Increased Hexokinase Activity, of Either Ectopic or Endogenous Origin, Protects Renal Epithelial Cells against Acute Oxidant-induced Cell Death

Abstract

Glucose (Glc) metabolism protects cells against oxidant injury. By virtue of their central position in both Glc uptake and utilization, hexokinases (HKs) are ideally suited to contribute to these effects. Compatible with this hypothesis, endogenous HK activity correlates inversely with injury susceptibility in individual renal cell types. We recently reported that ectopic HK expression mimics the anti-apoptotic effects of growth factors in cultured fibroblasts, but anti-apoptotic roles for HKs have not been examined in other cell types or in a cellular injury model. We therefore evaluated HK overexpression for the ability to mitigate acute oxidant-induced cell death in an established epithelial cell culture injury model. In parallel, we examined salutary heparinbinding epidermal growth factor (EGF)-like growth factor (HB-EGF) treatment for the ability to 1) increase endogenous HK activity and 2) mimic the protective effects of ectopic HK expression. Both HK overexpression and HB-EGF increased Glc-phosphorylating capacity and metabolism, and these changes were associated with markedly reduced susceptibility to acute oxidantinduced apoptosis. The uniform Glc dependence of these effects suggests an important adaptive role for Glc metabolism, and for HK activity in particular, in the promotion of epithelial cell survival. These findings also support the contention that HKs contribute to the protective effects of growth factors. Glucose (Glc)1 metabolism plays a critical role in the protection of a variety of cell types against oxidant-induced cell death (1-9). The mechanisms underlying these cytoprotective effects are poorly understood, but contributions by both altered energy metabolism and cellular redox status have been suggested. Hexokinases (HKs) play a central role in both the uptake and utilization of Glc by catalyzing the first committed step of its metabolism, the phosphorylation of Glc to yield Glc 6-phosphate. By this mechanism, HKs maintain the downhill concentration gradient that permits facilitated Glc entry into cells. They also initiate all major pathways of Glc utilization and are ideally positioned to influence metabolic flux through both the glycolytic and the pentose phosphate pathways. Glycolytic flux is intimately linked to cellular energy metabolism, whereas pentose phosphate pathway flux plays a pivotal role in maintaining the cellular redox state. In principle, therefore, HK activity may directly contribute to the salutary effects associated with Glc metabolism in the setting of oxidative stress.

Colony-stimulating factor-1 requires PI3-kinase-mediated metabolism for proliferation and survival in myeloid cells

“…40 In agreement, HKII overexpression in DKI cells, in collaboration with CSF-1, increased MTS activity and cell viability. Compared to p110*, HKII overexpression was only partially effective.…”

“…In WT cells, CSF-1 increased HK activity by 29%, comparable to numbers reported for other growth factors (20-50%). 40 A similar enhancement was seen in p110* and E40K, but not in DKI cells. Basal HK activity in p110* and E40K cells showed a small but statistically significant increase compared to WT cells.…”

“…40 One unit is the amount of activity that results in the coupled formation of 1 mmol of NADPH/min at 251C in the presence of glucose, G6PD, b-NADP and ATP.…”

Akt mediates mitochondrial protection in cardiomyocytes through phosphorylation of mitochondrial hexokinase-II

“…26 While our data demonstrate that mitochondrial HK-II is a key inhibitor of PT-pore (Ca 2 þ -mediated and Cs-A sensitive) induced cytochrome c release, and previous papers show that overexpression of HK is protective against stress. 37,38 Much additional study will be required to elucidate the mechanisms by which HK-II keeps PT pore opening in check.…”

The voltage-dependent anion channel-1 modulates apoptotic cell death

“…23 Recent studies indicate that in malignant cancer, HK-II not only improves the cells energy supply but also protects against cell death. 24 Moreover, HK-I has been shown to bind to a bilayer-reconstituted VDAC and to induce its closure, prevent mitochondrial PTP opening and prevent cytochrome c release.…”