Biology subjects

Schnabel, L. V.

Publications and source records attributed to Schnabel, L. V..

4 recordsLinked to original sources

bioRxiv2023

TGF-β downregulates antigen processing and presentation genes and MHC I surface expression through a Smad3-dependent mechanism.

Regulation of MHC I surface expression by TGF-{beta} is important for controlling cell-mediated immune responses, but how TGF-{beta} downregulates MHC I is unknown. We investigated this mechanism using flow cytometry and RNA-sequencing to identify the major TGF-{beta} signaling pathway and target genes involved. All three isoforms of TGF-{beta} were found to have similar abilities to downregulate constitutive MHC I surface expression. Inhibiting the type I TGF-{beta} receptor, ALK5, as well the canonical TGF-{beta} signaling molecule Smad3, prevented TGF-{beta} from downregulating MHC I surface expression. RNA-sequencing from horse and human mesenchymal stem cells revealed that multiple genes associated with antigen processing and presentation were downregulated in TGF-{beta}-treated cells with B2M and ERAP1 being downregulated in both species. While downregulation of MHC I surface expression a slow process that continued past 24 hours after TGF-{beta} treatment, downregulation of gene expression of ERAP1 occurred within 12 hours after treatment. B2M expression was not consistently downregulated until after 24 hours and TAP2 expression was inconsistent over a 72-hour period, although it was significantly downregulated at 12 hours after TGF-{beta} treatment. This data supports that TGF-{beta} downregulates antigen processing and presentation genes resulting in decreased surface expression of MHC I through a Smad3-dependent mechanism.

immunology↗

bioRxiv2023

Neo-natal castration leads to subtle differences in porcine anterior cruciate ligament morphology and function in adolescence

Female adolescent athletes are at a higher risk of tearing their anterior cruciate ligament (ACL) than male counterparts. While most work related to hormones has focused on the effects of estrogen to understand the increased risk of ACL injury, there are other understudied factors, including testosterone. The purpose of this study was to determine how surgical castration in the male porcine model influences ACL size and function across skeletal growth. Thirty-six male Yorkshire crossbreed pigs were raised to 3 (juvenile), 4.5 (early adolescent), and 6 months (adolescent) of age. Animals were either castrated (barrows) within 1-2 weeks after birth or were left intact (boars). Post-euthanasia, joint and ACL size were assessed via MRI, and biomechanics were assessed via a robotic testing system. Joint size increased throughout age, yet barrows had smaller joints than boars (p<0.001 for all measures). ACL cross-sectional area (CSA), length, volume, and stiffness increased with age (p<0.0001), as did ACL anteromedial (AM) bundle percent contribution to resisting loads (p=0.012). Boar ACL, AM bundle, and PL bundle volumes were 19% (p=0.002), 25% (p=0.003), and 15% (p=0.04) larger than barrows across ages. However, CSA, stiffness, and bundle contribution were similar between boars and barrows (p>0.05). The barrows had smaller temporal increases in AM bundle percent function than boars, but these data were highly variable. Thus, early and sustained loss in testosterone leads to subtle differences in ACL morphology, but may not influence measures associated with increased injury risk, such as CSA or bundle forces in response to applied loads.

bioengineering↗

bioRxiv2022

Degenerative changes are associated with severity of anterior cruciate ligament injury within the skeletally immature joint

Anterior cruciate ligament (ACL) injuries are a major problem in the pediatric and adolescent populations. Some of these injuries extend only partially through the tissue cross-section; yet, there is limited data to inform clinical treatment of such partial tears. In particular, it is unknown how injury severity impacts long-term degenerative changes in the joint. Here, we leverage a skeletally immature preclinical porcine model to evaluate joint biomechanics and degeneration after partial (isolated anteromedial (AM) or posterolateral (PL) bundle) or complete ACL injury. Six months after injury, joint laxity increases were minimal after PL bundle injury, minor after AM bundle injury, and major after ACL injury. Joint degeneration (evaluated in the cartilage and meniscus) was minimal after PL bundle injury, moderate after AM bundle injury, and substantial after ACL injury. With subjects grouped by clinical Lachman grade (indicating the extent of joint destabilization), degeneration was associated with increasing grade, irrespective of injury type. These findings point to the importance of considering joint laxity as a factor when treating young patients, particularly those with partial ACL injuries.

bioengineering↗

bioRxiv2020

The combination of mitogenic stimulation and cell cycle arrest induces senescence in equine and human cartilage explants

ObjectiveCellular senescence is a phenotypic state characterized by stable cell-cycle arrest, enhanced lysosomal activity, and the secretion of inflammatory molecules and matrix degrading enzymes. Senescence has been implicated in osteoarthritis (OA) pathophysiology; however, the mechanisms that drive senescence induction in cartilage and other joint tissues are unknown. While numerous physiological signals are capable of initiating the senescence phenotype, one emerging theme is that growth-arrested cells convert to senescence in response to sustained mitogenic stimulation. The goal of this study was to develop an in vitro articular cartilage explant model to investigate the mechanisms of senescence induction. DesignThis study utilized healthy articular cartilage derived from cadaveric equine stifles and human ankles. Explants were irradiated or treated with palbociclib to initiate cell cycle arrest, and mitogenic stimulation was provided by serum-containing medium (horse) and the inclusion of growth factors (human). The primary readout of senescence was a quantitative flow cytometry assay to detect senescence-associated {beta} galactosidase activity (SA-{beta}-gal). ResultsIrradiation of equine explants caused 25.39% of cells to express high levels of SA-{beta}-gal, as compared to 3.82% in control explants (p=0.0031). For human cartilage, explants that received both mitogenic stimulation and cell cycle arrest showed increased rates of senescence induction as compared to baseline control (7.16% vs. 2.34% SA-{beta}-gal high, p=0.0007). ConclusionsTreatment of cartilage explants with mitogenic stimuli in the context of cell-cycle arrest reliably induces high levels of SA-{beta} gal activity, which provides a physiologically relevant model system to investigate the mechanisms of senescence induction.

cell biology↗