Award details

Role of AKT1 & SIVA1 in resistance to avian salmonellosis

Reference	BB/J016837/1
Principal Investigator / Supervisor	Dr Mark Fife
Co-Investigators / Co-Supervisors
Institution	The Pirbright Institute
Department	Avian Infectious Diseases
Funding type	Research
Value (£)	108,941
Status	Completed
Type	Research Grant
Start date	01/07/2012
End date	30/06/2015
Duration	36 months

Abstract

Avian resistance to systemic salmonellosis is largely mediated by the SAL1 locus. Analysis of the segregation of SNPs in the progeny of a sixth generation back-cross of inbred lines that differ in resistance (6 and 15I), as well as F(13) inter-cross lines, has fine-mapped the QTL to a 0.4Mb region encoding AKT1 and SIVA1. In murine and human cells, these proteins have opposing effects on apoptosis and induction of innate immunity. In mammalian cells, Salmonella activates AKT via injection of SopB. This delays apoptosis and promotes net intracellular replication in vitro and in mice, as evidenced by studies with sopB mutants, null mice and specific inhibitors. By contrast, SIVA1 is pro-apoptotic and is proposed to control Salmonella via release of heterophil extracellular traps upon cell death. No evidence exists that these mechanisms are relevant in chickens and a need exists to unravel how resistance-associated SNPs exert their effect. We propose to define the kinetics of AKT1 and SIVA1 activation upon Salmonella infection using specific antisera, and associate this with the fate of infected cells ex vivo and in chickens by flow cytometry and immuno-staining. We will examine if levels or activities of AKT1 and SIVA1 explain the differential resistance of lines 6 and 15I. Net replication of Salmonella in such birds will be quantified in cells and tissues by fluorescence dilution, and visualised relative to AKT1 activation and apoptosis. We will further define if AKT1 plays a protective role in avian responses to Salmonella by use of sopB mutants, inhibitors and siRNA-mediated knock-down. Toward marker-assisted selection, we will survey the frequency of informative SNPs in a population of Hy-Line layers directly related to that exposed to a recent fowl typhoid outbreak. Birds of defined genotype will be challenged to associate genetic variation with AKT1/SIVA1 levels or activation, host responses and Salmonella replication.

Summary

Poultry are a key reservoir of human Salmonella infections owing to the ability of some strains to colonise the avian intestines and reproductive tract. Birds often carry the bacteria in the absence of overt symptoms; however some types of Salmonella cause severe typhoid-like diseases in poultry that exert substantial welfare and economic costs. Global population growth and rising affluence are fuelling demand for poultry meat and eggs, and a need exists to enhance the supply and safety of such. Though vaccines are used in layers in some countries, most of the 55 billion chickens reared annually worldwide lack protection against Salmonella infection. We and others have discovered that some chickens exhibit heritable differences in resistance to Salmonella. It may be feasible to selectively breed for birds with improved resilience to Salmonella infection; however this requires the identification of resistance-associated factors and knowledge of how they act. By analysing the genetic material of birds that differ in resistance, we have located a region of the chicken chromosome that confers protection against typhoidal salmonellosis, both in laboratory studies and commercial poultry populations. Recent studies have now resolved the region associated with resistance to just a handful of genes. It is highly plausible that variation affecting two genes in this region (AKT1 and SIVA1) explains why birds react to Salmonella in different ways, as the encoded proteins control host processes that impact on the fate of bacteria. For example, AKT1 and SIVA1 control the death of infected cells and the induction of immune responses, but have opposing activities. It is not possible for us to predict how the genetic changes affecting these genes will alter their expression or activity. Moreover, it is unclear how such factors may control the growth and spread of Salmonella in birds. We therefore propose to: 1. Examine if birds normally respond to Salmonella infection by activating the expression or function of AKT1 and SIVA1. We will examine this in cells cultured from chickens, as well as in intact birds, and associate any differences with host responses and the fate of the bacteria. 2. Examine if lines of chicken known to differ in resistance to Salmonella infection vary in the levels or activation of AKT1 and SIVA1. 3. Use specific inhibitors and bacterial strains to establish that AKT1 activation is necessary for Salmonella to grow and spread in birds. 4. Define the nature, frequency and consequences of genetic changes affecting AKT1 and SIVA1 in commercial poultry populations. This will aid the selective breeding of chickens that show improved resilience to Salmonella infection. We are fortunate to have the support of one of the world's largest poultry breeding companies (Erich Wesjohann Group), who will provide birds, genome sequences, expertise and 10% of total project costs. This reflects the value of the proposed studies to the industry. The consortium has productively collaborated and the proposed studies are a timely, logical and feasible extension of our recent joint research.

Impact Summary

Please see document submitted by lead applicant (joint ref. M1529404)

Committee	Research Committee A (Animal disease, health and welfare)
Research Topics	Animal Health, Immunology, Microbial Food Safety, Microbiology
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	Industrial Partnership Award (IPA)

Associated awards:

BB/J015296/1 Role of AKT1 & SIVA1 in resistance to avian salmonellosis

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