Biology subjects

Kronenberg, H. M.

Publications and source records attributed to Kronenberg, H. M..

7 recordsLinked to original sources

bioRxiv2026

Intermittent parathyroid hormone employs autonomous and non-autonomous mechanisms to drive osteogenesis from Ebf3-expressing skeletal progenitor cells

How systemic hormonal signals coordinate stem cell fate decisions in adult tissues remains incompletely understood. In bone marrow, Cxcl12-abundant reticular (CAR) cells, marked by Early B-cell Factor 3 (Ebf3) expression, are multipotent mesenchymal progenitors that maintain the hematopoietic stem cell niche and serves as a major osteoblast progenitor source during adult bone remodeling. Using inducible lineage tracing coupled with single-cell transcriptomics and conditional genetics in mice, we show that intermittent parathyroid hormone (iPTH; teriparatide) drives osteogenesis from CAR cells by simultaneously engaging cell-intrinsic and cell-extrinsic mechanisms. Directly, iPTH suppresses lineage-enforcing transcription factors Ebf3, Ebf1, and Foxc1, thereby destabilizing progenitor identity and priming CAR cells for osteogenic commitment. Simultaneously, iPTH stimulates osteoclastic bone resorption, releasing TGF{beta} which recruits these primed progenitors to bone surfaces, a process abolished by osteoclast depletion. Preventing CAR cell maturation via Sp7 deletion abrogates iPTH-induced bone gain, establishing these progenitors as essential mediators of bone anabolism. This coupled mechanism, in which intrinsic transcriptional priming converges with extrinsic niche remodeling, is conserved in human CAR cells from teriparatide-treated postmenopausal women, which show concordant suppression of EBF3 and FOXC1 and elevated TGF{beta}-responsive gene signatures. These findings reveal a general principle by which a systemic hormone orchestrates tissue remodeling through simultaneous reprogramming of progenitor identity and remodeling of the niche microenvironment.

physiology↗

bioRxiv2026

Inducible activation of PKA in osteoblasts causes a profound high bone turnover phenotype similar to human diseases

Protein kinase A (PKA) is involved in bone biology and is a key mediator of parathyroid hormone signaling in the osteoblast. However, the consequences of sustained PKA activation in bone are unclear. In this study, we inducibly activated PKA in osteoblasts by deleting its major regulatory subunit, Prkar1a, using a Col11-driven Cre system. Prkar1aob-/-mice demonstrated rapid and profound bone pathologies in their femurs, lumbar and caudal vertebrae with cortical bone breakdown and cortical trabecularization. This phenotype was characterized by increased bone turnover and elevated osteoblastic and osteoclastic activities. Transcriptomic and qPCR analyses showed an impairment of osteoblast differentiation with a defect in ossification, expansion of stromal cells, and numbers of both osteoblastic and osteoclastic precursors. Moreover, there were alterations in gene expression of chemokines and Wnt members with enhanced osteoclastogenesis. Altogether, activation of PKA in osteoblasts by inducible deletion of Prkar1a causes a profound high bone turnover phenotype resembling several human bone diseases.

pathology↗

bioRxiv2021

Control of osteocyte dendrite formation by Sp7 and its target gene osteocrin

Osteocytes use an elaborate network of dendritic connections to control bone remodeling. Some osteoblasts embed within mineralized bone matrix, change shape, and become osteocytes. The molecular circuitry that drives dendrite formation during "osteocytogenesis" is poorly understood. Here we show that deletion of Sp7, a gene linked to rare and common skeletal disease, in mature osteoblasts and osteocytes causes severe defects in osteocyte dendrites. Unbiased profiling of Sp7 target genes and binding sites reveals unexpected repurposing of this transcription factor to drive dendrite formation. Osteocrin is a Sp7 target gene that promotes osteocyte dendrite formation and rescues phenotypic and molecular defects in Sp7-deficient mice. Single-cell RNA-sequencing demonstrates overt defects in osteocyte maturation in vivo in the absence of Sp7. Sp7-dependent gene networks enriched in developing osteocytes are associated with rare and common human skeletal traits. Moreover, humans homozygous for the osteogenesis imperfecta-causing SP7R316C mutation show dramatic defects in osteocyte morphology. Genes that mark osteocytes in vivo and that are regulated by Sp7 in vitro are highly enriched in neurons, highlighting shared features between osteocytic and neuronal connectivity. Taken together, these findings reveal a crucial role for Sp7 and its target gene Osteocrin in osteocytogenesis, demonstrating that pathways that control osteocyte development influence human bone diseases.

molecular biology↗

bioRxiv2021

Dual targeting of salt inducible kinases and CSF1R uncouples bone formation and bone resorption

Bone formation and resorption are typically coupled, such that the efficacy of anabolic osteoporosis treatments may be limited by bone destruction. The multi-kinase inhibitor YKL-05-099 potently inhibits salt inducible kinases (SIKs) and may represent a promising new class of bone anabolic agents. Here we report that YKL-05-099 increases bone formation in hypogonadal female mice without increasing bone resorption. Postnatal mice with inducible, global deletion of SIK2 and SIK3 show increased bone mass, increased bone formation, and, distinct from the effects of YKL-05-099, increased bone resorption. No cell-intrinsic role of SIKs in osteoclasts was noted. In addition to blocking SIKs, YKL-05-099 also binds and inhibits CSF1R, the receptor for the osteoclastogenic cytokine M-CSF. Modeling reveals that YKL-05-099 binds to SIK2 and CSF1R in a similar manner. Dual targeting of SIK2/3 and CSF1R induces bone formation without concomitantly increasing bone resorption and thereby may overcome limitations of most current anabolic osteoporosis therapies.

physiology↗

bioRxiv2021

Genes with Specificity for Expression in the Round Cell Layer of the Growth Plate are Enriched in GWAS of Human Height

Human adult height reflects the outcome of childhood skeletal growth. Growth plate (epiphyseal) chondrocytes are key determinants of height. As epiphyseal chondrocytes mature and proliferate, they pass through three developmental stages, which are organized into three distinct layers in the growth plate: 1) resting (round), 2) proliferative (flat), and 3) hypertrophic. Recent genome-wide association studies (GWAS) of human height identified numerous associated loci, which are enriched for genes expressed in growth plate chondrocytes. However, it remains unclear which specific genes expressed in which layers of the growth plate regulate skeletal growth and human height. To connect the genetics of height and growth plate biology, we analyzed GWAS data through the lens of gene expression in the three dissected layers of murine newborn tibial growth plate. For each gene, we derived a specificity score for each growth plate layer and regressed these scores against gene-level p-values from recent height GWAS data. We found that specificity for expression in the round cell layer, which contains chondrocytes early in maturation, is significantly associated with height GWAS p-values (p=8.5x10-9); this association remains after conditioning on specificity for the other cell layers. The association also remains after conditioning on membership in an "OMIM gene set" (genes known to cause monogenic skeletal growth disorders, p<9.7x10-6). We replicated the association in RNA-seq data from maturing chondrocytes sampled at early and late time points during differentiation in vitro: we found that expression early in differentiation is significantly associated with p-values from height GWAS (p=6.1x10-10) and that this association remains after conditioning on expression at 10 days in culture and on the OMIM gene set (p<0.006). These findings newly implicate genes highlighted by GWAS of height and specifically expressed in the round cell layer as being potentially important regulators of skeletal biology.

genetics↗

bioRxiv2020

Chondrocytes in the resting zone of the growth plate are maintained in a Wnt-inhibitory environment

Chondrocytes in the resting zone of the postnatal growth plate are characterized by slow cell cycle progression, and encompass a population of parathyroid hormone-related protein (PTHrP)-expressing skeletal stem cells that contribute to the formation of columnar chondrocytes. However, how these chondrocytes are maintained in the resting zone remains undefined. We undertook a genetic pulse-chase approach to isolate slow cycling, label-retaining chondrocytes (LRCs) from the growth plate using a chondrocyte-specific doxycycline-controllable Tet-Off system regulating expression of histone 2B-linked GFP. Comparative RNA-seq analysis identified significant enrichment of inhibitors and activators for Wnt/{beta}-catenin signaling in LRCs and non-LRCs, respectively. Activation of Wnt/{beta}-catenin signaling in PTHrP+ resting chondrocytes using Pthrp-creER and Apc-floxed allele impaired their ability to form columnar chondrocytes. Therefore, slow-cycling chondrocytes are maintained in a canonical Wnt-inhibitory environment within the resting zone, unraveling a novel mechanism regulating maintenance and differentiation of PTHrP+ skeletal stem cells of the postnatal growth plate.

developmental biology↗

bioRxiv2019

Mesenchymal expression of activated K-ras yields Noonan Syndrome-like bone defects that are rescued by mid-gestational MEK inhibition.

Activating germline K-ras mutations cause Noonan syndrome (NS), which is characterized by several developmental deficits including cardiac defects, cognitive delays and skeletal abnormalities. NS patients have increased signaling through the MAPK pathway. To model NS skeletal defects and understand the effect of hyperactive K-ras signaling on normal limb development, we generated a mouse model in which activated K-rasG12D was expressed specifically in mesenchymal progenitors of the limb bud. These mice display short, abnormally mineralized long bones that phenocopy those of NS patients. This defect was first apparent at E14.5, and was characterized by a delay in bone collar formation. Coincident mutation of p53 had no effect on the K-rasG12D induced bone defect, arguing that it is does not result from senescence or apoptosis. Instead, our data revealed profound defects in the development of the committed osteoblasts; their appearance is delayed, concordant with the delay in bone collar formation, and they display an aberrant localization outside of the bone shaft. Additionally, we see growth plate defects including a reduction in the hypertrophic chondrocyte layer. Most importantly, we found that in utero delivery of a MEK inhibitor between E10.5 and E14.5 is sufficient to completely suppress the ability of activated K-ras to induce NS-like long bone defects in embryogenesis. These data define a critical point in mid-gestation in which elevated MAPK signaling impairs growth plate and bone collar formation and yield NS-like limb defects. Moreover, they offer insight into possible therapeutic strategies for skeletal defects in patients with Noonan Syndrome.\n\nSIGNIFICANCE STATEMENTNoonan syndrome is a genetic condition that is characterized by various developmental defects including skeletal abnormalities that lead to short stature. These patients carry mutations that activate Ras/MAPK signaling. We have generated a mouse model that recapitulates these Noonan Syndrome-like bone defects. Analysis of these animals establishes the developmental window in which bone formation goes awry, and reveals disruption of an early event that is critical for the longitudinal growth of bones. Additionally, we show that treatment with an inhibitor of Ras/MAPK signaling during this key developmental window is sufficient to completely suppress these Noonan Syndrome-like bone defects. This offers possible therapeutic strategies for skeletal defects in patients with Noonan Syndrome.

developmental biology↗