HIF-1α Promotes Glutamine-Mediated Redox Homeostasis and Glycogen-Dependent Bioenergetics to Support Postimplantation Bone Cell Survival

Abstract

Cell-based therapy is a promising strategy in regenerative medicine, but the poor survival rate of the implanted cells remains a major challenge and limits clinical translation. We preconditioned periosteal cells to the hypoxic and ischemic environment of the bone defect site by deleting prolyl hydroxylase domain-containing protein 2 (PHD2), resulting in hypoxia-inducible factor 1 alpha (HIF-1α) stabilization. This strategy increased postimplantation cell survival and improved bone regeneration. The enhanced cell viability was angiogenesis independent but relied on combined changes in glutamine and glycogen metabolism. HIF-1α stabilization stimulated glutaminase-mediated glutathione synthesis, maintaining redox homeostasis at baseline and during oxidative or nutrient stress. Simultaneously, HIF-1α signaling increased glycogen storage, preventing an energy deficit during nutrient or oxygen deprivation. Pharmacological inhibition of PHD2 recapitulated the adaptations in glutamine and glycogen metabolism and, consequently, the beneficial effects on cell survival. Thus, targeting cellular metabolism is an appealing strategy for bone regeneration and cell-based therapy in general.

Healing of a Large Long-Bone Defect through Serum-Free In Vitro Priming of Human Periosteum-Derived Cells

“…In addition, recent findings indicate that the majority of in vitro expanded cells undergo apoptosis upon implantation (Stegen et al., 2016). A cause may be the need to instantly adjust to a compromised environment, since current culture conditions represent a rather non-physiological and abundant nutritional source.…”

Wnt signaling and cellular metabolism in osteoblasts

“…Functionally, stimulating glycolysis through activation of Hif1α signaling in preosteoblasts increases bone formation in vivo , indicating that reprogramming glucose metabolism is sufficient to promote osteoblast differentiation [103]. Moreover, Hif1α activation has been shown to promote bone healing partly through reprogramming of glucose metabolism, highlighting the clinical implications of understanding metabolic regulation in osteoblasts [104]. Recent studies have demonstrated that aerobic glycolysis is directly stimulated in response to osteogenic signals such as PTH and Wnt [105, 106].…”

“…Decreased glutamine consumption by bone marrow stromal cells has been linked with impaired osteoblast differentiation associated with aging [147]. Moreover, increased glutathione production from glutamine in response to Hif1α has been shown to improve cell survival and bone repair in a critical-size tibial defect model [148]. In differentiating osteoblasts, glutamine anaplerosis fulfills part of the energetic requirement of bone formation in response to Wnt signaling.…”

Single-cell characterization and metabolic profiling of in vitro cultured human skeletal progenitors with enhanced in vivo bone forming capacity

“…In this setting, their energy and redox metabolism is adapted in order to survive in hypoxic and nutrient deprived conditions . These adaptations were previously characterized in mouse PDCs . Interestingly, hypoxic culture conditions were shown to provoke recruitment of the glycogen stores to maintain the energy balance.…”