Biology subjects

Howard, Z.

Publications and source records attributed to Howard, Z..

4 recordsLinked to original sources

bioRxiv2025

CCR2 recruits monocytes to the lung, while CX3CR1 modulates positioning of monocyte-derived CD11cpos cells in the lymph node during pulmonary tuberculosis

Infection by Mycobacterium tuberculosis (Mtb) continues to cause more than 1 million deaths annually, due to pathogen persistence in lung macrophages and dendritic cells derived from blood monocytes. While accumulation of monocyte-derived cells in the Mtb-infected lung partially depends on the chemokine receptor CCR2, the other chemoattractant receptors regulating trafficking remain undefined. We used mice expressing knock-in/knockout reporter alleles of Ccr2 and Cx3cr1 to interrogate their expression and function in monocyte-derived populations of the lungs and draining mediastinal lymph nodes during Mtb infection. CCR2 and CX3CR1 expression varied across monocyte-derived subsets stratified by cell surface Ly6C expression in both organs. We found that expression of CCR2 predicted dependence of monocyte-derived cells on the receptor for lung and lymph node accumulation. CCR2-deficient mice were also observed to have worsened lung and lymph node Mtb burden. While CX3CR1 deficiency, alone or in combination with CCR2 deficiency, did not affect cell frequencies or lung Mtb control, its absence was associated with altered positioning of monocyte-derived dendritic cells in mediastinal lymph nodes. We found that combined loss of Ccr2 and Cx3cr1 also worsened Mtb control in the mediastinal lymph node, suggesting a rationale for the persistent expression of CX3CR1 among monocyte-derived cells in pulmonary tuberculosis. IMPORTANCEMycobacterium tuberculosis is the respiratory pathogen responsible for the deadliest infectious disease worldwide. Susceptible humans exhibit ineffective immune responses, in which infected phagocytes are not able to eliminate the pathogen. Since recruited monocyte-derived cells serve as reservoirs for persistent infection, understanding how these phagocytes accumulate in the lung and why they are unable to eliminate Mtb can inform development of therapies that can synergize with antimicrobials to achieve faster and more durable Mtb elimination. Monocyte-derived cells express the chemokine receptors CCR2 and CX3CR1, but the role of the latter in Mtb infection remains poorly defined. The significance of our study is in elucidating the roles of these receptors in the trafficking of monocyte-derived cells in the infected lung and mediastinal lymph node. These data shed light on the host response in tuberculosis and in other pulmonary infections.

immunology↗

bioRxiv2023

A genome-wide cytotoxicity screen of Cluster F1 mycobacteriophage Girr reveals novel inhibitors of Mycobacterium smegmatis growth

Over the past decade, thousands of bacteriophage genomes have been sequenced and annotated. A striking observation from this work is that known structural features and functions cannot be assigned for >65% of the encoded proteins. One approach to begin experimentally elucidating the function of these uncharacterized gene products is genome-wide screening to identify phage genes that confer phenotypes of interest like inhibition of host growth. This study describes the results of a screen evaluating the effects of overexpressing each gene encoded by the temperate Cluster F1 mycobacteriophage Girr on the growth of the host bacterium Mycobacterium smegmatis. Overexpression of 29 of the 102 Girr genes ([~]28% of the genome) resulted in mild to severe cytotoxicity. Of the 29 toxic genes described, 12 have no known function (NKF) and are predominately small proteins of <125 amino acids. Overexpression of the majority of these 12 cytotoxic NKF proteins resulted in moderate to severe growth reduction and represent novel antimicrobial products. The remaining 17 toxic genes have predicted functions, encoding products involved in phage structure, DNA replication/modification, DNA binding/gene regulation, or other enzymatic activity. Comparison of this dataset with prior genome-wide cytotoxicity screens of mycobacteriophages Waterfoul and Hammy reveals some common functional themes, though several of the predicted Girr functions associated with cytotoxicity in our report, including genes involved in lysogeny, have not been described previously. This study, completed as part of the HHMI-supported SEA-GENES project, highlights the power of parallel, genome-wide overexpression screens to identify novel interactions between phages and their hosts.

microbiology↗

bioRxiv2023

Mycobacterium tuberculosis resides in lysosome-poor monocyte-derived lung cells during persistent infection

Mycobacterium tuberculosis (Mtb) infects cells in multiple lung myeloid cell subsets and causes chronic infection despite innate and adaptive immune responses. However, the mechanisms allowing Mtb to evade elimination are not fully understood. Here, using new methods, we determined that after T cell responses have developed, CD11clo monocyte-derived lung cells termed MNC1 (mononuclear cell subset 1), harbor more live Mtb compared to alveolar macrophages (AM), neutrophils, and less permissive CD11chi MNC2. Bulk RNA sequencing of sorted cells revealed that the lysosome biogenesis pathway is underexpressed in MNC1. Functional assays confirmed that Mtb-permissive MNC1 have less lysosome content, acidification, and proteolytic activity than AM, and less nuclear TFEB, a master regulator of lysosome biogenesis. Mtb infection does not drive lysosome deficiency in MNC1 in vivo. Instead, Mtb recruits MNC1 and MNC2 to the lungs for its spread from AM to these cell subsets as a virulence mechanism that requires the Mtb ESX-1 secretion system. The c-Abl tyrosine kinase inhibitor nilotinib activates TFEB and enhances lysosome function of primary macrophages in vitro and MNC1 and MNC2 in vivo, improving control of Mtb infection. Our results indicate that Mtb exploits lysosome-poor monocyte-derived cells for in vivo persistence, suggesting a potential target for host-directed tuberculosis therapy. One Sentence SummaryVirulent Mtb recruits and exploits intrinsically lysosome-deficient lung mononuclear cell subsets to resist elimination during chronic infection.

immunology↗

bioRxiv2019

Hierarchical learning of statistical regularities over multiple timescales of sound sequence processing: A dynamic causal modelling study

The nervous system is endowed with predictive capabilities, updating neural activity to reflect recent stimulus statistics in a manner which optimises processing of expected future states. This process has previously been formulated within a predictive coding framework, where sensory input is either \"explained away\" by accurate top-down predictions, or leads to a salient prediction error which triggers an update to the existing prediction when inaccurate. However, exactly how the brain optimises predictive processes in the stochastic and multi-faceted real-world environment remains unclear. Auditory evoked potentials have proven a useful measure of monitoring unsupervised learning of patterning in sound sequences through modulations of the mismatch negativity component which is associated with \"change detection\" and widely used as a proxy for indexing learnt regularities. Here we used dynamic causal modelling to analyse scalp-recorded auditory evoked potentials collected during presentation of sound sequences consisting of multiple, nested regularities and extend on previous observations of pattern learning restricted to the scalp level or based on single-outcome events. Patterns included the regular characteristics of the two tones presented, consistency in their relative probabilities as either common standard (p = .875) or rare deviant (p = .125), and the regular rate at which these tone probabilities alternated. Significant changes in connectivity reflecting a drop in the precision of prediction errors based on learnt patterns were observed at three points in the sound sequence, corresponding to the three hierarchical levels of nested regularities: (1) when an unexpected \"deviant\" sound was encountered; (2) when the probabilities of the two tonal states altered; and (3) when there was a change in rate at which probabilities in tonal state changed. These observations provide further evidence of simultaneous pattern learning over multiple timescales, reflected through changes in neural activity below the scalp.\n\nAuthor summaryOur physical environment is comprised of regularities which give structure to our world. This consistency provides the basis for experiential learning, where we can increasingly master our interactions with our surroundings based on prior experience. This type of learning also guides how we sense and perceive the world. The sensory system is known to reduce responses to regular and predictable patterns of input, and conserve neural resources for processing input which is new and unexpected. Temporal pattern learning is particularly important for auditory processing, in disentangling overlapping sound streams and deciphering the information value of sound. For example, understanding human language requires an exquisite sensitivity to the rhythm and tempo of speech sounds. Here we elucidate the sensitivity of the auditory system to concurrent temporal patterning during a sound sequence consisting of nested patterns over three timescales. We used dynamic causal modelling to demonstrate that the auditory system monitors short, intermediate and longer-timescale patterns in sound simultaneously. We also show that these timescales are each represented by distinct connections between different brain areas. These findings support complex interactions between different areas of the brain as responsible for the ability to learn sophisticated patterns in sound even without conscious attention.

neuroscience↗