Functional plasticity in oyster gut microbiomes along a eutrophication gradient in an urbanized estuary

Background

Oysters in coastal environments are subject to fluctuating environmental conditions that may impact the ecosystem services they provide. Oyster-associated microbiomes are responsible for some of these services, particularly nutrient cycling in benthic habitats. The effects of climate change on host-associated microbiome composition are well-known, but functional changes and how they may impact host physiology and ecosystem functioning are poorly characterized. We investigated how environmental parameters affect oyster-associated microbial community structure and function along a trophic gradient in Narragansett Bay, Rhode Island, USA. Adult eastern oyster, Crassostrea virginica, gut and seawater samples were collected at 5 sites along this estuarine nutrient gradient in August 2017. Samples were analyzed by 16S rRNA gene sequencing to characterize bacterial community structures and metatranscriptomes were sequenced to determine oyster gut microbiome responses to local environments.

Results

There were significant differences in bacterial community structure between the eastern oyster gut and water samples, suggesting selection of certain taxa by the oyster host. Increasing salinity, pH, and dissolved oxygen, and decreasing nitrate, nitrite and phosphate concentrations were observed along the North to South gradient. Transcriptionally active bacterial taxa were similar for the different sites, but expression of oyster-associated microbial genes involved in nutrient (nitrogen and phosphorus) cycling varied throughout the Bay, reflecting the local nutrient regimes and prevailing environmental conditions.

Conclusions

The observed shifts in microbial community composition and function inform how estuarine conditions affect host-associated microbiomes and their ecosystem services. As the effects of estuarine acidification are expected to increase due to the combined effects of eutrophication, coastal pollution, and climate change, it is important to determine relationships between host health, microbial community structure, and environmental conditions in benthic communities.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-020-00066-0.

Bacterial Community Dynamics in an Oyster Hatchery in Response to Probiotic Treatment

Larval oysters in hatcheries are susceptible to diseases caused by bacterial pathogens, including Vibrio spp. Previous studies have shown that daily addition of the probiotic Bacillus pumilus RI06-95 to water in rearing tanks increases larval survival when challenged with the pathogen Vibrio coralliilyticus. We propose that the presence of probiotics causes shifts in bacterial community structure in rearing tanks, leading to a net decrease in the relative abundance of potential pathogens. During three trials spanning the 2012-2015 hatchery seasons, larvae, tank biofilm, and rearing water samples were collected from control and probiotic-treated tanks in an oyster hatchery over a 12-day period after spawning. Samples were analyzed by 16S rRNA sequencing of the V4 or V6 regions followed by taxonomic classification, in order to determine bacterial community structures. There were significant differences in bacterial composition over time and between sample types, but no major effect of probiotics on the structure and diversity of bacterial communities (phylum level, Bray-Curtis k = 2, 95% confidence). Probiotic treatment, however, led to a higher relative percent abundance of Oceanospirillales and Bacillus spp. in water and oyster larvae. In the water, an increase in Vibrio spp. diversity in the absence of a net increase in relative read abundance suggests a likely decrease in the abundance of specific pathogenic Vibrio spp., and therefore lower chances of a disease outbreak. Co-occurrence network analysis also suggests that probiotic treatment had a systemic effect on targeted members of the bacterial community, leading to a net decrease in potentially pathogenic species.

From the raw bar to the bench: Bivalves as models for human health

Bivalves, from raw oysters to steamed clams, are popular choices among seafood lovers and once limited to the coastal areas. The rapid growth of the aquaculture industry and improvement in the preservation and transport of seafood have enabled them to be readily available anywhere in the world. Over the years, oysters, mussels, scallops, and clams have been the focus of research for improving the production, managing resources, and investigating basic biological and ecological questions. During this decade, an impressive amount of information using high-throughput genomic, transcriptomic and proteomic technologies has been produced in various classes of the Mollusca group, and it is anticipated that basic and applied research will significantly benefit from this resource. One aspect that is also taking momentum is the use of bivalves as a model system for human health. In this review, we highlight some of the aspects of the biology of bivalves that have direct implications in human health including the shell formation, stem cells and cell differentiation, the ability to fight opportunistic and specific pathogens in the absence of adaptive immunity, as source of alternative drugs, mucosal immunity and, microbiome turnover, toxicology, and cancer research. There is still a long way to go; however, the next time you order a dozen oysters at your favorite raw bar, think about a tasty model organism that will not only please your palate but also help unlock multiple aspects of molluscan biology and improve human health.

Developing tools for the study of molluscan immunity: The sequencing of the genome of the eastern oyster, Crassostrea virginica

The eastern oyster, Crassostrea virginica, provides important ecological and economical services, making it the target of restoration projects and supporting a significant fishery/aquaculture industry with landings valued at more than $100 million in 2012 in the United States of America. Due to the impact of infectious diseases on wild, restored, and cultured populations, the eastern oyster has been the focus of studies on host-pathogen interactions and immunity, as well as the target of selective breeding efforts for disease resistant oyster lines. Despite these efforts, relatively little is known about the genetic basis of resistance to diseases or environmental stress, not only in eastern oyster, but also in other molluscan species of commercial interest worldwide. In order to develop tools and resources to assist in the elucidation of the genomic basis of traits of commercial, biological, and ecological interest in oysters, a team of genome and bioinformatics experts, in collaboration with the oyster research community, is sequencing, assembling, and annotating the first reference genome for the eastern oyster and producing an exhaustive transcriptome from a variety of oyster developmental stages and tissues in response to a diverse set of environmentally-relevant stimuli. These transcriptomes and reference genome for the eastern oyster, added to the already available genome and transcriptomes for the Pacific oyster (Crassostrea gigas) and other bivalve species, will be an essential resource for the discovery of candidate genes and markers associated with traits of commercial, biological, and ecologic importance in bivalve molluscs, including those related to host-pathogen interactions and immunity.

Numerical quantification of Perkinsus marinus in the American oyster Crassostrea virginica (Gmelin, 1791) (Mollusca: Bivalvia) by modern stereology

Species of Perkinsus are responsible for high mortalities of bivalve molluscs world-wide. Techniques to accurately estimate parasites in tissues are required to improve understanding of perkinsosis. This study quantifies the number and tissue distribution of Perkinsus marinus in Crassostrea virginica by modern stereology and immunohistochemistry. Mean total number of trophozoites were (mean +/- SE) 11.80 +/- 3.91 million and 11.55 +/- 3.88 million for the optical disector and optical fractionator methods, respectively. The mean empirical error between both stereological approaches was 3.8 +/- 1.0%. Trophozoites were detected intracellularly in the following tissues: intestine (30.1%), Leydig tissue (21.3%), hemocytes (14.9%), digestive gland (11.4%), gills (6.1%), connective tissues (5.7%), gonads (4.1%), palps (2.2%), muscle (1.9%), mantle connective (0.8%), pericardium (0.7%), mantle epithelium (0.1%), and heart (0.1%). The remaining 0.6% were found extracellularly. Percentages of trophozoite stages were (mean +/- SE): large, log-phase trophonts, i.e., signet rings, 97.0 +/- 1.2%; meronts, 2.0 +/- 0.9%; clusters of small, log-phase trophonts, i.e., merozoites, 1.0 +/- 0.5%. Levels of infection in hemocytes and Leydig tissue were representative of total parasite intensity. These techniques are a powerful tool to follow parasite distribution and invasion, and to further explore mechanisms of Perkinsus spp. pathogenesis in bivalves.

Survival of eastern oysters Crassostrea virginica from three lines following experimental challenge with bacterial pathogens

Shellfish production is often affected by bacterial pathogens that cause high losses in hatcheries and nurseries. We evaluated the relative survival of larvae and juveniles of 3 Crassostrea virginica oyster lines: (1) GHP, a Rhode Island line; (2) NEHY, a line resistant to dermo and multinucleated sphere X diseases; and (3) FLOWERS, a line resistant to Roseovarius oyster disease, experimental challenge with Vibrio spp. isolates RE22 and RE101, causative agents of bacillary necrosis in Pacific oyster larvae, and the type strain of Roseovarius crassostreae, causative agent of Roseovarius oyster disease. All of the isolates were able to induce significant mortalities in oyster larvae and juveniles. Susceptibility to bacterial challenge in larvae was significantly higher at 25 degrees C than at 20 degrees C. Susceptibility decreased with oyster age; mean survival time ranged from 24 h in oyster larvae to more than 6 wk in juveniles. Significant differences in susceptibility to bacterial challenge were observed between oyster lines; NEHY was the most resistant line overall. Extracellular products (ECPs) from Vibrio sp. RE22 and R. crassostreae, as well as viable bacteria, were toxic to hemocytes from the 3 oyster lines, suggesting that ECPs are involved in pathogenesis and that external and mucosal barriers to infection are major contributors to resistance to bacterial challenge. These protocols will be useful in the elucidation of mechanisms of bacterial pathogenesis and resistance to infection in oysters.

Fundulus as the premier teleost model in environmental biology: opportunities for new insights using genomics

A strong foundation of basic and applied research documents that the estuarine fish Fundulus heteroclitus and related species are unique laboratory and field models for understanding how individuals and populations interact with their environment. In this paper we summarize an extensive body of work examining the adaptive responses of Fundulus species to environmental conditions, and describe how this research has contributed importantly to our understanding of physiology, gene regulation, toxicology, and ecological and evolutionary genetics of teleosts and other vertebrates. These explorations have reached a critical juncture at which advancement is hindered by the lack of genomic resources for these species. We suggest that a more complete genomics toolbox for F. heteroclitus and related species will permit researchers to exploit the power of this model organism to rapidly advance our understanding of fundamental biological and pathological mechanisms among vertebrates, as well as ecological strategies and evolutionary processes common to all living organisms.

Role of nitric oxide in the defenses of Crassostrea virginica to experimental infection with the protozoan parasite Perkinsus marinus

We investigated the role of nitric oxide (NO) in the responses of the Eastern oyster, Crassostrea virginica, to the protozoan parasite Perkinsus marinus, causative agent of Dermo disease. P. marinus induced a slight but significant increase in NO production by oyster hemocytes in vitro, comparable to the increase induced by the immune stimulants phorbol myristrate acetate (PMA) and lipopolysaccharide (LPS). P. marinus also activated the NO response in oysters in vivo, as shown by induction of a protein reacting with a universal NO synthase (NOS) antibody in hemocytes and the presence of high levels of nitrite in plasma. Treatment of experimentally infected oysters with the NOS inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) resulted in a transient decrease in NO levels in oyster plasma and a significant increase in the number of parasites at early time points after infection. The NO donor, S-nitroso-N-acetyl-penicillamine (SNAP) caused a significant inhibition in the proliferation of P. marinus cultured cells after 24 h of incubation. These results indicate that NO has a role in decreasing parasite loads at early time points after infection.

The major Aeromonas veronii outer membrane protein: gene cloning and sequence analysis

The gene encoding the major outer membrane protein (OMP) from Aeromonas veronii, Omp38, was cloned and characterized. Sequence analysis revealed an open reading frame of 1,047 nucleotides coding for a primary protein of 349 amino acids with a 20-amino-acid signal peptide at the N-terminal and the consensus sequence Ala-X-Ala (Ala-Asn-Ala) as the signal peptidase I recognition site. The mature protein is composed of 329 amino acids with a calculated molecular mass of 36,327 Da. The degree of identity of the deduced Omp38 amino acid sequence to porins from enteric bacteria (OmpF, PhoE, and OmpC) was only 30%. Nevertheless, Omp38 possesses typical features of Gram-negative porins, including acidic pI, high glycine and low proline content, no cysteine residues, and a carboxy-terminal Phe. On the basis of PhoE-OmpF three-dimensional structure and the Kyte-Doolittle hydrophobicity analysis, it seems likely that Omp38 secondary structure consists of 16 antiparallel beta-strands and 8 loops. Phylogenetic analyses among Omp38 and related porins from Gram-negative bacteria originate well-defined clusters that agree with the taxonomy of the corresponding organisms.

Protease activity in the plasma of American oysters, Crassostrea virginica, experimentally infected with the protozoan parasite Perkinsus marinus

Perkinsus marinus is responsible for disease and mortality of the American oyster, Crassostrea virginica. To investigate the interactions between P. marinus and oyster hemocytes, protease activity was measured in plasma of oysters collected 4 hr, 24 hr, 4 days, and 2 mo after experimental infection with P. marinus. A significant increase in protease activity was observed in oyster plasma 4 hr after injection with P. marinus, followed by a sharp decrease within 24 hr. Gelatin-impregnated gel electrophoresis showed the presence of 2 major bands (60 and 112 kDa) and 3 less prevalent bands (35, 92, and 200 kDa) with metalloproteinaselike activity in the plasma of noninfected oysters. Additional bands in the 40- to 60-kDa range, corresponding to P. marinus serine proteases, were observed in oyster plasma at early time points after infection. A transient, but significant, decrease in the activity of oyster metalloproteinases was observed at early time points after infection. Coincubation of oyster plasma with P. marinus extracellular products resulted in a decrease in oyster metalloproteinases and several P. marinus proteases. This study provides insights into the role of proteases in the pathogenesis of Dermo disease.

Molecular cloning, sequencing and characterization of omp48, the gene encoding for an antigenic outer membrane protein from Aeromonas veronii

AIMS

To clone, sequence and characterize the gene encoding the Omp48, a major outer membrane protein from Aeromonas veronii.

METHODS AND RESULTS

A genomic library of Aer. veronii was constructed and screened to detect omp48 gene sequences, but no positive clones were identified, even under low stringency conditions. The cloned gene probably was toxic to the host Escherichia coli strain, so the cloning of omp48 was achieved by inverse PCR. The nucleotide sequence of omp48 consisted of an open reading frame of 1278 base pairs. The predicted primary protein is composed of 426 amino acids, with a 25-amino-acid signal peptide and common Ala-X-Ala cleavage site. The mature protein is composed of 401 amino acids with a molecular mass of 44,256 Da.

CONCLUSIONS

The omp48 gene from Aer. veronii was cloned, sequenced and characterized in detail. BLAST analysis of Omp48 protein showed sequence similarity (over 50%) to the LamB porin family from other pathogenic Gram-negative bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial diseases are a major economic problem for the fish farming industry. Outer membrane proteins are potentially important vaccine components. The characterization of omp48 gene will allow further investigation of the potential of Omp48 as recombinant or DNA vaccine component to prevent Aer. veronii and related species infections in reared fish.

16S ribosomal DNA sequencing confirms the synonymy of Vibrio harveyi and V. carchariae

Seventeen bacterial strains previously identified as Vibrio harveyi (Baumann et al. 1981) or V. carchariae (Grimes et al. 1984) and the type strains of V. harveyi, V. carchariae and V. campbellii were analyzed by 16S ribosomal DNA (rDNA) sequencing. Four clusters were identified in a phylogenetic analysis performed by comparing a 746 base pair fragment of the 16S rDNA and previously published sequences of other closely related Vibrio species. The type strains of V. harveyi and V. carchariae and about half of the strains identified as V. harveyi or V. carchariae formed a single, well-supported cluster designed as 'bona fide' V. harveyi/carchariae. A second more heterogeneous cluster included most other strains and the V. campbellii type strain. Two remaining strains are shown to be more closely related to V. rumoiensis and V. mediterranei. 16S rDNA sequencing has confirmed the homogeneity and synonymy of V. harveyi and V. carchariae. Analysis of API20E biochemical profiles revealed that they are insufficient by themselves to differentiate V. harveyi and V. campbellii strains. 16S rDNA sequencing, however, can be used in conjunction with biochemical techniques to provide a reliable method of distinguishing V. harveyi from other closely related species.

Infectious necrotizing enteritis and mortality caused by Vibrio carchariae in summer flounder Paralichthys dentatus during intensive culture

An epizootic causing mortality among cultured summer flounder Paralichthys dentatus occurred in summer of 1998 at a land-based facility on Narragansett Bay, Rhode Island, USA. The disease, flounder infectious necrotizing enteritis (FINE), was characterized by reddening around the anal area, distended abdomens filled with opaque serosanguineous fluid, enteritis and necrosis of the posterior intestine. In extreme cases of the disease, the posterior intestine was detached from the anus and was observed coming out the vent. The intestine of individuals that recovered from the disease ended in a blind-sac; the abdomens of these fish were distended, due to food and water inside the intestinal blind-sac. A bacterium was isolated from ascites fluid and kidney of moribund flounder and identified as the causative agent in challenge experiments. The pathogen was identified as Vibrio carchariae by morphological and biochemical characteristics and sequence of the 16S rRNA. The LD50 estimate was 5 x 10(5) colony-forming units injected intraperitoneally into 100 to 200 g summer flounder.

Evaluation of eukaryotic promoters for the construction of DNA vaccines for aquaculture

We evaluated fish promoters as an alternative to viral promoters in the construction of DNA vaccines for aquaculture. A carp beta-actin promoter drove expression of the luciferase gene in live fish tissue to levels comparable to the CMVtk promoter.

Isolation and Characterization of an Actin Promoter from the Red Abalone (Haliotis rufescens)

: We have isolated and characterized the 5'-flanking and part of the coding region of an actin gene from the red abalone Haliotis rufescens. There is high sequence homology between the abalone actin coding region and actins from other species. The sequence of this abalone actin is more closely related to vertebrate cytoplasmic actins than to muscle actins. RNase protection assays located the position of the transcription start point 66 bp upstream of the initiation codon. Promoter prediction by neural network located a TATA box 30 bp upstream of the transcription start point. A search with the SIGNAL SCAN program identified several potential transcription factor binding sites in the abalone sequence. These sites include sequences highly conserved in other actin promoters, like several putative CAAT and E boxes and a modified CArG box. Transfection assays with a construct containing the 5' flanking region of the abalone actin coupled to a luciferase reporter gene showed that the promoter is functional in mammalian and fish cell lines, as well as in abalone gonad tissue. Expression vectors constructed with the abalone actin promoter will be useful for gene transfer studies into abalone and other mollusks.

Structural and functional differences in the promoter and 5' flanking region of Ldh-B within and between populations of the teleost Fundulus heteroclitus

We have investigated the mechanisms underlying differences in the transcriptional regulation of lactate dehydrogenase-B (Ldh-B) between northern and southern populations of a teleost fish, Fundulus heteroclitus. A 1-kb region immediately 5' of the gene was sequenced from populations throughout the species range. There were two major allele classes in the sample, one containing alleles from Maine and another containing those from Florida. Populations from intermediate localities contained both allele classes. Some individuals from Georgia had sequences intermediate between the two classes, representing either ancestral alleles or recombinants. Tests of neutrality were applied to determine whether observed variation was consistent with neutral expectations. Significant deviations from neutral expectations were detected for the 5' flanking region, but not for other loci. The functional consequences of flanking sequence variation were assessed by transfection of reporter gene constructs into cultured cells and injection into living fish. Consistent with observed variation in Ldh-B transcription rate between populations, significant differences in reporter gene activity were driven by flanking regions from northern and southern populations both in cell culture and in vivo. This functional differentiation, coupled with departures from neutral expectations, suggests that selection may have acted on the regulation of Ldh-B in F. heteroclitus.

Glomerular up-regulation of EIIIA and V120 fibronectin isoforms in proliferative immune complex nephritis

Fibronectin: (FNs) comprise a family of adhesive glycoproteins that are prominent components of mesangial extracellular matrix and accumulate during glomerular injury. By alternative splicing of an unique mRNA precursor, various FN isoforms can be originated. In rat, three regions of the molecule are involved: EIIIA, EIIIB and V. Because specific FN isoforms are expressed in embryogenesis and wound healing, conditions characterized by cell migration and adhesion, we examined the pattern of FN isoforms in the mild and severe phases of a progressive immune complex proliferative nephritis in rats. We constructed specific probes to analyze the splicing pattern of FN pre-mRNAs by ribonuclease protection assays. FN mRNAs containing EIIIA, EIIIB and V regions increased along, the progression of nephritis, though the increment of EIIIB-FN mRNA was modest. However, different regulation of all these isoforms was observed. The percentage of FN mRNA containing the EIIIA exon versus total FN increased with the severity of the disease, while the percentage of FN mRNA containing the EIIIB exon decreased. Relative V-FN mRNA expression versus total FN mRNA increased only in the severe phase. By means of specific antibodies we also studied the presence of EIIIA, EIIIB and V-FN proteins in the kidney. In the normal glomerutus, EIIIA-FN protein was barely detectable in the mesangium, increasing in the mild phase of nephritis. In the severe phase of nephritis, increased EIIIA-FN was localized in the mesangium, in Bowman's capsule and in crescents. By contrast, EIIIB-FN protein in the glomerulus was absent even in the severe phase. V120-FN protein, an isoform that mediates the attachment of leukocytes through the VLA-4 integrin, was present in the mesangium and glomerular capillary loops in control animals, and increased in the severe phase of nephritis, coinciding with a strong leukocyte infiltration. In conclusion, our results show that during immune glomerular injury there were marked changes in the pattern of FN isoforms expression. Since those isoforms, particularly V120 isoform, are important in cell adhesion and migration, their up-regulation may facilitate the recruitment of cells into the injured glomeruli. The blockade of the interaction between V120-FN and infiltrating leukocytes may represent a new approach to the treatment of nephritis.

Interferon-inducible protein-10 is highly expressed in rats with experimental nephrosis

Interferon-inducible protein (IP)-10 is a small glycoprotein member of a family of chemotactic cytokines structurally related to interleukin-8. We have recently described the induction of IP-10 mRNA in mouse mesangial cells stimulated with lipopolysacharide, interferon-gamma, and tumor necrosis factor-alpha. To further evaluate a possible role for this chemokine in renal injury, we have studied IP-10 in an experimental model of nephrosis induced in rats by adriamycin. High levels of glomerular IP-10 mRNA expression and glomerular and tubulointerstitial IP-10 protein were seen on day 21, coinciding with maximal proteinuria, glomerular tumor necrosis factor mRNA expression, and interstitial cellular infiltrates. Maintenance on a low protein diet not only delayed the appearance of proteinuria and interstitial cellular infiltrate but also decreased glomerular IP-10 mRNA expression. Isolated normal glomeruli and cultured glomerular epithelial and mesangial cells from normal rats expressed IP-10 mRNA upon stimulation with 100 U/ml interferon or 1 microgram/ml lipopolysaccharide for 3 hours. IP-10 mRNA expression was also inducible by lipopolysaccharide and cytokines in NRK 49F renal interstitial fibroblasts and, to a lesser extent, in NRK 52E tubular epithelial cells. Furthermore, IP-10 protein was inducible in murine mesangial cells. We conclude that IP-10 is highly inducible in vitro and in vivo in resident glomerular and tubulointerstitial cells. IP-10 may participate in the modulation of renal damage in experimental nephrosis.

Fibronectin (FN) decreases glomerular lesions and synthesis of tumour necrosis factor-alpha (TNF-alpha), platelet-activating factor (PAF) and FN in proliferative glomerulonephritis

We have studied the effect of therapy with plasma FN on glomerular synthesis of PAF, TNF-alpha and FN, in experimental proliferative glomerulonephritis. Glomerular PAF, TNF-alpha and FN production were increased in rats with nephritis. Peak glomerular PAF production preceded, while peak glomerular TNF-alpha bioactivity coincided with maximal proteinuria. Rats treated with FN (5 mg/kg per 48 h) for 15 days had less proteinuria, glomerular and interstitial cell infiltration and glomerular PAF, TNF-alpha and FN synthesis than non-treated rats. In order to characterize further the mechanisms of action of FN, healthy rats were injected with either FN or saline. Peripheral blood mononuclear cells and neutrophils from healthy rats injected with FN secreted less TNF-alpha and PAF, respectively, than those obtained from saline-treated rats. Our data suggest that the beneficial effect of FN may be related to decreased number of glomerular leucocytes and decreased synthesis of inflammatory mediators and extracellular matrix.

Involvement of tumor necrosis factor and platelet-activating factor in the pathogenesis of experimental nephrosis in rats

BACKGROUND

The experimental nephrosis induced in rats by adriamycin (ADR) or puromycin aminonucleoside (PA) provide a useful model to study the participation of inflammatory mediators in the pathogenesis of proteinuria.

EXPERIMENTAL DESIGN

We have measured tumor necrosis factor (TNF) and platelet-activating factor (PAF) production by glomeruli of rats with nephrosis, as well as the effect of treatment with the PAF antagonist, BN52021. We have also evaluated the in vitro effects of ADR, PA, and PAF on TNF and PAF production, cell viability, and protein synthesis in glomerular mesangial cells and glomerular epithelial cells (GEC) in culture.

RESULTS

In ADR nephrosis, the greatest production of PAF was on day 14, preceding maximal proteinuria, whereas the highest levels of TNF where observed on day 21 after ADR injection, the moment at which proteinuria reached maximal levels. In PA nephrosis, glomerular PAF production peaked twice (days 1 and 15), before and after maximal proteinuria (day 11), whereas TNF production peaked from days 2 to 11, and slowly declined until day 21. In both models, treatment with BN52021 induced a striking decrease in proteinuria, as well as a diminution in glomerular TNF and PAF production. Both ADR and PA induced TNF and PAF production in whole glomeruli, glomerular mesangial cells, and GEC in culture. As shown by a 51Cr release assay, ADR and PA were toxic to GEC. This effect was inhibited by PAF antagonists and by anti-TNF antibodies. Whereas TNF was moderately toxic to GEC, PAF had no effect on 51Cr release. TNF toxicity was abolished by anti-TNF antibodies and largely diminished by PAF antagonists.

CONCLUSIONS

TNF and PAF may participate in the induction of GEC damage and the development of proteinuria in two experimental models of nephrosis in rats.

The potential role of inflammatory and fibrogenic cytokines in the glomerular diseases

In recent years increasing evidence has been accumulated on the role of cytokines in mediating glomerular and renal damage. Many such cytokines are released in the inflamed glomeruli by leukocytes and intrinsic glomerular cells. Cytokines not only recruit inflammatory cells into the injured glomeruli, but also induce a variety of responses on glomerular cells that range from a direct toxic effect to shape changes, proliferation, and induction of the release of inflammatory mediators and extracellular matrix, and could promote further glomerular damage. Moreover, exogenous administration of cytokines has induced glomerular injury in healthy animals and has enhanced renal damage in animals with glomerulonephritis. Anti-cytokine strategies have proved to be effective therapeutical alternatives in experimental models of glomerular diseases and may provide a more specific approach to the management of human glomerulonephritis.

Expression of IP-10, a lipopolysaccharide- and interferon-gamma-inducible protein, in murine mesangial cells in culture

IP-10 is an early gene induced in multiple cell types by a variety of proinflammatory agents, notably interferons (IFNs) and lipopolysaccharide (LPS). To determine whether this protein might play a role in amplifying immune-mediated glomerular injury, we cultured mouse mesangial cells with several stimuli for various times. Increasing amounts of IFN-gamma (to 100 units/ml) elicited increasing levels of IP-10 messenger RNA (mRNA), sustained to 24 hours, but had no effect on tumor necrosis factor-alpha (TNF-alpha) mRNA. LPS induced transient IP-10 mRNA expression that peaked at 8 hours; TNF-alpha mRNA was also increased. TNF-alpha at doses up to 10 ng/ml and soluble immune complexes up to 150 micrograms/ml antibody evoked 3- to 5-fold increases in IP-10 mRNA expression, much less than the 30- to 70-fold increases seen with IFN-gamma and LPS. We conclude that IFN-gamma, LPS, and other agonists can amplify glomerular immune injury, perhaps via elevated expression of IP-10.