Abstract 849: Drp1-dependent Altered Mitochondrial Dynamics Contribute to Protein Aggregation and Mitochondrial Dysfunction in R120G αB-crystallin-induced Proteotoxicity

Introduction: αB-crystallin (CryAB) is a chaperone protein that plays a pivotal role in the maintenance of the structural and mechanical integrity of the sarcomere. Mutation in αB-crystallin (CryAB R120G) causes sarcomere disorganization leading to protein aggregation. Accumulation of toxic protein aggregates causes cardiac contractile dysfunction and perturbed mitochondrial spatial organization. However, the role of mitochondria in the pathogenesis of protein aggregation-induced cardiomyopathies remain obscure.

Objective: In this study, we investigated the role of mitochondrial dynamics and function in the development of R120G αB-crystallin induced cardiac proteotoxicity.

Methods and Results: CryAB R120G Tg hearts showed accumulation of toxic protein aggregates resulting in disruption of the sarcomere structure, development of cardiomyocyte hypertrophy, and contractile dysfunction. Hearts obtained from CryAB R120G Tg mice showed increased expression and localization of Drp1 on the mitochondrial membrane. Alteration in the expression of mitochondrial dynamics regulatory proteins was observed at two months age when these mice exhibited normal cardiac morphometry and systolic function. Adenoviral-mediated expression of CryAB R120G in cardiomyocytes also showed increased mitochondrial fission, expression dependent inhibition of mitochondrial respiration and activation of cellular toxicity. Inhibition mitochondrial fission by Drp1 partial knockdown in CryABR120G expressing cardiomyocytes significantly decreased protein aggregation and improved mitochondrial respiration.

Conclusion: Drp1-dependent excessive mitochondrial fission results in defects in mitochondrial respiration and accumulation of protein aggregates in CryABR120G expressing cardiomyocytes. Therefore, our study shows that maladaptive aberrant mitochondrial fission causes CryABR120G -induced mitochondrial dysfunction and cardiac proteotoxicity-associated cellular dysfunction.

Abstract 408: Defective Mitochondrial Dynamics Contribute to Cardiac Contractile Dysfunction in Desminopathy

Rational: Desmin plays a critical role in the maintenance of the structural and mechanical integrity of the sarcomere. Mutation in desmin causes disorganization of contractile apparatus leading to cardiomyopathy. Cardiomyocyte-specific expression of mutated desmin (a seven amino acid deletion R172-E178, D7-Des Tg) causes accumulations of toxic protein aggregates leading to cardiac contractile dysfunction. Whether these alterations result in maladaptive changes in mitochondrial dynamics and contribute to mitochondrial respiratory defects resulting in cardiomyopathies remains obscure.

Objective: In this study, we investigated whether altered mitochondrial dynamics play a causative role in the development of cardiac contractile dysfunction and cardiomyocyte death in D7-Des Tg mouse model of desminopathy.

Methods and results: D7-Des Tg hearts showed accumulation of desmin aggregates resulting in disruption of the desmin network, development of cardiomyocyte hypertrophy, and contractile dysfunction. Ultrastructural analysis by electron microscopy showed highly perturbed mitochondrial spatial organization and mitochondrial fragmentation in D7-Des Tg mice. D7-Des Tg mice hearts showed increased mtDNA copy number, increased expression of mitochondrial fission regulatory proteins, defects in mitochondrial respiration and activation of apoptotic cell death. Adenoviral-mediated expression of D7-Des in cardiomyocytes also showed increased mitochondrial fission, expression dependent inhibition of mitochondrial respiration and activation of cellular toxicity. Inhibition of mitochondrial fission by mitochondrial division inhibitor mdivi-1 significantly improved mitochondrial respiration and inhibited cellular toxicity associated with D7-Des expression in cardiomyocytes.

Conclusion: Aberrant mitochondrial fission results in mitochondrial respiratory defects and apoptotic cell death in a D7-Des Tg hearts. Inhibition of aberrant mitochondrial fission using mitochondrial division inhibitor significantly preserved mitochondrial function and decreased apoptotic cell death. Therefore, our study shows that maladaptive aberrant mitochondrial fission causes desminopathy-associated cellular dysfunction.

Risk of Acute Coronary Syndrome is Better Predicted by Apolipoprotein B in Young People than Dyslipidemic Parameter of Conventional Lipid Profile

The traditional lipidic parameters when present and clusters within reference range, often fails to predict the risk of acute coronary syndrome in young population in this region. Measurement of Apolipoprotein B (Apo B), a parameter of the lipoprotein-lipid profile, provides a method of quantifying the concentration of lipoproteins, rather than their cholesterol content. Present study aimed to quantify the risk of acute coronary syndrome (ACS) in young people with having none to less number of traditional lipidic parameters for dyslipidemia. This is a case control study among 50 cases of first attack of ACS among 18-45 years of age of both sexes, admitted in coronary care unit of Mymensingh Medical College Hospital, Mymensingh, Bangladesh from June 2009 to May 2010. Data was recently reanalyzed. Out of five sub-sets of lipid profile, namely TC, TG, HDL-C, LDL-C and non-HDL-C, 16(32%) cases were dyslipidemic by 0 (none) parameter, 13(26%) cases by one parameter, 7(14%) cases by two parameters, 4(8%) cases by three cases, 7(14%) cases by four parameters and 3(6%) cases by all five parameters. It was found that none to lesser the number of dyslipidemic parameters, greater the percentage of ACS cases and they are having hyper ApoB with statistically significant association (p<0.05).

Antimicrobial activity and cytotoxicity of Zanthoxylum budrunga

The petroleum ether, chloroform and methanol extracts of the leaves and barks of Zanthoxylum budrunga have been evaluated for their antibacterial, antifungal and cytotoxic properties.

Nystatin effects on vacuolar function in Saccharomyces cerevisiae

The effects of nystatin, a polyene antibiotic, was studied in Saccharomyces cerevisiae by isolating and characterizing nystatin-sensitive mutants. We isolated a number of nystatin-sensitive mutants by ethylmethane sulfonate mutagenesis. One of these mutants, the nss1 mutant, was characterized in detail. The mutant was sensitive to stresses such as high temperature or high concentrations of monovalent and divalent cations. The nss1 mutants showed severe vacuolar protein sorting and vacuolar morphology defects. The nss1 mutant was demonstrated to have a mutational lesion in the known VPS16 gene, which is essential for vacuolar protein sorting in S. cerevisiae. All of the vacuolar deficient mutants (vps11, vps16, vps18, and vps33) were sensitive to nystatin. Nystatin was found to cause extensive enlargement of the vacuole in wild-type S. cerevisiae cells. These results are discussed with special reference to the vacuolar function of S. cerevisiae.

Cell surface galactosylation is essential for nonsexual flocculation in Schizosaccharomyces pombe

We have isolated fission yeast mutants that constitutively flocculate upon growth in liquid media. One of these mutants, the gsf1 mutant, was found to cause dominant, nonsexual, and calcium-dependent aggregation of cells into flocs. Its flocculation was inhibited by the addition of galactose but was not affected by the addition of mannose or glucose, unlike Saccharomyces cerevisiae FLO mutants. The gsf1 mutant coflocculated with Schizosaccharomyces pombe wild-type cells, while no coflocculation was found with galactose-deficient (gms1Delta) cells. Moreover, flocculation of the gsf1 mutant was also inhibited by addition of cell wall galactomannan from wild-type cells but not from gms1Delta cells. These results suggested that galactose residues in the cell wall glycoproteins may be receptors of gsf1-mediated flocculation, and therefore cell surface galactosylation is required for nonsexual flocculation in S. pombe.

Post-thoracotomy paraplegia coincident with epidural anaesthesia

We report a case of paraplegia in the immediate postoperative period following right bilobectomy for carcinoma of the lung. An epidural catheter had been inserted following induction of anaesthesia and an infusion of bupivacaine 0.15% was used for postoperative pain relief. Magnetic resonance imaging failed to reveal any spinal or epidural haematoma or spinal cord ischaemia. The patient developed respiratory failure on the third postoperative day and required assisted ventilation. He was weaned from the ventilator on day 15. Two days later he sustained a cardiac arrest and died. Post-mortem examination demonstrated spinal cord infarction and severely stenosed spinal arteries. The thoracotomy position and/or intra-operative hypotension might have compromised the blood flow to the spinal cord and although suspected as a possible cause, the use of epidural analgesia was not implicated.

Isolation and characterization of an invertase and its repressor genes from Schizosaccharomyces pombe

PCR was used to isolate an invertase homolog gene from the fission yeast Schizosaccharomyces pombe. The cloned inv1(+) gene encodes a protein of 581 amino acids with 16 potential asparagine-linked glycosylation sites, and has 39% and 38% identity to the Schwanniomyces occidentalis and Saccharomyces cerevisiae SUC2 invertases. When the inv1(+) gene was disrupted, S. pombe strains lacked detectable invertase activity. This result showed that the inv1(+) gene encodes only one active invertase in S. pombe cells. The transcription of inv1(+) is repressed in the presence of glucose. The transcription of inv1(+) was not affected in cyr1Delta strain which lacks adenylate cyclase activity, unlike transcription of S. pombe fbp1(+) gene. We have identified an S. pombe gene (scr1(+)) that encodes a homolog of the Aspergillus nidulans CREA which is required for glucose repression of the glyconeogenic pathway. Although the deletion of scr1(+) did not influence the transcription of fbp1(+) gene, glucose repression of the inv1(+) gene was severely affected. These results showed that glucose repression of inv1(+) gene is dependent on scr1(+) gene, and S. pombe cAMP signalling pathway may not be essential for glucose repression of inv1(+) gene.