Virus-host interactions are multidimensional, they include the alterations in transcriptome, proteome, metabolome and lipidome of the host. In recent years, most of the high-throughput studies have focused majorly on the host transcriptomic responses and other host components have received less attention. This study presents a comprehensive characterization of the lung proteome, critical signaling pathways and proteomic determinants responsible for disease pathogenesis at the proteome level in chicken lung tissues infected with HPAI H5N1 virus over different time points post-infection.
Clinical signs
Chicken in the control group did not show any clinical signs during the experimental period. In the test group, the birds were normal up to 12 hr post-infection. Mild clinical symptoms like depression, decreased feed as well as water consumption and ruffled feathers were observed at 24 hr post-infection. The clinical symptoms like dullness, lacrimation, cyanotic combs and wattles, edema and red discoloration of the shanks and feet were seen in the birds at 48 hr post-infection.
Raw mass spectra dataset analysis
Total 15 fractions of WATERS QTOP raw data sets were generated, with data size 48 GB, including 1, 47,451 MS scans and 19,917 MS/MS scans. Total 19,917 MS/MS spectra were searched against chicken protein database by comet search engine. The iProphet algorithm identified 17,273 unique peptides and 8,516 unique proteins at minimum probability threshold of above 0.05 and minimum above 7 amino acids. In order to increase the accuracy of validation of peptides and proteins, we applied local FDR 5% level (probability cut off above 0.95) in the ProteinProphet output. At higher probability threshold cut off, we identified total 3313 proteins with the presence of at least one unique peptide. ProteinProphet predicted sensitivity and error rate information is shown in Fig.S1. This is the highest protein identification reported till date in chicken. Our proteomic approach identified H5N1 viral peptides such as NA, NP and PB1 in the chicken lung proteome. NA is a sialidase responsible for releasing sialic acid from glycoprotein and glycolipid sialoconjugates of bound influenza virus to assist virus release [30]. NP is an important viral protein responsible for the packaging of the viral RNA and also shown to be involved in many aspects of influenza viral replication [31, 32]. PB1 viral protein has been shown to be associated with the high pathogenicity of H5N1 viruses infection in ducks [33]. Influenza viral infection status of lung tissues was confirmed by virus isolation in embryonated egg inoculation and RT-PCR method as well as by identification of viral peptides in lung proteome dataset.
Differential protein expression analysis
At 12 hr post-infection, 820 proteins were upregulated and 2493 proteins were downregulated in chicken lung tissues. A total of 827 proteins were upregulated and 2441 proteins were downregulated at 24 hr post-infection. At 48 hr post-infection, 693 proteins were upregulated and 2620 proteins were downregulated in chicken lung proteome (Table 1). A total of 470 and 2235 proteins were found to be commonly upregulated and downregulated in all time intervals post-infection in chicken lungs infected with H5N1 virus, respectively (Fig. 1). The protein profile showed that 70, 70 and 101 proteins were exclusively up regulated in chicken lung tissue at 12hr, 24hr and 48hr post-infection, respectively (Fig. 1). Downregulation of 87, 35 and 245 proteins were observed exclusively at 12 hr, 24hr and 48hr post-infection, respectively (Fig. 1). The fold change value of the upregulated proteins ranged from 42 to 1. Interestingly, at 48 hr time point (fold change value below1.5), higher number of proteins were downregulated (n = 1754) as compare to 12 hr time point (n = 247) post-infection condition (Table 1, Fig. 2). This result indicates that most of the host proteins were downregulated at the later stage of infection.
Table 1
Differential protein expression analysis in chicken infected with HPAI H5N1 virus.
Condition
|
Upregulated proteins
|
Downregulated proteins
|
Upregulated proteins
(> 1.5 fold)
|
Downregulated Proteins
(< 1.5 fold)
|
12hr interval
|
820
|
2493
|
138
|
247
|
24hr interval
|
872
|
2441
|
157
|
222
|
48hr interval
|
693
|
2620
|
173
|
1754
|
Gene ontology analysis of the commonly upregulated and downregulated lung tissue proteins of H5N1 infected chicken lung enriched following GO terms such as cytoskeleton, regulation of cell cycle, regulation of protein kinase activity etc. (Table 2). The upregulation (KRT6A, MCPH1, MYH7, MICAL1 and MICAL3) and downregulation (ACTL9, CTNNB1, DNM1, FILIP1L, and MYO1B) of cytoskeletal proteins were observed in the lung tissue of chicken. Cytoskeletal proteins have been reported to interact with viral proteins to regulate viral replication and assembly as well as the transport of viral components in the cell [34, 35]. Similar associations of cytoskeletal proteins with influenza infection condition are also reported previously [10, 14, 36]. The cyclin-dependent kinases (CDKs) such as CDK13, DDB1, DRD3, FOXG1, and TCF3 that are involved in the regulation of cell cycle were all upregulated in chicken lung proteome. Söderholm et al. (2016) reported that the cyclin-dependent kinase activity is required for efficient viral replication and for activation of the host antiviral responses [37]. Protein kinase activity associated proteins, namely, JAK3, MARK3, TBK1, EIF2AK3, PRKCA, and TRPM6were downregulated in the chicken lung tissues. Differential expression of proteins including signal transduction molecules, kinases and other biochemical metabolism related enzymes that are associated with the repair of damaged lung tissues are reported in dogs infected with influenza virus infection [14]. In addition, some apoptosis and tumour-associated proteins (BCL6, FAF1, TBX5, AKAP13, TNFSF10 and TGFB1) were also identified in the chicken lung proteome. Further we did GO term analysis of proteins that were exclusively expressed in particular post-infection condition in chicken (Table 3). This analysis result provides information how the disease progress from onset of disease to outcome of disease in chicken. At 12 hr interval, most of cellular homeostasis were affected and at 48 hr post-infection condition the host activated critical pathways such as Influenza A, chemokine signaling pathway, Jak-STAT signaling pathway, apoptosis, MAPK signaling pathway (Table 3). These results indicate that the virus initially inhibit the cellular homeostasis and activates the critical pathways at the later stage of infection.
Table 2
Gene Ontology term analysis of commonly upregulated and downregulated lung tissue proteins in chicken infected with HPAI H5N1 virus.
GO terms
|
Count
|
P-Value
|
Upregulated proteins
|
|
|
Golgi apparatus
|
32
|
7.70E-04
|
Cellular homeostasis
|
21
|
1.10E-03
|
Protein heterodimerization activity
|
12
|
2.20E-03
|
Ion homeostasis
|
18
|
3.70E-03
|
Protein domain specific binding
|
15
|
4.40E-03
|
Acid-amino acid ligase activity
|
11
|
5.20E-03
|
Intracellular organelle lumen
|
50
|
6.40E-03
|
Fatty acid transport
|
4
|
1.80E-02
|
Regulation of cell cycle
|
13
|
3.50E-02
|
Vesicle-mediated transport
|
19
|
4.20E-02
|
Positive regulation of protein kinase cascade
|
8
|
5.10E-02
|
Negative regulation of gene expression
|
16
|
8.20E-02
|
Cytoskeleton
|
35
|
8.60E-02
|
Adenyl nucleotide binding
|
47
|
1.90E-03
|
ATP binding
|
43
|
4.90E-03
|
Downregulated proteins
|
|
|
Adenyl nucleotide binding
|
236
|
1.20E-13
|
ATP binding
|
222
|
5.40E-13
|
GTPase regulator activity
|
74
|
4.50E-08
|
Cytoskeleton
|
176
|
1.20E-06
|
Protein kinase activity
|
82
|
9.20E-04
|
Regulation of small GTPase mediated signal transduction
|
47
|
8.10E-06
|
Regulation of Rho protein signal transduction
|
25
|
1.10E-05
|
Proteinaceous extracellular matrix
|
51
|
8.80E-05
|
Regulation of Ras protein signal transduction
|
38
|
1.30E-04
|
Protein amino acid phosphorylation
|
89
|
6.20E-04
|
Cell death
|
93
|
1.30E-03
|
Enzyme linked receptor protein signalling pathway
|
49
|
3.10E-03
|
Endosome
|
44
|
4.10E-03
|
Intracellular signaling cascade
|
146
|
4.30E-03
|
Positive regulation of gene expression
|
70
|
2.50E-02
|
Calcium ion binding
|
105
|
3.20E-02
|
Negative regulation of translation
|
8
|
3.60E-02
|
Regulation of phosphorylation
|
56
|
4.60E-02
|
JUN kinase binding
|
3
|
4.70E-02
|
Proteolysis
|
114
|
7.20E-02
|
Positive regulation of MAP kinase activity
|
15
|
9.60E-02
|
Table 3
Functional annotation analysis of proteins exclusively expressed in chicken at different time points post infection with HPAI H5N1 virus.
Pathway activation
|
No. of proteins
|
P Value
|
12 hr post infection
|
|
|
Cell cycle
|
31
|
2.88E-26
|
mRNA surveillance pathway
|
21
|
4.95E-18
|
RNA transport
|
24
|
2.62E-17
|
p53 signaling pathway
|
11
|
1.22E-07
|
Pathways in cancer
|
13
|
0.0128
|
24 hr post infection
|
|
|
Cell cycle
|
12
|
1.17E-08
|
Gap junction
|
8
|
7.31E-06
|
RNA degradation
|
6
|
6.13E-05
|
T cell receptor signaling pathway
|
7
|
0.000127
|
Fc epsilon RI signaling pathway
|
6
|
0.000215
|
ErbB signaling pathway
|
6
|
0.000485
|
Phagosome
|
4
|
0.00326
|
Fc gamma R-mediated phagocytosis
|
5
|
0.00529
|
Chemokine signaling pathway
|
7
|
0.00615
|
B cell receptor signaling pathway
|
4
|
0.0112
|
Neurotrophin signaling pathway
|
5
|
0.0141
|
Natural killer cell mediated cytotoxicity
|
5
|
0.0221
|
Focal adhesion
|
6
|
0.0287
|
48 hr post infection
|
|
|
RNA transport
|
47
|
1.77E-18
|
T cell receptor signaling pathway
|
37
|
6.08E-15
|
Regulation of actin cytoskeleton
|
52
|
1.15E-14
|
Focal adhesion
|
54
|
4.67E-14
|
Pathways in cancer
|
70
|
1.13E-13
|
ErbB signaling pathway
|
31
|
6.41E-12
|
Adipocytokine signaling pathway
|
26
|
6.92E-12
|
B cell receptor signaling pathway
|
28
|
1.91E-11
|
Neurotrophin signaling pathway
|
35
|
3.79E-10
|
mRNA surveillance pathway
|
26
|
6.14E-09
|
Chemokine signaling pathway
|
41
|
7.57E-08
|
Influenza A
|
28
|
1.68E-07
|
Cell cycle
|
30
|
3.95E-07
|
Jak-STAT signaling pathway
|
25
|
1.62E-06
|
Fc epsilon RI signaling pathway
|
21
|
1.86E-06
|
mTOR signaling pathway
|
14
|
2.72E-05
|
Toll-like receptor signaling pathway
|
20
|
0.000377
|
Apoptosis
|
18
|
0.000385
|
Natural killer cell mediated cytotoxicity
|
24
|
0.00139
|
MAPK signaling pathway
|
38
|
0.00297
|
Leukocyte transendothelial migration
|
19
|
0.00374
|
RIG-I-like receptor signaling pathway
|
11
|
0.0039
|
Molecular pathogenesis of H5N1 infection in chicken
Previous transcriptomics study of our group found that highly pathogenic H5N1 virus induced excessive expression of type I IFNs, cytokine, chemokines and ISGs in the lung tissues. This atypical expression of immune genes (cytokine storm) might be the cause for the high mortality in chickens [28]. However, the information on the pathways activated, constituents of cytokine storm and therapeutic strategies against cytokine storm is lacking in avian species. Intensive molecular studies in humans and human animal models system have identified, (1) Activation of TLR3 and 7, as well as endosome (TLR3 and 7) and cytosolic (RIG-I) pathways; (2) activation of IL-1R signaling pathway; and (3)activation of MVAS/MyD88/TRIF signaling as essential pathways involved in the cytokine storm [38].
In order to check whether these pathways are activated and if activated what are the levels of expression of the immune genes in chicken lung tissues, we applied meta-analysis of lung transcriptome datasets. We utilised the previously published microarray datasets of chicken infected with HPAIVs, because transcriptomic data can capture the complete gene expression dynamics at a particular condition. We mapped the differentially expressed genes retrieved from meta-analysis results of chicken into influenza reference pathways in KEGG database. Activation of TLR signaling pathway, RIG I signaling pathway, NOD like receptor signaling pathway and JAK-STAT signaling pathway were observed in chicken lung transcriptome (Fig.S2). Similarly, activation of these pathways was evident in the chicken proteome datasets (Fig. 3). Further Bayesian networks (BN) were constructed with prior knowledge using chicken meta-analysis transcriptome datasets (Fig. 4, Fig. S3). The combined in silico analysis of transcriptome and proteome datasets confirmed the activation of TLR, RLR, NLR and Jak-STAT signaling pathways in lung tissues infected with HPAIVs in chickens. The fact that most of the influenza pathogenesis possesses abnormalities in all of these core pathways suggests they play a central role in the cytokine storm.
Next, we examined the cytokine storm responsive genes (i.e expression level of cytokines, chemokines and ISGs) as a result of activation of the above-mentioned pathways. Cytokine storm responsive genes lists were compiled for chickens based on information in literature [2]. The expression levels (fold change) of these genes were retrieved from meta-analysis transcriptome datasets of chicken. Cytokines, chemokines and ISGs genes were found to be upregulated in chicken lung tissues and these may be the basis of the increase in the severity of HPAI H5N1 infection in chickens (Fig. 5). In summary, we characterized the immune pathways involved in the cytokine storm and identified cytokine storm responsive genes in chicken lung tissues infected with HPAIVs.
Identification of proteomic determinants responsible for disease pathogenesis in chicken
To know the main driver or hub proteins responsible for disease pathogenesis, we constructed protein-protein interaction (PPI) network based on chicken lung proteome dataset (Fig. 6). The proteins such as MyD88, IKBKB, IRAK4, RELA, and MAVS involved in the TLRs, RLRs, IL1R and NLR signaling pathways were identified with high degree centrality and betweenness centrality measures (Table 4).
Table 4
Hub proteins identified in chicken PPI networks based on degree centrality and betweenness centrality measures.
Proteins
|
Degree centrality
|
Betweenness centrality
|
HNF4A
|
254
|
254342.21
|
ELAVL1
|
254
|
253172.78
|
FN1
|
117
|
79642.94
|
COPS5
|
117
|
73208.97
|
CUL1
|
105
|
55049.71
|
CAND1
|
105
|
45936.7
|
CTNNB1
|
80
|
75126.54
|
BRCA1
|
72
|
41422.24
|
FYN
|
65
|
35789.72
|
MYD88
|
10
|
2614.04
|
IKBKB
|
42
|
16555.52
|
RELA
|
48
|
23497.55
|
MAVS
|
6
|
1721.53
|
STAT1
|
81
|
46280.33
|
STAT2
|
14
|
1579.16
|
STAT3
|
90
|
66853.77
|
SOCS3
|
23
|
11524.2
|
IRAK4
|
8
|
311.94
|
MYD88 gene encodes a cytosolic adapter protein that plays a central role in the innate and adaptive immune response. This protein functions as an essential signal transducer in the IL1R and TLR signaling pathways. These pathways in turn regulate the activation of numerous proinflammatory genes [39]. The IKBKB protein phosphorylates the inhibitor in the inhibitor/NF-kappa-B complex, causing dissociation of the inhibitor and activation of NF-kB signaling pathway [40]. MAVS acts downstream of DDX58/RIG-I and IFIH1/MDA5 genes, as an essential signal transducer in the beta interferon signaling pathways and that contribute to antiviral immunity [41]. RELA/NF-kB is a ubiquitous transcription factor involved in several biological processes. This transcription factor is activated through degradation of its specific inhibitor in the cytoplasm; NF-kB moves to the nucleus and activates transcription of specific genes. The NF-kBp65-p65 complex appears to be involved in invasin-mediated activation of IL-8 expression [42]. Teijaro et al. (2014) reported that MyD88 and MAVS as the predominant signaling molecule required for innate immune cell recruitment and for the majority of cytokine amplification (i.e., cytokine storm) in mice infected with influenza virus [38]. Further they suggested that therapeutic control of cytokine storm is possible through a common pathway inhibition downstream of multiple innate pathogen-sensing molecules of cytokine amplification. In our study the identified hub proteins (MyD88, IKBKB, IRAK4, RELA, and MAVS) were all involved in different components of MyD88 and MVAS signaling pathways. Based on this literature, we suggest that successful therapeutic intervention for cytokine storm in chicken should target these proteins as drug targets to blunt the cytokine amplification. Further the S1P1R agonist therapy may suppress global cytokine amplification in chicken as in mice [38]. However biological validation of this hypothesis by in vivo experiment is needed.
In Jak-STAT signalling pathway, we found STAT1, STAT2, STAT3 and SOCS3 proteins as the main driving proteins in the PPI network (Table 4). However, these proteins had protein probability range from 0.63 to 0.90, hence were not evident in our main proteome dataset of chicken. The STAT1, STAT2 and STAT-3 proteins are a key constituents of JAK-STAT signalling pathway, play critical roles in the IFN signalling pathway and are required for a robust IFN-induced antiviral response [43, 44]. SOCS1 and SOCS3 are reported to be critical regulators of IFN responses through the inhibition of STAT phosphorylation and induction of ISGs through a RIG-I/MAVS/IFNAR1-dependent pathway [45, 46].
Further we identified some novel main driver/hub proteins with a very high degree of centrality and betweenness of centrality measures which are not reported previously to be associated with influenza infection condition in human, human models or avian species. These novel hub proteins are HNF4A, ELAVL1, FN1, COPS5, CUL1, CAND1, BRCA1, CTNNB1 and FYN (Table 4, Fig. 6). The HNF4A protein is a transcriptionally controlled transcription factor and required for the transcription of alpha 1-antitrypsin, apolipoprotein CIII, transthyretin genes and HNF1-alpha genes [47]. ELAVL1 is a member of the ELAVL family of RNA-binding proteins and selectively bind AU-rich elements (AREs) found in the 3' untranslated regions of mRNAs. The ELAVL family of proteins play a role in stabilizing ARE-containing mRNAs [48]. This gene has been implicated in a variety of biological processes and has been linked to a number of diseases, including cancer [49].
FN1 bind cell surfaces and various compounds including collagen, fibrin, heparin, DNA, and actin. FN1 is involved in cell adhesion and migration processes during embryogenesis, wound healing, blood coagulation, host defense, and metastasis [50]. COPS5 is one of the eight subunits of COP9 signalosome and functions as an important regulator in phosphorylation of p53/TP53, c-jun/JUN, IkappaBalpha/NFKBIA, ITPK1 and IRF8 signalling [51]. CUL1 is a core component of multiple cullin-RING-based SCF (SKP1-CUL1-F-box protein) E3 ubiquitin-protein ligase complexes, which mediate the ubiquitination of proteins involved in cell cycle progression, signal transduction and transcription [52].
BRCA1 encodes a nuclear phosphoprotein that has a role in maintaining genomic stability, and acts as a tumour suppressor. This protein is involved in transcription, DNA repair of double-stranded breaks, and recombination [53]. FYN gene encodes a membrane-associated tyrosine kinase that has been implicated in the control of cell growth [54]. In summary, many proteins involved in the TLRs, RLRs, NLR and Jak-STAT signaling pathways and other novel proteins were identified as main protein determinant and these proteins might be linked with disease pathogenesis in chicken H5N1 infection. However critical functional role of these proteins in avian influenza pathogenesis in chicken requires further biological validation by in vivo and in vitro experiments.