Identification and local manipulation of bone marrow vasculature during intravital imaging

Diabetes and the Microvasculature of the Bone and Marrow

PURPOSE OF REVIEW

The purpose of this review is to highlight the evidence of microvascular dysfunction in bone and marrow and its relation to poor skeletal outcomes in diabetes mellitus.

RECENT FINDINGS

Diabetes mellitus is characterized by chronic hyperglycemia, which may lead to microangiopathy and macroangiopathy. Micro- and macroangiopathy have been diagnosed in Type 1 and Type 2 diabetes, coinciding with osteopenia, osteoporosis, enhanced fracture risk and delayed fracture healing. Microangiopathy has been reported in the skeleton, correlating with reduced blood flow and perfusion, vasomotor dysfunction, microvascular rarefaction, reduced angiogenic capabilities, and augmented vascular permeability. Microangiopathy within the skeleton may be detrimental to bone and manifest as, among other clinical abnormalities, reduced mass, enhanced fracture risk, and delayed fracture healing. More investigations are required to elucidate the various mechanisms by which diabetic microvascular dysfunction impacts the skeleton.

Advances and challenges in intravital imaging of craniofacial and dental progenitor cells

Craniofacial and appendicular bone homeostasis is dynamically regulated by a balance between bone formation and resorption by osteoblasts and osteoclasts, respectively. Despite the developments in multiple imaging techniques in bone biology, there are still technical challenges and limitations in the investigation of spatial/anatomical location of rare stem/progenitor cells and their molecular regulation in tooth and craniofacial bones of living animals. Recent advances in live animal imaging techniques for the craniofacial and dental apparatus can provide new insights in real time into bone stem/progenitor cell dynamics and function in vivo. Here, we review the current inventions and applications of the noninvasive intravital imaging technique and its practical uses and limitations in the analysis of stem/progenitor cells in craniofacial and dental apparatus in vivo. Furthermore, we also explore the potential applications of intravital microscopy in the dental field.

Quantitative analysis of sympathetic and nociceptive innervation across bone marrow regions in mice

Bone marrow (BM) innervation regulates the mobilization of hematopoietic stem and progenitor cells (HSPCs) from BM and stress hematopoiesis by either acting directly on HSPCs or by altering the niche function of mesenchymal and endothelial cells. However, the spatial distribution of BM innervation across bone regions is yet to be fully elucidated. Thus, we aimed to characterize the distribution of sympathetic and nociceptive nerves in each bone and BM region, using three-dimensional quantitative microscopy. We discovered that sympathetic and nociceptive nerves were the major fibers throughout the BM. Compared to other femoral regions, central parts of the femoral BM were more densely innervated by both sympathetic and nociceptive nerves. Each region of the sternum was similarly innervated by sympathetic and nociceptive nerves. Further, the majority of sympathetic and nociceptive nerves in the BM ran parallel with arteries and arterioles, whereas the degree varied according to the bone types or BM regions. In conclusion, this study provides spatial, topological, and functional information on BM innervation in a quantitative manner and demonstrates that sympathetic and nociceptive nerves are two major components in BM innervation, mostly associated with arteries and arterioles.

Inhibition of canonical Wnt signaling promotes ex vivo maintenance and proliferation of hematopoietic stem cells in zebrafish

The maintenance and proliferation of hematopoietic stem cells (HSCs) are tightly regulated by their niches in the bone marrow. The analysis of niche cells or stromal cell lines that can support HSCs has facilitated the finding of novel supporting factors for HSCs. Despite large efforts in the murine bone marrow, however, HSC expansion is still difficult ex vivo, highlighting the need for new approaches to elucidate the molecular elements that regulate HSCs. The zebrafish provides a unique model to study hematopoietic niches as HSCs are maintained in the kidney, allowing for a parallel view of hematopoietic niches over evolution. Here, using a stromal cell line from the zebrafish kidney, zebrafish kidney stromal (ZKS), we uncover that an inhibitor of canonical Wnt signaling, IWR-1-endo, is a potent regulator of HSCs. Co-culture assays revealed that ZKS cells were in part supportive of maintenance, but not expansion, of gata2a:GFP+runx1:mCherry+ (gata2a+runx1+) HSCs. Transcriptome analysis revealed that, compared to candidate niche cells in the kidney, ZKS cells weakly expressed HSC maintenance factor genes, thpo and cxcl12, but highly expressed canonical Wnt ligand genes, wnt1, 7bb, and 9a. Thpo supplementation in ZKS culture slightly increased, but inhibition of canonical Wnt signaling by IWR-1-endo treatment largely increased the number of gata2a+runx1+ cells (> 2-fold). Moreover, we found that gata2a+runx1+ cells can be maintained by supplementing both IWR-1-endo and Thpo without stromal cells. Collectively, our data provide evidence that IWR-1-endo can be used as a novel supporting factor for HSCs.

Tracking Strain-Specific Morphogenesis and Angiogenesis of Murine Calvaria with Large-Scale Optoacoustic and Ultrasound Microscopy

Skull bone development is a dynamic and well-coordinated process playing a key role in maturation and maintenance of the bone marrow (BM), fracture healing, and progression of diseases such as osteoarthritis or osteoporosis. At present, dynamic transformation of the growing bone (osteogenesis) as well as its vascularization (angiogenesis) remain largely unexplored due to the lack of suitable in vivo imaging techniques capable of noninvasive visualization of the whole developing calvaria at capillary-level resolution. We present a longitudinal study on skull bone development using ultrasound-aided large-scale optoacoustic microscopy (U-LSOM). Skull bone morphogenesis and microvascular growth patterns were monitored in three common mouse strains (C57BL/6J, CD-1, and Athymic Nude-Foxn1nu) at the whole-calvaria scale over a 3-month period. Strain-specific differences in skull development were revealed by quantitative analysis of bone and vessel parameters, indicating the coupling between angiogenesis and osteogenesis during skull bone growth in a minimally invasive and label-free manner. The method further enabled identifying BM-specific sinusoidal vessels, and superficial skull vessels penetrating into BM compartments. Our approach furnishes a new high-throughput longitudinal in vivo imaging platform to study morphological and vascular skull alterations in health and disease, shedding light on the critical links between blood vessel formation, skull growth, and regeneration. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Fluorescence Microscopy-An Outline of Hardware, Biological Handling, and Fluorophore Considerations

Fluorescence microscopy has become a critical tool for researchers to understand biological processes at the cellular level. Micrographs from fixed and live-cell imaging procedures feature in a plethora of scientific articles for the field of cell biology, but the complexities of fluorescence microscopy as an imaging tool can sometimes be overlooked or misunderstood. This review seeks to cover the three fundamental considerations when designing fluorescence microscopy experiments: (1) hardware availability; (2) amenability of biological models to fluorescence microscopy; and (3) suitability of imaging agents for intended applications. This review will help equip the reader to make judicious decisions when designing fluorescence microscopy experiments that deliver high-resolution and informative images for cell biology.

Stressed Out About Plasmodium falciparum Gametocytogenesis

Blocking malaria transmission is critical to malaria control programs but remains a major challenge especially in endemic regions with high levels of asymptomatic infections. New strategies targeting the transmissible sexual stages of the parasite, called gametocytes, are needed. This review focuses on P. falciparum gametocytogenesis in vivo and in vitro. Highlighting advances made elucidating genes required for gametocyte production and identifying key questions that remain unanswered such as the factors and regulatory mechanisms that contribute to gametocyte induction, and the mechanism of sequestration. Tools available to begin to address these issues are also described to facilitate advances in our understanding of this important stage of the life cycle.