Petri Ylipaasto

Enterovirus infection in human pancreatic islet cells, islet tropism in vivo and receptor involvement in cultured islet beta cells

Aims/hypothesisIt is thought that enterovirus infections cause beta-cell damage and contribute to the development of Type 1 diabetes by replicating in the pancreatic islets. We sought evidence for this through autopsy studies and by investigating known enterovirus receptors in cultured human islets.MethodsAutopsy pancreases from 12 newborn infants who died of fulminant coxsackievirus infections and from 65 Type 1 diabetic patients were studied for presence of enteroviral ribonucleic acid by in situ hybridisation. Forty non-diabetic control pancreases were included in the study. The expression and role of receptor candidates in cultured human islets were investigated with receptor-specific antibodies using immunocytochemistry and functional assays.ResultsEnterovirus-positive islet cells were found in some of both autopsy specimen collections, but not in control pancreases. No infected cells were seen in exocrine tissue. The cell surface molecules, poliovirus receptor and integrin αvβ3, which act as enterovirus receptors in established cell lines, were expressed in beta cells. Antibodies to poliovirus receptor, human coxsackievirus and adenovirus receptor and integrin αvβ3 protected islets and beta cells from adverse effects of poliovirus, coxsackie B viruses, and several of the arginine-glycine-aspartic acid motifs containing enteroviruses and human parechovirus 1 respectively. No evidence was found for expression of the decay-accelerating factor which acts as a receptor for several islet-cell-replicating echoviruses in established cell lines.Conclusions/interpretationThe results show a definite islet-cell tropism of enteroviruses in the human pancreas. Some enteroviruses seem to use previously identified cell surface molecules as receptors in beta cells, whereas the identity of receptors used by other enteroviruses remains unknown.

Functional impairment and killing of human beta cells by enteroviruses: the capacity is shared by a wide range of serotypes, but the extent is a characteristic of individual virus strains

AbstractAims/hypothesis. Direct infection of beta cells could explain the diabetogenic effect of enteroviruses. Primary adult human beta cells are susceptible to coxsackievirus infections, which could result in impaired beta-cell function or cell death (coxsackieviruses B3, B4, B5) or both, or no apparent immediate adverse effects (coxsackievirus A9). We extended these studies to additional enterovirus serotypes including several echoviruses, some of which have been associated clinically with the development of Type I (insulin-dependent) diabetes mellitus. Methods. The patterns and consequences of enterovirus infections were investigated in cultured adult human isolated islets. Cell type-specific infection and viability were assessed by immunocytochemical methods. Beta-cell function was studied by perifusion. Results. Poliovirus type 1/Mahoney, coxsackievirus A13, human parechovirus 1 and several echoviruses (serotypes 6, 7, 11) were capable of causing significant functional impairment (p<0.05) and beta-cell death. In contrast, echovirus serotypes 9 and 30 were not destructive. However, when several different field isolates of echovirus 30 were investigated, some of them were found to be clearly more destructive than the corresponding prototype strain. This was also true for echovirus 9. A strain isolated from a 6-week-old baby suffering from acute Type I diabetes was functionally more destructive than either of the echovirus 9 prototype strains. Conclusion/interpretation. These observations indicate that the capacity of an enterovirus to kill human beta cells or impair their function is not entirely defined by the serotype, but in addition by as yet unidentified characteristics of the virus strain involved. Moreover, any serotype could potentially be diabetogenic.

Cellular tropism of human enterovirus D species serotypes EV-94, EV-70, and EV-68 in vitro: implications for pathogenesis.

Enterovirus 94 (EV‐94) is an enterovirus serotype described recently which, together with EV‐68 and EV‐70, forms human enterovirus D species. This study investigates the seroprevalences of these three serotypes and their abilities to infect, replicate, and damage cell types considered to be essential for enterovirus‐induced diseases. The cell types studied included human leukocyte cell lines, primary endothelial cells, and pancreatic islets. High prevalence of neutralizing antibodies against EV‐68 and EV‐94 was found in the Finnish population. The virus strains studied had wide leukocyte tropism. EV‐94 and EV‐68 were able to produce infectious progeny in leukocyte cell lines with monocytic, granulocytic, T‐cell, or B‐cell characteristics. EV‐94 and EV‐70 were capable of infecting primary human umbilical vein endothelial cells, whereas EV‐68 had only marginal progeny production and did not induce cytopathic effects in these cells. Intriguingly, EV‐94 was able to damage pancreatic islet β‐cells, to infect, replicate, and cause necrosis in human pancreatic islets, and to induce proinflammatory and chemoattractive cytokine expression in endothelial cells. These results suggest that HEV‐D viruses may be more prevalent than has been thought previously, and they provide in vitro evidence that EV‐94 may be a potent pathogen and should be considered a potentially diabetogenic enterovirus type. J. Med. Virol. 82:1940–1949, 2010.

Enterovirus-induced gene expression profile is critical for human pancreatic islet destruction.

Aims/hypothesisVirally induced inflammatory responses, beta cell destruction and release of beta cell autoantigens may lead to autoimmune reactions culminating in type 1 diabetes. Therefore, viral capability to induce beta cell death and the nature of virus-induced immune responses are among key determinants of diabetogenic viruses. We hypothesised that enterovirus infection induces a specific gene expression pattern that results in islet destruction and that such a host response pattern is not shared among all enterovirus infections but varies between virus strains.MethodsThe changes in global gene expression and secreted cytokine profiles induced by lytic or benign enterovirus infections were studied in primary human pancreatic islet using DNA microarrays and viral strains either isolated at the clinical onset of type 1 diabetes or capable of causing a diabetes-like condition in mice.ResultsThe expression of pro-inflammatory cytokine genes (IL-1-α, IL-1-β and TNF-α) that also mediate cytokine-induced beta cell dysfunction correlated with the lytic potential of a virus. Temporally increasing gene expression levels of double-stranded RNA recognition receptors, antiviral molecules, cytokines and chemokines were detected for all studied virus strains. Lytic coxsackievirus B5 (CBV-5)-DS infection also downregulated genes involved in glycolysis and insulin secretion.Conclusions/interpretationThe results suggest a distinct, virus-strain-specific, gene expression pattern leading to pancreatic islet destruction and pro-inflammatory effects after enterovirus infection. However, neither viral replication nor cytotoxic cytokine production alone are sufficient to induce necrotic cell death. More likely the combined effect of these and possibly cellular energy depletion lie behind the enterovirus-induced necrosis of islets.

In vitro toxicity of cereulide on porcine pancreatic Langerhans islets

Cereulide is a K(+) ionophore cytotoxic and mitochondriotoxic to primary cells and cell lines of human and other mammalian origins. It is a heat-stable, highly lipophilic (logK(ow) 5.96) peptide (1152 g mol(-1)) produced by certain strains of Bacillus cereus, a bacterium connected to emetic food poisonings. In this study the pancreatic toxicity of purified cereulide, and cereulide-containing bacterial extracts, was studied using fetal porcine Langerhans islets in culture. Exposure to 1ngml(-1) of purified cereulide caused necrotic cell death of the islet cells impairing their insulin content within 2 days. Cell extracts of cereulide-positive B. cereus strains connected to food poisoning or isolated from foodstuffs were toxic, corresponding to their measured cereulide content. Extracts of B. cereus strains producing or not producing the B. cereus diarrheal toxin, but no cereulide, were tolerated by the porcine islet cultures up to concentrations 1000-fold higher compared to extracts from strains containing cereulide, and up to exposure times of 7d. Cereulide thus was identified as the B. cereus-produced substance toxic towards porcine fetal Langerhans islets and beta cells.

Diabetogenic Effects of the Most Prevalent Enteroviruses in Finnish Sewage

Common enterovirus infections appear to initiate or facilitate the pathogenetic processes leading to type 1 diabetes (T1D) and also sometimes precipitate the clinical disease. We have recently demonstrated that (1) enterovirus‐positive islet cells were seen on postmortem pancreatic specimens of several T1D patients but not in the corresponding samples of nondiabetic controls, and (2) several different enteroviruses can be associated with T1D. Enterovirus infections are transmitted from person to person by fecal–oral or respiratory routes, which means that infections usually start from the respiratory or gastrointestinal mucosa. Regardless of the clinical symptoms of the disease, viral replication continues in the submucosal lymphatic tissue for several weeks, up to a couple of months, and during that time the virus is excreted into the feces and translocated to the environment. Monitoring of sewage samples for enteroviruses can be used as a tool in epidemiologic studies of enterovirus. Finland has successfully used environmental control data in poliovirus surveillance for decades. About 24 samples have been collected annually from the Helsinki region, which covers about 20% of the population. In the present study, we have reanalyzed the sewage samples of the years 1993–2004 for nonpolio enteroviruses by inoculating them into five different continuous cell lines known to cover a wide range of serotypes. Isolated strains were identified by RT‐PCR and VP1 sequencing. The most commonly detected serotypes were coxsackie B viruses (CBV1–5) and echoviruses (E6, 7, 11, 25, 30). Diabetogenic effects of the most prevalent enterovirus serotypes were studied in primary human β cells.

An enterovirus strain isolated from diabetic child belongs to a genetic subcluster of echovirus 11, but is also neutralised with monotypic antisera to coxsackievirus A9

An enterovirus strain (designated D207) isolated from a Slovakian diabetic child and originally serotyped as coxsackievirus A9 (CAV-9) was found to cause rapid cytolysis coinciding with severe functional damage of the surviving cells in primary cultures of human pancreatic islets. This finding prompted us to clone the isolate for full-length genome sequencing and molecular characterization as the prototype strain of CAV-9 is known to cause only minimal damage to insulin-producing beta-cells. Based on capsid-coding sequence comparisons, the isolate turned out to be echovirus 11 (E-11). Phylogenetic analyses demonstrated that E-11/D207 was closely related to a specific subgroup B of E-11 strains known to cause uveitis. To study further antigenic properties of isolate E-11/D207 and uveitis-causing E-11 strains, neutralization experiments were carried out with CAV-9- and E-11-specific antisera. Unlike the prototype strains, the isolate E-11/D207 and uveitis-causing E-11 strains were well neutralized with both CAV-9- and E-11-specific antisera. Attempts to identify recombination of the capsid coding sequences as a reason for double-reactivity using the Simplot analysis failed to reveal major transferred motifs. However, peptide scanning technique was able to identify antigenic regions of capsid proteins of E-11/D207 as well as regions cross-reacting with an antiserum raised to CAV-9. Thus, double specificity of E-11/D207 seems to be a real characteristic shared by the phylogenetically closely related virus strains in the genetic subgroup B of E-11.

Amino acids of coxsackie B5 virus are critical for infection of the murine insulinoma cell line, MIN-6

It was shown recently that 15 successive passages of a laboratory strain of the Coxsackie B virus 5 in a mouse pancreas (CBV‐5‐MPP) resulted in apparent changes in the virus phenotype, which led to the capacity to induce a diabetes‐like syndrome in mice. For further characterization of islet cell interactions with a passaged virus strain, a murine insulinoma cell line, MIN‐6, was selected as an experimental model. The CBV‐5‐MPP virus strain was not able to replicate in MIN‐6 cells in vitro but required adaptation over a few days for progeny production and the generation of cytopathic effects. In order to determine the genetic characteristics required for virus growth in MIN‐6 cells, the whole genome of the MIN‐6‐adapted virus variant was sequenced, and critical amino acids were identified by comparing the sequence with that of a virus strain passaged repeatedly in the mouse pancreas. The results of site‐directed mutagenesis demonstrated that only one residue, amino acid 94 of VP1, is a major determinant for virus adaptation to MIN‐6 cells. J. Med. Virol. 81:296–304, 2009.

Screening enteroviruses for Beta-cell tropism using foetal porcine Beta-cells

Primary adult human insulin-producing beta-cells are susceptible to infection by prototype strains of coxsackieviruses (CV) and infection may result in impaired beta-cell function and/or cell death, as shown for coxsackie B virus (CVB) types 4 and 5, or have no apparent immediate adverse effects, as shown for CVA-9. Because of the limited availability of human pancreatic beta-cells, the aim of this study was to find out if foetal porcine pancreatic islets could be used as a substitute in enterovirus (EV) screening. These cells resemble human beta-cells in several biological properties. CVB infection resulted in a rapid progressive decline of insulin content and reponsiveness to insulin release. The amount of virus inoculum sufficient for this destruction was small, corresponding to only 55 infectious units per pancreas. In contrast to CVBs, CVA-9 replicated poorly, and sometimes not at all, in foetal porcine beta-cells. The first signs of functional impairment and cell destruction, if present at all, were seen only after 1-3 weeks of incubation. Furthermore, CVA-16, several strains of echoviruses and human parechovirus type 1 were unable to replicate in foetal porcine pancreatic beta-cells. Based on these results, foetal porcine islets are somewhat more sensitive to CVB infection than adult human islets, whereas many other human EV strains do not infect porcine beta-cells. Therefore, foetal porcine beta-cells cannot be used for systematic screening of human EV strains and isolates for beta-cell tropism, but they might provide a useful model for detailed studies on the interaction of CVBs with beta-cells.

A single amino acid substitution in viral VP1 protein alters the lytic potential of clone-derived variants of echovirus 9 DM strain in human pancreatic islets.

In vitro studies with primary human pancreatic islets suggest that several enterovirus serotypes are able to infect and replicate in beta cells. Some enterovirus strains are highly cytolytic in vitro whereas others show virus replication with no apparent islet destruction. The capability to induce islet destruction is determined only partially by the virus serotype, since strain specific differences have been detected within some serotypes including echovirus 9 (E‐9). In this study, the viral genetic factors determining the outcome of islet infection (i.e., destructive vs. benign) were investigated by constructing parallel infectious clones of lytic E‐9‐DM strain that was isolated from a small child at the clinical onset of type 1 diabetes. The capabilities of these clone‐derived viruses to induce islet destruction were monitored and the lytic potential of clones was modified by site‐directed mutagenesis. The lytic capabilities of these clone‐derived viruses in human pancreatic islets were modified by a single amino acid substitution (T81A) in the capsid protein VP1. The data presented outline the importance of amino acid point mutations in the pathogenetic process leading to islet necrosis. However, although the amino acid substitution (T81A) modifies the lytic capabilities of E‐9‐DM strain‐derived microvariant strains, it is likely that additional viral genetic determinants of pancreatic islet pathogenicity exist in other E‐9 strains. J. Med. Virol. 85:1267–1273, 2013.