Biology subjects

Johnson, B. M.

Publications and source records attributed to Johnson, B. M..

6 recordsLinked to original sources

bioRxiv2026

MyD88 deficiency modestly attenuates disease in a Leigh syndrome mouse model while enrofloxacin accelerates disease

Primary genetic mitochondrial diseases (GMDs) are a clinically and genetically diverse group of diseases estimated to impact over 1 in 4,000 individuals. Leigh syndrome (LS) is the most common pediatric presentation of GMD. LS typically presents within the first years of life and is a severe progressive multi-system disorder. Symmetric progressive inflammatory brain lesions are a defining feature of the disease. Patients can also present with seizures, metabolic dysfunction, muscle weakness, and other symptoms. No effective clinical treatments currently exist. Recent data from the Ndufs4(-/-) mouse model shows that peripheral macrophages contribute to brain lesions in LS, that disease is causally driven by innate immune populations, and that depletion of innate immune cells prevents LS disease. However, the precise mechanisms underlying immune activation remain unknown. Certain mitochondrial macromolecules retain bacterial signatures and can act as potent agonists for innate immune pathways. For example, cytoplasmic mitochondrial RNA and mitochondrial DNA are detected by Toll-like receptors (TLRs) 7 and 9, respectively, at the endosome. Accordingly, these are considered strong candidates for mediating innate immune activation in LS. Here, we generated TLR signaling deficient Ndufs4(-/-)/MyD88(-/-) animals to assess whether TLR signaling plays a role in disease onset or progression in LS. Loss of MyD88 in Ndufs4(-/-) animals statistically significantly increased survival and delayed the onset of some symptoms, but the benefits were modest compared to CSF1R inhibition from prior work. We conclude that Myd88-mediated immune signaling is not a primary driver of LS. Notably, prophylactic enrofloxacin treatment, which was necessary for production of innate immune deficient MyD88(-/-) animals, modestly decreased survival and accelerated disease. The impact of enrofloxacin and similar drugs in the context of mitochondrial disease warrants further investigation.

neuroscience↗

bioRxiv2025

Gut colonization by Bacteroides fragilis at juvenile age alters microbiota composition and accelerates type 1 diabetes progression in non-obese diabetic mice

Type 1 diabetes (T1D) in humans is associated with higher Bacteroidetes : Firmicutes ratio and higher abundance of Bacteroides genus members. Bacteroides fragilis (BF) is an integral component of the human colonic commensal microbiota. Here, we show that gut colonization of specific pathogen-free (SPF) non-obese diabetic (NOD) mice by BF at a juvenile age induces a pro-inflammatory immune response and accelerated disease progression. NOD mice born to BF-monocolonized parents not only showed rapid disease progression compared to germ-free (GF) controls but also preserved accelerated disease onset and higher disease incidence upon conventionalization, suggesting that BF contributes to a pro-inflammatory response and autoimmunity in T1D. Interestingly, we found that while gut microbiota composition was different in control and BF-colonized SPF mice, presence of BF alone could significantly impact the acquisition of microbial communities upon conventionalization of gnotobiotic mice. Bulk RNAseq analysis of colon tissues revealed profound differences in the gene expression pattern of GF and BF-monocolonized mice as well as their conventionalized counterparts, shedding light on the probable mechanisms contributing to accelerated disease onset in mice that are exposed to BF. We found that mucin production is downregulated and the abundance of mucin degraders such as Akkermansia muciniphila is profoundly lower in BF-colonized mice that are conventionalized. Overall, these studies demonstrate that early life acquisition of BF-like distal gut commensals could have profound modulatory effects on the eventual overall gut microbiota structure, immune function, and {beta}-cell specific autoimmune outcomes under genetic susceptibility.

immunology↗

bioRxiv2021

Leukocyte proliferation mediates disease pathogenesis in the Ndufs4(KO) mouse model of Leigh syndrome

Symmetric, progressive, necrotizing lesions in the brainstem are a defining feature of Leigh syndrome (LS). A mechanistic understanding of the pathogenesis of these lesions has been elusive. Here, we report that leukocyte proliferation is causally involved in the pathogenesis of Leigh syndrome. Directly depleting leukocytes with a colony-stimulating factor 1 receptor (CSF1R) inhibitor dramatically attenuates disease, including complete prevention of CNS lesion formation and substantial extension of survival. Leukocyte depletion rescues a range of symptoms including hyperlactemia, seizures, respiratory function, and neurologic symptoms. These data provide a mechanistic explanation for the beneficial effects of mTOR inhibition. More importantly, these findings dramatically alter our understanding of the pathogenesis of LS, demonstrating that immune involvement directly drives disease. These findings have significant implication for the mechanisms of disease resulting from mitochondrial dysfunction, and may lead to novel therapeutic strategies. One-Sentence SummaryPharmacologic targeting of leukocytes prevents CNS lesions, neurological disease, and metabolic dysfunction in the Ndufs4(KO) mouse model of Leigh syndrome.

pathology↗

bioRxiv2019

Impacts of Gut Microbiota on Gender Bias in Intestinal Pro-Inflammatory Immune Phenotype and Systemic Autoimmune Progression in Lupus-prone SNF1 mice

1.The risk of developing systemic lupus erythematosus (SLE) is about 9 times higher among women compared to men. Our recent report, which used (SWRxNZB) F1 (SNF1) mouse model of spontaneous lupus, showed a potential link between immune response initiated in the gut mucosa at juvenile age (sex hormone independent) and SLE susceptibility. Here, this mouse model, we show that gut microbiota contributes to a pro-inflammatory immune response in the intestine and autoimmune progression, primarily in females, leading to an associated gender bias. We found that gut microbiota composition in male and female littermates are significantly different only at adult age and depletion of gut microbes causes suppression of autoimmune progression only in females. In agreement, microbiota depletion suppressed the pro-inflammatory cytokine response of gut mucosa in both juvenile and adult females. In male SNF1 mice, on the other hand, orchidectomy (castration) caused changes in the composition of gut microbiota and a modest acceleration of autoimmune progression. However, cecum microbiota transplantation studies failed to show superior protection of females from autoimmunity by androgen-influenced gut microbiota. Overall, our work shows that microbiota-dependent pro-inflammatory immune response in the gut mucosa of females initiated at juvenile ages and androgen-dependent protection of males contributes to gender differences in the intestinal immune phenotype and systemic autoimmune progression.

immunology↗

bioRxiv2018

Polysaccharide A-dependent opposing effects of mucosal and systemic exposures to human gut commensal Bacteroides fragilis in type 1 diabetes

Bacteroides fragilis (BF) is an integral component of the human colonic commensal microbiota. BF is also the most commonly isolated organism from clinical cases of intra-abdominal abscesses suggesting its potential to induce pro-inflammatory responses, upon accessing the systemic compartment. Hence, we examined the impact of mucosal and systemic exposures to BF on type 1 diabetes (T1D) incidence in non-obese diabetic (NOD) mice. The impact of intestinal exposure to BF under chemically-induced enhanced gut permeability condition, which permits microbial translocation, in T1D was also examined. While oral administration of pre-diabetic mice with heat-killed (HK) BF caused enhanced immune regulation and suppression of autoimmunity resulting in delayed hyperglycemia, mice that received HK BF by i.v. injection showed rapid disease progression. Importantly, polysaccharide-A deficient ({Delta}PSA) BF failed to produce these opposing effects upon oral and systemic deliveries. Further, BF induced modulation of disease progression was observed in WT, but not TLR2-deficient, NOD mice. Interestingly, oral administration of BF under enhanced gut permeability condition resulted in accelerated disease progression and rapid onset of hyperglycemia in NOD mice. Overall, these observations suggest that BF-like gut commensals can cause pro-inflammatory responses upon gaining access to systemic compartment and contribute to T1D in at-risk subjects.

immunology↗

bioRxiv2018

Complex dietary-polysaccharide modulates gut immune function and microbiota, and promotes protection from autoimmune diabetes

Since the dietary supplement and prebiotic value of {beta}-glucan-rich products have been widely recognized and the dietary approaches for modulating autoimmunity have been increasingly explored, we assessed the impact of oral administration of high-pure yeast {beta}-glucan (YBG) on gut immune function, microbiota and type 1 diabetes (T1D) using mouse models. Oral administration of this non-digestible complex polysaccharide caused a Dectin-1-dependent immune response involving increased expression of IL10, retinaldehyde dehydrogenase (Raldh) and pro-inflammatory cytokines in the gut mucosa. YBG-exposed intestinal DCs induced/expanded primarily Foxp3+, IL10+ and IL17+ T cells, ex vivo. Importantly, prolonged oral administration of low-dose YBG at pre-diabetic stage suppressed insulitis and significantly delayed the T1D incidence in non-obese diabetic (NOD) mice. Further, prolonged treatment with YBG showed increased Foxp3+ T cell frequencies, and a significant change in the gut microbiota, particularly an increase in the abundance of Bacteroidetes and a decrease in the Firmicute members. Oral administration of YBG, together with Raldh-substrate and {beta}-cell antigen, resulted in a better protection of NOD mice from T1D. These observations suggest that YBG not only has a prebiotic property, but also has an oral tolerogenic-adjuvant-like effect, and these features could be exploited for modulating autoimmunity in T1D.

immunology↗