Display omitted
Partially mineralized fibrous tissue situated between tendon and bone is believed to be tougher than either tendon or bone, possibly serving as a compliant, energy absorptive, ...protective barrier between the two. This tissue does not reform following surgical repair (e.g., rotator cuff tendon-to-bone re-attachment) and might be a factor in the poor outcomes following such surgeries. Towards our long-term goal of tissue engineered solutions to functional tendon-to-bone re-attachment, we tested the hypotheses that partially mineralized fibrous matrices can derive toughness from mobility of mineral along their fibers, and that in such cases toughness is maximized at levels of mineralization sufficiently low to allow substantial mobility. Nanofibrous electrospun poly(lactic–co-glycolic acid) (PLGA) scaffolds mineralized for prescribed times were fabricated as model systems to test these hypotheses. Tensile tests performed at varying angles relative to the dominant fiber direction confirmed that mineral cross-linked PLGA nanofibers without adhering to them. Peel tests revealed that fracture toughness increased with mineralization time up to a peak value, then subsequently decreased with increasing mineralization time back to the baseline toughness of unmineralized scaffolds. These experimental results were predicted by a theoretical model combining mineral growth kinetics with fracture energetics, suggesting that toughness increased with mineralization time until mineral mobility was attenuated by steric hindrance, then returned to baseline levels following the rigid percolation threshold. Results supported our hypotheses, and motivate further study of the roles of mobile mineral particles in toughening the tendon-to-bone attachment.
Effective surgical repair of interfaces between tendon and bone remains an unmet clinical need, in part due to a lack of understanding of how toughness is achieved in the healthy tissue. Using combined synthesis, experiment, and modeling approaches, the current work supported the hypothesis that toughening of a fibrous scaffold arises from brittle mineral particles that crosslink the fibers, but only if the particles are free to slide relative to the fibers. In the case of the tendon-to-bone interface, this suggests that partially mineralized tissue between tendon and bone, with mobile mineral but relatively low stiffness, may serve as a compliant, energy-absorbing barrier that guards against injury. These results suggest an opportunity for fabrication of tough and strong fibrous scaffolds for tissue engineering applications.
In intimate ecological interactions, the interdependency of species may result in correlated demographic histories. For species of conservation concern, understanding the long-term dynamics of such ...interactions may shed light on the drivers of population decline. Here, we address the demographic history of the monarch butterfly, Danaus plexippus, and its dominant host plant, the common milkweed Asclepias syriaca (A. syriaca), using broad-scale sampling and genomic inference. Because genetic resources for milkweed have lagged behind those for monarchs, we first release a chromosome-level genome assembly and annotation for common milkweed. Next, we show that despite its enormous geographic range across eastern North America, A. syriaca is best characterized as a single, roughly panmictic population. Using approximate Bayesian computation with random forests (ABC-RF), a machine learning method for reconstructing demographic histories, we show that both monarchs and milkweed experienced population expansion during the most recent recession of North American glaciers 10,000–20,000 years ago. Our data also identify concurrent population expansions in both species during the large-scale clearing of eastern forests (∼200 years ago). Finally, we find no evidence that either species experienced a reduction in effective population size over the past 75 years. Thus, the well-documented decline of monarch abundance over the past 40 years is not visible in our genomic dataset, reflecting a possible mismatch of the overwintering census population to effective population size in this species.
•A new, chromosome-level assembly and annotation is provided for common milkweed•Milkweed forms an enormous, panmictic population across its North American range•Monarchs and milkweeds both had two concurrent population expansions in the past•Neither species shows signs of recent declines in effective population size
Boyle et al. find correlated population histories for the monarch butterfly and its common milkweed food plant over the past 25,000 years. Using genomic data and a new, chromosome-level milkweed assembly, they find expansions in both species corresponding to the recession of glaciers and to the more recent clearing of North American forests.
Telomere maintenance is essential for the long-term proliferation of human pluripotent stem cells, while their telomere length set point determines the proliferative capacity of their differentiated ...progeny. The shelterin protein TPP1 is required for telomere stability and elongation, but its role in establishing a telomere length set point remains elusive. Here, we characterize the contribution of the shorter isoform of TPP1 (TPP1S) and the amino acid L104 outside the TEL patch, TPP1's telomerase interaction domain, to telomere length control. We demonstrate that cells deficient for TPP1S (TPP1S knockout KO), as well as the complete TPP1 KO cell lines, undergo telomere shortening. However, TPP1S KO cells are able to stabilize short telomeres, while TPP1 KO cells die. We compare these phenotypes with those of TPP1
mutant cells, which have short and stable telomeres similar to the TPP1S KO. In contrast to TPP1S KO cells, TPP1
cells respond to increased telomerase levels and maintain protected telomeres. However, TPP1
shows altered sensitivity to expression changes of shelterin proteins suggesting the mutation causes a defect in telomere length feedback regulation. Together this highlights TPP1
as the first shelterin mutant engineered at the endogenous locus of human stem cells with an altered telomere length set point.
Mutations in the skeletal muscle ryanodine receptor gene (RYR1) can cause susceptibility to malignant hyperthermia (MH), a potentially lethal genetic condition triggered by volatile anesthetics. MH ...is associated with hypermetabolism, which has directed research interest into oxidative phosphorylation and muscle bioenergetics. The most common cause of MH in the United Kingdom is the c.7300G>A RYR1 variant, which is present in ∼16% of MH families. Our study focuses on the MH susceptible G2435R-RYR1 knock-in mouse model, which is the murine equivalent of the human c.7300G>A genotype. Using a combination of transcriptomics, protein expression, and functional analysis, we investigated adult muscle fiber bioenergetics in this mouse model. RNA-Seq data showed reduced expression of genes associated with mitochondria and fatty acid oxidation in RYR1 mutants when compared with WT controls. Mitochondrial function was assessed by measuring oxygen consumption rates in permeabilized muscle fibers. Comparisons between WT and homozygous G2435R-RYR1 mitochondria showed a significant increase in complex I–facilitated oxidative phosphorylation in mutant muscle. Furthermore, we observed a gene-dose-specific increase in reactive oxygen species production in G2435R-RYR1 muscle fibers. Collectively, these findings provide evidence of metabolic defects in G2435R-RYR1 knock-in mouse muscle under basal conditions. Differences in metabolic profile could be the result of differential gene expression in metabolic pathways, in conjunction with mitochondrial damage accumulated from chronic exposure to increased oxidative stress.
Ion channels represent a large and growing family of target proteins regulated by gasotransmitters such as nitric oxide, carbon monoxide and, as described more recently, hydrogen sulfide. Indeed, ...many of the biological actions of these gases can be accounted for by their ability to modulate ion channel activity. Here, we report recent evidence that H2S is a modulator of low voltage‐activated T‐type Ca2+ channels, and discriminates between the different subtypes of T‐type Ca2+ channel in that it selectively modulates Cav3.2, whilst Cav3.1 and Cav3.3 are unaffected. At high concentrations, H2S augments Cav3.2 currents, an observation which has led to the suggestion that H2S exerts its pro‐nociceptive effects via this channel, since Cav3.2 plays a central role in sensory nerve excitability. However, at more physiological concentrations, H2S is seen to inhibit Cav3.2. This inhibitory action requires the presence of the redox‐sensitive, extracellular region of the channel which is responsible for tonic metal ion binding and which particularly distinguishes this channel isoform from Cav3.1 and 3.3. Further studies indicate that H2S may act in a novel manner to alter channel activity by potentiating the zinc sensitivity/affinity of this binding site. This review discusses the different reports of H2S modulation of T‐type Ca2+ channels, and how such varying effects may impact on nociception given the role of this channel in sensory activity. This subject remains controversial, and future studies are required before the impact of T‐type Ca2+ channel modulation by H2S might be exploited as a novel approach to pain management.
Schematic diagram showing the linear structure of the transmembrane domain I of the Cav3.2 T‐type Ca2+ channel α subunit. In the ‘tonic’ channel state (middle), zinc partially occupies a binding site formed by interacting residues (indicated by white dots) present in IS1–IS2 and IS3–IS4 linkers, including H191. Under these conditions, zinc causes tonic inhibition of evoked currents (as illustrated by example current shown below). Chelation of zinc by TPEN (left) augments current amplitudes via relief of tonic zinc inhibition. In the presence of H2S, zinc affinity appears augmented, leading to increased zinc binding and a reduction in current amplitude.
Magnetic and geochemical core data spanning the last 17,000
years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective ...precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3
cal
kyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5
cal
kyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5
cal
kyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2
cal
kyr BP. Precipitation declined after 6.8
cal
kyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~
4.2
cal
kyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.
► 17,000
years of climate change at the source of the Blue Nile, Lake Tana, Ethiopia. ► Southerly suppression of the ITCZ and monsoon front at the time of the Younger Dryas. ► Drought at 8.4
cal
kyr BP preceded and was more significant than the “8.2 event”. ► No abrupt end to the so-called African Humid Period. ► Drought at Nile source a factor in the demise of the Egyptian Old Kingdom.
Lung cancer remains the most common cause of both cancer mortality and brain metastases (BM). The purpose of this study was to assess the effect of gene alterations and tyrosine kinase inhibition ...(TKI) on median survival (MS) and cause of death (CoD) in patients with BM from lung adenocarcinoma (L-adeno).
A multi-institutional retrospective database of patients with L-adeno and newly diagnosed BM between 2006 and 2014 was created. Demographics, gene alterations, treatment, MS, and CoD were analyzed. The treatment patterns and outcomes were compared with those in prior trials.
Of 1521 L-adeno patients, 816 (54%) had known alteration status. The gene alteration rates were 29%, 10%, and 26% for EGFR, ALK, and KRAS, respectively. The time from primary diagnosis to BM for EGFR-/+ was 10/15 months (P=.02) and for ALK-/+ was 10/20 months (P<.01), respectively. The MS for the group overall (n=1521) was 15 months. The MS from first treatment for BM for EGFR and ALK-, EGFR+, ALK+ were 14, 23 (P<.01), and 45 (P<.0001) months, respectively. The MS after BM for EGFR+ patients who did/did not receive TKI before BM was 17/30 months (P<.01), respectively, but the risk of death was not statistically different between TKI-naïve patients who did/did not receive TKI after the diagnosis of BM (EGFR/ALK hazard ratios: 1.06 P=.84/1.60 P=.45, respectively). The CoD was nonneurologic in 82% of patients with known CoD.
EGFR and ALK gene alterations are associated with delayed onset of BM and longer MS relative to patients without these alterations. The CoD was overwhelmingly nonneurologic in patients with known CoD.
Tumor cell survival and proliferation is attributable in part to suppression of apoptotic pathways, yet the mechanisms by which cancer cells resist apoptosis are not fully understood. Many cancer ...cells constitutively express heme oxygenase-1 (HO-1), which catabolizes heme to generate biliverdin, Fe2+, and carbon monoxide (CO). These breakdown products may play a role in the ability of cancer cells to suppress apoptotic signals. K+ channels also play a crucial role in apoptosis, permitting K+ efflux which is required to initiate caspase activation. Here, we demonstrate that HO-1 is constitutively expressed in human medulloblastoma tissue, and can be induced in the medulloblastoma cell line DAOY either chemically or by hypoxia. Induction of HO-1 markedly increases the resistance of DAOY cells to oxidant-induced apoptosis. This effect was mimicked by exogenous application of the heme degradation product CO. Furthermore we demonstrate the presence of the pro-apoptotic K+ channel, Kv2.1, in both human medulloblastoma tissue and DAOY cells. CO inhibited the voltage-gated K+ currents in DAOY cells, and largely reversed the oxidant-induced increase in K+ channel activity. p38 MAPK inhibition prevented the oxidant-induced increase of K+ channel activity in DAOY cells, and enhanced their resistance to apoptosis. Our findings suggest that CO-mediated inhibition of K+ channels represents an important mechanism by which HO-1 can increase the resistance to apoptosis of medulloblastoma cells, and support the idea that HO-1 inhibition may enhance the effectiveness of current chemo- and radiotherapies.
Background: Heme oxygenase-1 (HO-1) is constitutively expressed in many cancers which are highly resistant to apoptosis.
Results: CO, a product of HO-1, inhibits K+ channels in the medulloblastoma cell line DAOY and protects against apoptosis.
Conclusion: HO-1 increases resistance to apoptosis in cancer cells via CO generation.
Significance: targeting HO-1 expression may increase the effectiveness of cancer therapies.
Here we develop a novel method for quantifying sediment components, e.g. biogenic silica, organic or mineral matter, from near infrared (NIR) spectra based on fitting by multiple regression of ...measured spectra for end-member materials. We show that with suitable end-members our new open-source multiple regression routine gives excellent simultaneous quantification of the major components of a sediment, the concentrations comparing well with independent methods of quantification. Widely used partial least squares regression approaches rely on large environmental training data sets; our method produces comparable results, but with the advantages of negating the need for a training dataset and with greater simplicity and theoretical robustness. We demonstrate that component NIR spectra are additive, a prerequisite for use of multiple regression to un-mix the compound spectra, and show that a number of environmental materials make suitable end-members for this analysis. We show that spectral mixing is not conservative with respect to mass proportion, but rather to the relative chromatic intensity of contributing sediment components. Concentrations can be calculated using the measured spectra by correction using a chromatic intensity factor, the value of which can be measured independently. We have applied our approach to a postglacial sediment sequence from Loch Grannoch (SW Scotland) and reveal a down-core pattern of varying dominance by biogenic silica, organic and mineral content from the late glacial to present. With isolation and measurement of appropriate end-members this multivariate regression approach to interrogating NIR spectra has utility across a wide range of sedimentary environments and potentially for other spectral analytical methods.
PDF
