Viral infections in the acquired immunodeficiency syndrome

Atg2, Atg9 and Atg18 in mitochondrial integrity, cardiac function and healthspan in Drosophila

In yeast, the Atg2-Atg18 complex regulates Atg9 recycling from phagophore assembly site during autophagy; their function in higher eukaryotes remains largely unknown. In a targeted screening in Drosophila melanogaster, we show that Mef2-GAL4-RNAi-mediated knockdown of Atg2, Atg9 or Atg18 in the heart and indirect flight muscles led to shortened healthspan (declined locomotive function) and lifespan. These flies displayed an accelerated age-dependent loss of cardiac function along with cardiac hypertrophy (increased heart tube wall thickness) and structural abnormality (distortion of the lumen surface). Using the Mef2-GAL4-MitoTimer mitochondrial reporter system and transmission electron microscopy, we observed significant elongation of mitochondria and reduced number of lysosome-targeted autophagosomes containing mitochondria in the heart tube but exaggerated mitochondrial fragmentation and reduced mitochondrial density in indirect flight muscles. These findings provide the first direct evidence of the importance of Atg2-Atg18/Atg9 autophagy complex in the maintenance of mitochondrial integrity and, regulation of heart and muscle functions in Drosophila, raising the possibility of augmenting Atg2-Atg18/Atg9 activity in promoting mitochondrial health and, muscle and heart function.

A novel MitoTimer reporter gene for mitochondrial content, structure, stress, and damage in vivo

Mitochondrial dysfunction plays important roles in many diseases, but there is no satisfactory method to assess mitochondrial health in vivo. Here, we engineered a MitoTimer reporter gene from the existing Timer reporter gene. MitoTimer encodes a mitochondria-targeted green fluorescent protein when newly synthesized, which shifts irreversibly to red fluorescence when oxidized. Confocal microscopy confirmed targeting of the MitoTimer protein to mitochondria in cultured cells, Caenorhabditis elegans touch receptor neurons, Drosophila melanogaster heart and indirect flight muscle, and mouse skeletal muscle. A ratiometric algorithm revealed that conditions that cause mitochondrial stress led to a significant shift toward red fluorescence as well as accumulation of pure red fluorescent puncta of damaged mitochondria targeted for mitophagy. Long term voluntary exercise resulted in a significant fluorescence shift toward green, in mice and D. melanogaster, as well as significantly improved structure and increased content in mouse FDB muscle. In contrast, high-fat feeding in mice resulted in a significant shift toward red fluorescence and accumulation of pure red puncta in skeletal muscle, which were completely ameliorated by voluntary wheel running. Hence, MitoTimer allows for robust analysis of multiple parameters of mitochondrial health under both physiological and pathological conditions and will be highly useful for future research of mitochondrial health in multiple disciplines in vivo.

PGC-1alpha plays a functional role in exercise-induced mitochondrial biogenesis and angiogenesis but not fiber-type transformation in mouse skeletal muscle

Endurance exercise stimulates peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) expression in skeletal muscle, and forced expression of PGC-1alpha changes muscle metabolism and exercise capacity in mice. However, it is unclear if PGC-1alpha is indispensible for endurance exercise-induced metabolic and contractile adaptations in skeletal muscle. In this study, we showed that endurance exercise-induced expression of mitochondrial enzymes (cytochrome oxidase IV and cytochrome c) and increases of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31)-positive endothelial cells in skeletal muscle, but not IIb-to-IIa fiber-type transformation, were significantly attenuated in muscle-specific Pgc-1alpha knockout mice. Interestingly, voluntary running effectively restored the compromised mitochondrial integrity and superoxide dismutase 2 (SOD2) protein expression in skeletal muscle in Pgc-1alpha knockout mice. Thus, PGC-1alpha plays a functional role in endurance exercise-induced mitochondrial biogenesis and angiogenesis, but not IIb-to-IIa fiber-type transformation in mouse skeletal muscle, and the improvement of mitochondrial morphology and antioxidant defense in response to endurance exercise may occur independently of PGC-1alpha function. We conclude that PGC-1alpha is required for complete skeletal muscle adaptations induced by endurance exercise in mice.

Oxidative phenotype protects myofibers from pathological insults induced by chronic heart failure in mice

The fiber specificity of skeletal muscle abnormalities in chronic heart failure (CHF) has not been defined. We show here that transgenic mice (8 weeks old) with cardiac-specific overexpression of calsequestrin developed CHF (50.9% decrease in fractional shortening and 56.4% increase in lung weight, P<0.001), cachexia (37.8% decrease in body weight, P<0.001), and exercise intolerance (69.3% decrease in running distance to exhaustion, P<0.001) without a significant change in muscle fiber-type composition. Slow oxidative soleus muscle maintained muscle mass, whereas fast glycolytic tibialis anterior and plantaris muscles underwent atrophy (11.6 and 13.3%, respectively; P<0.05). In plantaris muscle, glycolytic type IId/x and IIb, but not oxidative type I and IIa, fibers displayed significant decreases in cross-sectional area (20.3%, P<0.05). Fast glycolytic white vastus lateralis muscle showed sarcomere degeneration and decreased cytochrome c oxidase IV (39.5%, P<0.01) and peroxisome proliferator-activated receptor gamma co-activator 1alpha protein expression (30.3%, P<0.01) along with a dramatic induction of the MAFbx/Atrogin-1 mRNA. These findings suggest that exercise intolerance can occur in CHF without fiber type switching in skeletal muscle and that oxidative phenotype renders myofibers resistant to pathological insults induced by CHF.

Identification of viral infection by confocal microscopy

Confocal microscopy is a valuable adjunct to electron microscopy in the fields of diagnostic and investigative virology. Confocal imaging can be used to examine large amounts of tissue stained by a variety of methods for evidence of viral infection. Areas thus identified can then be processed for ultrastructural study, allowing a highly focused search for viral pathogens. With the possible exception of the vibrating microtome, all of the equipment and reagents necessary for the preparation of specimens for confocal scanning are available in any well-stocked histology laboratory. Although originally developed to facilitate viral diagnosis by EM, the methods described herein can be applied to the ultrastructural study of any focal pathologic process.

Identification of focal viral infections by confocal microscopy for subsequent ultrastructural analysis

A correlative microscopy method for the ultrastructural analysis of focal viral tissue infections is presented. Using a confocal scanning laser microscope, foci of infection are identified in tissue sections prior to embedment; a variety of techniques can be employed for viral detection, including staining with standard histochemical reagents and fluorescently labeled antibodies. Areas of infection identified using confocal microscopy are excised from the tissue sections, embedded, and examined by transmission electron microscopy. Applications of this technique in both diagnostic and basic research settings are described.

Chronic acquired immunodeficiency syndrome-associated arthritis: a synovial ultrastructural study

We describe a patient who developed acquired immunodeficiency syndrome-related complex, complicated by chronic, symmetric polyarthritis. Synovial biopsy showed large areas of plasma cell infiltration subjacent to the synovial lining. Ultrastructural study demonstrated tubuloreticular structures within endothelial cells, crystal-like inclusions in plasma cells, and virus-like particles located around synoviocyte fragments. Although immunologic and morphologic studies did not permit classification of these virus-like structures, the role of these possible virions in the pathogenesis of the observed synovitis remains to be determined. Surprisingly, the patient's chronic arthritis resolved with anti-retroviral treatment (azidothymidine: AZT).

Helminthic infections in the acquired immunodeficiency syndrome

Strongyloides stercoralis, the only helminthic parasite that can complete its life cycle in the human host, is also the only helminthic parasite that has been reported with any frequency in AIDS patients. Symptoms include hives, skin eruptions, abdominal pain, perianal pruitis, diarrhea, and pneumonitis. Diagnosis is made by demonstrating rhabditiform larvae in the stool or female parasitic worms and eggs in the small intestinal mucosa; in disseminated cases, rhabditiform or filariform larvae can be found in liver, heart, lungs, thyroid, kidneys, adrenals, pancreas, lymph nodes, and central nervous system. Successful treatment has been achieved with thiabendazol. Strongyloidiasis is uncommon, but since cell-mediated immunity is important in combatting this organism, and since T-lymphocyte function is impaired in AIDS patients, strongyloidiasis should not be overlooked in the diagnosis of opportunistic illnesses in these individuals.

Malignancies in the acquired immunodeficiency syndrome

Malignancies frequently arise in patients infected with human immunodeficiency virus (HIV), including those patients classified as having the acquired immunodeficiency syndrome (AIDS). Currently, Kaposi's sarcoma and certain types of lymphoma are considered to develop as a result of HIV infection, and other cancers have also been reported in these patients. For the most part, ultrastructural study of HIV-associated malignancies has been limited to Kaposi's sarcoma; the ultrastructural features of the epidemic form of this disease are generally the same as those of the classical form. The occurrence of these cancers in HIV-infected individuals appears to be related to the immunodeficiency caused by this virus, but the basic etiologic mechanisms remain unknown. In general, only palliative treatments are presently available for HIV-associated malignancies.