Citrate-based materials fuel human stem cells by metabonegenic regulation

Abstract

A comprehensive understanding of the key microenvironmental signals regulating bone regeneration is pivotal for the effective design of bioinspired orthopedic materials. Here, we identified citrate as an osteopromotive factor and revealed its metabonegenic role in mediating citrate metabolism and its downstream effects on the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Our studies show that extracellular citrate uptake through solute carrier family 13, member 5 (SLC13a5) supports osteogenic differentiation via regulation of energy-producing metabolic pathways, leading to elevated cell energy status that fuels the high metabolic demands of hMSC osteodifferentiation. We next identified citrate and phosphoserine (PSer) as a synergistic pair in polymeric design, exhibiting concerted action not only in metabonegenic potential for orthopedic regeneration but also in facile reactivity in a fluorescent system for materials tracking and imaging. We designed a citrate/phosphoserine-based photoluminescent biodegradable polymer (BPLP-PSer), which was fabricated into BPLP-PSer/hydroxyapatite composite microparticulate scaffolds that demonstrated significant improvements in bone regeneration and tissue response in rat femoral-condyle and cranial-defect models. We believe that the present study may inspire the development of new generations of biomimetic biomaterials that better recapitulate the metabolic microenvironments of stem cells to meet the dynamic needs of cellular growth, differentiation, and maturation for use in tissue engineering.

The membrane protein ANKH is crucial for bone mechanical performance by mediating cellular export of citrate and ATP

“…The altered eccentricity and perimeter of Ank ank/ank femora are most likely a result of compensatory bone remodeling to retain whole bone strength. Interestingly, Ma et al recently reported that local levels of extracellular citrate are important for the osteogenic development of human mesenchymal stem cells [16]. Kim et al showed that differentiation of osteoblast is delayed in mice lacking Ank, which was attributed to reduced extracellular levels of PPi [11].…”

Ankylosis homologue (ANKH) controls extracellular citrate and pyrophosphate homeostasis and affects bone mechanical performance

“…Like PPi, citrate is also one of the major organic compounds present in bone and also strongly associates with hydroxyapatite 16 . With 90% of the body’s citrate content present in bone, this tissue is thought to play a central role in extracellular citrate homeostasis 17 . Therefore, we determined if bone citrate levels depend on ANK.…”

“…The altered eccentricity and perimeter of Ank ank/ank femora are most likely a result of compensatory bone remodeling to retain whole bone strength without increasing total bone mass. Interestingly, Ma et al recently reported that local levels of extracellular citrate are also important for the osteogenic development of human mesenchymal stem cells 17 . It is therefore conceivable that ANKH-dependent citrate release into bone is not only important for the material properties of hydroxyapatite, but also contributes to osteogenic differentiation.…”

Biomaterial‐Based Metabolic Regulation in Regenerative Engineering

“…Intuitively, one can envisage that the releasing of metabolic regulators, such as ions, metabolites and O 2 , which are inherently embedded or incorporated in biomaterials, may modulate intracellular metabolic flux after entering cells. In fact, metabolic regulator release represents the primary conduit through which biomaterials affect cell metabolism and subsequently influence cell functions, which is of particular interest for regenerative engineering.…”

“…Within the pool of degradation products that are gradually and dynamically released into the extracellular space in situ overtime, there may be metabolic regulators including regulatory metabolites, cofactors, and key substrates for energy production or biosynthesis that can impact intracellular metabolic events. Indeed, we recently identified citrate in the degradation products of citrate‐based biomaterials (CBBs) as this type of inherent metabolic regulator for hMSCs bioenergetics toward facilitated osteogenic differentiation via a mechanism named “metabonegenic” regulation ( Figure Ai) . Intracellular citrate is well‐known as an intermediate metabolite, playing an important role in regulating energy homeostasis, since it not only modulates the activity of key enzymes in both catabolic and anabolic pathways, but also could convert to acetyl–CoA, the direct substrate for fatty acid biosynthesis and histone acetylation .…”