Fusion-Independent Satellite Cell Communication to Muscle Fibers During Load-Induced Hypertrophy

The "canonical" function of Pax7+ muscle stem cells (satellite cells) during hypertrophic growth of adult muscle fibers is myonuclear donation via fusion to support increased transcriptional output. In recent years, however, emerging evidence suggests that satellite cells play an important secretory role in promoting load-mediated growth. Utilizing genetically modified mouse models of delayed satellite cell fusion and in vivo extracellular vesicle (EV) tracking, we provide evidence for satellite cell communication to muscle fibers during hypertrophy. Myogenic progenitor cell-EV-mediated communication to myotubes in vitro influences extracellular matrix (ECM)-related gene expression, which is congruent with in vivo overload experiments involving satellite cell depletion, as well as in silico analyses. Satellite cell-derived EVs can transfer a Cre-induced, cytoplasmic-localized fluorescent reporter to muscle cells as well as microRNAs that regulate ECM genes such as matrix metalloproteinase 9 (Mmp9), which may facilitate growth. Delayed satellite cell fusion did not limit long-term load-induced muscle hypertrophy indicating that early fusion-independent communication from satellite cells to muscle fibers is an underappreciated aspect of satellite cell biology. We cannot exclude the possibility that satellite cell-mediated myonuclear accretion is necessary to maintain prolonged growth, specifically in the later phases of adaptation, but these data collectively highlight how EV delivery from satellite cells can directly contribute to mechanical load-induced muscle fiber hypertrophy, independent of cell fusion to the fiber.

Elevated myonuclear density during skeletal muscle hypertrophy in response to training is reversed during detraining

Myonuclei gained during exercise-induced skeletal muscle hypertrophy may be long-lasting and could facilitate future muscle adaptability after deconditioning, a concept colloquially termed "muscle memory." The evidence for this is limited, mostly due to the lack of a murine exercise-training paradigm that is nonsurgical and reversible. To address this limitation, we developed a novel progressive weighted-wheel-running (PoWeR) model of murine exercise training to test whether myonuclei gained during exercise persist after detraining. We hypothesized that myonuclei acquired during training-induced hypertrophy would remain following loss of muscle mass with detraining. Singly housed female C57BL/6J mice performed 8 wk of PoWeR, while another group performed 8 wk of PoWeR followed by 12 wk of detraining. Age-matched sedentary cage-dwelling mice served as untrained controls. Eight weeks of PoWeR yielded significant plantaris muscle fiber hypertrophy, a shift to a more oxidative phenotype, and greater myonuclear density than untrained mice. After 12 wk of detraining, the plantaris muscle returned to an untrained phenotype with fewer myonuclei. A finding of fewer myonuclei simultaneously with plantaris deconditioning argues against a muscle memory mechanism mediated by elevated myonuclear density in primarily fast-twitch muscle. PoWeR is a novel, practical, and easy-to-deploy approach for eliciting robust hypertrophy in mice, and our findings can inform future research on the mechanisms underlying skeletal muscle adaptive potential and muscle memory.

Clinical trials in veterinary oncology: a clinician's viewpoint

Review of the veterinary oncology literature is important for keeping up-to-date, but it can be time-consuming and sometimes frustrating. Results of clinical trials are published in a variety of formats, including case descriptions, review articles, retrospective studies, and prospective trials. They may be found as abstracts, which usually present preliminary data and interpretation, as interesting items or commentary in a newsletter, or as articles in referred journals. In this "clinician's viewpoint," a practical approach to sifting through the mountains of literature is offered.

Concurrent renal adenocarcinoma and polycythemia in a dog

Concurrent renal adenocarcinoma and polycythemia were diagnosed in a 19-month-old, female Rhodesian ridgeback. An unusually early presentation for this neoplasm, it is the second reported case of renal adenocarcinoma in a dog less than two years of age. Concurrent renal adenocarcinoma and polycythemia have been reported previously in four older dogs. In the dog of this report, clinical signs included brick-red mucous membranes, lethargy, a periodic systolic heart murmur, and engorged retinal vessels. A large retroperitoneal mass and pulmonary metastatic nodules were present at the time of diagnosis. Red blood cell count, packed cell volume, and hemoglobin concentration were greatly increased (12,940,000 red blood cells/microliter; 73.2%; and 26.6 g/dl, respectively). Histopathological diagnosis was renal adenocarcinoma. Polycythemia was the result of excessive erythropoietin production by the neoplasm.

Natural killer cell activity in untreated and treated dogs with lymphoma

Natural killer (NK) cell activity and function were determined for 11 untreated and treated dogs with lymphoma. Concurrent chromium release and single cell binding assays, methods used to measure overall cytotoxic activity and that from individual cells, respectively, were performed at effector-to-target cell ratios of 50:1 and 100:1, with incubation periods of 12 and 16 hours. Significant reduction was achieved in overall activity for untreated dogs, using a 16-hour incubation period and an effector-to-target ratio of 100:1 (P less than 0.05). Decreased activity (P less than 0.025) was also achieved for those dogs that were administered combination chemotherapy, consisting of such drugs as cyclophosphamide, vincristine, prednisone, and doxorubicin. There was no significant difference in binding or cytotoxic activity by individual cells in the untreated or treated dogs, compared with the healthy controls. Short- or long-term treatment with glucocorticoids did not influence overall NK cll activity or individual cell cytotoxicity. The overall cytotoxic activity in untreated dogs was reduced, but these dogs had relatively normal numbers of NK cells compared with paracontrols. This suggests that a defect in recycling or the ability to kill targets repetitively, may be involved. A similar defect was found in NK cells of dogs treated aggressively with combination chemotherapy.

Severe hypophosphatemia associated with diabetes mellitus in six dogs and one cat

Severe hypophosphatemia was found in 6 diabetic dogs and in one diabetic cat. The cat suffered from hemolysis, and one dog had seizures, both apparently as a result of the severe hypophosphatemia. Clinical signs were not determined solely by the serum concentration of phosphorus, as seen in 5 other patients that did not have signs of disease despite similar serum phosphorus concentrations.

Immunologic profiles of cats with persistent, naturally acquired feline leukemia virus infection

Several immunologic responses were measured in 13 healthy cats with naturally acquired, persistent feline leukemia virus (FeLV) viremia from 4 multiple-cat households and were compared with responses from 28 of their healthy, non-FeLV-viremic housemates. Significant differences (P = less than 0.05) were not observed between results of FeLV-viremic and nonviremic cats for peripheral blood leukocyte or lymphocyte count, percentage of peripheral blood mononuclear cells able to form rosettes with guinea pig RBC or with antibody- and complement-coated sheep RBC, lymphocyte proliferative response to concanavalin A or pokeweed mitogen, or serum immunoglobulin G concentration. Seemingly, persistent FeLV viremia, when naturally acquired, may exist for some time without lymphopenia or a marked loss of mitogen-induced lymphocyte proliferation.

Tumors of the alimentary tract

Neoplasms of the canine and feline alimentary tract represent diagnostic and therapeutic challenges for the veterinarian in practice. Careful attention to historical details and thorough and repeated examination are of paramount importance in evaluating animals with chronic digestive disturbances. By judicious use of ancillary studies such as plain and contrast radiography, endoscopy, and exploratory surgery, the clinician may arrive at a diagnosis earlier in the course of a neoplasm. This in turn may facilitate more efficacious treatment. A particularly interesting aspect of tumors of the gastrointestinal tract is their frequent association with environmental carcinogens. By being aware of these relationships, veterinarians stand a better chance of reaching the ultimate goal of cancer therapists--the prevention of malignant disease.

Uptake of exogenous aspartate into circumventricular organs but not other regions of adult mouse brain

Adult mice were treated intraperitoneally with aspartate (Asp) at one of several doses (0.47-3.75 mmol/kg) and 30 min later given a subcutaneous Asp injection at the same dose. This treatment regimen resulted in steady state blood Asp elevations, a given dose producing the same degree of elevation at both 30 and 60 min. The lowest and highest doses, respectively, produced four-fold and 55-fold elevations of serum Asp. In selected circumventricular organ (CVO) regions of brain which lack blood brain barriers, tissue Asp levels rose 1.5 and 3 times above control values following the lowest and highest doses, respectively, whereas tissue Asp remained unchanged in non-CVO brain regions. Thus, even very moderate Asp dosing causes marked increases in CVO Asp. In order to analyze the pattern of Asp uptake into CVO, Asp was assayed in numerous subdivisions of each CVO, and maps were constructed which reflected microregional concentration differences. The pattern of Asp distribution suggests that Asp enters brain via fenestrated capillaries serving certain portions of CVO and then spreads into adjacent brain tissue. In separate experiments, we administered a single high dose of Asp (15 mmol/kg) to both adult and infant mice and measured Asp in serum and select brain regions 60 min later. Asp concentrations in serum and CVO (but not other brain regions) rose markedly at both ages but the increases were greater in serum and therefore also in CVO of infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemoimmunotherapy for canine lymphosarcoma: a prospective evaluation of specific and nonspecific immunomodulation

Fifty-six dogs were given chemoimmunotherapy for spontaneous lymphosarcoma. The dogs had been given identical combination chemotherapy (8 weeks) for induction of remission, and after achieving complete clinical remission, they were randomly assigned to one of three treatment groups to evaluate immunotherapy as a method ancillary to chemotherapy to maintain or extend the remission. For immunostimulation, one-third of the dogs were given chemically modified autochthonous tumor cell extract in Freund's complete adjuvant (FCA), one-third were given nonmodified tumor cell extract in FCA, and one-third were given FCA alone. A historical control population of dogs given the same chemotherapy was used for comparison. Of the 56 dogs, 50 (89.3%) achieved initial remission, but 18 of the latter relapsed clinically during the initial 8-week-chemotherapy regimen. The remaining 32 dogs (or 57.1% of the original 56 dogs) were subsequently given immunotherapy. Duration of remission and survival time were recorded. The median remission duration and survival time for all dogs given immunotherapy following cytoreductive chemotherapy were significantly longer than the historical control population given chemotherapy alone. However, there was no significant difference in remission duration or survival among the three immunotherapy groups.

Infectious peritonitis in a cat that subsequently developed a myeloproliferative disorder

The effusive form of feline infectious peritonitis was diagnosed clinically and serologically in a 3-year-old male domestic cat. The cat responded to treatment for 9 months, then developed a myeloproliferative disorder with cytologic characteristics of reticuloendotheliosis.

Chemoimmunotherapy for canine lymphosarcoma

Thirty-two dogs with naturally occurring multicentric lymphosarcoma were randomly assigned to one of two treatment groups. One half of the animals received combination chemotherapy plus vitamin injections (controls) while the other half received indentical chemotherapy plus injections of chemically-modified tumor cell extract in Freund's complete adjuvant (vaccinates). Clinical staging revealed no bias between groups but showed that prognosis could be closely correlated with the severity of disease at initial presentation. Twenty dogs (62%), including 11 vaccinates and 9 controls, responded favorably to chemotherapy and were evaluated for length of first remission and total survival time. Both parameters were significantly longer in vaccinated dogs than in controls. These data suggest that immunological stimulation may be a helpful adjunct to conventional therapy in selected types of cancer when immunological principles are observed.

Treatment of feline myelogenous leukemia: four case reports

Of 4 cats with myelogenous leukemia, 3 had the neutrophilic type and 1 had the basophilic type. Partial remission was achieved with chemotherapy in 2 of the cats. Their survival times, however, were 77 and 31 days from time of diagnosis. The other 2 cats did not respond to treatment and died 16 days from time of diagnosis.

Monocytic leukemia in three cats

Of 3 cats with monocytic leukemia, 1 responded favorably to treatment with cytosine arabinoside. With supportive therapy, it lived 78 days from the time of diagnosis, at which time it developed dyspnea and signs of toxicosis and died. The other 2 cats did not respond to treatment and died 4 and 16 days from time of diagnosis. Prior to death, they were bleeding from injection sites, and their blood had greater than 200,000 WBC/mm3. Necropsy of those 2 cats revealed extensive perivascular hemorrhagic infarcts within the cerebellum, medulla, and cerebrum.