Biology subjects

Knapp, E.

Publications and source records attributed to Knapp, E..

5 recordsLinked to original sources

bioRxiv2020

Improved prediction of femoral fracture toughness in mice by combining standard medical imaging with Raman spectroscopy

Bone fragility and fracture risk are assessed by measuring the areal bone mineral density (aBMD) using dual-energy X-ray absorptiometry (DXA). While aBMD correlates with bone strength, it is a poor predictor of fragility fracture risk. Alternatively, fracture toughness assesses the bones resistance to crack propagation and fracture, making it a suitable bone quality metric. Here, we explored how femoral midshaft measurements from DXA, micro-computed tomography (CT), and Raman spectroscopy could predict fracture toughness. We hypothesized that ovariectomy (OVX) decreases aBMD and fracture toughness compared to controls and we can optimize a multivariate assessment of bone quality by combining results from X-ray and Raman spectroscopy. Female mice underwent an OVX (n=5) or sham (n=5) surgery at 3 months of age. Femurs were excised 3 months after ovariectomy and assessed with Raman spectroscopy, CT, and DXA. Subsequently, a notch was created on the anterior side of the mid-diaphysis of the femurs. Three-point bending induced a controlled fracture that initiated at the notch. The OVX mice had a significantly lower aBMD, cortical thickness, and fracture toughness when compared to controls (p<0.05). A leave one out cross-validated (LOOCV) partial least squares regression (PLSR) model based only on the combination of aBMD and cortical thickness showed no significant predictive correlations with fracture toughness, whereas a PLSR model based on principal components derived from the full Raman spectra yielded significant prediction (r2=0.71, p<0.05). Further, the PLSR model was improved by incorporating aBMD, cortical thickness, and principal components from Raman spectra (r2=0.92, p<0.001). This exploratory study demonstrates combining X-ray with Raman spectroscopy leads to a more accurate assessment of bone fracture toughness and could be a useful diagnostic tool for the assessment of fragility fracture risk.

bioengineering↗

bioRxiv2020

Tendon Cell Deletion of IKKβ/NF-κB Drives Functionally Deficient Tendon Healing and Altered Cell Survival Signaling In Vivo

Acute tendon injuries are characterized by excessive matrix deposition that impedes regeneration and disrupts functional improvements. Inflammation is postulated to drive pathologic scar tissue formation, with nuclear factor kappa B (NF-{kappa}B) signaling emerging as a candidate pathway in this process. However, characterization of the spatial and temporal activation of canonical NF-{kappa}B signaling during tendon healing in vivo, including identification of the cell populations activating NF-{kappa}B, is currently unexplored. Therefore, we aimed to determine which cell populations activate canonical NF-{kappa}B signaling following flexor tendon repair with the goal of delineating cell-specific functions of NF-{kappa}B signaling during scar mediated tendon healing. Immunofluorescence revealed that both tendon cells and myofibroblasts exhibit prolonged activation of canonical NF-{kappa}B signaling into the remodeling phase of healing. Using cre-mediated knockout of the canonical NF-{kappa}B kinase (IKK{beta}), we discovered that suppression of canonical NF-{kappa}B signaling in Scleraxis-lineage cells increased myofibroblast content and scar tissue formation. Interestingly, Scleraxis-lineage specific knockout of IKK{beta} increased the incidence of apoptosis, suggesting that canonical NF-{kappa}B signaling may be mediating cell survival during tendon healing. These findings suggest indispensable roles for canonical NF-{kappa}B signaling during flexor tendon healing. One Sentence SummaryScleraxis-lineage specific knockdown of persistent canonical IKK{beta}/NF-{kappa}B drives scar formation and apoptotic signaling during flexor tendon healing.

molecular biology↗

bioRxiv2019

Inhibition of the mitochondrial permeability transition exerts sex-specific stimulatory effect on fracture repair

Bone fracture is accompanied by mechanical stresses and inflammation - conditions that impair mitochondria via the phenomenon of permeability transition. This phenomenon occurs due to opening of the mitochondrial permeability transition pore (MPTP) promoted by cyclophilin D (CypD). MPTP opening exacerbates inflammation and cell death and, thus can disrupt fracture repair. Here we tested a hypothesis that protecting mitochondria from MPTP opening via inhibition of CypD improves fracture repair. Our data indicate that osteoblast activity, bone formation, and biomechanical properties of repaired bones were significantly increased in CypD knock-out mice when compared to controls during fracture repair. These effects were observed in male but not female mice, thus showing sexual dimorphism. Pharmacological inhibition of CypD with NIM811 in male mice also stimulated fracture repair. In addition, CypD knock-out or pharmacological inhibition produced pro-osteogenic effect in isolated bone marrow osteoprogenitors. This in vitro effect was associated with higher mitochondrial respiration and increased {beta}-catenin activity regulated by mitochondria-dependent acetylation. Our findings implicate a sex-specific role of MPTP in bone fracture and suggest CypD inhibition as a modality to promote fracture repair.

biochemistry↗

bioRxiv2019

Cell non-autonomous functions of S100a4 drive fibrotic tendon healing

Identification of pro-regenerative approaches to improve tendon healing is of critical importance given the diminished quality of life and physical function that accompanies the typical fibrotic response to tendon injury. S100a4 modulates fibrosis through tissue-type dependent mechanisms, and the role of S100a4 in fibrotic, scar-mediated tendon healing has not been established. In the present study we tested the hypothesis that inhibition of S100a4 improves tendon function following acute injury and surgical repair. We demonstrate cell non-autonomous functions of S100a4 as S100a4 haploinsufficiency promotes regenerative tendon healing, including decreased scar formation and improved mechanical properties. Moreover, inhibition of S100a4 via antagonism of its putative receptor, the Receptor for Advanced Glycation Endproducts (RAGE), also decreases scar formation. Mechanistically, knock-down of S100a4 decreases myofibroblast and macrophage content at the site of injury, with both cell populations being key drivers of fibrotic progression. In contrast, S100a4+ cell depletion displays time-dependent effects on scar formation, and consistent impairments in restoration of mechanical properties, indicating a critical role for these cells in re-establishing tendon strength after injury. Finally, we demonstrate, that S100a4-lineage cells become -SMA+ myofibroblasts, via loss of S100a4 expression. Using a combination of genetic mouse models, small molecule inhibitors and in vitro studies we have defined S100a4 as a novel, promising therapeutic candidate to improve tendon function after acute injury.

cell biology↗

bioRxiv2018

Insulin Receptor Deletion in S100a4-lineage cells accelerates age-related bone loss

Type I and Type II Diabetes dramatically impair skeletal health. Altered Insulin Receptor (IR) signaling is a common feature of both diseases, and insulin has potent bone anabolic functions. Several previous studies have demonstrated that loss of IR in bone cells results in disrupted bone homeostasis during early post-natal growth. Here we have deleted IR in S100a4-lineage cells (IRcKOS100a4) and assessed the effects on bone homeostasis at both young (15 weeks) and older adult (48 weeks) mice. S100a4-cre has previously been shown to target the perichondrium during bone development, and here we show that S100a4 is expressed by adult trabecular and cortical bone cells, and that S100a4-Cre effectively targets adult bone, resulting in efficient deletion of IR. Deletion of IR in S100a4-lineage cells does effect initial bone acquisition or homeostasis with no changes in cortical, trabecular or mechanical properties at 15-weeks of age, relative to wild type (WT) littermates. However, by 48-weeks of age, IRcKOS100a4 mice display substantial declines in trabecular bone volume, bone volume fraction and torsional rigidity, relative to age-matched WT controls. This work establishes the utility of using S100a4-cre to target bone and demonstrates that IR in S100a4-lineage cells is required for maintenance of bone homeostasis in adult mice.

cell biology↗