Biology subjects

Nick, J. A.

Publications and source records attributed to Nick, J. A..

5 recordsLinked to original sources

bioRxiv2025

Tobramycin enhances Mycobacterium abscessus fitness through whiB7 induction

Nontuberculous mycobacteria (NTM) are opportunistic pathogens that cause pulmonary disease (PD) in people with bronchiectasis and other chronic airways diseases. Difficulty treating and eradicating NTM-PD highlights the need for improved understanding of bacterial mechanisms to establish chronic infections. People with the genetic disorder cystic fibrosis (CF) develop bronchiectasis and are the population at highest risk of NTM-PD, caused mainly by Mycobacterium avium or Mycobacterium abscessus (Mabsc). The majority of people with CF (pwCF) and bronchiectasis develop chronic Pseudomonas aeruginosa airway infections. We hypothesized that antibiotics used to treat P. aeruginosa infections could enhance Mabsc persistence in the CF airway. Here we demonstrate that clinically relevant concentrations of tobramycin, which does not kill Mabsc but is frequently administered to pwCF with chronic P. aeruginosa infections, induced Mabsc expression of whiB7, a transcription factor that activates genes associated with resistance to host defenses. Tobramycin promoted Mabsc resistance to killing by hydrogen peroxide (H2O2) and survival in both human macrophages and mice. Deletion of whiB7 increased Mabsc susceptibility to killing by H2O2, decreased ability of Mabsc to persist in macrophages, and disrupted ability of tobramycin to enhance Mabsc survival. Transcriptomic data defining the tobramycin associated WhiB7 regulon revealed differential gene expression of factors that could enhance Mabsc resistance to stress conditions such as those in found in the CF lung. Overall, our data indicate that administration of tobramycin to pwCF may have unexpected off-target effects, enhancing Mabsc whiB7 expression and promoting Mabsc persistent infection. Significance StatementPulmonary infections caused by Mycobacterium abscessus (Mabsc) are increasing in prevalence, especially in people with cystic fibrosis (pwCF) and bronchiectasis, and are very challenging to treat. Risk factors that predispose to Mabsc pulmonary infections remain poorly defined. This study demonstrates that tobramycin, an antibiotic commonly used to treat chronic Pseudomonas aeruginosa infections in pwCF, promotes Mabsc persistence by inducing Mabsc expression of the transcription factor whiB7. WhiB7 enhances Mabsc resistance to oxidative stress and survival in host macrophages. Transcriptome analysis reveals that tobramycin activates a large WhiB7 dependent regulon linked to stress tolerance and immune evasion. These findings highlight a clinically relevant off-target effect of tobramycin that may contribute to Mabsc persistence in polymicrobial infections.

microbiology↗

bioRxiv2024

A Novel Early Onset Spinocerebellar Ataxia 13 BAC Mouse Model with Cerebellar Hypoplasia, Tremor, and Ataxic Gait

Spinocerebellar ataxia 13 (SCA13) is an autosomal dominant neurological disorder caused by mutations in KCNC3. Our previous studies revealed that KCNC3 mutation R423H results in an early-onset form of SCA13. Previous biological models of SCA13 include zebrafish and Drosophila but no mammalian systems. More recently, mouse models with KCNC3 mutations presented behavioral abnormalities but without obvious pathological changes in the cerebellum, a hallmark of patients with SCA13. Here, we present a novel transgenic mouse model by bacterial artificial chromosome (BAC) recombineering to express the full-length mouse Kcnc3 expressing the R424H mutation. This BAC-R424H mice exhibited behavioral and pathological changes mimicking the clinical phenotype of the disease. The BAC-R424H mice (homologous to R423H in human) developed early onset clinical symptoms with aberrant gait, tremor, and cerebellar hypoplasia/atrophy. Histopathological analysis of the cerebellum in BAC-R424H mice showed progressive Purkinje cell loss and thinning of the molecular cell layer. Additionally, Purkinje cells of BAC-R424H mice showed significantly lower spontaneous firing frequency with a corresponding increase in inter-spike interval compared to that of wild-type mice. Our SCA13 transgenic mice recapitulate both neuropathological and behavioral changes manifested in human SCA13 R423H patients and provide an advantageous approach to understanding the role of voltage-gated potassium channel in cerebellar morphogenesis and function. This mammalian in vivo model will lead to further understanding of the R423H allelic form of SCA13 from the molecular to the behavioral level and serve as a platform for testing potential therapeutic compounds.

neuroscience↗

bioRxiv2024

Association of cerebellar inflammation and neurodegeneration in a novel spinocerebellar ataxia type 13 mouse model

BackgroundNeuroinflammation is a recognized pathological characteristic of neurodegenerative diseases. Spinocerebellar ataxia 13 (SCA13) is a progressive neurodegenerative disease with no effective treatments. Our previous studies reported human mutations in KCNC3 gene are causative for SCA13. Human R423H allelic mutation induces early-onset neurodegeneration and aberrant intracellular retention of Epidermal Growth Factor Receptor (EGFR) in drosophila. However, the neurodegeneration and inflammatory response induced by the R424H allele are unknown in a mammalian model of disease. MethodIn this study, a single Kcnc3 R424H mutation (Analogous to the human SCA13 R423H isoform) transgenic mice were created using CRISPR/Cas 9 technique. Motor function (gait, tremor, coordination and balance) and cerebellar volume (scanned and imaged with 7T MRI) of the R424H transgenic mice were evaluated at multiple timepoints. Neurodegeneration (Purkinje cells loss) as well as cerebellar (astroglia, microglia and macrophage activation) and peripheral (plasma cytokines levels) inflammatory responses were examined and analyzed. ResultThe R424H transgenic mice showed marked neurological motor dysfunction with high-frequency tremor, aberrant gait, and short latency to fall in Rotarod testing at 3 and 6 months of age. Abnormal spontaneous firing was recorded in electrophysiology of Purkinje cells. Pathological changes in our R424H transgenic mice included progressive Purkinje cell degeneration and cerebellar atrophy. Over-active microglia, astrocytes, and macrophages were observed in the cerebella of transgenic mice. Pearson correlation analyses indicated that the number of Calbindin positive cells, a Purkinje cell marker, showed a strong inverse correlation with the positive cell number of EGFR, phosphorylated EGFR (pEGFR), and CD68. The expression of EGFR/pEGFR was positively correlated with CD68 and Glial Fibrillary Acidic Protein. ConclusionTransgenic R424H mice provide a novel SCA13 model showing significant motor deficits, Purkinje cells loss, cerebellar inflammation, and atrophy. Our study suggests that the activation of inflammatory immune cells (astroglia, microglia and macrophages) and strong expression of EGFR/ pEGFR signal in these immune cells are associated with Purkinje cell loss in the cerebellum. This abnormal neuroinflammation may play a significant role in the aggressive procession of neurodegeneration.

neuroscience↗

bioRxiv2023

Divergent host innate immune response to the smooth-to-rough M. abscessus adaptation to chronic infection

Mycobacterium abscessus is a nontuberculous mycobacterium emerging as a significant pathogen for individuals with chronic lung disease, including cystic fibrosis and chronic obstructive pulmonary disease. Current therapeutics have poor efficacy. New strategies of bacterial control based on host defenses are appealing, but anti-mycobacterial immune mechanisms are poorly understood and are complicated by the appearance of smooth and rough morphotypes with distinct host responses. We explored the role of the complement system in the clearance of M. abscessus morphotypes by neutrophils, an abundant cell in these infections. M. abscessus opsonized with plasma from healthy individuals promoted greater killing by neutrophils compared to opsonization in heat-inactivated plasma. Rough clinical isolates were more resistant to complement but were still efficiently killed. Complement C3 associated strongly with the smooth morphotype while mannose-binding lectin 2 was associated with the rough morphotype. M. abscessus killing was dependent on C3, but not on C1q or Factor B; furthermore, competition of mannose-binding lectin 2 binding with mannan or N-acetyl-glucosamine during opsonization did not inhibit killing. These data suggest that M. abscessus does not canonically activate complement through the classical, alternative, or lectin pathways. Complement-mediated killing was dependent on IgG and IgM for smooth and on IgG for rough M. abscessus. Both morphotypes were recognized by Complement Receptor 3 (CD11b), but not CR1 (CD35), and in a carbohydrate- and calcium-dependent manner. These data suggest the smooth-to-rough adaptation changes complement recognition of M. abscessus and that complement is an important factor for M. abscessus infection.

immunology↗

bioRxiv2019

Population Genomics of Nontuberculous Mycobacteria Recovered from United States Cystic Fibrosis Patients

Nontuberculous mycobacteria (NTM) pose a threat to individuals with cystic fibrosis (CF) due to an increased prevalence of pulmonary infections, innate drug resistance of the bacteria, and potential transmission between CF patients. To explore the genetic diversity of NTM isolated from CF patients within the United States (US) and to identify potential transmission events, we sequenced and analyzed the genomes of 341 NTM isolates from 191 CF patients as part of a nationwide surveillance study. The most abundant species in the isolate cohort were Mycobacterium abscessus (59.5%), followed by species in the Mycobacterium avium complex (37.5%). Phylogenomic analyses of the three M. abscessus subspecies revealed that more than half of CF patients had isolates in one of four dominant clones, including two dominant clones of M. abscessus subspecies abscessus and two dominant clones of M. abscessus subspecies massiliense. M. avium isolates from US CF patients, however, do not have dominant clones and are phylogenetically diverse. Longitudinal NTM isolates were compared to determine genome-wide single nucleotide polymorphisms (SNPs) that occur within patients over time. This information was used to compare between and within-patient SNP distributions, to quantitatively define SNP thresholds suggestive of transmission, and calculate a posterior probability of recent transmission given the SNP distance between two isolates from different patients. Out of 114 patients with M. abscessus subspecies, ten clusters of highly similar isolates from 26 patients were identified. Among the 26 patients in the M. abscessus clusters, 12 attended the same CF care centers. No highly similar isolate clusters were observed in M. avium. Our study reveals the contrasting genomic diversity and epidemiology of two major NTM taxa and the potential for between-patient exposure and cross-transmission of these emerging pathogens.

microbiology↗