Protective Effect of Geranylgeranylacetone via Enhancement of HSPB8 Induction in Desmin-Related Cardiomyopathy

An arg120gly (R120G) missense mutation in HSPB5 (alpha-beta-crystallin ), which belongs to the small heat shock protein (HSP) family, causes desmin-related cardiomyopathy (DRM), a muscle disease that is characterized by the formation of inclusion bodies, which can contain pre-amyloid oligomer intermediates (amyloid oligomer). While we have shown that small HSPs can directly interrupt amyloid oligomer formation, the in vivo protective effects of the small HSPs on the development of DRM is still uncertain.In order to extend the previous in vitro findings to in vivo, we used geranylgeranylacetone (GGA), a potent HSP inducer. Oral administration of GGA resulted not only in up-regulation of the expression level of HSPB8 and HSPB1 in the heart of HSPB5 R120G transgenic (R120G TG) mice, but also reduced amyloid oligomer levels and aggregates. Furthermore, R120G TG mice treated with GGA exhibited decreased heart size and less interstitial fibrosis, as well as improved cardiac function and survival compared to untreated R120G TG mice. To address possible mechanism(s) for these beneficial effects, cardiac-specific transgenic mice expressing HSPB8 were generated. Overexpression of HSPB8 led to a reduction in amyloid oligomer and aggregate formation, resulting in improved cardiac function and survival. Treatment with GGA as well as the overexpression of HSPB8 also inhibited cytochrome c release from mitochondria, activation of caspase-3 and TUNEL-positive cardiomyocyte death in the R120G TG mice.Expression of small HSPs such as HSPB8 and HSPB1 by GGA may be a new therapeutic strategy for patients with DRM

A Genomewide Screen for Tolerance to Cationic Drugs Reveals Genes Important for Potassium Homeostasis in Saccharomyces cerevisiae ▿ †

Potassium homeostasis is crucial for living cells. In the yeast Saccharomyces cerevisiae, the uptake of potassium is driven by the electrochemical gradient generated by the Pma1 H+-ATPase, and this process represents a major consumer of the gradient. We considered that any mutation resulting in an alteration of the electrochemical gradient could give rise to anomalous sensitivity to any cationic drug independently of its toxicity mechanism. Here, we describe a genomewide screen for mutants that present altered tolerance to hygromycin B, spermine, and tetramethylammonium. Two hundred twenty-six mutant strains displayed altered tolerance to all three drugs (202 hypersensitive and 24 hypertolerant), and more than 50% presented a strong or moderate growth defect at a limiting potassium concentration (1 mM). Functional groups such as protein kinases and phosphatases, intracellular trafficking, transcription, or cell cycle and DNA processing were enriched. Essentially, our screen has identified a substantial number of genes that were not previously described to play a direct or indirect role in potassium homeostasis. A subset of 27 representative mutants were selected and subjected to diverse biochemical tests that, in some cases, allowed us to postulate the basis for the observed phenotypes