Abstract 355: Snf1-related kinase is Upregulated in the Ischemic Heart and Regulates Cellular Metabolism and Death
Sucrose non-fermenting (Snf1)-related kinase (SNRK) is a novel kinase homologous to the Snf1 kinase of yeast and the AMP-activated protein kinases (AMPK) of mammals. SNRK is expressed in a variety of tissues; however, its role in the cardiovascular system is unclear. While AMPK and Snf1 regulate metabolism, the primary function of SNRK is not known. We hypothesized that like AMPK, SNRK regulates cellular metabolism and influences cell survival. Western blots of protein extracts from several cell types showed that SNRK is widely expressed and exists in different forms in the nucleus and cytoplasm. We next assessed the effects of ischemia, hypoglycemia and increased AMP on SNRK levels. Dog hearts subjected to ischemia displayed a 41% increase in SNRK levels (P<0.01), while explanted hearts from patients with ischemic cardiomyopathy showed a 220% increase compared to controls (P<0.05). SNRK mRNA levels and subcellular location were altered by hypoglycemia and increased AMP levels. The role of SNRK on cell death and metabolism was then assessed by transfecting HEK293 cells with GFP, a SNRKGFP fusion construct, or SNRKGFP containing a mutation in the nuclear localization sequence (SNRKnls). SNRKGFP overexpression increased cell death by 10% (P=0.007) compared to controls both in the absence and presence of oxidant stress. Nuclear respiratory factors (NRF)2α and -2β (transcription factors that induce mitochondrial biogenesis) were upregulated with SNRK overexpression by 30% and 90%, respectively (P<0.05). SNRKnls did not induce a significant change. SNRK overexpression, but not SNRKnls, resulted in a 15% reduction in cellular ATP content compared to controls (P=0.0001). A gene array performed on cells overexpressing either SNRKGFP or GFP showed that SNRK overexpression strongly correlates with numerous nuclear and metabolic functions. These data show that SNRK is upregulated in ischemic heart disease and suggest that it induces cell death. SNRK also appears to be a component of the cellular metabolic machinery, likely exerting its actions via entry into the nucleus. Thus, by altering cellular metabolism, SNRK may play an important role in the response of the heart to ischemia, and may provide a novel target for cardiovascular therapeutic interventions.