A Contrast in Pathogenic Responses between C57BL/6J and BALB/cJ Mice Using a Model of Retinal Injury

Spaceflight causes strain-dependent gene expression changes associated with lipid and extracellular matrix dysregulation in the mouse kidney in vivo

To explore new worlds we must ensure humans can survive and thrive in the space environment. Incidence of kidney stones in astronauts is a major risk factor associated with long term missions, caused by increased blood calcium levels due to bone demineralisation triggered by microgravity and space radiation. Transcriptomic changes have been observed in other tissues during spaceflight, including the kidney. We analysed kidney transcriptome patterns in two different strains of mice flown on the International Space Station, C57BL/6J and BALB/c. Here we show a link between spaceflight and transcriptome patterns associated with dysregulation of lipid and extracellular matrix metabolism and altered transforming growth factor-beta signalling. A stronger response was seen in C57BL/6J mice than BALB/c. Genetic differences in hyaluronan metabolism between strains may confer protection against extracellular matrix remodelling through downregulation of epithelial-mesenchymal transition. We intend for our findings to contribute to development of new countermeasures against kidney disease in astronauts and people here on Earth.

Highlights

Spaceflight has a significant effect on gene expression in the kidney.Responses in the BALB/c indicate milder transcriptomic perturbations than C57BL/6J.Lipid metabolism was altered in both strains of mice.Extracellular matrix metabolism and TGF-β signalling up in BALB/c down in C57BL/6J.Reduced gene expression of hyaluronan synthesis pathway in BALB/c but not in C57BL/6J.

A Method for Real-Time Assessment of Mitochondrial Respiration Using Murine Corneal Biopsy

Purpose

To develop and optimize a method to monitor real-time mitochondrial function by measuring the oxygen consumption rate (OCR) in murine corneal biopsy punches with a Seahorse extracellular flux analyzer.

Methods

Murine corneal biopsies were obtained using a biopsy punch immediately after euthanasia. The corneal metabolic profile was assessed using a Seahorse XFe96 pro analyzer, and mitochondrial respiration was analyzed with specific settings.

Results

Real-time adenosine triphosphate rate assay showed that mitochondrial oxidative phosphorylation is a major source of adenosine triphosphate production in ex vivo live murine corneal biopsies. Euthanasia methods (carbon dioxide asphyxiation vs. overdosing on anesthetic drugs) did not affect corneal OCR values. Mouse corneal biopsy punches in 1.5-mm diameter generated higher and more reproducible OCR values than those in 1.0-mm diameter. The biopsy punches from the central and off-central cornea did not show significant differences in OCR values. There was no difference in OCR reading by the tissue orientations (the epithelium side up vs. the endothelium side up). No significant differences were found in corneal OCR levels between sexes, strains (C57BL/6J vs. BALB/cJ), or ages (4, 8, and 32 weeks). Using this method, we showed that the wound healing process in the mouse cornea affected mitochondrial activity.

Conclusions

The present study validated a new strategy to measure real-time mitochondrial function in fresh mouse corneal tissues. This procedure should be helpful for studies of the ex vivo live corneal metabolism in response to genetic manipulations, disease conditions, or pharmacological treatments in mouse models.

Adjunctive Thymosin Beta-4 Treatment Influences PMN Effector Cell Function during Pseudomonas aeruginosa-Induced Corneal Infection

Previous work examining the therapeutic efficacy of adjunct thymosin beta 4 (Tβ4) to ciprofloxacin for ocular infectious disease has revealed markedly reduced inflammation (inflammatory mediators and innate immune cells) with increased activation of wound healing pathways. Understanding the therapeutic mechanisms of action have further revealed a synergistic effect with ciprofloxacin to enhance bacterial killing along with a regulatory influence over macrophage effector cell function. As a natural extension of the aforementioned work, the current study uses an experimental model of P. aeruginosa-induced keratitis to examine the influence of Tβ4 regarding polymorphonuclear leukocyte (PMN/neutrophil) cellular function, contributing to improved disease response. Flow cytometry was utilized to phenotypically profile infiltrating PMNs after infection. The generation of reactive oxygen species (ROS), neutrophil extracellular traps (NETs), and PMN apoptosis were investigated to assess the functional activities of PMNs in response to Tβ4 therapy. In vitro work using peritoneal-derived PMNs was similarly carried out to verify and extend our in vivo findings. The results indicate that the numbers of infiltrated PMNs into infected corneas were significantly reduced with adjunctive Tβ4 treatment. This was paired with the downregulated expression of proinflammatory markers on these cells, as well. Data generated from PMN functional studies suggested that the corneas of adjunctive Tβ4 treated B6 mice exhibit a well-regulated production of ROS, NETs, and limited PMN apoptosis. In addition to confirming the in vivo results, the in vitro findings also demonstrated that neutrophil elastase (NE) was unnecessary for NETosis. Collectively, these data provide additional evidence that adjunctive Tβ4 + ciprofloxacin treatment is a promising option for bacterial keratitis that addresses both the infectious pathogen and cellular-mediated immune response, as revealed by the current study.

Multiple modes of action mediate the therapeutic effect of IVIg in experimental epidermolysis bullosa acquisita

Substitution of IgG in antibody deficiency or application of high-dose intravenous IgG (IVIg) in patients with autoimmunity are well-established treatments. Data on the mode of action of IVIg are, however, controversial and may differ for distinct diseases. In this study, we investigated the impact and molecular mechanism of high-dose IgG treatment in murine autoantibody-induced skin inflammation, namely, epidermolysis bullosa acquisita (EBA). EBA is caused by antibodies directed against type VII collagen (COL7) and is mediated by complement activation, release of reactive oxygen species, and proteases by myeloid cells. In murine experimental EBA the disease can be induced by injection of anti-COL7 IgG. Here, we substantiate that treatment with high-dose IgG improves clinical disease manifestation. Mechanistically, high-dose IgG reduced the amount of anti-COL7 in skin and sera, which is indicative for an FcRn-dependent mode-of-action. Furthermore, in a non-receptor-mediated fashion, high-dose IgG showed antioxidative properties by scavenging extracellular reactive oxygen species. High-dose IgG also impaired complement activation and served as substrate for proteases, both key events during EBA pathogenesis. Collectively, the non-receptor-mediated anti-inflammatory properties of high-dose IgG may explain the therapeutic benefit of IVIg treatment in skin autoimmunity.

Immuno-histological detection of resistant columnar units and vulnerable networks in the rat retina after asphyxia-induced transient cardiac arrest

BACKGROUND

Stroke-related loss of vision is one of the residual impairments, restricting the quality of life. However, studies of the ocular manifestations of asphyxia cardiac arrest/resuscitation (ACA/R) have reported very heterogeneous results.

OBJECTIVE

We aimed to evaluate the ACA/R-induced degeneration pattern of the different retinal cell populations in rats using different immuno-histological stainings.

METHODS

The staining pattern of toluidine blue and the ganglion cell markers β-III-tubulin and NeuN; the calcium-binding protein parvalbumin, indicating ganglion, amacrine, and horizontal cells; calretinin D28k, indicating ganglion and amacrine cells; calbindin, indicating horizontal cells; Chx 10, indicating cone bipolar cells; PKCα, indicating ON-type rod bipolar cells; arrestin, indicating cones; and rhodopsin, a marker of rods, as well as the glial cell markers GFAP (indicating astroglia and Müller cells) and IBA1 (indicating microglia), were evaluated after survival times of 7 and 21 days in an ACA/R rat model. Moreover, quantitative morphological analysis of the optic nerve was performed. The ACA/R specimens were compared with those from sham-operated and completely naïve rats.

RESULTS

ACA/R-induced effects were: (i) a significant reduction of retinal thickness after long-term survival; (ii) ganglion cell degeneration, including their fiber network in the inner plexiform layer; (iii) degeneration of amacrine and cone bipolar cells; (iv) degeneration of cone photoreceptors; (v) enhanced resistance to ACA/R by rod photoreceptors, ON-type rod bipolar and horizontal cells, possibly caused by the strong upregulation of the calcium-binding proteins calretinin, parvalbumin, and calbindin, counteracting the detrimental calcium overload; (vi) significant activation of Müller cells as further element of retinal anti-stress self-defense mechanisms; and (vii) morphological alterations of the optic nerve in form of deformed fibers.

CONCLUSIONS

Regardless of the many defects, the surviving neuronal structures seemed to be able to maintain retinal functionality, which can be additionally improved by regenerative processes true to the "use it or lose it" dogma.

Evaluation of Susceptibility and Innate Immune Response in C57BL/6 and BALB/c Mice During Candida albicans Endophthalmitis

Purpose

Candida remains the leading cause of fungal endophthalmitis. However, the pathobiology and innate immune responses in this disease are not well characterized. Here, we developed two murine models of candida endophthalmitis and evaluated their disease susceptibility and differential immune response.

Methods

Endophthalmitis was induced in C57BL/6 (B6) and BALB/c mice by intravitreal injection of Candida albicans (CA). Disease progression was monitored by slit-lamp examination and clinical scoring, followed by retinal function assessment using electroretinography (ERG). Enucleated eyes were used to estimate fungal burden and retinal tissue damage by hematoxylin and eosin and TUNEL staining. The level of inflammatory mediators were determined by quantitative Polymerase Chain Reaction (qPCR) and enzyme-linked immunosorbent assay, whereas neutrophil infiltration was assessed by flow cytometry and immunostaining.

Results

Intravitreal injection of CA at 6500 colony-forming units resulted in sustained (non-resolving) ocular inflammation in both B6 and BALB/c mice as evidenced by increased levels of inflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6) and chemokine (CXCL2/MIP-2). In both mouse strains, fungal burden peaked at 24 to 48 hours post-infection (hpi) and decreased by 72 to 96 hpi. CA-infected eyes exhibited increased polymorphonuclear neutrophils (PMN) infiltration and retinal tissue damage. Overall retinal function declined rapidly, with a significant reduction in ERG response at 12 hpi and near-total loss by 24 hpi. Differential analyses revealed increased pathology in BALB/c versus B6 mice.

Conclusions

C. albicans was able to cause endophthalmitis in mice. Although BALB/c mice were found to be more susceptible to CA endophthalmitis, both BALB/c and B6 models could be used to study fungal endophthalmitis and test therapeutic modalities.

Disparate expression of autophagy in corneas of C57BL/6 mice and BALB/c mice after Aspergillus fumigatus infection

AIM

To determine the disparate expression of autophagy in the Aspergillus fumigatus (A. fumigatus) keratitis between susceptible C57BL/6 mice and resistant BALB/c mice.

METHODS

C57BL/6 and BALB/c mice were used to establish fungal keratitis models. Disease severity and inflammatory response were observed by slit lamp microscopy in A. fumigatus-infected corneas of C57BL/6 and BALB/c mice at 1, 3 and 5d. Hematoxylin-eosin (H&E) staining was used to detect pathological changes of corneas. The expression of autophagy-related proteins Beclin-1, LC3, SQSTM1/p62, and LAMP-1 was assessed by Western blot in C57BL/6 and BALB/c mice at 1, 3 and 5d post infection (p.i.). Immunofluorescent staining was used to test the expression of LC3 in corneas after A. fumigatus infection.

RESULTS

Keratitis severity was higher in C57BL/6 mice versus BALB/c mice at 1, 3 and 5d p.i. H&E staining showed that the number of inflammatory cells was larger and the severity of ulcer was higher in C57BL/6 mice than in BALB/c mice after stimulation with A. fumigatus. Higher expression of LAMP-1, Beclin-1, and LC3 was shown in C57BL/6 mice corneas than in BALB/c mice corneas at 1, 3 and 5d p.i., while the expression of p62 was lower in C57BL/6 mice. The fluorescence of LC3 was significantly increased in corneas of C57BL/6 mice compared with BALB/c mice after A. fumigatus infection.

CONCLUSION

The expression of autophagy is higher in corneas of C57BL/6 mice than in BALB/c mice after A. fumigatus infection. Autophagy may be positively correlated with keratitis severity and pathological changes.

Application of a Flow-Based Hollow-Fiber Co-Culture System to Study Cellular Influences under Hyperglycemic Conditions

Elucidation of the basic mechanisms underlying human disease pathogenesis depends on the findings afforded to us through in vivo and in vitro approaches. While there are inherent limitations in any model system, 2D in vitro culture systems tend to be particularly restricted due to their static nature. Here, we adapted a flow-based hollow-fiber cartridge system to better understand the cellular influences of human retinal microvascular endothelial cells and mouse-derived neutrophils under high glucose conditions similar to those observed in diabetes. Analyses by western blot and flow cytometry indicate that pro-inflammatory molecules known to be associated with the pathogenesis of diabetic retinopathy were significantly elevated following high glucose exposure, including VEGF, ICAM-1, and ROS. Changes in mitochondrial potential were also observed. Further, we demonstrate that this innovative system allows for cross-species co-culture as well as long-term culturing conditions. This in vitro modeling system not only mimics the retinal microvasculature, it also allows for the examination of cellular interactions and mechanisms that contribute to diabetic retinopathy, a visually debilitating complication of diabetes.