Biology subjects

Ignatius, A.

Publications and source records attributed to Ignatius, A..

4 recordsLinked to original sources

bioRxiv2026

Mitochondrial dysfunction and impaired osteogenic capacity define stress-induced osteoblast senescence

Cellular senescence has emerged as a key contributor to age-related skeletal deterioration; however, the defining characteristics of senescent osteoblasts remain incompletely understood, hindering efforts to identify the cellular mechanisms that drive age-associated bone loss and potential therapeutic targets. Here, we compared doxorubicin- and hydrogen peroxide-induced senescence and established a robust in vitro osteoblast model that enables the stable maintenance of stress-induced premature senescence. Doxorubicin-treated MC3T3-E1 cells exhibited persistent growth arrest, a pronounced senescence-associated secretory phenotype (SASP), and impaired osteogenic function accompanied by marked mitochondrial dysfunction, including reduced respiratory capacity and altered mitochondrial morphology. Transcriptomic comparison with aged murine bone revealed a partial overlap with in vivo aging-associated gene expression signatures, particularly among genes involved in extracellular matrix organization and skeletal development, supporting the physiological relevance of the model. Importantly, key features of senescence, including the senescence-associated mitochondrial phenotype and impaired osteogenic capacity, were recapitulated in primary human osteoblasts. Collectively, these findings establish a robust model of stress-induced osteoblast senescence and demonstrate that senescent osteoblasts exhibit mitochondrial dysfunction, impaired osteogenic capacity, and molecular features that resemble aspects of skeletal aging.

cell biology↗

bioRxiv2025

Using artificial intelligence-based software for an unbiased discrimination of immune cell subtypes in the fracture hematoma and bone marrow of non-osteoporotic and osteoporotic mice

It is well established that the early inflammatory response following fracture is essential for initiating subsequent bone regeneration. An imbalance in inflammation, whether within the innate or adaptive immune response, can result in impaired fracture healing. In our previous studies, we demonstrated that, for example, mice with ovariectomy-induced osteoporosis exhibit altered immune cell populations in the early fracture hematoma and bone marrow, leading to delayed healing. These analyses were conducted using conventional FACS/flow cytometry software, where surface marker expression was assessed using a single threshold based on isotype controls--a binary "yes or no" decision. Recent advances have highlighted that immune cell populations are often more heterogeneous, with distinct phenotypic subgroups depending on their polarization status. This has been particularly well documented for macrophage subpopulations (M1, M2, and intermediate polarization states). In light of this, we employed a commercially available artificial intelligence-based clustering software (Cytolution) to more accurately and objectively identify immune cell subpopulations. We re-analyzed flow cytometry raw data from fracture hematoma and bone marrow of non-osteoporotic and osteoporotic mice at day 1 after fracture. Our findings revealed distinct subclusters for granulocytes (27 subclusters), macrophages (7 subclusters), B cells (4 subclusters), and T cells (6 subclusters) within the fracture hematoma and bone marrow. Comparing osteoporotic and non-osteoporotic mice, we observed an increased abundance of a specific B cell subpopulation in osteoporotic mice, alongside a significant reduction of a particular granulocyte subpopulation in the early fracture hematoma. Several subclusters of granulocytes, T cells, and macrophages were also altered in the bone marrow. The specific role of these immune cell subclusters remains to be investigated in the future. These results suggest that AI-based clustering may provide a powerful tool for identifying immune cell phenotypes during bone regeneration, offering a more nuanced understanding of flow cytometry data.

immunology↗

bioRxiv2022

Zebrafish fin regeneration requires generic and regeneration-specific responses of osteoblasts to trauma

Successful regeneration requires the coordinated execution of multiple cellular responses to injury. In amputated zebrafish fins, mature osteoblasts dedifferentiate, migrate towards the injury and form proliferative osteogenic blastema cells. We show that osteoblast migration is preceded by cell elongation and alignment along the proximodistal axis, which require actomyosin, but not microtubule turnover. Surprisingly, osteoblast dedifferentiation and migration can be uncoupled. Using pharmacological and genetic interventions, we found that NF-{kappa}B and retinoic acid signalling regulate dedifferentiation without affecting migration, while the complement system and actomyosin dynamics are required for migration but not dedifferentiation. Furthermore, by removing bone at two locations within a fin ray, we established a trauma model containing two injury sites. We found that osteoblasts dedifferentiate at and migrate towards both sites, while accumulation of osteogenic progenitor cells and regenerative bone formation only occur at the distal-facing injury. Together, these data indicate that osteoblast dedifferentiation and migration represent generic injury responses that are differentially regulated and can occur independently of each other and of regenerative growth. Successful bone regeneration appears to require the coordinated execution of generic and regeneration-specific responses of osteoblast to trauma. O_FIG O_LINKSMALLFIG WIDTH=131 HEIGHT=200 SRC="FIGDIR/small/481466v1_ufig1.gif" ALT="Figure 1"> View larger version (67K): org.highwire.dtl.DTLVardef@c1145org.highwire.dtl.DTLVardef@41f525org.highwire.dtl.DTLVardef@4569eaorg.highwire.dtl.DTLVardef@12c85e4_HPS_FORMAT_FIGEXP M_FIG C_FIG

developmental biology↗

bioRxiv2021

G6b-B regulates an essential step in megakaryocyte maturation

G6b-B is a megakaryocyte lineage-specific immunoreceptor tyrosine-based inhibition motif (ITIM)-containing receptor, essential for platelet homeostasis. Mice with a genomic deletion of the entire Mpig6b locus develop severe macrothrombocytopenia and myelofibrosis, which is reflected in humans with null-mutations in MPIG6B. The current model proposes that megakaryocytes lacking G6b-B develop normally, while proplatelet release is hampered, but the underlying molecular mechanism remains unclear. Here, we report on a spontaneous recessive single nucleotide mutation in C57BL/6 mice, localized within the intronic region of the Mpig6b locus that abolishes G6b-B expression and reproduces macrothrombocytopenia, myelofibrosis and osteosclerosis. As the mutation is based on a single nucleotide exchange, Mpig6bmut mice represent an ideal model to study the role of G6b-B. Megakaryocytes from these mice were smaller in size, displayed a less developed demarcation membrane system and reduced expression of receptors. RNA sequencing revealed a striking global reduction in the level of megakaryocyte-specific transcripts, in conjunction with decreased protein levels of the transcription factor GATA-1, and impaired thrombopoietin signaling. The reduced number of mature MKs in the bone marrow was corroborated on a newly developed Mpig6b null mouse strain. Our findings highlight an unexpected essential role of G6b-B in the early differentiation within the megakaryocytic lineage.

cell biology↗