression of the gE cytoplasmic domain had several notable phenotypes. First, the truncated gE proteins expressed from these mutants are not found in virion envelopes. Second, the mutants retain the ability to spread to all retinorecipient regions of the rodent brain after retinal infection of rats. Third, the mutants have the reduced virulence phenotype of a gE deletion mutant in rats. Finally, the mutants have distinct plaque-size phenotypes on MDBK cells but not PK15 cells. Based on these observations, we suggest that gE-mediated virulence and spread may reflect separate functions that are not mediated by gE on virus particles.