Biology subjects

Divieti Pajevic, P.

Publications and source records attributed to Divieti Pajevic, P..

2 recordsLinked to original sources

bioRxiv2026

An Ex Vivo Muscle Physiology Method for Robust Measurement of Supraspinatus Muscle Function in Mouse Models

The supraspinatus is the most frequently injured rotator cuff muscle, but its anatomical characteristics such as larger size, complex fiber architecture, and a single exposed tendon have limited the development of reproducible ex vivo contractility assays. In this study, we establish a robust method for ex vivo assessment of murine supraspinatus contractile function and characterize its physiological properties across age and injury conditions. We additionally adapt a barium chloride (BaCl2)-induced injury protocol for the supraspinatus, an approach not previously described, to evaluate how acute myofiber degeneration affects muscle performance. Male C57BL/6 mice (4 months) underwent 1.2% BaCl2 injection directly into the supraspinatus to induce controlled myofiber necrosis, allowing comparison of contractile behavior between injured and uninjured muscles. Using our injury ex vivo physiological testing protocol, we quantified optimal length (L0), twitch kinetics, force-frequency responses, peak tetanic force, and preliminary fatigue-recovery dynamics. Our protocol consistently generated fused tetanic contractions and reproducible force-frequency curves in the supraspinatus. We observed differences in supraspinatus contractility between young and old mice, consistent with well-established age-related changes in hindlimb muscle contractility. In addition, BaCl2 injury produced significant impairments in contractility 48 hours post-injection, demonstrating the sensitivity of this method to acute muscle damage. This study provides a novel and reliable method for evaluating the contractile function of the murine supraspinatus muscle ex vivo, overcoming previous anatomical challenges.

bioengineering↗

bioRxiv2019

Single Cell RNA Sequencing of Calvarial and Long Bone Endocortical Cells

Single cell RNA-seq (scRNA-seq) is emerging as a powerful technology to examine transcriptomes of individual cells. We determined whether scRNA-seq could be used to detect the effect of environmental and pharmacologic perturbations on osteoblasts. We began with a commonly used in vitro system in which freshly isolated neonatal mouse calvarial cells are expanded and induced to produce a mineralized matrix. We used scRNA-seq to compare the relative cell type abundances and the transcriptomes of freshly isolated cells to those that had been cultured for 12 days in vitro. We observed that the percentage of macrophage-like cells increased from 6% in freshly isolated calvarial cells to 34% in cultured cells. We also found that Bglap transcripts were abundant in freshly isolated osteoblasts but nearly undetectable in the cultured calvarial cells. Thus, scRNA-seq revealed significant differences between heterogeneity of cells in vivo and in vitro. We next performed scRNA-seq on freshly recovered long bone endocortical cells from mice that received either vehicle or Sclerostin-neutralizing antibody for 1 week. Bone anabolism-associated transcripts were also not significantly increased in immature and mature osteoblasts recovered from Sclerostin-neutralizing antibody treated mice; this is likely a consequence of being underpowered to detect modest changes in gene expression, since only 7% of the sequenced endocortical cells were osteoblasts, and a limited portion of their transcriptomes were sampled. We conclude that scRNA-seq can detect changes in cell abundance, identity, and gene expression in skeletally derived cells. In order to detect modest changes in osteoblast gene expression at the single cell level in the appendicular skeleton, larger numbers of osteoblasts from endocortical bone are required.

cell biology↗