Biology subjects

Surface, L. E.

Publications and source records attributed to Surface, L. E..

4 recordsLinked to original sources

bioRxiv2025

TGF-β signaling regulates the response of the skeleton to phosphate

Inorganic phosphate (Pi) homeostasis is crucial to organismal health, yet the mechanisms underlying the regulation of it remain unclear. Critically, we lack a clear understanding of the Pi response circuitry in osteogenic cells that identifies altered serum Pi levels and transmits this information to changes in serum FGF23 levels, a key hormone regulating circulating Pi. We utilized genome-wide CRISPR screens in osteogenic Pi-responsive fluorescent reporter cell lines to identify regulators of the response to high phosphate, intersecting those results with loci associated with circulating FGF23 levels by genome-wide association studies (GWAS) and identified a potential role for TGF-{beta}2. We found that each of the three ligands (TGF-{beta}1, 2, 3) can enhance the response to Pi in osteogenic cell lines and ex vivo cultures of calvariae, while inhibitors of TGF{beta} receptor signaling dampen it. Co-treatment of Pi with TGF{beta} ligands led to an elevated, synergistic transcriptional induction of Slc20a1, which encodes a key Pi importer, which corresponded with an increased intracellular uptake of phosphate. Furthermore, in mice, blocking TGF{beta} signaling disrupted the induction of FGF23 in mice on a high phosphate diet, resulting in disrupted downstream endocrine control of phosphate homeostasis. Together, these findings reveal a role for TGF{beta} signaling in the regulation of phosphate homeostasis in osteogenic cells through regulation of cellular phosphate uptake, which in turn contributes to the maintenance of organismal phosphate homeostasis.

molecular biology↗

bioRxiv2025

Genome-wide CRISPR interference screen identifies Clip2 as a novel regulator of osteocyte maturation and morphology

Osteocytes play critical roles in bone, making them attractive targets for therapeutics to improve bone mass and strength. The genes driving osteocyte maturation and function are not fully understood. Here we aimed to identify novel genes responsible for osteocyte differentiation and dendrite development by performing a genome-wide CRISPR-interference (CRISPRi) screen in the Ocy454 osteocyte-like cell line. We identify CD61 (integrin {beta}3) as a marker of osteocyte maturation: surface CD61 expression increases during osteocyte maturation, and CD61high cells express higher levels of osteocyte marker genes. We then developed a flow cytometry-based assay to quantify surface CD61 protein levels as a phenotypic endpoint for functional genomic screening. In a genome-wide screen, we identified Clip2, which encodes a microtubule binding protein, as one of dozens of genes necessary for CD61 expression. Clip2 inhibition decreased surface CD61 expression, reduced expression of osteocyte-specific genes Dmp1 and Sost, and impaired dendrite morphology in vitro. Together, these results highlight the utility of surface CD61 as a marker of osteocyte maturity and identify a role of the microtubule cytoskeleton for osteocyte differentiation, form, and function.

cell biology↗

bioRxiv2025

Accelerated osteocytic citrate production in chronic kidney disease is associated with protection of the kidney

Patients with chronic kidney disease (CKD) face elevated fracture incidences, but mechanisms underlying CKD-related bone loss remain unclear. Using the adenine-induced chronic kidney injury (AdKI) murine model, we identified that AdKI induces dysregulated glucose metabolism in bones and kidneys via in vivo and ex vivo metabolic tracing. Ex vivo 13C-metabolic tracing of osteocyte-enriched femora revealed accelerated citrate production from [1,2-13C]-glucose and [U-13C]-glutamine in AdKI mice. These metabolic changes were observed together with increased circulating citrate and Slc13a5 overexpression in bones from AdKI mice. Thus, to explore the role of citrate in AdKI, we utilized mice harboring a loss of function mutation in the citrate importer SLC13A5 (Slc13a5R337*/R337*). Mutant mice displayed elevated osteocytic citrate production, and elevated circulating citrate, without significantly worsened AdKI-related bone loss. Coincident with this, Slc13a5R337*/R337* mutant mice were significantly protected from loss of kidney function with attenuated AdKI-induced nephrolithiasis. We also confirmed that Slc13a5 is highly expressed in cortical bone compared to the kidney, suggesting the effect of the mutation is mediated by SLC13A5s function outside the kidney. Altogether, this study finds that accelerated osteocytic citrate production in CKD is associated with protection of kidney function, and modulation of citrate handling may be a site for therapeutic intervention in CKD.

physiology↗

bioRxiv2018

Identification and characterization of a transporter complex responsible for the cytosolic entry of nitrogen-containing bisphosphonates

AbstractNitrogen-containing-bisphosphonates (N-BPs) are a class of drugs widely prescribed to treat osteoporosis and other bone-related diseases. Although previous studies have established that N-BPs function by inhibiting the mevalonate pathway in osteoclasts, the mechanism by which N-BPs enter the cytosol from the extracellular space to reach their molecular target is not understood. Here we implemented a CRISPRi-mediated genome-wide screen and identified SLC37A3 (solute carrier family 37 member A3) as a gene required for the action of N-BPs. We observed that SLC37A3 forms a complex with ATRAID (all-trans retinoic acid-induced differentiation factor), a previously identified genetic target of N-BPs. SLC37A3 and ATRAID localize to lysosomes and are required for releasing N-BP molecules that have trafficked to lysosomes through fluid-phase endocytosis into the cytosol. Our results elucidate the route by which N-BPs are delivered to their molecular target, addressing a key aspect of the mechanism of action of N-BPs that may have significant clinical relevance.

biochemistry↗