Corrigendum: Persisting Cryptococcus yeast species Vishniacozyma victoriae and Cryptococcus neoformans elicit unique airway inflammation in mice following repeated exposure

[This corrects the article DOI: 10.3389/fcimb.2023.1067475.].

Optimization of Aspergillus versicolor Culture and Aerosolization in a Murine Model of Inhalational Fungal Exposure

Aspergillus versicolor is ubiquitous in the environment and is particularly abundant in damp indoor spaces. Exposure to Aspergillus species, as well as other environmental fungi, has been linked to respiratory health outcomes, including asthma, allergy, and even local or disseminated infection. However, the pulmonary immunological mechanisms associated with repeated exposure to A. versicolor have remained relatively uncharacterized. Here, A. versicolor was cultured and desiccated on rice then placed in an acoustical generator system to achieve aerosolization. Mice were challenged with titrated doses of aerosolized conidia to examine deposition, lymphoproliferative properties, and immunotoxicological response to repeated inhalation exposures. The necessary dose to induce lymphoproliferation was identified, but not infection-like pathology. Further, it was determined that the dose was able to initiate localized immune responses. The data presented in this study demonstrate an optimized and reproducible method for delivering A. versicolor conidia to rodents via nose-only inhalation. Additionally, the feasibility of a long-term repeated exposure study was established. This experimental protocol can be used in future studies to investigate the physiological effects of repeated pulmonary exposure to fungal conidia utilizing a practical and relevant mode of delivery. In total, these data constitute an important foundation for subsequent research in the field.

Persisting Cryptococcus yeast species Vishniacozyma victoriae and Cryptococcus neoformans elicit unique airway inflammation in mice following repeated exposure

Background

Allergic airway disease (AAD) is a growing concern in industrialized nations and can be influenced by fungal exposures. Basidiomycota yeast species such as Cryptococcus neoformans are known to exacerbate allergic airway disease; however, recent indoor assessments have identified other Basidiomycota yeasts, including Vishniacozyma victoriae (syn. Cryptococcus victoriae), to be prevalent and potentially associated with asthma. Until now, the murine pulmonary immune response to repeated V. victoriae exposure was previously unexplored.

Objective

This study aimed to compare the immunological impact of repeated pulmonary exposure to Cryptococcus yeasts.

Methods

Mice were repeatedly exposed to an immunogenic dose of C. neoformans or V. victoriae via oropharyngeal aspiration. Bronchoalveolar lavage fluid (BALF) and lungs were collected to examine airway remodeling, inflammation, mucous production, cellular influx, and cytokine responses at 1 day and 21 days post final exposure. The responses to C. neoformans and V. victoriae were analyzed and compared.

Results

Following repeated exposure, both C. neoformans and V. victoriae cells were still detectable in the lungs 21 days post final exposure. Repeated C. neoformans exposure initiated myeloid and lymphoid cellular infiltration into the lung that worsened over time, as well as an IL-4 and IL-5 response compared to PBS-exposed controls. In contrast, repeated V. victoriae exposure induced a strong CD4+ T cell-driven lymphoid response that started to resolve by 21 days post final exposure.

Discussion

C. neoformans remained in the lungs and exacerbated the pulmonary immune responses as expected following repeated exposure. The persistence of V. victoriae in the lung and strong lymphoid response following repeated exposure were unexpected given its lack of reported involvement in AAD. Given the abundance in indoor environments and industrial utilization of V. victoriae, these results highlight the importance to investigate the impact of frequently detected fungal organisms on the pulmonary response following inhalational exposure. Moreover, it is important to continue to address the knowledge gap involving Basidiomycota yeasts and their impact on AAD.

Mycobiota and the Contribution of Yeasts in Floor Dust of 50 Elementary Schools Characterized with Sequencing Internal Transcribed Spacer Region of Ribosomal DNA

The assemblage of fungi including unicellular yeasts in schools is understudied. We conducted an environmental study to characterize fungal communities in classroom floor dust. We collected 500 samples from 50 elementary schools in Philadelphia, PA, and evaluated room dampness/mold conditions. Genomic DNA from dust was extracted for internal transcribed spacer 1 Illumina MiSeq sequencing to identify operational taxonomic units (OTUs) organized from DNA sequences. Differential abundance analyses were performed to examine significant differences in abundance among groups. We identified 724 genera from 1490 OTUs. The genus Epicoccum was not diverse but the most abundant (relative abundance = 18.9%). Fungi were less diverse but most dissimilar in composition in the most water-damaged classrooms compared to the least water-damaged, indicating differential effects of individual classroom water-damage on fungal compositions. We identified 62 yeast genera, representing 19.6% of DNA sequences. Cyberlindnera was the most abundant (6.1%), followed by Cryptococcus, Aureobasidium, Rhodotorula, and Candida. The average relative abundance of yeasts tended to increase with increasing dampness and mold score and was significantly (p-value = 0.048) higher in the most water-damaged classrooms (22.4%) than the least water-damaged classrooms (18.2%). Our study suggests the need for further research on the potential health effects associated with exposures to yeasts in schools.

Exposure to Vishniacozyma victoriae elicits airway inflammation and a CD4+ T cell-driven lymphocytic response

Like the pathogenic yeast Cryptococcus neoformans, Vishniacozyma victoriae (syn. Cryptococcus victoriae), a non-pathogenic yeast, has been associated with allergic airway disease. Although V. victoriae is frequently detected in indoor environments, the impact of repeated exposure is currently unknown. In this study, mice were exposed via oropharyngeal aspiration to V. victoriae or C. neoformans every other day for a total of six exposures, and responses were analyzed 1 day and 21 days post final exposure. As expected, repeated exposure to C. neoformans resulted in an increase of myeloid and lymphoid cells in the bronchoalveolar lavage fluid (BALF), granuloma formation with intralesional yeast, and peribronchiolar and perivascular inflammation 1 day post exposure. This response was exacerbated 21 days post exposure as the yeast cells replicated. Repeated exposure to V. victoriae resulted in an increase in eosinophils, Ly6Chi/int monocytes, and CD103+ dendritic cells in the BALF, and mild perivascular and peribronchiolar inflammation 1 day post exposure. Surprisingly, V. victoriae cells were present in the lungs of exposed mice 21 days post exposure, and the response shifted toward a nodular lymphocytic response with an increase of CD4+ T cells in the BALF. Lastly, C. neoformans exposure was predicted to activate antigen presentation, B cell development and Th2 proteomic pathways, whereas V. victoriae was predicted to activate VDR/RXR activation, Granzyme A signaling, and IGF-1 signaling pathways 21 days post exposure. The results of this study suggest that exposure to environmentally ubiquitous V. victoriae may exacerbate allergic airway disease, although not to the extent of exposure to pathogenic C. neoformans.

Interagency Agreement between NIEHS & NIOSH: AES 12007001-1-0-6

Vishniacozyma victoriae (syn. Cryptococcus victoriae) in the homes of asthmatic and non-asthmatic children in New York City

BACKGROUND

Indoor environments contain a broad diversity of non-pathogenic Basidiomycota yeasts, but their role in exacerbating adverse health effects has remained unclear.

OBJECTIVE

To understand the role of Vishniacozyma victoriae exposure and its impact on human health.

METHODS

A qPCR assay was developed to detect and quantify an abundant indoor yeast species, Vishniacozyma victoriae (syn. Cryptococcus victoriae), from homes participating in the New York City Neighborhood Asthma and Allergy Study (NAAS). We evaluated the associations between V. victoriae, housing characteristics, and asthma relevant health endpoints.

RESULTS

V. victoriae was quantified in 236 of the 256 bedroom floor dust samples ranging from less than 300-45,918 cell equivalents/mg of dust. Higher concentrations of V. victoriae were significantly associated with carpeted bedroom floors (P = 0.044), mean specific humidity (P = 0.004), winter (P < 0.0001) and spring (P = 0.001) seasons, and the presence of dog (P = 0.010) and dog allergen Can f 1 (P = 0.027). V. victoriae concentrations were lower in homes of children with asthma vs. without asthma (P = 0.027), an association observed only among the non-seroatopic children.

Aspergillus versicolor Inhalation Triggers Neuroimmune, Glial, and Neuropeptide Transcriptional Changes

Increasing evidence associates indoor fungal exposure with deleterious central nervous system (CNS) health, such as cognitive and emotional deficits in children and adults, but the specific mechanisms by which it might impact the brain are poorly understood. Mice were exposed to filtered air, heat-inactivated Aspergillus versicolor (3 × 10⁵ spores), or viable A. versicolor (3 × 10⁵ spores) via nose-only inhalation exposure 2 times per week for 1, 2, or 4 weeks. Analysis of cortex, midbrain, olfactory bulb, and cerebellum tissue from mice exposed to viable A. versicolor spores for 1, 2, and 4 weeks revealed significantly elevated pro-inflammatory (Tnf and Il1b) and glial activity (Gdnf and Cxc3r1) gene expression in several brain regions when compared to filtered air control, with the most consistent and pronounced neuroimmune response 48H following the 4-week exposure in the midbrain and frontal lobe. Bulk RNA-seq analysis of the midbrain tissue confirmed that 4 weeks of A. versicolor exposure resulted in significant transcriptional enrichment of several biological pathways compared to the filtered air control, including neuroinflammation, glial cell activation, and regulation of postsynaptic organization. Upregulation of Drd1, Penk, and Pdyn mRNA expression was confirmed in the 4-week A. versicolor exposed midbrain tissue, highlighting that gene expression important for neurotransmission was affected by repeated A. versicolor inhalation exposure. Taken together, these findings indicate that the brain can detect and respond to A. versicolor inhalation exposure with changes in neuroimmune and neurotransmission gene expression, providing much needed insight into how inhaled fungal exposures can affect CNS responses and regulate neuroimmune homeostasis.

Inhalation of Stachybotrys chartarum Fragments Induces Pulmonary Arterial Remodeling

Stachybotrys chartarum is a fungal contaminant within the built environment and a respiratory health concern in the United States. The objective of this study was to characterize the mechanisms influencing pulmonary immune responses to repeatedly inhaled S. chartarum. Groups of B6C3F1/N mice repeatedly inhaled viable trichothecene-producing S. chartarum conidia (strain A or strain B), heat-inactivated conidia, or high-efficiency particulate absolute-filtered air twice per week for 4 and 13 weeks. Strain A was found to produce higher amounts of respirable fragments than strain B. Lung tissue, serum, and BAL fluid were collected at 24 and 48 hours after final exposure and processed for histology, flow cytometry, and RNA and proteomic analyses. At 4 weeks after exposure, a T-helper cell type 2-mediated response was observed. After 13 weeks, a mixed T-cell response was observed after exposure to strain A compared with a T-helper cell type 2-mediated response after strain B exposure. After exposure, both strains induced pulmonary arterial remodeling at 13 weeks; however, strain A-exposed mice progressed more quickly than strain B-exposed mice. BAL fluid was composed primarily of eosinophils, neutrophils, and macrophages. Both the immune response and the observed pulmonary arterial remodeling were supported by specific cellular, molecular, and proteomic profiles. The immunopathological responses occurred earlier in mice exposed to high fragment-producing strain A. The rather striking induction of pulmonary remodeling by S. chartarum appears to be related to the presence of fungal fragments during exposure.

Resolution of Pulmonary Inflammation Induced by Carbon Nanotubes and Fullerenes in Mice: Role of Macrophage Polarization

Pulmonary exposure to certain engineered nanomaterials (ENMs) causes chronic lesions like fibrosis and cancer in animal models as a result of unresolved inflammation. Resolution of inflammation involves the time-dependent biosynthesis of lipid mediators (LMs)-in particular, specialized pro-resolving mediators (SPMs). To understand how ENM-induced pulmonary inflammation is resolved, we analyzed the inflammatory and pro-resolving responses to fibrogenic multi-walled carbon nanotubes (MWCNTs, Mitsui-7) and low-toxicity fullerenes (fullerene C60, C60F). Pharyngeal aspiration of MWCNTs at 40 μg/mouse or C60F at a dose above 640 μg/mouse elicited pulmonary effects in B6C3F1 mice. Both ENMs stimulated acute inflammation, predominated by neutrophils, in the lung at day 1, which transitioned to histiocytic inflammation by day 7. By day 28, the lesion in MWCNT-exposed mice progressed to fibrotic granulomas, whereas it remained as alveolar histiocytosis in C60F-exposed mice. Flow cytometric profiling of whole lung lavage (WLL) cells revealed that neutrophil recruitment was the greatest at day 1 and declined to 36.6% of that level in MWCNT- and 16.8% in C60F-treated mice by day 7, and to basal levels by day 28, suggesting a rapid initiation phase and an extended resolution phase. Both ENMs induced high levels of proinflammatory leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) with peaks at day 1, and high levels of SPMs resolvin D1 (RvD1) and E1 (RvE1) with peaks at day 7. MWCNTs and C60F induced time-dependent polarization of M1 macrophages with a peak at day 1 and subsequently of M2 macrophages with a peak at day 7 in the lung, accompanied by elevated levels of type 1 or type 2 cytokines, respectively. M1 macrophages exhibited preferential induction of arachidonate 5-lipoxygenase activating protein (ALOX5AP), whereas M2 macrophages had a high level expression of arachidonate 15-lipoxygenase (ALOX15). Polarization of macrophages in vitro differentially induced ALOX5AP in M1 macrophages or ALOX15 in M2 macrophages resulting in increased preferential biosynthesis of proinflammatory LMs or SPMs. MWCNTs increased the M1- or M2-specific production of LMs accordingly. These findings support a mechanism by which persistent ENM-induced neutrophilic inflammation is actively resolved through time-dependent polarization of macrophages and enhanced biosynthesis of specialized LMs via distinct ALOX pathways.

Subchronic inhalation of Aspergillus versicolor conidia leads to sustained innate immune responses and is associated with irreversible remodeling of pulmonary arterial tissue following recovery

Aspergillus versicolor is an environmentally ubiquitous fungal species that is particularly abundant in environments with water infiltration. Respiration of fungal products, including conidia, hyphal fragments, mycotoxins, and other secondary metabolites may cause adverse pulmonary health effects including asthma and allergy. In the present study, pulmonary immune responses in B6C3F1 mice were examined following 1, 2, 4, 8, and 13 weeks of repeated respiratory challenge to 3×105A. versicolor conidia. Increased alveolar macrophages, inflammatory monocytes, neutrophils, and eosinophils, which peaked between 4 and 8 weeks, were detected in the lungs of mice exposed to viable conidia. Type 2 innate lymphoid cells (ILC2s) peaked between 8 and 13 weeks compared to total T cells which increased between 2 and 8 weeks and decreased at 13 weeks. Protein concentrations of the Th2 cytokines IL4, IL5, and IL13 were highest in bronchoaveolar lavage fluid of exposed mice following 4 weeks and exhibited a time-dependent reduction at 8 and 13 weeks. Inhalation of conidia for 13 weeks led to goblet cell hyperplasia, vascular wall thickening, and perivascular inflammation. Finally, mixed perivascular inflammation and smooth muscle hypertrophy were sustained at 4 weeks post-exposure. These data indicate that exposure to A. versicolor elicits a Th2-biased immune response that is driven by innate cell populations and is associated with the induction of remodeling of the pulmonary vasculature.

Cultivation and aerosolization of Stachybotrys chartarum for modeling pulmonary inhalation exposure

Objective: Stachybotrys chartarum is a hydrophilic fungal species commonly found as a contaminant in water-damaged building materials. Although several studies have suggested that S. chartarum exposure elicits a variety of adverse health effects, the ability to characterize the pulmonary immune responses to exposure is limited by delivery methods that do not replicate environmental exposure. This study aimed to develop a method of S. chartarum aerosolization to better model inhalation exposures. Materials and methods: An acoustical generator system (AGS) was previously developed and utilized to aerosolize and deliver fungal spores to mice housed in a multi-animal nose-only exposure chamber. In this study, methods for cultivating, heat-inactivating, and aerosolizing two macrocyclic trichothecene-producing strains of S. chartartum using the AGS are described. Results and discussion: In addition to conidia, acoustical generation of one strain of S. chartarum resulted in the aerosolization of fungal fragments (<2 µm aerodynamic diameter) derived from conidia, phialides, and hyphae that initially comprised 50% of the total fungal particle count but was reduced to less than 10% over the duration of aerosolization. Acoustical generation of heat-inactivated S. chartarum did not result in a similar level of fragmentation. Delivery of dry, unextracted S. chartarum using these aerosolization methods resulted in pulmonary inflammation and immune cell infiltration in mice inhaling viable, but not heat-inactivated S. chartarum. Conclusions: These methods of S. chartarum growth and aerosolization allow for the delivery of fungal bioaerosols to rodents that may better simulate natural exposure within water-damaged indoor environments.

Investigating local and systemic immune changes following sub-chronic inhalation of Aspergillus versicolor spores

Fungi are environmentally ubiquitous, and can be particularly abundant in damp indoor locations which may lead to pulmonary fungal exposure via inhalation of bioaerosols. Some of the adverse pulmonary health effects associated with fungal challenges include asthma, allergy, hypersensitivity pneumonitis, and local or disseminated infection. Here, we study the innate immune effects following 13 weeks sub-chronic inhalation exposures to spores derived from a common indoor fungal contaminant, Aspergillus versicolor. Compared to air-only control mice, A. versicolor-exposed B6C3F1 mice exhibited increased recruitment of leukocytes to the lung, particularly eosinophils and type 2 innate lymphoid cells (ILC2s), but also alveolar macrophages, inflammatory monocytes, and neutrophils following 13 weeks of exposure in nose-only inhalation chambers. Local expression of ccl2, ccl7, eotaxin, and il13 mRNA was increased in lung tissue. In addition, IL-4, CCL3, CCL4, CXCL1, and CXCL5 were increased in bronchoaveolar lavage fluid of A. versicolor-exposed mice compared to controls. Systemically, circulating CCL7, CXCL1, CXCL5, and CXCL10 were increased in serum of mice following inhalation of spores. Taken together, these data indicate A. versicolor elicits a Th2-biased immune response that is driven by multiple innate immune cell populations, including monocytes, eosinophils, and ILC2s.

Aspergillus fumigatus viability drives allergic responses to inhaled conidia

BACKGROUND

Aspergillus fumigatus-induced allergic airway disease has been shown to involve conidial germination in vivo, but the immunological mechanisms remain uncharacterized.

OBJECTIVE

A subchronic murine exposure model was used to examine the immunological mediators that are regulated in response to either culturable or nonculturable A fumigatus conidia.

METHODS

Female B6C3F1/N mice were repeatedly dosed via inhalation with 1 × 105 viable or heat-inactivated conidia (HIC), twice per week for 13 weeks (26 exposures). Control mice inhaled high-efficiency particulate arrestor-filtered air. The influence of A fumigatus conidial germination on the pulmonary immunopathological outcomes was evaluated by flow cytometry analysis of cellular infiltration in the airways, assessment of lung messenger RNA expression, quantitative proteomics, and histopathology of whole lung tissue.

RESULTS

Repeated inhalation of viable conidia, but not HIC, resulted in allergic inflammation marked by vascular remodeling, extensive eosinophilia, and accumulation of alternatively activated macrophages (AAMs) in the murine airways. More specifically, mice that inhaled viable conidia resulted in a mixed TH1 and TH2 (IL-13) cytokine response. Recruitment of eosinophils corresponded with increased Ccl11 transcripts. Furthermore, genes associated with M2 or alternatively activated macrophage polarization (eg, Arg1, Chil3, and Retnla) were significantly up-regulated in viable A fumigatus-exposed mice. In mice inhaling HIC, CD4+ T cells expressing IFN-γ (TH1) dominated the lymphocytic infiltration. Quantitative proteomics of the lung revealed metabolic reprogramming accompanied by mitochondrial dysfunction and endoplasmic reticulum stress stimulated by oxidative stress from repetitive microbial insult.

CONCLUSION

Our studies demonstrate that A fumigatus conidial viability in vivo is critical to the immunopathological presentation of chronic fungal allergic disease.

MicroRNA Regulation of Host Immune Responses following Fungal Exposure

Fungal bioaerosols are ubiquitous in the environment and human exposure can result in a variety of health effects ranging from systemic, subcutaneous, and cutaneous infections to respiratory morbidity including allergy, asthma, and hypersensitivity pneumonitis. Recent research has focused on the role of microRNAs (miRNAs) following fungal exposure and is overlooked, yet important, group of regulators capable of influencing fungal immune responses through a variety of cellular mechanisms. These small non-coding ribose nucleic acids function to regulate gene expression at the post-transcriptional level and have been shown to participate in multiple disease pathways including cancer, heart disease, apoptosis, as well as immune responses to microbial hazards and occupational allergens. Recent animal model studies have characterized miRNAs following the exposure to inflammatory stimuli. Studies focused on microbial exposure, including bacterial infections, as well as exposure to different allergens have shown miRNAs, such as miR-21, miR-146, miR-132, miR-155, and the let-7 family members, to be involved in immune and inflammatory responses. Interestingly, the few studies have assessed that the miRNA profiles following fungal exposure have identified the same critical miRNAs that have been characterized in other inflammatory-mediated and allergy-induced experimental models. Review of available in vitro, animal and human studies of exposures to Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Paracoccidioides brasiliensis, and Stachybotrys chartarum identified several miRNAs that were shared between responses to these species including miR-125 a/b (macrophage polarization/activation), miR-132 [toll-like receptor (TLR)2-mediated signaling], miR-146a (TLR mediated signaling, alternative macrophage activation), and miR-29a/b (natural killer cell function, C-leptin signaling, inhibition of Th1 immune response). Although these datasets provide preliminary insight into the role of miRNAs in fungal exposed models, interpretation of miRNA datasets can be challenging for researchers. To assist in navigating this rapidly evolving field, the aim of this review is to describe miRNAs in the framework of host recognition mechanisms and provide initial insight into the regulatory pathways in response to fungal exposure.

Influence of Aspergillus fumigatus conidia viability on murine pulmonary microRNA and mRNA expression following subchronic inhalation exposure

BACKGROUND

Personal exposure to fungal bioaerosols derived from contaminated building materials or agricultural commodities may induce or exacerbate a variety of adverse health effects. The genomic mechanisms that underlie pulmonary immune responses to fungal bioaerosols have remained unclear.

OBJECTIVE

The impact of fungal viability on the pulmonary microRNA and messenger RNA profiles that regulate murine immune responses was evaluated following subchronic inhalation exposure to Aspergillus fumigatus conidia.

METHODS

Three groups of naïve B6C3F1/N mice were exposed via nose-only inhalation to A. fumigatus viable conidia, heat-inactivated conidia (HIC), or HEPA-filtered air twice a week for 13 weeks. Total RNA was isolated from whole lung 24 and 48 h postfinal exposure and was further processed for gene expression and microRNA array analysis. The molecular network pathways between viable and HIC groups were evaluated.

RESULTS

Comparison of data sets revealed increased Il4, Il13 and Il33 expression in mice exposed to viable vs. HIC. Of 415 microRNAs detected, approximately 50% were altered in mice exposed to viable vs. HIC 48 h postexposure. Significantly down-regulated (P ≤ 0.05) miR-29a-3p was predicted to regulate TGF-β3 and Clec7a, genes involved in innate responses to viable A. fumigatus. Also significantly down-regulated (P ≤ 0.05), miR-23b-3p regulates genes involved in pulmonary IL-13 and IL-33 responses and SMAD2, downstream of TGF-β signalling. Using Ingenuity Pathway Analysis, a novel interaction was identified between viable conidia and SMAD2/3.

CONCLUSIONS AND CLINICAL RELEVANCE

Examination of the pulmonary genetic profiles revealed differentially expressed genes and microRNAs following subchronic inhalation exposure to A. fumigatus. MicroRNAs regulating genes involved in the pulmonary immune responses were those with the greatest fold change. Specifically, germinating A. fumigatus conidia were associated with Clec7a and were predicted to interact with Il13 and Il33. Furthermore, altered microRNAs may serve as potential biomarkers to evaluate fungal exposure.

Early detection of cardiac dysfunction in the type 1 diabetic heart using speckle-tracking based strain imaging

Enhanced sensitivity in echocardiographic analyses may allow for early detection of changes in cardiac function beyond the detection limits of conventional echocardiographic analyses, particularly in a small animal model. The goal of this study was to compare conventional echocardiographic measurements and speckle-tracking based strain imaging analyses in a small animal model of type 1 diabetes mellitus. Conventional analyses revealed differences in ejection fraction, fractional shortening, cardiac output, and stroke volume in diabetic animals relative to controls at 6-weeks post-diabetic onset. In contrast, when assessing short- and long-axis speckle-tracking based strain analyses, diabetic mice showed changes in average systolic radial strain, radial strain rate, radial displacement, and radial velocity, as well as decreased circumferential and longitudinal strain rate, as early as 1-week post-diabetic onset and persisting throughout the diabetic study. Further, we performed regional analyses for the LV and found that the free wall region was affected in both the short- and long-axis when assessing radial dimension parameters. These changes began 1-week post-diabetic onset and remained throughout the progression of the disease. These findings demonstrate the use of speckle-tracking based strain as an approach to elucidate cardiac dysfunction from a global perspective, identifying left ventricular cardiac regions affected during the progression of type 1 diabetes mellitus earlier than contractile changes detected by conventional echocardiographic measurements.

IL-15Rα deficiency in skeletal muscle alters respiratory function and the proteome of mitochondrial subpopulations independent of changes to the mitochondrial genome

Interleukin-15 receptor alpha knockout (IL15RαKO) mice exhibit a greater skeletal muscle mitochondrial density with an altered mitochondrial morphology. However, the mechanism and functional impact of these changes have not been determined. In this study, we characterized the functional, proteomic, and genomic alterations in mitochondrial subpopulations isolated from the skeletal muscles of IL15RαKO mice and B6129 background control mice. State 3 respiration was greater in interfibrillar mitochondria and whole muscle ATP levels were greater in IL15RαKO mice supporting the increases in respiration rate. However, the state 3/state 4 ratio was lower, suggesting some degree of respiratory uncoupling. Proteomic analyses identified several markers independently in mitochondrial subpopulations that are associated with these functional alterations. Next Generation Sequencing of mtDNA revealed a high degree of similarity between the mitochondrial genomes of IL15RαKO mice and controls in terms of copy number, consensus coding and the presence of minor alleles, suggesting that the functional and proteomic alterations we observed occurred independent of alterations to the mitochondrial genome. These data provide additional evidence to implicate IL-15Rα as a regulator of skeletal muscle phenotypes through effects on the mitochondrion, and suggest these effects are driven by alterations to the mitochondrial proteome.

Translational Regulation of the Mitochondrial Genome Following Redistribution of Mitochondrial MicroRNA in the Diabetic Heart

BACKGROUND

Cardiomyocytes are rich in mitochondria which are situated in spatially distinct subcellular regions, including those under the plasma membrane, subsarcolemmal mitochondria, and those between the myofibrils, interfibrillar mitochondria. We previously observed subpopulation-specific differences in mitochondrial proteomes following diabetic insult. The objective of this study was to determine whether mitochondrial genome-encoded proteins are regulated by microRNAs inside the mitochondrion and whether subcellular spatial location or diabetes mellitus influences the dynamics.

METHODS AND RESULTS

Using microarray technology coupled with cross-linking immunoprecipitation and next generation sequencing, we identified a pool of mitochondrial microRNAs, termed mitomiRs, that are redistributed in spatially distinct mitochondrial subpopulations in an inverse manner following diabetic insult. Redistributed mitomiRs displayed distinct interactions with the mitochondrial genome requiring specific stoichiometric associations with RNA-induced silencing complex constituents argonaute-2 (Ago2) and fragile X mental retardation-related protein 1 (FXR1) for translational regulation. In the presence of Ago2 and FXR1, redistribution of mitomiR-378 to the interfibrillar mitochondria following diabetic insult led to downregulation of mitochondrially encoded F0 component ATP6. Next generation sequencing analyses identified specific transcriptome and mitomiR sequences associated with ATP6 regulation. Overexpression of mitomiR-378 in HL-1 cells resulted in its accumulation in the mitochondrion and downregulation of functional ATP6 protein, whereas antagomir blockade restored functional ATP6 protein and cardiac pump function.

CONCLUSIONS

We propose mitomiRs can translationally regulate mitochondrially encoded proteins in spatially distinct mitochondrial subpopulations during diabetes mellitus. The results reveal the requirement of RNA-induced silencing complex constituents in the mitochondrion for functional mitomiR translational regulation and provide a connecting link between diabetic insult and ATP synthase function.

Functional deficiencies of subsarcolemmal mitochondria in the type 2 diabetic human heart

The mitochondrion has been implicated in the development of diabetic cardiomyopathy. Examination of cardiac mitochondria is complicated by the existence of spatially distinct subpopulations including subsarcolemmal (SSM) and interfibrillar (IFM). Dysfunction to cardiac SSM has been reported in murine models of type 2 diabetes mellitus; however, subpopulation-based mitochondrial analyses have not been explored in type 2 diabetic human heart. The goal of this study was to determine the impact of type 2 diabetes mellitus on cardiac mitochondrial function in the human patient. Mitochondrial subpopulations from atrial appendages of patients with and without type 2 diabetes were examined. Complex I- and fatty acid-mediated mitochondrial respiration rates were decreased in diabetic SSM compared with nondiabetic (P ≤ 0.05 for both), with no change in IFM. Electron transport chain (ETC) complexes I and IV activities were decreased in diabetic SSM compared with nondiabetic (P ≤ 0.05 for both), with a concomitant decline in their levels (P ≤ 0.05 for both). Regression analyses comparing comorbidities determined that diabetes mellitus was the primary factor accounting for mitochondrial dysfunction. Linear spline models examining correlative risk for mitochondrial dysfunction indicated that patients with diabetes display the same degree of state 3 and electron transport chain complex I dysfunction in SSM regardless of the extent of glycated hemoglobin (HbA1c) and hyperglycemia. Overall, the results suggest that independent of other pathologies, mitochondrial dysfunction is present in cardiac SSM of patients with type 2 diabetes and the degree of dysfunction is consistent regardless of the extent of elevated HbA1c or blood glucose levels.

Evaluation of the cardiolipin biosynthetic pathway and its interactions in the diabetic heart

AIMS

We have previously reported alterations in cardiolipin content and inner mitochondrial membrane (IMM) proteomic make-up specifically in interfibrillar mitochondria (IFM) in the type 1 diabetic heart; however, the mechanism underlying this alteration is unknown. The goal of this study was to determine how the cardiolipin biosynthetic pathway and cardiolipin-IMM protein interactions are impacted by type 1 diabetes mellitus.

MAIN METHODS

Male FVB mice were made diabetic by multiple low-dose streptozotocin injections and sacrificed five weeks post-diabetic onset. Messenger RNA was measured and cardiac mitochondrial subpopulations were isolated. Further mitochondrial functional experimentation included evaluating the protein expression of the enzymes directly responsible for cardiolipin biosynthesis, as well as ATP synthase activity. Interactions between cardiolipin and ATP synthase subunits were also examined.

KEY FINDINGS

Western blot analysis revealed a significant decrease in cardiolipin synthase (CRLS) protein content in diabetic IFM, with a concomitant decrease in its activity. ATP synthase activity was also significantly decreased. We identified two novel direct interactions between two subunits of the ATP synthase F0 complex (ATP5F1 and ATP5H), both of which were significantly decreased in diabetic IFM.

SIGNIFICANCE

Overall, these results indicate that type 1 diabetes mellitus negatively impacts the cardiolipin biosynthetic pathway specifically at CRLS, contributing to decreased cardiolipin content and loss of interactions with key ATP synthase F0 complex constituents in the IFM.

Reversal of mitochondrial proteomic loss in Type 1 diabetic heart with overexpression of phospholipid hydroperoxide glutathione peroxidase

Mitochondrial dysfunction is a contributor to diabetic cardiomyopathy. Previously, we observed proteomic decrements within the inner mitochondrial membrane (IMM) and matrix of diabetic cardiac interfibrillar mitochondria (IFM) correlating with dysfunctional mitochondrial protein import. The goal of this study was to determine whether overexpression of mitochondria phospholipid hydroperoxide glutathione peroxidase 4 (mPHGPx), an antioxidant enzyme capable of scavenging membrane-associated lipid peroxides in the IMM, could reverse proteomic alterations, dysfunctional protein import, and ultimately, mitochondrial dysfunction associated with the diabetic heart. MPHGPx transgenic mice and controls were made diabetic by multiple low-dose streptozotocin injections and examined after 5 wk of hyperglycemia. Five weeks after hyperglycemia onset, in vivo analysis of cardiac contractile function revealed decreased ejection fraction and fractional shortening in diabetic hearts that was reversed with mPHGPx overexpression. MPHGPx overexpression increased electron transport chain function while attenuating hydrogen peroxide production and lipid peroxidation in diabetic mPHGPx IFM. MPHGPx overexpression lessened proteomic loss observed in diabetic IFM. Posttranslational modifications, including oxidations and deamidations, were attenuated in diabetic IFM with mPHGPx overexpression. Mitochondrial protein import dysfunction in diabetic IFM was reversed with mPHGPx overexpression correlating with protein import constituent preservation. Ingenuity Pathway Analyses indicated that oxidative phosphorylation, tricarboxylic acid cycle, and fatty acid oxidation processes most influenced in diabetic IFM were preserved by mPHGPx overexpression. Specific mitochondrial networks preserved included complex I and II, mitochondrial ultrastructure, and mitochondrial protein import. These results indicate that mPHGPx overexpression can preserve the mitochondrial proteome and provide cardioprotective benefits to the diabetic heart.

miR-141 as a regulator of the mitochondrial phosphate carrier (Slc25a3) in the type 1 diabetic heart

Dysfunctional mitochondria are central in the pathogenesis of diabetic cardiomyopathy. Mitochondrial proteomic alterations resulting from diabetes mellitus have been reported although the mechanisms driving changes in proteomic signatures are unknown. microRNAs (miRNAs) have been considered as potential regulators of proteins. The goal of this study was to determine whether miRNAs play a role in diabetes-induced mitochondrial proteomic alterations. Quanitative RT-PCR miRNA screening in diabetic mice, 5 wk following multiple low-dose streptozotocin treatment was associated with alteration in the expression of 29 miRNAs in the diabetic heart compared with control. Among those miRNAs upregulated in the diabetic heart was miR-141 (P < 0.002). miRNA target prediction analyses identified miR-141 as a potential regulator of the inner mitochondrial membrane phosphate transporter, solute carrier family 25 member 3 (Slc25a3), which provides inorganic phosphate to the mitochondrial matrix and is essential for ATP production. With the use of a luciferase reporter construct with a Slc25a3 3'-untranslated region (UTR) target sequence, overexpression of miR-141 downregulated luciferase activity levels confirming miR-141/Slc25a3 3'-UTR binding. miR-141 overexpression in HL-1 cells elicited a decrease in Slc25a3 protein content, ATP production and a decrease in ATP synthase activity, similar to the diabetic phenotype (P < 0.05, for both). Diabetic interfibrillar mitochondria (IFM) displayed decreased Slc25a3 protein content, which was inversely correlated with increased miR-141 expression. Further, diabetic IFM ATP synthase activity was also decreased (P < 0.05). Together these results indicate that miR-141 can regulate Slc25a3 protein expression in the diabetic heart. Further, diabetes-induced miRNA changes may influence mitochondrial proteomes and functional processes such as mitochondrial ATP production.

Proteomic alterations of distinct mitochondrial subpopulations in the type 1 diabetic heart: contribution of protein import dysfunction

Diabetic cardiomyopathy is associated with increased risk of heart failure in type 1 diabetic patients. Mitochondrial dysfunction is suggested as an underlying contributor to diabetic cardiomyopathy. Cardiac mitochondria are characterized by subcellular spatial locale, including mitochondria located beneath the sarcolemma, subsarcolemmal mitochondria (SSM), and mitochondria situated between the myofibrils, interfibrillar mitochondria (IFM). The goal of this study was to determine whether type 1 diabetic insult in the heart influences proteomic make-up of spatially distinct mitochondrial subpopulations and to evaluate the role of nuclear encoded mitochondrial protein import. Utilizing multiple proteomic approaches (iTRAQ and two-dimensional-differential in-gel electrophoresis), IFM proteomic make-up was impacted by type 1 diabetes mellitus to a greater extent than SSM, as evidenced by decreased abundance of fatty acid oxidation and electron transport chain proteins. Mitochondrial phosphate carrier and adenine nucleotide translocator, as well as inner membrane translocases, were decreased in the diabetic IFM (P < 0.05 for both). Mitofilin, a protein involved in cristae morphology, was diminished in the diabetic IFM (P < 0.05). Posttranslational modifications, including oxidations and deamidations, were most prevalent in the diabetic IFM. Mitochondrial heat shock protein 70 (mtHsp70) was significantly decreased in diabetic IFM (P < 0.05). Mitochondrial protein import was decreased in the diabetic IFM with no change in the diabetic SSM (P < 0.05). Taken together, these results indicate that mitochondrial proteomic alterations in the type 1 diabetic heart are more pronounced in the IFM. Further, proteomic alterations are associated with nuclear encoded mitochondrial protein import dysfunction and loss of an essential mitochondrial protein import constituent, mtHsp70, implicating this process in the pathogenesis of the diabetic heart.

Enhanced apoptotic propensity in diabetic cardiac mitochondria: influence of subcellular spatial location

Cardiovascular complications, such as diabetic cardiomyopathy, account for the majority of deaths associated with diabetes mellitus. Mitochondria are particularly susceptible to the damaging effects of diabetes mellitus and have been implicated in the pathogenesis of diabetic cardiomyopathy. Cardiac mitochondria consist of two spatially distinct subpopulations, termed subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The goal of this study was to determine whether subcellular spatial location is associated with apoptotic propensity of cardiac mitochondrial subpopulations during diabetic insult. Swiss Webster mice were subjected to intraperitoneal injection of streptozotocin or citrate saline vehicle. Ten weeks following injection, diabetic hearts displayed increased caspase-3 and caspase-9 activities, indicating enhanced apoptotic signaling (P < 0.05, for both). Mitochondrial size (forward scatter) and internal complexity (side scatter) were decreased in diabetic IFM (P < 0.05, for both) but not in diabetic SSM. Mitochondrial membrane potential (Delta(Psim)) was lower in diabetic IFM (P < 0.01) but not in diabetic SSM. Mitochondrial permeability transition pore (mPTP) opening was increased in diabetic compared with control IFM (P < 0.05), whereas no differences were observed in diabetic compared with control SSM. Examination of mPTP constituents revealed increases in cyclophilin D in diabetic IFM. Furthermore, diabetic IFM possessed lower cytochrome c and BcL-2 levels and increased Bax levels (P < 0.05, for all 3). No significant changes in these proteins were observed in diabetic SSM compared with control. These results indicate that diabetes mellitus is associated with an enhanced apoptotic propensity in IFM, suggesting a differential apoptotic susceptibility of distinct mitochondrial subpopulations based upon subcellular location.