Excess glucose alone depress young mesenchymal stromal/stem cell osteogenesis and mitochondria activity within hours/days via NAD⁺/SIRT1 axis

Background: The impact of global overconsumption of simple sugars on bone health, which peaks in adolescence/early adulthood and correlates with osteoporosis (OP) and fracture risk decades, is unclear. Mesenchymal stromal/stem cells (MSCs) are the progenitors of osteoblasts/bone-forming cells, and known to decrease their osteogenic differentiation capacity with age. Alarmingly, while there is correlative evidence that adolescents consuming greatest amounts of simple sugars have the lowest bone mass, there is no mechanistic understanding on the causality of this correlation.

Methods: Bioinformatics analyses for energetics pathways involved during MSC differentiation using human cell information was performed. In vitro dissection of normal versus high glucose (HG) conditions on osteo-/adipo-lineage commitment and mitochondrial function was assessed using multi-sources of non-senescent human and murine MSCs; for in vivo validation, young mice was fed normal or HG-added water with subsequent analyses of bone marrow CD45^- MSCs.

Results: Bioinformatics analyses revealed mitochondrial and glucose-related metabolic pathways as integral to MSC osteo-/adipo-lineage commitment. Functionally, in vitro HG alone without differentiation induction decreased both MSC mitochondrial activity and osteogenesis while enhancing adipogenesis by 8 h' time due to depletion of nicotinamide adenine dinucleotide (NAD⁺), a vital mitochondrial co-enzyme and co-factor to Sirtuin (SIRT) 1, a longevity gene also involved in osteogenesis. In vivo, HG intake in young mice depleted MSC NAD⁺, with oral NAD⁺ precursor supplementation rapidly reversing both mitochondrial decline and osteo-/adipo-commitment in a SIRT1-dependent fashion within 1 ~ 5 days.

Conclusions: We found a surprisingly rapid impact of excessive glucose, a single dietary factor, on MSC SIRT1 function and osteogenesis in youthful settings, and the crucial role of NAD⁺-a single molecule-on both MSC mitochondrial function and lineage commitment. These findings have strong implications on future global OP and disability risks in light of current worldwide overconsumption of simple sugars.