Alternate splicing of transcripts shape macrophage response to Mycobacterium tuberculosis infection

Gingipain regulates isoform switches of PD-L1 in macrophages infected with Porphyromonas gingivalis

Periodontal pathogen Porphyromonas gingivalis (P. gingivalis) is believed to possess immune evasion capabilities, but it remains unclear whether this immune evasion is related to host gene alternative splicing (AS). In this study, RNA-sequencing revealed significant changes in both AS landscape and transcriptomic profile of macrophages following P. gingivalis infection with/without knockout of gingipain (a unique toxic protease of P. gingivalis). P. gingivalis infection increased the PD-L1 transcripts expression and selectively upregulated a specific coding isoform that more effectively binds to PD-1 on T cells, thereby inhibiting immune function. Biological experiments also detected AS switch of PD-L1 in P. gingivalis-infected or gingipain-treated macrophages. AlphaFold 3 predictions indicated that the protein docking compatibility between PD-1 and P. gingivalis-upregulated PD-L1 isoform was over 80% higher than another coding isoform. These findings suggest that P. gingivalis employs gingipain to modulate the AS of PD-L1, facilitating immune evasion.

Enhanced packaging of U6 small nuclear RNA and splicing-related proteins into extracellular vesicles during HIV infection

U6 small nuclear RNA (U6 snRNA), a critical spliceosome component primarily found in the nucleus, plays a vital role in RNA splicing. Our previous study, using the simian immunodeficiency virus (SIV) macaque model, revealed an increase of U6 snRNA in plasma extracellular vesicles (EVs) in acute retroviral infection. Given the limited understanding of U6 snRNA dynamics across cells and EVs, particularly in SIV infection, this research explores U6 snRNA trafficking and its association with splicing proteins in the nucleus, cytoplasm, and EVs. We observed a redistribution of U6 snRNA from the nucleus to EVs post-infection, accompanied by distinct protein profile changes and alterations in nucleic acid metabolism and spliceosome pathways. In addition, U6 machinery proteins changed in cells and EVs in a contrasting manner. The redistribution of U6 and related proteins we observed could be part of a viral strategy to redirect host splicing machinery, suggesting that U6 may have regulatory roles and be part of retroviral infection signature.

Global proteomics reveals pathways of mesenchymal stem cells altered by Mycobacterium tuberculosis

Mycobacterium tuberculosis (M. tb) has a remarkable ability to persist inside host cells. Several studies showed that M. tb infects and survives inside bone marrow mesenchymal stem cells (BM-MSCs) escaping the host immune system. Here, we have identified various cellular pathways that are modulated in human BM-MSCs upon infection with virulent M. tb and the proteomic profile of these cells varies from that of avirulent M. tb infected cells. We found that virulent M. tb infection reshapes host pathways such as stem cell differentiation, alternative splicing, cytokine production, mitochondrial function etc., which might be modulated by M. tb to persist inside this unconventional niche of human BM-MSCs. Additionally, we observed that virulent M. tb infection suppresses various cellular processes. This study uncovers the differences in the host proteomic profiles resulting from the virulent versus avirulent M. tb infection that can pave the way to identify host-directed therapeutic targets for the treatment of tuberculosis.

Profiling genetically driven alternative splicing across the Indonesian archipelago

One of the regulatory mechanisms influencing the functional capacity of genes is alternative splicing (AS). Previous studies exploring the splicing landscape of human tissues have shown that AS has contributed to human biology, especially in disease progression and the immune response. Nonetheless, this phenomenon remains poorly characterized across human populations, and it is unclear how genetic and environmental variation contribute to AS. Here, we examine a set of 115 Indonesian samples from three traditional island populations spanning the genetic ancestry cline that characterizes Island Southeast Asia. We conduct a global AS analysis between islands to ascertain the degree of functionally significant AS events and their consequences. Using an event-based statistical model, we detected over 1,500 significant differential AS events across all comparisons. Additionally, we identify over 6,000 genetic variants associated with changes in splicing (splicing quantitative trait loci [sQTLs]), some of which are driven by Papuan-like genetic ancestry, and only show partial overlap with other publicly available sQTL datasets derived from other populations. Computational predictions of RNA binding activity reveal that a fraction of these sQTLs directly modulate the binding propensity of proteins involved in the splicing regulation of immune genes. Overall, these results contribute toward elucidating the role of genetic variation in shaping gene regulation in one of the most diverse regions in the world.

Host factor RBMX2 promotes epithelial cell apoptosis by downregulating APAF-1's Retention Intron after Mycobacterium bovis infection

The Mycobacterium tuberculosis variant bovis (M. bovis) is a highly pathogenic environmental microorganism that causes bovine tuberculosis (bTB), a significant zoonotic disease. Currently, "test and culling" is the primary measure for controlling bTB, but it has been proven to be inadequate in animals due to their high susceptibility to the pathogen. Selective breeding for increased host resistance to bTB to reduce its prevalence is feasible. In this study, we found a vital host-dependent factor, RBMX2, that can potentially promote M. bovis infection. By knocking RBMX2 out, we investigated its function during M. bovis infection. Through transcriptome sequencing and alternative splicing transcriptome sequencing, we concluded that after M. bovis infection, embryo bovine lung (EBL) cells were significantly enriched in RNA splicing associated with apoptosis compared with wild-type EBL cells. Through protein/molecular docking, molecular dynamics simulations, and real-time quantitative PCR, we demonstrated that RBMX2 promotes the apoptosis of epithelial cells by upregulating and binding to apoptotic peptidase activating factor 1 (APAF-1), resulting in the alternative splicing of APAF-1 as a retention intron. To our knowledge, this is the first report of M. bovis affecting host epithelial cell apoptosis by hijacking RBMX2 to promote the intron splicing of downstream APAF-1. These findings may represent a significant contribution to the development of novel TB prevention and control strategies.

The Role of mRNA Alternative Splicing in Macrophages Infected with Mycobacterium tuberculosis: A Field Needing to Be Discovered

Mycobacterium tuberculosis (Mtb) is one of the major causes of human death. In its battle with humans, Mtb has fully adapted to its host and developed ways to evade the immune system. At the same time, the human immune system has developed ways to respond to Mtb. The immune system responds to viral and bacterial infections through a variety of mechanisms, one of which is alternative splicing. In this study, we summarized the overall changes in alternative splicing of the transcriptome after macrophages were infected with Mtb. We found that after infection with Mtb, cells undergo changes, including (1) directly reducing the expression of splicing factors, which affects the regulation of gene expression, (2) altering the original function of proteins through splicing, which can involve gene truncation or changes in protein domains, and (3) expressing unique isoforms that may contribute to the identification and development of tuberculosis biomarkers. Moreover, alternative splicing regulation of immune-related genes, such as IL-4, IL-7, IL-7R, and IL-12R, may be an important factor affecting the activation or dormancy state of Mtb. These will help to fully understand the immune response to Mtb infection, which is crucial for the development of tuberculosis biomarkers and new drug targets.

Alternative splicing of pre-mRNA modulates the immune response in Holstein cattle naturally infected with Mycobacterium avium subsp. paratuberculosis

Little is known about the role of alternative splicing (AS) in regulating gene expression in Mycobacteria-infected individuals in distinct stages of infection. Pre-mRNA AS consists of the removal of introns and the assembly of exons contained in eukaryotic genes. AS events can influence transcript stability or structure with important physiological consequences. Using RNA-Seq data from peripheral blood (PB) and ileocecal valve (ICV) samples collected from Holstein cattle with focal and diffuse paratuberculosis (PTB)-associated histopathological lesions in gut tissues and without lesions (controls), we detected differential AS profiles between the infected and control groups. Four of the identified AS events were experimentally validated by reverse transcription-digital droplet PCR (RT-ddPCR). AS events in several genes correlated with changes in gene expression. In the ICV of animals with diffuse lesions, for instance, alternatively spliced genes correlated with changes in the expression of genes involved in endocytosis, antigen processing and presentation, complement activation, and several inflammatory and autoimmune diseases in humans. Taken together, our results identified common mechanisms of AS involvement in the pathogenesis of PTB and human diseases and shed light on novel diagnostic and therapeutic interventions to control these diseases.

Large-scale analysis reveals splicing biomarkers for tuberculosis progression and prognosis

BACKGROUND

Emerging evidence suggests that aberrant alternative splicing (AS) may play an important role in tuberculosis (TB). However, current knowledge regarding the value of AS in TB progression and prognosis remains unclear.

METHOD

Public RNA-seq datasets related to TB progression and prognosis were searched and AS analyses were conducted based on SUPPA2. Percent spliced in (PSI) was used for quantifying AS events and multiple machine learning (ML) methods were employed to construct predictive models. Area under curve (AUC), sensitivity and specificity were calculated to evaluate the model performance.

RESULTS

A total of 1587 samples from 7 datasets were included. Among 923 TB-progression related differential AS events (DASEs), 3 events (GET1-skipping exon (SE), TPD52-alternative first exons (AF) and TIMM10-alternative 5' splice site (A5)) were selected as candidate biomarkers; however, their predictive performance was limited. For TB prognosis, 5 events (PHF23-AF, KIF1B-SE, MACROD2-alternative 3' splice site (A3), CD55-retained intron (RI) and GALNT11-AF) were selected as candidates from the 1282 DASEs. Six ML methods were used to integrate these 5 events and XGBoost outperformed than others. AUC, sensitivity and specificity of XGBoost model were 0.875, 81.1% and 83.5% in training set, while they were 0.805, 68.4% and 73.2% in test set.

CONCLUSION

GET1-SE, TPD52-AF and TIMM10-A5 showed limited role in predicting TB progression, while PHF23-AF, KIF1B-SE, MACROD2-A3, CD55-RI and GALNT11-AF could well predict TB prognosis and work as candidate biomarkers. This work preliminarily explored the value of AS in predicting TB progression and prognosis and offered potential targets for further research.

Alternative Splicing, An Overlooked Defense Frontier of Plants with Respect to Bacterial Infection

Disease represents a major problem in sustainable agricultural development. Plants interact closely with various microorganisms during their development and in response to the prevailing environment. In particular, pathogenic microorganisms can cause plant diseases, affecting the fertility, yield, and longevity of plants. During the long coevolution of plants and their pathogens, plants have evolved both molecular pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) signaling networks in order to regulate host cells in response to pathogen infestation. Additionally, in the postgenomic era, alternative splicing (AS) has become uncovered as one of the major drivers of proteome diversity, and abnormal RNA splicing is closely associated with bacterial infections. Currently, the complexity of host-bacteria interactions is a much studied area of research that has shown steady progress over the past decade. Although the development of high-throughput sequencing technologies and their application in transcriptomes have revolutionized our understanding of AS, many mechanisms related to host-bacteria interactions remain still unclear. To this end, this review summarizes the changes observed in AS during host-bacteria interactions and outlines potential therapeutics for bacterial diseases based on existing studies. In doing so, we hope to provide guidelines for plant disease management in agriculture.

Alternative splicing in Atlantic salmon head kidney and SHK-1 cell line during the Piscirickettsia salmonis infection: A comparative transcriptome survey

Piscirickettsia salmonis, an intracellular bacterium in salmon aquaculture, is a big challenge because it is responsible for 54.2% of Atlantic salmon mortalities. In recent years, the high relevance of Alternative Splicing (AS) as a molecular mechanism associated with infectious conditions and host-pathogen interaction processes, especially in host immune activation, has been observed. Several studies have highlighted the role of AS in the host's immune response during viral, bacterial, and endoparasite infection. In the present study, we evaluated AS transcriptome profiles during P. salmonis infection in the two most used study models, SHK-1 cell line and salmon head kidney tissue. First, the SHK-1 cell line was exposed to P. salmonis infection at 0-, 7-, and 14-days post-infection (dpi). Following, total RNA was extracted for Illumina sequencing. On the other hand, RNA-Seq datasets of Atlantic salmon head kidney infected with the same P. salmonis strayingwase used. For both study models, the highest number of differentially alternative splicing (DAS) events was observed at 7 dpi, 16,830 DAS events derived from 9213 DAS genes in SHK-1 cells, and 13,820 DAS events from 7684 DAS genes in salmon HK. Alternative first exon (AF) was the most abundant AS type in the three infection times analyzed, representing 31% in SHK-1 cells and 228.6 in salmon HK; meanwhile, mutually exclusive exon (MX) was the least abundant. Notably, functional annotation of DAS genes in SHK-1 cells infected with P. salmonis showed a high presence of genes related to nucleotide metabolism. In contrast, the salmon head kidney exhibited many GO terms associated with immune response. Our findings reported the role of AS during P. salmonis infection in Atlantic salmon. These studies would contribute to a better understanding of the molecular bases that support the pathogen-host interaction, evidencing the contribution of AS regulating the transcriptional host response.

Talaromyces marneffei suppresses macrophage inflammation by regulating host alternative splicing

Talaromyces marneffei (T. marneffei) immune escape is essential in the pathogenesis of talaromycosis. It is currently known that T. marneffei achieves immune escape through various strategies. However, the role of cellular alternative splicing (AS) in immune escape remains unclear. Here, we depict the AS landscape in macrophages upon T. marneffei infection via high-throughput RNA sequencing and detect a truncated protein of NCOR2 / SMRT, named NCOR2-013, which is significantly upregulated after T. marneffei infection. Mechanistic analysis indicates that NCOR2-013 forms a co-repression complex with TBL1XR1 / TBLR1 and HDAC3, thereby inhibiting JunB-mediated transcriptional activation of pro-inflammatory cytokines via the inhibition of histone acetylation. Furthermore, we identify TUT1 as the AS regulator that regulates NCOR2-013 production and promotes T. marneffei immune evasion. Collectively, these findings indicate that T. marneffei escapes macrophage killing through TUT1-mediated alternative splicing of NCOR2 / SMRT, providing insight into the molecular mechanisms of T. marneffei immune evasion and potential targets for talaromycosis therapy.

SARS-CoV-2 infection severity and mortality is modulated by repeat-mediated regulation of alternative splicing

Like single-stranded RNA viruses, SARS-CoV-2 hijacks the host transcriptional machinery for its own replication. Numerous traditional differential gene expression-based investigations have examined the diverse clinical symptoms caused by SARS-CoV-2 infection. The virus, on the other hand, also affects the host splicing machinery, causing host transcriptional dysregulation, which can lead to diverse clinical outcomes. Hence, in this study, we performed host transcriptome sequencing of 125 hospital-admitted COVID-19 patients to understand the transcriptomic differences between the severity sub-phenotypes of mild, moderate, severe, and mortality. We performed transcript-level differential expression analysis, investigated differential isoform usage, looked at the splicing patterns within the differentially expressed transcripts (DET), and elucidated the possible genome regulatory features. Our DTE analysis showed evidence of diminished transcript length and diversity as well as altered promoter site usage in the differentially expressed protein-coding transcripts in the COVID-19 mortality patients. We also investigated the potential mechanisms driving the alternate splicing and discovered a compelling differential enrichment of repeats in the promoter region and a specific enrichment of SINE (Alu) near the splicing sites of differentially expressed transcripts. These findings suggested a repeat-mediated plausible regulation of alternative splicing as a potential modulator of COVID-19 disease severity. In this work, we emphasize the role of scarcely elucidated functional role of alternative splicing in influencing COVID-19 disease severity sub-phenotypes, clinical outcomes, and its putative mechanism. IMPORTANCE The wide range of clinical symptoms reported during the COVID-19 pandemic inherently highlights the numerous factors that influence the progression and prognosis of SARS-CoV-2 infection. While several studies have investigated the host response and discovered immunological dysregulation during severe infection, most of them have the common theme of focusing only up to the gene level. Viruses, especially RNA viruses, are renowned for hijacking the host splicing machinery for their own proliferation, which inadvertently puts pressure on the host transcriptome, exposing another side of the host response to the pathogen challenge. Therefore, in this study, we examine host response at the transcript-level to discover a transcriptional difference that culminates in differential gene-level expression. Importantly, this study highlights diminished transcript diversity and possible regulation of transcription by differentially abundant repeat elements near the promoter region and splicing sites in COVID-19 mortality patients, which together with differentially expressed isoforms hold the potential to elaborate disease severity and outcome.

NCoR1 controls Mycobacterium tuberculosis growth in myeloid cells by regulating the AMPK-mTOR-TFEB axis

Mycobacterium tuberculosis (Mtb) defends host-mediated killing by repressing the autophagolysosome machinery. For the first time, we report NCoR1 co-repressor as a crucial host factor, controlling Mtb growth in myeloid cells by regulating both autophagosome maturation and lysosome biogenesis. We found that the dynamic expression of NCoR1 is compromised in human peripheral blood mononuclear cells (PBMCs) during active Mtb infection, which is rescued upon prolonged anti-mycobacterial therapy. In addition, a loss of function in myeloid-specific NCoR1 considerably exacerbates the growth of M. tuberculosis in vitro in THP1 differentiated macrophages, ex vivo in bone marrow-derived macrophages (BMDMs), and in vivo in NCoR1MyeKO mice. We showed that NCoR1 depletion controls the AMPK-mTOR-TFEB signalling axis by fine-tuning cellular adenosine triphosphate (ATP) homeostasis, which in turn changes the expression of proteins involved in autophagy and lysosomal biogenesis. Moreover, we also showed that the treatment of NCoR1 depleted cells by Rapamycin, Antimycin-A, or Metformin rescued the TFEB activity and LC3 levels, resulting in enhanced Mtb clearance. Similarly, expressing NCoR1 exogenously rescued the AMPK-mTOR-TFEB signalling axis and Mtb killing. Overall, our data revealed a central role of NCoR1 in Mtb pathogenesis in myeloid cells.

Identification of host regulators of Mycobacterium tuberculosis phenotypes uncovers a role for the MMGT1-GPR156 lipid droplet axis in persistence

The ability of Mycobacterium tuberculosis (Mtb) to establish latency affects disease and response to treatment. The host factors that influence the establishment of latency remain elusive. We engineered a multi-fluorescent Mtb strain that reports survival, active replication, and stressed non-replication states and determined the host transcriptome of the infected macrophages in these states. Additionally, we conducted a genome-wide CRISPR screen to identify host factors that modulated the phenotypic state of Mtb. We validated hits in a phenotype-specific manner and prioritized membrane magnesium transporter 1 (MMGT1) for a detailed mechanistic investigation. Mtb infection of MMGT1-deficient macrophages promoted a switch to persistence, upregulated lipid metabolism genes, and accumulated lipid droplets during infection. Targeting triacylglycerol synthesis reduced both droplet formation and Mtb persistence. The orphan G protein-coupled receptor GPR156 is a key inducer of droplet accumulation in ΔMMGT1 cells. Our work uncovers the role of MMGT1-GPR156-lipid droplets in the induction of Mtb persistence.

Roles of alternative splicing in infectious diseases: from hosts, pathogens to their interactions

ABSTRACT

Alternative splicing (AS) is an evolutionarily conserved mechanism that removes introns and ligates exons to generate mature messenger RNAs (mRNAs), extremely improving the richness of transcriptome and proteome. Both mammal hosts and pathogens require AS to maintain their life activities, and inherent physiological heterogeneity between mammals and pathogens makes them adopt different ways to perform AS. Mammals and fungi conduct a two-step transesterification reaction by spliceosomes to splice each individual mRNA (named cis -splicing). Parasites also use spliceosomes to splice, but this splicing can occur among different mRNAs (named trans -splicing). Bacteria and viruses directly hijack the host's splicing machinery to accomplish this process. Infection-related changes are reflected in the spliceosome behaviors and the characteristics of various splicing regulators (abundance, modification, distribution, movement speed, and conformation), which further radiate to alterations in the global splicing profiles. Genes with splicing changes are enriched in immune-, growth-, or metabolism-related pathways, highlighting approaches through which hosts crosstalk with pathogens. Based on these infection-specific regulators or AS events, several targeted agents have been developed to fight against pathogens. Here, we summarized recent findings in the field of infection-related splicing, including splicing mechanisms of pathogens and hosts, splicing regulation and aberrant AS events, as well as emerging targeted drugs. We aimed to systemically decode host-pathogen interactions from a perspective of splicing. We further discussed the current strategies of drug development, detection methods, analysis algorithms, and database construction, facilitating the annotation of infection-related splicing and the integration of AS with disease phenotype.

From tuberculosis bedside to bench: UBE2B splicing as a potential biomarker and its regulatory mechanism

Alternative splicing (AS) is an important approach for pathogens and hosts to remodel transcriptome. However, tuberculosis (TB)-related AS has not been sufficiently explored. Here we presented the first landscape of TB-related AS by long-read sequencing, and screened four AS events (S100A8-intron1-retention intron, RPS20-exon1-alternaitve promoter, KIF13B-exon4-skipping exon (SE) and UBE2B-exon7-SE) as potential biomarkers in an in-house cohort-1. The validations in an in-house cohort-2 (2274 samples) and public datasets (1557 samples) indicated that the latter three AS events are potential promising biomarkers for TB diagnosis, but not for TB progression and prognosis. The excellent performance of classifiers further underscored the diagnostic value of these three biomarkers. Subgroup analyses indicated that UBE2B-exon7-SE splicing was not affected by confounding factors and thus had relatively stable performance. The splicing of UBE2B-exon7-SE can be changed by heat-killed mycobacterium tuberculosis through inhibiting SRSF1 expression. After heat-killed mycobacterium tuberculosis stimulation, 231 ubiquitination proteins in macrophages were differentially expressed, and most of them are apoptosis-related proteins. Taken together, we depicted a global TB-associated splicing profile, developed TB-related AS biomarkers, demonstrated an optimal application scope of target biomarkers and preliminarily elucidated mycobacterium tuberculosis-host interaction from the perspective of splicing, offering a novel insight into the pathophysiology of TB.

Mycobacterium tuberculosis PE_PGRS1 promotes mycobacteria intracellular survival via reducing the concentration of intracellular free Ca2+ and suppressing endoplasmic reticulum stress

Mycobacterium tuberculosis (M. tuberculosis) is the causative agent of tuberculosis (TB). And the PE_PGRS family members of M. tuberculosis are closely associated with virulence and antigen presentation but with function largely elusive. PE_PGRS1(Rv0109) contained 7 Ca²⁺ binding domains of GGXGXD/NXUX (X is any amino acid), which can reduce intracellular Ca²⁺ surge. In addition, PE_PGRS1 can mitigate the activation of PERK branch in endoplasmic reticulum (ER) stress by down-regulating the expression of CHOP, Bip, p-PERK, p-eIF2α, and ATF4. Interestingly, we found that two splicing variations of Bax/Bcl-2, Baxβ, and Bcl-2α, were differentially expressed after infection with Ms_PE_PGRS1, and may be involved in the regulation of apoptosis. Hence, this study identified that PE_PGRS1 is a novel calcium-associated protein that can decrease intracellular Ca²⁺ levels and the PERK axis. And the weakening of the PERK-eIF2α-ATF4 axis reduces THP-1 macrophages apoptosis, promotes the survival of mycobacteria in macrophages.

Regulation and function of alternative polyadenylation in development and differentiation

Alternative processing of nascent mRNAs is widespread in eukaryotic organisms and greatly impacts the output of gene expression. Specifically, alternative cleavage and polyadenylation (APA) is a co-transcriptional molecular process that switches the polyadenylation site (PAS) at which a nascent mRNA is cleaved, resulting in mRNA isoforms with different 3'UTR length and content. APA can potentially affect mRNA translation efficiency, localization, stability, and mRNA seeded protein-protein interactions. APA naturally occurs during development and cellular differentiation, with around 70% of human genes displaying APA in particular tissues and cell types. For example, neurons tend to express mRNAs with long 3'UTRs due to preferential processing at PASs more distal than other PASs used in other cell types. In addition, changes in APA mark a variety of pathological states, including many types of cancer, in which mRNAs are preferentially cleaved at more proximal PASs, causing expression of mRNA isoforms with short 3'UTRs. Although APA has been widely reported, both the function of APA in development and the mechanisms that regulate the choice of 3'end cut sites in normal and pathogenic conditions are still poorly understood. In this review, we summarize current understanding of how APA is regulated during development and cellular differentiation and how the resulting change in 3'UTR content affects multiple aspects of gene expression. With APA being a widespread phenomenon, the advent of cutting-edge scientific techniques and the pressing need for in-vivo studies, there has never been a better time to delve into the intricate mechanisms of alternative cleavage and polyadenylation.

Host-directed therapy against tuberculosis: Concept and recent developments

Tuberculosis (TB) continues to remain at the forefront of the infectious disease burden globally, albeit with some aberrations during the COVID-19 pandemic. Among many factors, the emergence of drug resistance or antimicrobial resistance (AMR) has necessitated a renewed focus on developing novel and repurposed drugs against TB. Host-directed therapy (HDT) has emerged as an attractive alternative and a complementary strategy to the conventional antibiotic-based therapy of tuberculosis since HDT enjoys the advantage of disarming the pathogen of its ability to develop drug resistance. Considering the imminent threat of AMR across the spectrum of bacterial pathogens, HDT promises to overcome the drug shortage against superbugs. While all these make HDT a very attractive strategy, identifying the right set of host targets to develop HDT remains a challenge, despite remarkable development in the field over the past decade. In this review, we examine the host mechanisms, that either inadvertently or through targeted perturbation by the pathogen, help TB pathogenesis, and we discuss the latest developments in the targeting of some of the key pathways to achieve newer TB therapeutics.

Bovine Immunity and Vitamin D3: An Emerging Association in Johne's Disease

Mycobacterium avium subspecies paratuberculosis (MAP) is an environmentally hardy pathogen of ruminants that plagues the dairy industry. Hallmark clinical symptoms include granulomatous enteritis, watery diarrhea, and significant loss of body condition. Transition from subclinical to clinical infection is a dynamic process led by MAP which resides in host macrophages. Clinical stage disease is accompanied by dysfunctional immune responses and a reduction in circulating vitamin D3. The immunomodulatory role of vitamin D3 in infectious disease has been well established in humans, particularly in Mycobacterium tuberculosis infection. However, significant species differences exist between the immune system of humans and bovines, including effects induced by vitamin D3. This fact highlights the need for continued study of the relationship between vitamin D3 and bovine immunity, especially during different stages of paratuberculosis.

PRMT5 epigenetically regulates the E3 ubiquitin ligase ITCH to influence lipid accumulation during mycobacterial infection

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), triggers enhanced accumulation of lipids to generate foamy macrophages (FMs). This process has been often attributed to the surge in the expression of lipid influx genes with a concomitant decrease in those involved in lipid efflux. Here, we define an Mtb-orchestrated modulation of the ubiquitination of lipid accumulation markers to enhance lipid accretion during infection. We find that Mtb infection represses the expression of the E3 ubiquitin ligase, ITCH, resulting in the sustenance of key lipid accrual molecules viz. ADRP and CD36, that are otherwise targeted by ITCH for proteasomal degradation. In line, overexpressing ITCH in Mtb-infected cells was found to suppress Mtb-induced lipid accumulation. Molecular analyses including loss-of-function and ChIP assays demonstrated a role for the concerted action of the transcription factor YY1 and the arginine methyl transferase PRMT5 in restricting the expression of Itch gene by conferring repressive symmetrical H4R3me2 marks on its promoter. Consequently, siRNA-mediated depletion of YY1 or PRMT5 rescued ITCH expression, thereby compromising the levels of Mtb-induced ADRP and CD36 and limiting FM formation during infection. Accumulation of lipids within the host has been implicated as a pro-mycobacterial process that aids in pathogen persistence and dormancy. In line, we found that perturbation of PRMT5 enzyme activity resulted in compromised lipid levels and reduced mycobacterial survival in mouse peritoneal macrophages (ex vivo) and in a therapeutic mouse model of TB infection (in vivo). These findings provide new insights into the role of PRMT5 and YY1 in augmenting mycobacterial pathogenesis. Thus, we posit that our observations could help design novel adjunct therapies and combinatorial drug regimen for effective anti-TB strategies.

Mycobacterium tuberculosis infection leads to the formation of lipid-laden cells (foamy macrophages-FMs) that offer a favorable shelter for its persistence. During infection, we observe a significant reduction in the expression of the E3 ubiquitin ligase, ITCH. This repression allows the sustenance of key lipid accretion molecules (ADRP and CD36), by curbing their proteasomal degradation. Further, we show the repression of ITCH to be dependent on the concerted action of the bifunctional transcription factor, YY1 and the arginine methyl transferase, PRMT5. NOTCH signaling pathway was identified as a master-regulator of YY1 expression. In vitro and in vivo analyses revealed the significance of PRMT5 in regulating FM formation and consequently mycobacterial burden.

Impacts and mechanisms of alternative mRNA splicing in cancer metabolism, immune response, and therapeutics

Alternative pre-mRNA splicing (AS) provides the potential to produce diversity at RNA and protein levels. Disruptions in the regulation of pre-mRNA splicing can lead to diseases. With the development of transcriptome and genome sequencing technology, increasing diseases have been identified to be associated with abnormal splicing of mRNAs. In tumors, abnormal alternative splicing frequently plays critical roles in cancer pathogenesis and may be considered as new biomarkers and therapeutic targets for cancer intervention. Metabolic abnormalities and immune disorders are important hallmarks of cancer. AS produces multiple different isoforms and diversifies protein expression, which is utilized by the immune and metabolic reprogramming systems to expand gene functions. The abnormal splicing events contributed to tumor progression, partially due to effects on immune response and metabolic reprogramming. Herein, we reviewed the vital role of alternative splicing in regulating cancer metabolism and immune response. We discussed how alternative splicing regulates metabolic reprogramming of cancer cells and antitumor immune response, and the possible strategies to targeting alternative splicing pathways or splicing-regulated metabolic pathway in the context of anticancer immunotherapy. Further, we highlighted the challenges and discuss the perspectives for RNA-based strategies for the treatment of cancer with abnormally alternative splicing isoforms.

Exogenous Vitamin D3 Modulates Response of Bovine Macrophages to Mycobacterium avium subsp. paratuberculosis Infection and Is Dependent Upon Stage of Johne’s Disease

Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of ruminant enteritis, targets intestinal macrophages. During infection, macrophages contribute to mucosal inflammation and development of granulomas in the small intestine which worsens as disease progression occurs. Vitamin D₃ is an immunomodulatory steroid hormone with beneficial roles in host-pathogen interactions. Few studies have investigated immunologic roles of 25-hydroxyvitamin D₃ (25(OH)D₃) and 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) in cattle, particularly cattle infected with MAP. This study examined the effects of exogenous vitamin D₃ on immune responses of monocyte derived macrophages (MDMs) isolated from dairy cattle naturally infected with MAP. MDMs were pre-treated with ± 100 ng/ml 25(OH)D₃ or ± 4 ng/ml 1,25(OH)₂D₃, then incubated 24 hrs with live MAP in the presence of their respective pre-treatment concentrations. Following treatment with either vitamin D₃ analog, phagocytosis of MAP by MDMs was significantly greater in clinically infected animals, with a greater amount of live and dead bacteria. Clinical cows had significantly less CD40 surface expression on MDMs compared to subclinical cows and noninfected controls. 1,25(OH)₂D₃ also significantly increased nitrite production in MAP infected cows. 1,25(OH)₂D₃ treatment played a key role in upregulating secretion of pro-inflammatory cytokines IL-1β and IL-12 while downregulating IL-10, IL-6, and IFN-γ. 1,25(OH)₂D₃ also negatively regulated transcripts of CYP24A1, CYP27B1, DEFB7, NOS2, and IL10. Results from this study demonstrate that vitamin D₃ compounds, but mainly 1,25(OH)₂D₃, modulate both pro- and anti-inflammatory immune responses in dairy cattle infected with MAP, impacting the bacterial viability within the macrophage.

Spotted Fever Group Rickettsia Trigger Species-Specific Alterations in Macrophage Proteome Signatures with Different Impacts in Host Innate Inflammatory Responses

The molecular details underlying differences in pathogenicity between Rickettsia species remain to be fully understood. Evidence points to macrophage permissiveness as a key mechanism in rickettsial virulence. Different studies have shown that several rickettsial species responsible for mild forms of rickettsioses can also escape macrophage-mediated killing mechanisms and establish a replicative niche within these cells. However, their manipulative capacity with respect to host cellular processes is far from being understood. A deeper understanding of the interplay between mildly pathogenic rickettsiae and macrophages and the commonalities and specificities of host responses to infection would illuminate differences in immune evasion mechanisms and pathogenicity. We used quantitative proteomics by sequential windowed data independent acquisition of the total high-resolution mass spectra with tandem mass spectrometry (SWATH-MS/MS) to profile alterations resulting from infection of THP-1 macrophages with three mildly pathogenic rickettsiae: Rickettsia parkeri, Rickettsia africae, and Rickettsia massiliae, all successfully proliferating in these cells. We show that all three species trigger different proteome signatures. Our results reveal a significant impact of infection on proteins categorized as type I interferon responses, which here included several components of the retinoic acid-inducible gene I (RIG-1)-like signaling pathway, mRNA splicing, and protein translation. Moreover, significant differences in protein content between infection conditions provide evidence for species-specific induced alterations. Indeed, we confirm distinct impacts on host inflammatory responses between species during infection, demonstrating that these species trigger different levels of beta interferon (IFN-β), differences in the bioavailability of the proinflammatory cytokine interleukin 1β (IL-1β), and differences in triggering of pyroptotic events. This work reveals novel aspects and exciting nuances of macrophage-Rickettsia interactions, adding additional layers of complexity between Rickettsia and host cells' constant arms race for survival. IMPORTANCE The incidence of diseases caused by Rickettsia has been increasing over the years. It has long been known that rickettsioses comprise diseases with a continuous spectrum of severity. There are highly pathogenic species causing diseases that are life threatening if untreated, others causing mild forms of the disease, and a third group for which no pathogenicity to humans has been described. These marked differences likely reflect distinct capacities for manipulation of host cell processes, with macrophage permissiveness emerging as a key virulence trait. However, what defines pathogenicity attributes among rickettsial species is far from being resolved. We demonstrate that the mildly pathogenic Rickettsia parkeri, Rickettsia africae, and Rickettsia massiliae, all successfully proliferating in macrophages, trigger different proteome signatures in these cells and differentially impact critical components of innate immune responses by inducing different levels of beta interferon (IFN-β) and interleukin 1β (IL-1β) and different timing of pyroptotic events during infection. Our work reveals novel nuances in rickettsia-macrophage interactions, offering new clues to understand Rickettsia pathogenicity.

Identification and characterization of novel infection associated transcripts in macrophages

By analysis of lncRNA expression profiles of macrophages in response to Mycobacterium tuberculosis (Mtb) infection, we identified novel highly expressed transcripts, unique in encompassing a protein coding transcript- Cytidine Monophosphate Kinase 2 (CMPK2) and a previously identified lncRNA- Negative Regulator of Interferon Response (NRIR). While these transcripts (TILT1, 2,3 - TLR4 and Infection induced Long Transcript) are induced by virulent Mtb as well as lipopolysaccharide (LPS) early, lack of/delayed expression in non-viable Mtb/BCG infected cells, respectively, suggest an important role in macrophage responses. The elevated expression by 3 hr in response to fast growing bacteria further emphasizes the importance of these RNAs in the macrophage infection response. Overall, we provide evidence for the presence of multiple transcripts that form a part of the early infection response programme of macrophages.Abbreviations: IFN: Interferon; NRIR: negative regulator of interferon response; CMPK2: cytidine/ uridine monophosphate kinase; LPS: lipopolysaccharide; LAM: Lipoarabinomannan; PIMs: Phosphatidylinositol Mannosides; TILT1, 2,3: TLR4 and Infection induced Long Transcript; TLR4: Toll-like receptor 4; Mtb: Mycobacterium tuberculosis; BCG: Mycobacterium bovis BCG; MDMs: human monocyte derived macrophages.

A Trifecta of New Insights into Ovine Footrot for Infection Drivers, Immune Response, and Host-Pathogen Interactions

Footrot is a polymicrobial infectious disease in sheep causing severe lameness, leading to one of the industry's largest welfare problems. The complex etiology of footrot makes in situ or in vitro investigations difficult. Computational methods offer a solution to understanding the bacteria involved and how they may interact with the host, ultimately providing a way to identify targets for future hypothesis-driven investigative work. Here, we present the first combined global analysis of bacterial community transcripts together with the host immune response in healthy and diseased ovine feet during a natural polymicrobial infection state using metatranscriptomics. The intratissue and surface bacterial populations and the most abundant bacterial transcriptomes were analyzed, demonstrating that footrot-affected skin has reduced diversity and increased abundances of not only the causative bacterium Dichelobacter nodosus but also other species such as Mycoplasma fermentans and Porphyromonas asaccharolytica. Host transcriptomics reveals the suppression of biological processes related to skin barrier function, vascular functions, and immunosurveillance in unhealthy interdigital skin, supported by histological findings that type I collagen (associated with scar tissue formation) is significantly increased in footrot-affected interdigital skin compared to outwardly healthy skin. Finally, we provide some interesting indications of host and pathogen interactions associated with virulence genes and the host spliceosome, which could lead to the identification of future therapeutic targets.

The three as: Alternative splicing, alternative polyadenylation and their impact on apoptosis in immune function

The latest advances in next-generation sequencing studies and transcriptomic profiling over the past decade have highlighted a surprising frequency of genes regulated by RNA processing mechanisms in the immune system. In particular, two control steps in mRNA maturation, namely alternative splicing and alternative polyadenylation, are now recognized to occur in the vast majority of human genes. Both have the potential to alter the identity of the encoded protein, as well as control protein abundance or even protein localization or association with other factors. In this review, we will provide a summary of the general mechanisms by which alternative splicing (AS) and alternative polyadenylation (APA) occur, their regulation within cells of the immune system, and their impact on immunobiology. In particular, we will focus on how control of apoptosis by AS and APA is used to tune cell fate during an immune response.

Chinese Traditional Medicine NiuBeiXiaoHe (NBXH) Extracts Have the Function of Antituberculosis and Immune Recovery in BALB/c Mice

Background

The Traditional Chinese Medicine NiuBeiXiaoHe (NBXH) is a valid antituberculosis (TB) prescription from the experience of clinical practice. However, the mechanism of NBXH extracts' immunotherapy has been poorly understood. Herein, the immunotherapeutic efficacy and the differentially expressed (DE) genes of NBXH extracts were evaluated and identified in BALB/c mice.

Methods

The total RNA was extracted from peripheral blood mononuclear cells, and the DE genes were identified by gene chip. The enrichment and signaling pathway analyses were performed using Gene Ontology (GO) and KEGG database.

Results

It was shown that the treatment of NBXH extracts (high dose) significantly reduced mycobacteria loads and histopathological lesions in mice infected by Mycobacterium tuberculosis and resulted in 3,454 DE upregulated genes and 3,594 downregulated DE genes. Furthermore, NBXH extracts killed mycobacteria by inhibiting the supply of necessary ingredients for their growth and proliferation. They restored the disordered immune microenvironments by up- or downregulating immune and inflammation-related pathways.

Conclusions

Taken together, NBXH extracts not only efficiently decreased the mycobacteria loads but also balanced the immune disorders in mice. These new findings provide a fresh perspective for elucidating the immunotherapeutic mechanism of NBXH extracts and pointed out the direction for improving the treatment efficacy of NBXH extracts.

Identification of loci associated with susceptibility to bovine paratuberculosis and with the dysregulation of the MECOM, eEF1A2, and U1 spliceosomal RNA expression

Although genome-wide association studies have identified single nucleotide polymorphisms (SNPs) associated with the susceptibility to Mycobacterium avium subsp. paratuberculosis (MAP) infection, only a few functional mutations for bovine paratuberculosis (PTB) have been characterized. Expression quantitative trait loci (eQTLs) are genetic variants typically located in gene regulatory regions that alter gene expression in an allele-specific manner. eQTLs can be considered as functional links between genomic variants, gene expression, and ultimately phenotype. In the current study, peripheral blood (PB) and ileocecal valve (ICV) gene expression was quantified by RNA-Seq from fourteen Holstein cattle with no lesions and with PTB-associated histopathological lesions in gut tissues. Genotypes were generated from the Illumina LD EuroG10K BeadChip. The associations between gene expression levels (normalized read counts) and genetic variants were analyzed by a linear regression analysis using R Matrix eQTL 2.2. This approach allowed the identification of 192 and 48 cis-eQTLs associated with the expression of 145 and 43 genes in the PB and ICV samples, respectively. To investigate potential relationships between these cis-eQTLs and MAP infection, a case–control study was performed using the genotypes for all the identified cis-eQTLs and phenotypical data (histopathology, ELISA for MAP-antibodies detection, tissue PCR, and bacteriological culture) of 986 culled cows. Our results suggested that the heterozygous genotype in the cis-eQTL-rs43744169 (T/C) was associated with the up-regulation of the MDS1 and EVI1 complex (MECOM) expression, with positive ELISA, PCR, and bacteriological culture results, and with increased risk of progression to clinical PTB. As supporting evidence, the presence of the minor allele was associated with higher MECOM levels in plasma samples from infected cows and with increased MAP survival in an ex-vivo macrophage killing assay. Moreover, the presence of the two minor alleles in the cis-eQTL-rs110345285 (C/C) was associated with the dysregulation of the eukaryotic elongation factor 1-α2 (eEF1A2) expression and with increased ELISA (OD) values. Finally, the presence of the minor allele in the cis-eQTL rs109859270 (C/T) was associated with the up-regulation of the U1 spliceosomal RNA expression and with an increased risk of progression to clinical PTB. The introduction of these novel functional variants into marker-assisted breeding programs is expected to have a relevant effect on PTB control.

Skipped Over: Tuning Natural Killer Cells Toward HIV Through Alternative Splicing

Natural killer (NK) cells provide some of the earliest immune responses to infection, but when viruses manipulate or perturb the immune environment to alter NK cell function, this places the host at a disadvantage. Indeed, others and we observe that in the context of HIV/simian immunodeficiency virus (SIV) infection, although NK cells are not infected, they can become dysfunctional over time. Several studies have characterized protein and transcriptional profiles of NK cells during HIV/SIV infection, but none have examined whether the production of alternative transcripts and corresponding isoforms is modulated. This phenomenon occurs broadly in normal biology and in other disease states, and could provide a novel avenue of investigation that may yield better targets to restore or augment NK cell responses to HIV/SIV. Herein, we briefly summarize published and new data that may provide a perspective on how to target NK cell splice variants.

Is targeting dysregulation in apoptosis splice variants in Mycobacterium tuberculosis (MTB) host interactions and splicing factors resulting in immune evasion by MTB strategies a possibility?

Mycobacterium tuberculosis (Mtb), is one of the foremost organisms causing mortality in humans, and has been for most of human history. When faced with an infection the human immune system is ordinarily very competent in killing both extracellular and intracellular bacilli. However, Mtb is able to evade the host immune system and is even able to establish a persistent infectious reservoir by "hiding" in the immune cells of the host. While the mechanisms by which the bacteria accomplishes this are not fully understood, it is known that the bacterium can subvert cellular processes in cells such as macrophages that prevent the lysis of the bacteria or the cell undergoing apoptosis. They are also able to interfere with immune cell signalling. One of the greatest effects that Mtb has is too alter the transcriptome of the macrophage. An easy way for the bacterium to accomplish this is to alter the alternative splicing patterns of the host. This can lead to a large change in the population of different protein isoforms, some of which have very different functions when compared to the original protein. At the same time the long history of Mtb infecting humans have led to specific immune reactions that occur in the host immune system in order to fight the infection. Many of these specific reactions involve new isoforms of host defence proteins. In this way the human host can use alternate splicing to create new isoforms of immune- related proteins that are more effective in defending against Mtb.

From Gene to Protein-How Bacterial Virulence Factors Manipulate Host Gene Expression During Infection

Bacteria evolved many strategies to survive and persist within host cells. Secretion of bacterial effectors enables bacteria not only to enter the host cell but also to manipulate host gene expression to circumvent clearance by the host immune response. Some effectors were also shown to evade the nucleus to manipulate epigenetic processes as well as transcription and mRNA procession and are therefore classified as nucleomodulins. Others were shown to interfere downstream with gene expression at the level of mRNA stability, favoring either mRNA stabilization or mRNA degradation, translation or protein stability, including mechanisms of protein activation and degradation. Finally, manipulation of innate immune signaling and nutrient supply creates a replicative niche that enables bacterial intracellular persistence and survival. In this review, we want to highlight the divergent strategies applied by intracellular bacteria to evade host immune responses through subversion of host gene expression via bacterial effectors. Since these virulence proteins mimic host cell enzymes or own novel enzymatic functions, characterizing their properties could help to understand the complex interactions between host and pathogen during infections. Additionally, these insights could propose potential targets for medical therapy.

Characterization of Full-Length Transcriptome Sequences and Splice Variants of Lateolabrax maculatus by Single-Molecule Long-Read Sequencing and Their Involvement in Salinity Regulation

Transcriptome complexity plays crucial roles in regulating the biological functions of eukaryotes. Except for functional genes, alternative splicing and fusion transcripts produce a vast expansion of transcriptome diversity. In this study, we applied PacBio single-molecule long-read sequencing technology to unveil the whole transcriptome landscape of Lateolabrax maculatus. We obtained 28,809 high-quality non-redundant transcripts, including 18,280 novel isoforms covering 8,961 annotated gene loci within the current reference genome and 3,172 novel isoforms. A total of 10,249 AS events were detected, and intron retention was the predominant AS event. In addition, 1,359 alternative polyadenylation events, 3,112 lncRNAs, 29,609 SSRs, 365 fusion transcripts, and 1,194 transcription factors were identified in this study. Furthermore, we performed RNA-Seq analysis combined with Iso-Seq results to investigate salinity regulation mechanism at the transcripts level. A total of 518 transcripts were differentially expressed, which were further divided into 8 functional groups. Notably, transcripts from the same genes exhibited similar or opposite expression patterns. Our study provides a comprehensive view of the transcriptome complexity in L. maculatus, which significantly improves current gene models. Moreover, the diversity of the expression patterns of transcripts may enhance the understanding of salinity regulatory mechanism in L. maculatus and other euryhaline teleosts.

The Splicing Factor hnRNP M Is a Critical Regulator of Innate Immune Gene Expression in Macrophages

While transcriptional control of innate immune gene expression is well characterized, almost nothing is known about how pre-mRNA splicing decisions influence, or are influenced by, macrophage activation. Here, we demonstrate that the splicing factor hnRNP M is a critical repressor of innate immune gene expression and that its function is regulated by pathogen sensing cascades. Loss of hnRNP M led to hyperinduction of a unique regulon of inflammatory and antimicrobial genes following diverse innate immune stimuli. While mutating specific serines on hnRNP M had little effect on its ability to control pre-mRNA splicing or transcript levels of housekeeping genes in resting macrophages, it greatly impacted the protein's ability to dampen induction of specific innate immune transcripts following pathogen sensing. These data reveal a previously unappreciated role for pattern recognition receptor signaling in controlling splicing factor phosphorylation and establish pre-mRNA splicing as a critical regulatory node in defining innate immune outcomes.

Time-Course Transcriptome Analysis for Drug Repositioning in Fusobacterium nucleatum-Infected Human Gingival Fibroblasts

Fusobacterium nucleatum (F. nucleatum) is a crucial periodontal pathogen and human gingival fibroblasts (GFs) are the first line of defense against oral pathogens. However, the research on potential molecular mechanisms of host defense and effective treatment of F. nucleatum infection in GFs remains scarce. In this study, we undertook a time-series experiment and performed an RNA-seq analysis to explore gene expression profiles during the process of F. nucleatum infection in GFs. Differentially expressed genes (DEGs) could be divided into three coexpression clusters. Functional analysis revealed that the immune-related signaling pathways were more overrepresented at the early stage, while metabolic pathways were mainly enriched at the late stage. We computationally identified several U.S. Food and Drug Administration (FDA)-approved drugs that could protect the F. nucleatum infected GFs via a coexpression-based drug repositioning approach. Biologically, we confirmed that six drugs (etravirine, zalcitabine, wortmannin, calcium D-pantothenate, ellipticine, and tanespimycin) could significantly decrease F. nucleatum-induced reactive oxygen species (ROS) generation and block the Protein Kinase B (PKB/AKT)/mitogen-activated protein kinase signaling pathways. Our study provides more detailed molecular mechanisms of the process by which F. nucleatum infects GFs and illustrates the value of the cogena-based drug repositioning method and the potential therapeutic application of these tested drugs in the treatment of F. nucleatum infection.

Gut Microbiota Has a Widespread and Modifiable Effect on Host Gene Regulation

The composition of the gut microbiome has been associated with various aspects of human health, but the mechanism of this interaction is still unclear. We utilized a cellular system to characterize the effect of the microbiome on human gene expression. We showed that some of these changes in expression may be mediated by changes in chromatin accessibility. Furthermore, we validate the role of a specific microbe and show that changes in its abundance can modify the host gene expression response. These results show an important role of gut microbiota in regulating host gene expression and suggest that manipulation of microbiome composition could be useful in future therapies.

Variation in gut microbiome is associated with wellness and disease in humans, and yet the molecular mechanisms by which this variation affects the host are not well understood. A likely mechanism is that of changing gene regulation in interfacing host epithelial cells. Here, we treated colonic epithelial cells with live microbiota from five healthy individuals and quantified induced changes in transcriptional regulation and chromatin accessibility in host cells. We identified over 5,000 host genes that change expression, including 588 distinct associations between specific taxa and host genes. The taxa with the strongest influence on gene expression alter the response of genes associated with complex traits. Using ATAC-seq, we showed that a subset of these changes in gene expression are associated with changes in host chromatin accessibility and transcription factor binding induced by exposure to gut microbiota. We then created a manipulated microbial community with titrated doses of Collinsella, demonstrating that manipulation of the composition of the microbiome under both natural and controlled conditions leads to distinct and predictable gene expression profiles in host cells. Taken together, our results suggest that specific microbes play an important role in regulating expression of individual host genes involved in human complex traits. The ability to fine-tune the expression of host genes by manipulating the microbiome suggests future therapeutic routes.

IMPORTANCE The composition of the gut microbiome has been associated with various aspects of human health, but the mechanism of this interaction is still unclear. We utilized a cellular system to characterize the effect of the microbiome on human gene expression. We showed that some of these changes in expression may be mediated by changes in chromatin accessibility. Furthermore, we validate the role of a specific microbe and show that changes in its abundance can modify the host gene expression response. These results show an important role of gut microbiota in regulating host gene expression and suggest that manipulation of microbiome composition could be useful in future therapies.

Role of two-component regulatory systems in intracellular survival of Mycobacterium tuberculosis

The typical two-component regulatory systems (TCSs), consisting of response regulator and histidine kinase, play a central role in survival of pathogenic bacteria under stress conditions such as nutrient starvation, hypoxia, and nitrosative stress. A total of 11 complete paired two-component regulatory systems have been found in Mycobacterium tuberculosis, including a few isolated kinase and regulatory genes. Increasing evidence has shown that TCSs are closely associated with multiple physiological process like intracellular persistence, pathogenicity, and metabolism. This review gives the two-component signal transduction systems in M. tuberculosis and their signal transduction roles in adaption to the environment.

Defining the genetic and evolutionary architecture of alternative splicing in response to infection

Host and environmental factors contribute to variation in human immune responses, yet the genetic and evolutionary drivers of alternative splicing in response to infection remain largely uncharacterised. Leveraging 970 RNA-sequencing profiles of resting and stimulated monocytes from 200 individuals of African- and European-descent, we show that immune activation elicits a marked remodelling of the isoform repertoire, while increasing the levels of erroneous splicing. We identify 1,464 loci associated with variation in isoform usage (sQTLs), 9% of them being stimulation-specific, which are enriched in disease-related loci. Furthermore, we detect a longstanding increased plasticity of immune gene splicing, and show that positive selection and Neanderthal introgression have both contributed to diversify the splicing landscape of human populations. Together, these findings suggest that differential isoform usage has been an important substrate of innovation in the long-term evolution of immune responses and a more recent vehicle of population local adaptation.

Genetic ancestry might influence immunological response to infection at different regulatory levels. Here, the authors use RNA-Seq to investigate the variability of alternative splicing patterns in resting and stimulated monocytes of African- and European-descent.

RNA Splicing: A New Paradigm in Host-Pathogen Interactions

RNA splicing brings diversity to the eukaryotic proteome. Different spliced variants of a gene may differ in their structure, function, localization, and stability influencing protein stoichiometry and physiological outcomes. Alternate spliced variants of different genes are known to associate with various chronic pathologies including cancer. Emerging evidence suggests precise regulation of splicing as fundamental to normal well-being. In this context, infection-induced alternative splicing has emerged as a new pivot of host function, which pathogenic microbes can alter-directly or indirectly-to tweak the host immune responses against the pathogen. The implications of these findings are vast, and although not explored much in the case of pathogenic infections, we present here examples from splicing mediated regulation of immune responses across a variety of conditions and explore how this fascinating finding brings a new paradigm to host-pathogen interactions.

Arthropod venoms: Biochemistry, ecology and evolution

Comprising of over a million described species of highly diverse invertebrates, Arthropoda is amongst the most successful animal lineages to have colonized aerial, terrestrial, and aquatic domains. Venom, one of the many fascinating traits to have evolved in various members of this phylum, has underpinned their adaptation to diverse habitats. Over millions of years of evolution, arthropods have evolved ingenious ways of delivering venom in their targets for self-defence and predation. The morphological diversity of venom delivery apparatus in arthropods is astounding, and includes extensively modified pedipalps, tail (telson), mouth parts (hypostome), fangs, appendages (maxillulae), proboscis, ovipositor (stinger), and hair (urticating bristles). Recent investigations have also unravelled an astonishing venom biocomplexity with molecular scaffolds being recruited from a multitude of protein families. Venoms are a remarkable bioresource for discovering lead compounds in targeted therapeutics. Several components with prospective applications in the development of advanced lifesaving drugs and environment friendly bio-insecticides have been discovered from arthropod venoms. Despite these fascinating features, the composition, bioactivity, and molecular evolution of venom in several arthropod lineages remains largely understudied. This review highlights the prevalence of venom, its mode of toxic action, and the evolutionary dynamics of venom in Arthropoda, the most speciose phylum in the animal kingdom.

Increased Alternative Splicing as a Host Response to Edwardsiella ictaluri Infection in Catfish

Alternative splicing is the process of generating multiple transcripts from a single pre-mRNA used by eukaryotes to regulate gene expression and increase proteomic complexity. Although alternative splicing profiles have been well studied in mammalian species, they have not been well studied in aquatic species, especially after biotic stresses. In the present study, genomic information and RNA-Seq datasets were utilized to characterize alternative splicing profiles and their induced changes after bacterial infection with Edwardsiella ictaluri in channel catfish (Ictalurus punctatus). A total of 27,476 alternative splicing events, derived from 9694 genes, were identified in channel catfish. Exon skipping was the most abundant while mutually exclusive exon was the least abundant type of alternative splicing. Alternative splicing was greatly induced by E. ictaluri infection with 21.9% increase in alternative splicing events. Interestingly, genes involved in RNA binding and RNA splicing themselves were significantly enriched in differentially alternatively spliced genes after infection. Sequence analyses of splice variants of a representative alternatively spliced gene, splicing factor srsf2, revealed that certain spliced transcripts may undergo nonsense-mediated decay (NMD), suggesting functional significance of the induced alternative splicing. Although statistical analysis was not possible with such large datasets, results from quantitative real-time PCR from representative differential alternative splicing events provided general validation of the bacterial infection-induced alternative splicing. This is the first comprehensive study of alternative splicing and its changes in response to bacterial infection in fish species, providing insights into the molecular mechanisms of host responses to biotic stresses.

Alternate splicing of transcripts upon Mycobacterium tuberculosis infection impacts the expression of functional protein domains

Previously, we reported that infection of human macrophages with Mycobacterium tuberculosis (Mtb) results in massive alterations in the pattern of RNA splicing in the host. The finding gained significance since alternate spliced variants of a same gene may have substantially different structure, function, stability, interaction partners, localization, and so forth, owing to inclusion or exclusion of specific exons. To establish a proof-of-concept; on how infection-induced RNA splicing could impact protein functions, here we used RNA-seq data from THP-1 macrophages that were infected with clinical isolate of Mtb. In addition to re-establishing the fact that Mtb infection may cause strain specific alterations in RNA splicing, we also developed a new analysis pipeline resulting in characterization of domain maps of the transcriptome postinfection. For the sake of simplicity, we restricted our analysis to all the kinases in the human genome and considered only pfam classified protein domains and checked their frequency of inclusion or exclusion due to alternate splicing across the conditions and time points. We report massive alterations in the domain architecture of most regulated proteins across the entire kinases highlighting the physiological importance of such an understanding. This study paves way for more detailed analysis of different functional classes of proteins and perturbations to their domain architecture as a consequence of mycobacterial infections. Such analysis would yield unprecedented depth to our understanding of host-pathogen interaction and allow in a more systematic manner targeting of host pathways for controlling the infections.

Conserved temporal ordering of promoter activation implicates common mechanisms governing the immediate early response across cell types and stimuli

The promoters of immediate early genes (IEGs) are rapidly activated in response to an external stimulus. These genes, also known as primary response genes, have been identified in a range of cell types, under diverse extracellular signals and using varying experimental protocols. Whereas genomic dissection on a case-by-case basis has not resulted in a comprehensive catalogue of IEGs, a rigorous meta-analysis of eight genome-wide FANTOM5 CAGE (cap analysis of gene expression) time course datasets reveals successive waves of promoter activation in IEGs, recapitulating known relationships between cell types and stimuli: we obtain a set of 57 (42 protein-coding) candidate IEGs possessing promoters that consistently drive a rapid but transient increase in expression over time. These genes show significant enrichment for known IEGs reported previously, pathways associated with the immediate early response, and include a number of non-coding RNAs with roles in proliferation and differentiation. Surprisingly, we also find strong conservation of the ordering of activation for these genes, such that 77 pairwise promoter activation orderings are conserved. Using the leverage of comprehensive CAGE time series data across cell types, we also document the extensive alternative promoter usage by such genes, which is likely to have been a barrier to their discovery until now. The common activation ordering of the core set of early-responding genes we identify may indicate conserved underlying regulatory mechanisms. By contrast, the considerably larger number of transiently activated genes that are specific to each cell type and stimulus illustrates the breadth of the primary response.

Transcriptome Analysis of Porcine PBMCs Reveals the Immune Cascade Response and Gene Ontology Terms Related to Cell Death and Fibrosis in the Progression of Liver Failure

BACKGROUND

The key gene sets involved in the progression of acute liver failure (ALF), which has a high mortality rate, remain unclear. This study aims to gain a deeper understanding of the transcriptional response of peripheral blood mononuclear cells (PBMCs) following ALF.

METHODS

ALF was induced by D-galactosamine (D-gal) in a porcine model. PBMCs were separated at time zero (baseline group), 36 h (failure group), and 60 h (dying group) after D-gal injection. Transcriptional profiling was performed using RNA sequencing and analysed using DAVID bioinformatics resources.

RESULTS

Compared with the baseline group, 816 and 1,845 differentially expressed genes (DEGs) were identified in the failure and dying groups, respectively. A total of five and two gene ontology (GO) term clusters were enriched in 107 GO terms in the failure group and 154 GO terms in the dying group. These GO clusters were primarily immune-related, including genes regulating the inflammasome complex and toll-like receptor signalling pathways. Specifically, GO terms related to cell death, including apoptosis, pyroptosis, and autophagy, and those related to fibrosis, coagulation dysfunction, and hepatic encephalopathy were enriched. Seven Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, cytokine-cytokine receptor interaction, hematopoietic cell lineage, lysosome, rheumatoid arthritis, malaria, and phagosome and pertussis pathways were mapped for DEGs in the failure group. All of these seven KEGG pathways were involved in the 19 KEGG pathways mapped in the dying group.

CONCLUSION

We found that the dramatic PBMC transcriptome changes triggered by ALF progression was predominantly related to immune responses. The enriched GO terms related to cell death, fibrosis, and so on, as indicated by PBMC transcriptome analysis, seem to be useful in elucidating potential key gene sets in the progression of ALF. A better understanding of these gene sets might be of preventive or therapeutic interest.

Alternative Splicing of Differentiated Myeloid Cell Transcripts after Infection by Anaplasma phagocytophilum Impacts a Selective Group of Cellular Programs

Eukaryotic proteome diversity exceeds that encoded within individual genes, and results in part from alternative splicing events of pre-messenger RNA. The diversity of these splicing events can shape the outcome in development and differentiation of normal tissues, and is important in pathogenic circumstances such as cancer and some heritable conditions. A role for alternative splicing of eukaryotic genes in response to viral and intracellular bacterial infections has only recently been recognized, and plays an important role in providing fitness for microbial survival, while potentially enhancing pathogenicity. Anaplasma phagocytophilum survives within mammalian neutrophils by reshaping transcriptional programs that govern cellular functions. We applied next generation RNAseq to ATRA-differentiated HL-60 cells established to possess transcriptional and functional responses similar to A. phagocytophilum-infected human neutrophils. This demonstrated an increase in transcripts with infection and high proportion of alternatively spliced transcript events (ASEs) for which predicted gene ontology processes were in part distinct from those identified by evaluation of single transcripts or gene-level analyses alone. The alternative isoforms are not on average shorter, and no alternative splicing in genes encoding spliceosome components is noted. Although not evident at gene-level analyses, individual spliceosome transcripts that impact nearly all spliceosome components were significantly upregulated. How the distinct GO processes predicted by ASEs are regulated by infection and whether they are relevant to fitness or pathogenicity of A. phagocytophilum should be addressed in more detailed studies.

Mycobacterium tuberculosis H37Rv infection regulates alternative splicing in Macrophages

Objective: The objective of this study was to evaluate the expression of genes encoding SR proteinsand alternative splicing of IL4 and TLR4 in Mycobacterium tuberculosis (M. tb) H37Rv-infected macrophages.

Materials and methods: THP-1 cells were induced to differentiate into macrophages with 200 nM PMA, and H37Rv strains were used for macrophage infection. After RNA extraction, qRT-PCR was performed to evaluate the expression of many SR proteins as well as the alternative splicing of IL4 and TLR4.

Results: IL4 and TLR4 play significant roles in host immunity to tuberculosis. The level of IL-4 splice variants in THP-1 cells increased after M. tb H37Rv infection. Three splice variants of TLR4 were detected in M. tb-infected THP-1 cells, when compared with uninfected controls; the expression level of these splicing variants in M. tb-infected THP-1 cell was down-regulated. Since SR proteins are RNA-binding proteins that regulate RNA splicing, the expression of SR proteins was examined, and SRSF2 and SRSF3 were significantly down-regulated. In addition, splicing factors SRp75 and SF3a were also significantly down-regulated post M. tb infection.

Conclusion: Our findings indicate that alternative splicing may be involved in host gene regulation post M. tb infection of macrophage cells.