Biology subjects

White, K. E.

Publications and source records attributed to White, K. E..

5 recordsLinked to original sources

bioRxiv2025

Klotho deficiency promotes skeletal muscle weakness and is associated with impaired motor unit connectivity

Muscle wasting and weakness are important clinical problems that impact quality of life and health span by restricting mobility and independence, and by increasing the risk for physical disability. The molecular basis for this has not been fully determined. Klotho expression is downregulated in conditions associated with muscle wasting, including aging, chronic kidney disease, and myopathy. The objective of this study was to investigate a mechanistic role for Klotho in regulating muscle wasting and weakness. Body weight, lean mass, muscle mass, and myofiber caliber were reduced in Klotho-deficient mice. In the tibialis anterior muscle of Klotho null mice, type IIa myofibers were resistant to changes in size, and muscle composition differed with a higher concentration of type IIb fibers to the detriment of type IIx fibers. Glycolytic enzymatic activity also increased. The composition of the soleus muscle was unaffected and myofiber caliber was reduced comparably in type I, IIa, and IIx fibers. Muscle contractile function declined in Klotho-deficient mice, as evidenced by reduced absolute twitch and torque, and decreased rates of contraction and relaxation. RNA-sequencing analysis identified increased transcriptional expression of synaptic and fetal sarcomeric genes, which prompted us to test effects on muscle innervation. Klotho-deficiency induced morphological remodeling of the neuromuscular junction, myofiber denervation, and a functional loss of motor units. Loss of motor units correlated with absolute torque. Collectively, our findings have uncovered a novel mechanism through which Klotho-deficiency leads to alterations to the muscle synapse affecting motor unit connectivity that likely influences muscle wasting and weakness. Key points summaryO_LIMaintaining skeletal muscle mass and function is critical to preserve physical capacity and independence. Clinical observations implicate longevity factor Klotho as a key regulator of muscle mass and weakness. Low Klotho levels are reported to correlate with muscle weakness and frailty. C_LIO_LIUsing Klotho null mice, our study shows that Klotho-deficiency promotes skeletal muscle weakness and impaired motor unit connectivity. C_LIO_LIRNA-sequencing analysis identified altered expression of sarcomeric and synaptic genes suggesting changes to the muscle synapse in Klotho-deficient mice. C_LIO_LIHistopathological analyses revealed Klotho-deficiency is associated with reduced myofiber caliber, altered muscle composition, and increased prevalence of NCAM+ denervated fibers. Imaging of the NMJ further showed morphological changes and reduced area of synaptic contact. C_LIO_LIOverall, our findings show that Klotho regulates the structure and function of the NMJ affecting motor unit connectivity which may have an important role in the pathogenesis of muscle wasting and weakness. C_LI

physiology↗

bioRxiv2022

Single Cell Cortical Bone Transcriptomics Defines Novel Osteolineage Gene Sets Altered in Chronic Kidney Disease

Due to a lack of spatial-temporal resolution at the single cell level, the etiologies of the bone dysfunction caused by diseases such as normal aging, osteoporosis, and the metabolic bone disease associated with chronic kidney disease (CKD) remain largely unknown. To this end, flow cytometry and scRNAseq were performed on long bone cells from Sost-cre/Ai9+ mice, and pure osteolineage transcriptomes were identified, including novel osteocyte-specific gene sets. Clustering analysis isolated osteoblast precursors that expressed Tnc, Mmp13, and Spp1, and a mature osteoblast population defined by Smpd3, Col1a1, and Col11a1. Osteocytes were demarcated by Cd109, Ptprz1, Ramp1, Bambi, Adamts14, Spns2, Bmp2, WasI, and Phex. We validated our in vivo scRNAseq using integrative in vitro promoter occupancy via ATACseq coupled with transcriptomic analyses of a conditional, temporally differentiated MSC cell line. Further, trajectory analyses predicted osteoblast-to-osteocyte transitions via defined pathways associated with a distinct metabolic shift as determined by single-cell flux estimation analysis (scFEA). Using the adenine mouse model of CKD, at a time point prior to major skeletal alterations, we found that gene expression within all stages of the osteolineage was disturbed. In sum, distinct populations of osteoblasts/osteocytes were defined at the single cell level. Using this roadmap of gene assembly, we demonstrated unrealized molecular defects across multiple bone cell populations in a mouse model of CKD, and our collective results suggest a potentially earlier and more broad bone pathology in this disease than previously recognized.

cell biology↗

bioRxiv2022

Gabapentin Disrupts Binding of Perlecan to the α2δ1 Voltage Sensitive Calcium Channel Subunit and Impairs Skeletal Mechanosensation

Our understanding of how osteocytes, the principal mechanosensors within bone, sense and perceive force remains unclear. Previous work identified "tethering elements" (TEs) spanning the pericellular space of osteocytes and transmitting mechanical information into biochemical signals. While we identified the heparan sulfate proteoglycan perlecan (PLN) as a component of these TEs, PLN must attach to the cell surface to induce biochemical responses. As voltage-sensitive calcium channels (VSCCs) are critical for bone mechanotransduction, we hypothesized that PLN binds the extracellular 2{delta}1 subunit of VSCCs to couple the bone matrix to the osteocyte membrane. Here, we showed co-localization of PLN and 2{delta}1 along osteocyte dendritic processes. Additionally, we quantified the molecular interactions between 2{delta}1 and PLN domains and demonstrated for the first time that 2{delta}1 strongly associates with PLN via its domain III. Furthermore, 2{delta}1 is the binding site for the commonly used pain drug, gabapentin (GBP), which is associated with adverse skeletal effects when used chronically. We found that GBP disrupts PLN::2{delta}1 binding in vitro, and GBP treatment in vivo results in impaired bone mechanosensation. Our work identified a novel mechanosensory complex within osteocytes composed of PLN and 2{delta}1, necessary for bone force transmission and sensitive to the drug GBP. This work provides insights into the mechanisms underlying mechanotransduction and will inform future studies to understand the mechanisms responsible for the negative effects of GBP on bone.

molecular biology↗

bioRxiv2020

Generation of two Multipotent Mesenchymal Progenitor Cell Lines Capable of Osteogenic, Mature Osteocyte, Adipogenic, and Chondrogenic Differentiation

Differentiation of multi-potent mesenchymal progenitor cells give rise to several tissue types including bone, cartilage, and adipose. In addition to the complication arising from the numerous spatial, temporal, and hormonal factors that regulate lineage allocation, targeting of these cells in vivo is challenging, making mesenchymal progenitor cell lines valuable tools to study both tissue development and the differentiated cell types. Mesenchymal stem cells (MSCs) can be isolated from humans and animals; however, obtaining homogenous, responsive cells in a reproducible fashion can be problematic. As such, we have developed two novel mesenchymal progenitor cell (MPC) lines, MPC1 and MPC2, which were generated from the bone marrow of male C57BL/6 mice. These cells were immortalized using the temperature sensitive large T-antigen, allowing for thermal control of proliferation and differentiation. Both MPC1 and MPC2 cell lines are capable of osteogenic, adipogenic, and chondrogenic differentiation. Under osteogenic conditions both cell lines formed discrete mineralized nodules, staining for alizarin red and alkaline phosphatase, while expressing high levels of osteogenic genes including Sost, Fgf23, and Dmp1. Sost and Dmp1 mRNA levels were drastically reduced with parathyroid hormone, thus recapitulating in vivo responses. MPC cells secreted both the intact (iFGF23) and C-terminal (cFGF23) forms of endocrine hormone FGF23, which was upregulated in the presence of 1,25 dihydroxy vitamin D (1,25D). In addition to osteogenic differentiation, both cell lines also rapidly entered the adipogenic lineage, expressing several adipose markers after only 4 days in adipogenic media. MPC cells were also capable of chondrogenic differentiation, displaying increased expression of common cartilage genes including aggrecan, sox9, and cartilage oligomeric matrix protein. With the ability to differentiate into multiple mesenchymal lineages and mimic in vivo responses of key regulatory genes/proteins, MPC cells are a valuable model to study factors that regulate mesenchymal lineage allocation as well as the mechanisms that dictate transcription, protein modification, and secretion of these factors.

cell biology↗

bioRxiv2017

A lineage-related reciprocal inhibition circuitry for sensory-motor action selection

The insect central complex and vertebrate basal ganglia are forebrain centres involved in selection and maintenance of behavioural actions. However, little is known about the formation of the underlying circuits, or how they integrate sensory information for motor actions. Here, we show that paired embryonic neuroblasts generate central complex ring neurons that mediate sensory-motor transformation and action selection in Drosophila. Lineage analysis resolves four ring neuron subtypes, R1-R4, that form GABAergic inhibition circuitry among inhibitory sister cells. Genetic manipulations, together with functional imaging, demonstrate subtype-specific R neurons mediate the selection and maintenance of behavioural activity. A computational model substantiates genetic and behavioural observations suggesting that R neuron circuitry functions as salience detector using competitive inhibition to amplify, maintain or switch between activity states. The resultant gating mechanism translates facilitation, inhibition and disinhibition of behavioural activity as R neuron functions into selection of motor actions and their organisation into action sequences.

neuroscience↗