Hif-1α Knockdown Reduces Glycolytic Metabolism and Induces Cell Death of Human Synovial Fibroblasts Under Normoxic Conditions

Increased glycolysis and HIF-1 alpha activity are characteristics of cells under hypoxic or inflammatory conditions. Besides, in normal O-2 environments, elevated rates of glycolysis support critical cellular mechanisms such as cell survival. The purpose of this study was to analyze the contribution of HIF-1 alpha to the energy metabolism and survival of human synovial fibroblasts (SF) under normoxic conditions. HIF-1 alpha was silenced using lentiviral vectors or small-interfering RNA (siRNA) duplexes. Expression analysis by qRT-PCR and western blot of known HIF-1 alpha target genes in hypoxia demonstrated the presence of functional HIF-1 alpha in normoxic SF and confirmed the glycolytic enzyme glyceraldehyde3-phosphate dehydrogenase (GAPDH) as a HIF-1 alpha target even in normoxia. HIF-1 alpha silencing induced apoptotic cell death in cultured SF and, similarly, treatment with glycolytic, but not with OXPHOS inhibitors, induced SF death. Finally, in vivo HIF-1 alpha targeting by siRNA showed a significant reduction in the viability of human SF engrafted into a murine air pouch. Our results demonstrate that SF are highly dependent on glycolytic metabolism and that HIF-1 alpha plays a regulatory role in glycolysis even under aerobic conditions. Local targeting of HIF-1 alpha provides a feasible strategy to reduce SF hyperplasia in chronic arthritic diseases.