Mitochondrial haplotype modulates genome expression and mitochondrial structure/function in cardiomyocytes following volume overload

Mitochondrial DNA (mtDNA) haplotype regulates mitochondrial structure/function and reactive oxygen species in aortocaval fistula (ACF) in mice. Here, we unravel the mitochondrial haplotype effects on cardiomyocyte mitochondrial ultrastructure and transcriptome response to ACF in vivo. Phenotypic responses and quantitative transmission electron microscopy (TEM) and RNA sequence at 3 days were determined after sham surgery or ACF in vivo in cardiomyocytes from wild-type (WT) C57BL/6J (C57n:C57mt) and C3H/HeN (C3Hn:C3Hmt) and mitochondrial nuclear exchange mice (C57n:C3Hmt or C3Hn:C57mt). Quantitative TEM of cardiomyocyte mitochondria C3HWT hearts have more electron-dense compact mitochondrial cristae compared with C57WT. In response to ACF, mitochondrial area and cristae integrity are normal in C3HWT; however, there is mitochondrial swelling, cristae lysis, and disorganization in both C57WT and MNX hearts. Tissue analysis shows that C3HWT hearts have increased autophagy, antioxidant, and glucose fatty acid oxidation-related genes compared with C57WT. Comparative transcriptomic analysis of cardiomyocytes from ACF was dependent upon mtDNA haplotype. C57mtDNA haplotype was associated with increased inflammatory/protein synthesis pathways and downregulation of bioenergetic pathways, whereas C3HmtDNA showed upregulation of autophagy genes. In conclusion, ACF in vivo shows a protective response of C3Hmt haplotype that is in large part driven by mitochondrial nuclear genome interaction.NEW & NOTEWORTHY The results of this study support the effects of mtDNA haplotype on nuclear gene expression in cardiomyocytes. Currently, there is no acceptable therapy for volume overload due to mitral regurgitation. The findings of this study could suggest that mtDNA haplotype activates different pathways after ACF warrants further investigations on human population of heart disease from different ancestry backgrounds.

Interstitial Collagen Loss, Myocardial Remodeling, and Function in Primary Mitral Regurgitation

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The stretch of volume overload in PMR initiates interstitial collagen loss and decrease in LV sphericity index.

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LV chamber diastolic function is normal whereas LA function, LV twist/volume slope, early LV untwist, and myocardial circumferential strain are impaired.

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There is increased oxidative stress in the cardiomyocyte with cytoskeletal breakdown and myofibrillar loss in PMR.

Interstitial collagen loss and cardiomyocyte ultrastructural damage accounts for left ventricular (LV) sphericity and decrease in LV twist and circumferential strain. Normal LV diastolic function belies significantly abnormal left atrial (LA) function and early LV diastolic untwist rate. This underscores the complex interplay of LV and LA myocardial remodeling and function in the pathophysiology of primary mitral regurgitation. In this study, we connect LA function with LV systolic and diastolic myocardial remodeling and function using cardiac magnetic resonance tissue tagging in primary mitral regurgitation.

Reduced Left Atrial Emptying Fraction and Chymase Activation in Pathophysiology of Primary Mitral Regurgitation

Increasing left atrial (LA) size predicts outcomes in patients with isolated mitral regurgitation (MR). Chymase is plentiful in the human heart and affects extracellular matrix remodeling. Chymase activation correlates to LA fibrosis, LA enlargement, and a decreased total LA emptying fraction in addition to having a potential intracellular role in mediating myofibrillar breakdown in LA myocytes. Because of the unreliability of the left ventricular ejection fraction in predicting outcomes in MR, LA size and the total LA emptying fraction may be more suitable indicators for timing of surgical intervention.

Disruption of desmin-mitochondrial architecture in patients with regurgitant mitral valves and preserved ventricular function

OBJECTIVE

Recent studies have demonstrated improved outcomes in patients receiving early surgery for degenerative mitral regurgitation (MR) rather than adhering to conventional guidelines for surgical intervention. However, studies providing a mechanistic basis for these findings are limited.

METHODS

Left ventricular (LV) myocardium from 22 patients undergoing mitral valve repair for American Heart Association class I indications was evaluated for desmin, the voltage-dependent anion channel, α-B-crystallin, and α, β-unsaturated aldehyde 4-hydroxynonenal by fluorescence microscopy. The same was evaluated in 6 normal control LV autopsy specimens. Cardiomyocyte ultrastructure was examined by transmission electron microscopy. Magnetic resonance imaging with tissue tagging was performed in 55 normal subjects and 22 MR patients before and 6 months after mitral valve repair.

RESULTS

LV end-diastolic volume was 1.5-fold (P < .0001) higher and LV mass-to-volume ratio was lower in MR (P = .004) hearts versus normal hearts and showed improvement 6 months after mitral valve surgery. However, LV ejection fraction decreased from 65% ± 7% to 52% ± 9% (P < .0001) and LV circumferential (P < .0001) and longitudinal strain decreased significantly below normal values (P = .002) after surgery. Hearts with MR had a 53% decrease in desmin (P < .0001) and a 2.6-fold increase in desmin aggregates (P < .0001) versus normal, along with substantial, intense perinuclear staining of α, β-unsaturated aldehyde 4-hydroxynonenal in areas of mitochondrial breakdown and clustering. Transmission electron microscopy demonstrated numerous electron-dense deposits, myofibrillar loss, Z-disc abnormalities, and extensive granulofilamentous debris identified as desmin-positive by immunogold transmission electron microscopy.

CONCLUSIONS

Despite well-preserved preoperative LV ejection fraction, severe oxidative stress and disruption of cardiomyocyte desmin-mitochondrial sarcomeric architecture may explain postoperative LV functional decline and further supports the move toward earlier surgical intervention.

The effect of virus dose on the development of Marek's disease in two strains of chickens

The effect of inoculating different doses of Marek's disease virus on the consequent lymphocyte-associated viraemia titres, survival time and mortality was studied in two strains of chickens, one highly susceptible (a strain of Rhode Island Red) and one moderately resistant (a strain of Light Sussex) to Marek's disease. In both strains an increase in the infecting dose of virus increased the ensuing viraemia, and there was an inverse relationship between virus dose and survival time. There was a negative correlation between viraemia titres and survival time. The modulation of infecting dose had no effect on overall mortality among the susceptible, Rhode Island Red strain, chickens, but did influence the mortality of the Light Sussex strain chickens. It was suggested that the outcome of infection within an individual may be determined by a rather subtle interaction between the infection and transformation of a limiting number of target cells and an immune response directed against such infected or transformed cells, and that in different breeds of chickens these two factors may differ in importance.

Coronary vascular morphology in pressure-overload left ventricular hypertrophy

To attempt to explain the loss of subendocardial coronary reserve in chronic pressure-overload cardiac hypertrophy on a morphologic basis, we measured capillary capacity and coronary artery and arteriole medial wall area in dogs with moderately severe chronic (1 year) left ventricular hypertrophy (LVH). Aortic bands were placed on the ascending aorta of 8-10-week-old puppies of either sex, and hearts were perfusion fixed with 2% glutaraldehyde 8-16 months later after hemodynamic study while fully conscious. Left ventricular (LV) mass/body weight ratio in 11 banded dogs with LV end-diastolic pressure < 12 mmHg was 72% greater than in 15 controls (C). There was a decrease in subendocardial coronary reserve during adenosine-induced vasodilation with a shift away from the subendocardium (endo/epi flow ratio: C = 0.68 +/- 0.05; LVH = 0.34 +/- 0.06; P < 0.05). In spite of the extensive hypertrophy, image analysis revealed capillary density to be equally reduced by only 10-15% in endo, mid and epicardial LV regions compared to control dogs, while increased capillary cross-sectional area resulted in no change in capillary surface area/myocyte volume or volume percentage capillary space. In addition to these data suggesting capillary angiogenesis, there was no reduction in arteriolar density, indicating transmural increase in arteriolar number, and, as a consequence, increased total length of the resistance vessels. Medial area of arterioles and arteries showed a graduated increase according to size. We concluded that due to the lack of transmural difference in vascular morphology in chronic (1 year) moderately severe LVH, these anatomic bases do not play a major role as a cause for the loss of coronary reserve. Regional functional differences as a consequence of the morphologic alterations, however, cannot be excluded.

Aberrant expression of Ia-like antigens on tumor cells of regressing but not of progressing Rous sarcomas

Unlike many other tumors, experimentally induced Rous sarcomas in chickens have a definite tendency to regress spontaneously. Regression is under genetic control, but it is immunologically mediated although the target antigens that stimulate an immune response are unknown. Tumor cells in regressing sarcomas were found to express class II major histocompatibility complex (Ia-like) antigens while tumor cells from progressing sarcomas were negative. This suggests that the induction of Ia-like antigen expression has a role in the initiation or perpetuation of regression, similar to that postulated for class II antigen expression in a variety of autoimmune diseases.

Immune mechanisms in infections of poultry

Resistance to infectious agents may depend upon innate mechanisms or acquired immune responses. Inflammation, phagocytosis, cell-mediated immunity and antibodies are components of a complex reaction which result either in resistance or in susceptibility. Most infectious organisms stimulate immune responses within every compartment of the immune system. In rather few infections of poultry, it is possible to pinpoint a limited number of immune reactions that are primarily responsible for resistance. In some situations, autoimmunity may contribute to the pathology associated with infections.

Isolation of very virulent pathotypes of Marek's disease virus from vaccinated chickens in Europe

Two very virulent strains of Marek's disease virus were isolated from two separate farms in northern Italy that had experienced outbreaks of Marek's disease in vaccinated flocks. The isolates were similar to very virulent strains reported in the USA in terms of their enhanced pathogenicity, both for chickens vaccinated with the herpesvirus of turkeys, and for genetically resistant chickens. This first description of very virulent strains of Marek's disease virus from outside the USA suggests that at least some of the increasingly frequent disease outbreaks reported in Europe may be associated with such strains and that the adoption of bivalent or polyvalent vaccines containing, for example, attenuated Marek's disease virus plus herpesvirus of turkeys may be beneficial in the field.

Studies on the role of macrophages in Marek's disease of the chicken

Macrophage activity in relation to Marek's disease was investigated by determining phagocytic indices in vivo and by examining virus plaque-inhibiting activity of peritoneal macrophages in vitro. No correlation was observed between phagocytic index and resistance in different genetic strains of chickens. Infection with Marek's disease virus increased both phagocytic indices and the plaque-inhibiting activity of peritoneal macrophages, more so in susceptible than in resistant chickens. There was an association between increased macrophage activity and virus replication, and it is suggested that the enhancement of macrophage activity results from activation indirectly caused by the presence of Marek's disease virus or viral antigens.

Susceptibility of Marek's disease lymphoblastoid cell lines to infection with influenza and pseudorabies viruses and the protective effect of immunization with influenza virus-infected lymphoblastoid cells

The susceptibility of 3 lymphoblastoid cell lines (MDCC-MSB1, MDCC-HP1 and MDCC-RP1) derived from Marek's disease tumours to infection with influenza (AoPR8) and pseudorabies viruses was studied. MSB1 and HP1 were more susceptible to infection with influenza virus than was RP1. It was shown in the case of HP1, which was studied in greater detail, that although the majority of the cells synthesized influenza virus haemagglutinin when infected at high multiplicity, only a small proportion produced mature infectious particles. The results obtained from both high and low multiplicities of infection suggested that infection with AoPRs was abortive in the majority of the cells of all 3 cell lines. Infected cultures remained viable when subcultured over several days. All 3 cell lines were resistant to pseudorabies virus. The block in pseudorabies virus replication probably occurred after adsorption. Immunization of chickens with HP1 lymphoblastoid cells superinfected with influenza virus AoPR8 and inactivated with glutaraldehyde gave better protection against Marek's disease than immunization with uninfected HP1 cells.

The mechanism of genetic resistance to Marek's disease in chickens

Genetic resistance to Marek's disease in RPL line-6 chickens is expressed not only at the level of host immunological responses against virus an tumour antigens, but also at the level of target lymphoid cells for virus infection and transformation. The nature of the target cell involved was investigated. Spleen cells from susceptible line-7 chickens adsorbed more Marek's disease virus and turkey herpesvirus in vitro than line-6 spleen cells. In the case of Marek's disease virus this was reflected in the replicative ability of the virus in vivo. Transplantation of thymus fragments from 1-day-old line-7 chickens into thymectomized line-6 chickens conferred a high degree of susceptibility on the latter, but the transplantation of spleen or fragments had no significant effect. The reverse procedure, i.e. grafting of line-6 thymi into line-7 chickens, did not diminish the susceptibility of the recipients. In each treatment group the observed titres of leukocyte-associated viraemia correlated with the susceptibility of the group to Marek's disease. Histologically the grafted thymus fragments became depleted of lymphocytes immediately after transplantation. By 6 days there was substantial recovery, apparently as a result of re-population of the thymic epithelium by host stem cells. This was confirmed by transplanting thymus fragments between individuals of opposite sexes. Karyotype analysis showed that the thymus contained lymphocytes of the sex of the recipient. However, karyotype analysis of lymphoma cells taken from recipient line-6 chickens that had received thymus grafts from line-7 birds of the opposite sex showed that, in the majority of cases, the lymphomas consisted of cells of donor origin. It is concluded that the susceptibility of line-7 chickens is largely attributable to the greater susceptibility of their T-lymphocytes to infection and transformation by Marek's disease virus, and that this susceptibility can be transferred to genetically resistant line-6 birds by adoptive transfer of the cells in the form of thymus fragments.

Nature of genetic resistance to Marek's disease in chickens

Infection of line 6 resistant and line 7 susceptible chickens with Marek's disease virus (MDV) resulted in a depressed phytohemagglutinin (PHA) response and the presence of Marek's disease (MD) tumor-associated surface antigen (MATSA) in the spleens. At 6-10 weeks after infection, recovery in PHA response, diminution in the number of MATSA cells, and the presence of significant anti-MATSA immunity were observed in line 6 but not in line 7 chickens. Both lines had antibody-dependent cell-mediated antiviral immunity, but T-cell-mediated antiviral immunity was detected only in line 6 and the surviving line 7 chickens. Lymphoproliferative lesions were found only in line 7 chickens, an virus titers were significantly higher in line 7 than in line 6 chickens and embryos. Lymphoid organ weights and the number of lymphocytes of line 6 were significantly lower than those of line 7. These data suggests that resistance to MD in line 6 chickens was due to a) a deficiency in the aggregate number of target lymphocytes, b) a restriction in the ability to lymphocytes to nonproductively replicate MDV, and c) the involvement of cellular antiviral and antitumor immune responses.

The effect of bursectomy on the adoptive transfer of resistance to Marek's disease

Immunization with inactivated viral antigens protected chickens against Marek's disease. Non-immunized chickens could be protected by injections of spleen cells but not of serum from immunized, histocompatible donors. Chickens rendered agamma-globulinaemic by bursectomy and irradiation could also be immunized against Marek's disease by inoculation with viral antigens, but spleen cells from these immunized, bursectomized and irradiated donors did not confer protection on the recipients into which they were injected. It was concluded that, although in the bursectomized, immunized donors cell-mediated immunity alone was able to provide a fair degree of protection against Marek's disease, the protection afforded against the disease by spleen-cell transfer was at least partly attributable to the transfer of antibody-producing cells, and that humoral immunity, while not being an absolute requirement for resistance, is normally an important component of the resistance mechanism.

An isolator for avian disease research

An isolator is described, fabricated in glass-reinforced plastic, suitable for housing 25-30 chicks to 6 weeks of age, or for fewer older birds, for use in experiments involving infectious agents.

Marek's disease tumour-specific antigen induced by the herpesvirus of turkeys in vaccinated chickens

The herpesvirus of turkeys, a supposedly apathogenic virus commonly used for vaccination against Marek's disease, was found to induce Marek's disease tumour-specific antigens on spleen and peripheral blood lymphocytes in vaccinated chickens. Herpesvirus of turkeys may be able to induce the neoplastic transformation of lymphocytes and the consequential stimulation of an anti-tumour immune response may be an important component of vaccinal immunity.

Dissociation of antiviral and antitumor immunity in resistance to Marek's disease

Immunization of chickens either with gluteral-dehyde-inactivated chicken kidney cells infected with Marek's disease (MD) virus or with glutaraldehyde-inactivated cells of MD lymphoma-derived continuous lymphoblastoid cell lines protected against MD. The former type of immunity was associated with an immunologic suppression of virus replication and virus antigen production after challenge with virulent virus, but lymphocytes specifically cytotoxic to cells bearing MD tumor antigens were not detected. In the latter type of immunity, virus multiplication was not affected; some evidence of the stimulation of cell-mediated antitumor immunity was found. The results supported the view that immunity to MD may be directed against either virus-specific or tumor-specific antigens and that in natural resistance to MD both mechanisms may be operative.

The ultrastructure of lymphoblastoid cell lines from Marek's disease lymphomata

The ultrastructure of two lymphoblastoid cell lines derived from Marek's disease lymphomata has been studied. The cells varied from 5 to 12 mum in diameter and had large round or oval nuclei. A nucleolus was occasionally present and about 3% of cells showed projections of the nuclear envelope. The cytoplasm contained many ribosomes and several mitochondria but endoplasmic reticulum was sparse. A small number of cells contained annulate lamellae and crystalline structures were occasionally seen. Cells with immature intranuclear herpesvirus particles were rarely present. The cells had many ultrastructural features in common with Burkitt's lymphoma-derived cell lines.