Rheb (Ras Homologue Enriched in Brain)-dependent Mammalian Target of Rapamycin Complex 1 (mTORC1) Activation Becomes Indispensable for Cardiac Hypertrophic Growth after Early Postnatal Period

Cardiomyocytes proliferate during fetal life but lose their ability to proliferate soon after birth and further increases in cardiac mass are achieved through an increase in cell size or hypertrophy. Mammalian target of rapamycin complex 1 (mTORC1) is critical for cell growth and proliferation. Rheb (Ras homologue enriched in brain) is one of the most important upstream regulators of mTORC1. Here, we attempted to clarify the role of Rheb in the heart using cardiac-specific Rheb-deficient mice (Rheb^−/−). Rheb^−/− mice died from postnatal day 8 to 10. The heart-to-body weight ratio, an index of cardiomyocyte hypertrophy, in Rheb^−/− was lower than that in the control (Rheb^+/+) at postnatal day 8. The cell surface area of cardiomyocytes isolated from the mouse hearts increased from postnatal days 5 to 8 in Rheb^+/+ mice but not in Rheb^−/− mice. Ultrastructural analysis indicated that sarcomere maturation was impaired in Rheb^−/− hearts during the neonatal period. Rheb^−/− hearts exhibited no difference in the phosphorylation level of S6 or 4E-BP1, downstream of mTORC1 at postnatal day 3 but showed attenuation at postnatal day 5 or 8 compared with the control. Polysome analysis revealed that the mRNA translation activity decreased in Rheb^−/− hearts at postnatal day 8. Furthermore, ablation of eukaryotic initiation factor 4E-binding protein 1 in Rheb^−/− mice improved mRNA translation, cardiac hypertrophic growth, sarcomere maturation, and survival. Thus, Rheb-dependent mTORC1 activation becomes essential for cardiomyocyte hypertrophic growth after early postnatal period.     

Immunohistochemical Localization of Manserin,a Novel Neuropeptide Derived from Secretogranin II,in Rat Adrenal Gland,and its Upregulation by Physical Stress

We recently identified a novel 40-amino acid neuropeptide designated manserin from the rat brain (Yajima in NeuroReport 15: 1755–1759, 2004). Manserin is highly expressed in pituitary and hypothalamic nuclei, which suggests that it plays a role in the endocrine system. In this study, we employed immunohistochemical methods to investigate the presence of manserin in rat adrenal glands, as well as its regulation by physical stress. Immunohistochemical analysis using anti-manserin antibody showed that manserin is present in the rat adrenal medulla but not in the cortex. When the colocalization of manserin and phenylethanolamine N-methyltransferase (PNMT), an epinephrine-synthesizing enzyme, was examined, virtually all PNMT-positive cells expressed manserin. Interestingly, the immunoreactivity of manserin was significantly increased when the rats were exposed to water-immersion restraint stress. These results demonstrate for the first time that adrenal manserin, a novel neuropeptide, may have a potential physiological role under stress-inducing conditions.     

Astrocytes with previous chronic exposure to amyloid β‐peptide fragment 1–40 suppress excitatory synaptic transmission

Synaptic dysfunction and neuronal death are responsible for cognitive and behavioral deficits in Alzheimer's disease (AD). It is well known that such neurological abnormalities are preceded by long‐term exposure of amyloid β‐peptide (Aβ) and/or hyperphosphorylated tau prior. In addition to the neurological deficit, astrocytes as a major glial cell type in the brain, significantly participate in the neuropathogenic mechanisms underlying synaptic modulation. Although astrocytes play a significant key role in modulating synaptic transmission, little is known on whether astrocyte dysfunction caused by such long‐term Aβ exposure affects synapse formation and function. Here, we show that synapse formation and synaptic transmission are attenuated in hippocampal‐naïve neurons co‐cultured with astrocytes that have previously experienced chronic Aβ_1‐40 exposure. In this abnormal astrocytic condition, hippocampal neurons exhibit decrements of evoked excitatory post‐synaptic currents (EPSCs) and miniature EPSC frequency. Furthermore, size of readily releasable synaptic pools and number of excitatory synapses were also significantly decreased. Contrary to these negative effects, release probability at individual synapses was significantly increased in the same astrocytic condition. Taken together, our data indicate that lower synaptic transmission caused by astrocytes previously, and chronically, exposed to Aβ1–40 is attributable to a small number of synapses with higher release probability.

     

Purification capability of tobacco transformed with enzymes from a methylotrophic bacterium for formaldehyde

Plants have the ability to remediate environmental pollution. Especially, they have a high purification capability for airpollution. We have measured the purification characteristics of foliage plants for indoor airpollutants--for example, formaldehyde (HCHO), toluene, and xylene--using a tin oxide gas sensor. HCHO is an important intermediate for biological fixation of C1 compounds in methylotrophs. The ribulose monophosphate pathway of HCHO fixation is inherent in many methylotrophic bacteria, which can grow on Cl compounds. Two genes for the key enzymes, HPS and PHI, from the methylotrophic bacterium Mycobacterium gastri MB19 were introduced into tobacco. In this article, the HCHO-removal characteristic of the transformant was examined by using the gas sensor in order to evaluate quantitatively. The purification characteristics of the transformant for toluene, xylene, and styrene were also measured. The results confirmed an increase of 20% in the HCHO-removal capability. The differences of the purification capabilities for toluene, xylene, and styrene were not recognized.     

Purification characteristics of golden pothos for atmospheric gasoline

Previous studies have shown that plants have the ability to purify various atmospheric chemicals. Gasoline is one of the more serious pollutants. Soil and atmospheric pollution caused by gasoline is increasing due to the widespread use of automobiles. In this article, the purification characteristic of the pothos plant for atmospheric gasoline is investigated using a tin oxide gas sensor. The purification rate (Pr), defined as the purification ability per hour as described by a differential coefficient, has a maximum value at longer time intervals as the pollutant concentration becomes higher. Pr can be represented by an exponential function of lapsed time and its characteristic in soil is similar. A golden pothos plant growing in a 30-cm diameter pot of was placed in a 300-I experimental chamber to examine its purification ability. Pr had a maximum value 40 h after a 0.04-ml injection of gasoline into the chamber. The total purification ability (Pa) is also used in this study and is derived using the peak value (h) and the full width (tw) at half maximum of the tin oxide gas-sensor characteristic, namely Pa = h/tw x 100. The Pa of the pothos for gasoline was about 7, with the value decreasing as the pollutant concentration increased.     

Calpain protects the heart from hemodynamic stress

Calpains make up a family of Ca(2+)-dependent intracellular cysteine proteases that include ubiquitously expressed μ- and m-calpains. Both are heterodimers consisting of a distinct large catalytic subunit (calpain 1 for μ-calpain and calpain 2 for m-calpain) and a common regulatory subunit (calpain 4). The physiological roles of calpain remain unclear in the organs, including the heart, but it has been suggested that calpain is activated by Ca(2+) overload in diseased hearts, resulting in cardiac dysfunction. In this study, cardiac-specific calpain 4-deficient mice were generated to elucidate the role of calpain in the heart in response to hemodynamic stress. Cardiac-specific deletion of calpain 4 resulted in decreased protein levels of calpains 1 and 2 and showed no cardiac phenotypes under base-line conditions but caused left ventricle dilatation, contractile dysfunction, and heart failure with interstitial fibrosis 1 week after pressure overload. Pressure-overloaded calpain 4-deficient hearts took up a membrane-impermeant dye, Evans blue, indicating plasma membrane disruption. Membrane repair assays using a two-photon laser-scanning microscope revealed that calpain 4-deficient cardiomyocytes failed to reseal a plasma membrane that had been disrupted by laser irradiation. Thus, the data indicate that calpain protects the heart from hemodynamic stresses, such as pressure overload.     

Autophagy-mediated degradation is necessary for regression of cardiac hypertrophy during ventricular unloading

Cardiac hypertrophy occurs in response to a variety of stresses as a compensatory mechanism to maintain cardiac output and normalize wall stress. Prevention or regression of cardiac hypertrophy can be a major therapeutic target. Although regression of cardiac hypertrophy occurs after control of etiological factors, the molecular mechanisms remain to be clarified. In the present study, we investigated the role of autophagy in regression of cardiac hypertrophy. Wild-type mice showed cardiac hypertrophy after continuous infusion of angiotensin II for 14 days using osmotic minipumps, and regression of cardiac hypertrophy was observed 7 days after removal of the minipumps. Autophagy was induced during regression of cardiac hypertrophy, as evidenced by an increase in microtubule-associated protein 1 light chain 3 (LC3)-II protein level. Then, we subjected cardiac-specific Atg5-deficient (CKO) and control mice (CTL) to angiotensin II infusion for 14 days. CKO and CTL developed cardiac hypertrophy to a similar degree without contractile dysfunction. Seven days after removal of the minipumps, CKO showed significantly less regression of cardiac hypertrophy compared with CTL. Regression of pressure overload-induced cardiac hypertrophy after unloading was also attenuated in CKO. These results suggest that autophagy is necessary for regression of cardiac hypertrophy during unloading of neurohumoral and hemodynamic stress.