Lin28a maintains a subset of adult muscle stem cells in an embryonic-like state.

During homeostasis and after injury, adult muscle stem cells (MuSCs) activate to mediate muscle regeneration. However, much remains unclear regarding the heterogeneous capacity of MuSCs for self-renewal and regeneration. Here, we show that Lin28a is expressed in embryonic limb bud muscle progenitors, and that a rare reserve subset of Lin28a+Pax7- skeletal MuSCs can respond to injury at adult stage by replenishing the Pax7+ MuSC pool to drive muscle regeneration. Compared with adult Pax7+ MuSCs, Lin28a+ MuSCs displayed enhanced myogenic potency in vitro and in vivo upon transplantation. The epigenome of adult Lin28a+ MuSCs showed resemblance to embryonic muscle progenitors. In addition, RNA-sequencing revealed that Lin28a+ MuSCs co-expressed higher levels of certain embryonic limb bud transcription factors, telomerase components and the p53 inhibitor Mdm4, and lower levels of myogenic differentiation markers compared to adult Pax7+ MuSCs, resulting in enhanced self-renewal and stress-response signatures. Functionally, conditional ablation and induction of Lin28a+ MuSCs in adult mice revealed that these cells are necessary and sufficient for efficient muscle regeneration. Together, our findings connect the embryonic factor Lin28a to adult stem cell self-renewal and juvenile regeneration.

Muscle Injuries Induce a Prostacyclin-PPARγ/PGC1a-FAO Spike That Boosts Regeneration.

It is well-known that muscle regeneration declines with aging, and aged muscles undergo degenerative atrophy or sarcopenia. While exercise and acute injury are both known to induce muscle regeneration, the molecular signals that help trigger muscle regeneration have remained unclear. Here, mass spectrometry imaging (MSI) is used to show that injured muscles induce a specific subset of prostanoids during regeneration, including PGG1, PGD2, and the prostacyclin PGI2. The spike in prostacyclin promotes skeletal muscle regeneration via myoblasts, and declines with aging. Mechanistically, the prostacyclin spike promotes a spike in PPARγ/PGC1a signaling, which induces a spike in fatty acid oxidation (FAO) to control myogenesis. LC-MS/MS and MSI further confirm that an early FAO spike is associated with normal regeneration, but muscle FAO became dysregulated during aging. Functional experiments demonstrate that the prostacyclin-PPARγ/PGC1a-FAO spike is necessary and sufficient to promote both young and aged muscle regeneration, and that prostacyclin can synergize with PPARγ/PGC1a-FAO signaling to restore aged muscles' regeneration and physical function. Given that the post-injury prostacyclin-PPARγ-FAO spike can be modulated pharmacologically and via post-exercise nutrition, this work has implications for how prostacyclin-PPARγ-FAO might be fine-tuned to promote regeneration and treat muscle diseases of aging.

Adult progenitor rejuvenation with embryonic factors.

During ageing, adult stem cells' regenerative properties decline, as they undergo replicative senescence and lose both their proliferative and differentiation capacities. In contrast, embryonic and foetal progenitors typically possess heightened proliferative capacities and manifest a more robust regenerative response upon injury and transplantation, despite undergoing many rounds of mitosis. How embryonic and foetal progenitors delay senescence and maintain their proliferative and differentiation capacities after numerous rounds of mitosis, remains unknown. It is also unclear if defined embryonic factors can rejuvenate adult progenitors to confer extended proliferative and differentiation capacities, without reprogramming their lineage-specific fates or inducing oncogenic transformation. Here, we report that a minimal combination of LIN28A, TERT, and sh-p53 (LTS), all of which are tightly regulated and play important roles during embryonic development, can delay senescence in adult muscle progenitors. LTS muscle progenitors showed an extended proliferative capacity, maintained a normal karyotype, underwent myogenesis normally, and did not manifest tumorigenesis nor aberrations in lineage differentiation, even in late passages. LTS treatment promoted self-renewal and rescued the pro-senescence phenotype of aged cachexia patients' muscle progenitors, and promoted their engraftment for skeletal muscle regeneration in vivo. When we examined the mechanistic basis for LIN28A's role in the LTS minimum combo, let-7 microRNA suppression could not fully explain how LIN28A promoted muscle progenitor self-renewal. Instead, LIN28A was promoting the translation of oxidative phosphorylation mRNAs in adult muscle progenitors to optimize mitochondrial reactive oxygen species (mtROS) and mitohormetic signalling. Optimized mtROS induced a variety of mitohormetic stress responses, including the hypoxic response for metabolic damage, the unfolded protein response for protein damage, and the p53 response for DNA damage. Perturbation of mtROS levels specifically abrogated the LIN28A-driven hypoxic response in Hypoxia Inducible Factor-1α (HIF1α) and glycolysis, and thus LTS progenitor self-renewal, without affecting normal or TS progenitors. Our findings connect embryonically regulated factors to mitohormesis and progenitor rejuvenation, with implications for ageing-related muscle degeneration.

Assessing the commutability of candidate reference materials for the harmonization of neurofilament light measurements in blood.

OBJECTIVES: Neurofilament light chain (NfL) concentration in blood is a biomarker of neuro-axonal injury in the nervous system and there now exist several assays with high enough sensitivity to measure NfL in serum and plasma. There is a need for harmonization with the goal of creating a certified reference material (CRM) for NfL and an early step in such an effort is to determine the best matrix for the CRM. This is done in a commutability study and here the results of the first one for NfL in blood is presented. METHODS: Forty paired individual serum and plasma samples were analyzed for NfL on four different analytical platforms. Neat and differently spiked serum and plasma were evaluated for their suitability as a CRM using the difference in bias approach. RESULTS: The correlation between the different platforms with regards to measured NfL concentrations were very high (Spearman's ρ≥0.96). Samples spiked with cerebrospinal fluid (CSF) showed higher commutability compared to samples spiked with recombinant human NfL protein and serum seems to be a better choice than plasma as the matrix for a CRM. CONCLUSIONS: The results from this first commutability study on NfL in serum/plasma showed that it is feasible to create a CRM for NfL in blood and that spiking should be done using CSF rather than with recombinant human NfL protein.

Mitral annular calcification: The incremental diagnostic value of 3D transesophageal echocardiography.

Three-dimensional (3D) echocardiography is an important tool in the evaluation of mitral valve anatomy. We illustrate a case of a 67-year-old female who was admitted for non-ST-elevation myocardial infarction (NSTEMI) and underwent two-vessel coronary artery bypass grafting for surgical disease. Her two-dimensional (2D) echocardiographic images intraoperatively demonstrated a mass on the posterior mitral valve leaflet which created a diagnostic challenge; 3D transesophageal imaging was crucial in identifying the true nature of the pathology to be mitral annular calcification with supra-annular extension.

Characterization of convergent thickening, a major convergence force producing morphogenic movement in amphibians.

The morphogenic process of convergent thickening (CT) was originally described as the mediolateral convergence and radial thickening of the explanted ventral involuting marginal zone (IMZ) of Xenopus gastrulae (Keller and Danilchik, 1988). Here, we show that CT is expressed in all sectors of the pre-involution IMZ, which transitions to expressing convergent extension (CE) after involution. CT occurs without CE and drives symmetric blastopore closure in ventralized embryos. Assays of tissue affinity and tissue surface tension measurements suggest CT is driven by increased interfacial tension between the deep IMZ and the overlying epithelium. The resulting minimization of deep IMZ surface area drives a tendency to shorten the mediolateral (circumblastoporal) aspect of the IMZ, thereby generating tensile force contributing to blastopore closure (Shook et al., 2018). These results establish CT as an independent force-generating process of evolutionary significance and provide the first clear example of an oriented, tensile force generated by an isotropic, Holtfreterian/Steinbergian tissue affinity change.

Assessment of different strategies for scalable production and proliferation of human myoblasts.

OBJECTIVES: Myoblast transfer therapy (MTT) is a technique to replace muscle satellite cells with genetically repaired or healthy myoblasts, to treat muscular dystrophies. However, clinical trials with human myoblasts were ineffective, showing almost no benefit with MTT. One important obstacle is the rapid senescence of human myoblasts. The main purpose of our study was to compare the various methods for scalable generation of proliferative human myoblasts. METHODS: We compared the immortalization of primary myoblasts with hTERT, cyclin D1 and CDK4R24C , two chemically defined methods for deriving myoblasts from pluripotent human embryonic stem cells (hESCs), and introduction of viral MyoD into hESC-myoblasts. RESULTS: Our results show that, while all the strategies above are suboptimal at generating bona fide human myoblasts that can both proliferate and differentiate robustly, chemically defined hESC-monolayer-myoblasts show the most promise in differentiation potential. CONCLUSIONS: Further efforts to optimize the chemically defined differentiation of hESC-monolayer-myoblasts would be the most promising strategy for the scalable generation of human myoblasts, for applications in MTT and high-throughput drug screening.

Blunt Trauma Abdominal and Pelvic Computed Tomography Has Low Yield for Injuries in More Than One Anatomic Region.

INTRODUCTION: Most trauma centers order abdominal and pelvic computed tomography (CT) as an automatically paired CT for adult blunt trauma evaluation. However, excessive CT utilization adds risks of excessive exposure to ionizing radiation, the need to work up incidental findings (leading to unnecessary and invasive tests), and greater costs. Examining a cohort of adult blunt trauma patients that received paired abdominal and pelvic (A/P) CT, we sought to determine the diagnostic yield of clinically significant injuries (CSI) in the following: 1) the abdomen alone; 2) the pelvis alone; 3) the lumbosacral spine alone; and 4) more than one of these anatomic regions concomitantly. METHODS: In this retrospective study, we reviewed the imaging and hospital course of a consecutive sample of blunt trauma activation patients older than 14 years of age who received paired A/P CT during their blunt trauma assessments at an urban Level I trauma center from April through October 2014. Categorization of CSI was determined according to an a priori, expert panel-derived classification scheme. RESULTS: The median age of the 689 patients who had A/P CT was 48 years old; 68.1% were male; 64.0% were admitted, and hospital mortality was 3.6%. CSI yields were as follows: abdomen 2.2% (95% confidence interval [CI] [1.3-3.6%]); pelvis 2.9% (95% CI [1.9-4.4%]); lumbosacral spine 0.6% (95% CI [0.2-1.5%]); both abdomen and pelvis 0.3% (95% CI [0.1-1.1%]); both the abdomen and lumbosacral spine 0.6% (0.2-1.5%); both the pelvis and lumbosacral spine 0.1% (0.0-0.8%); all three regions - abdomen, pelvis and lumbosacral spine - 0.1% (0.0-0.8%). CONCLUSION: Automatic pairing of A/P CT has very low diagnostic yield for CSI in both the abdomen and pelvis. These data suggest a role for selective CT imaging protocols that image these regions individually instead of automatically as a pair.

Potable Water Reuse through Advanced Membrane Technology.

Recycling water from municipal wastewater offers a reliable and sustainable solution to cities and regions facing shortage of water supply. Places including California and Singapore have developed advanced water reuse programs as an integral part of their water management strategy. Membrane technology, particularly reverse osmosis, has been playing a key role in producing high quality recycled water. This feature paper highlights the current status and future perspectives of advanced membrane processes to meet potable water reuse. Recent advances in membrane materials and process configurations are presented and opportunities and challenges are identified in the context of water reuse.

Hospitalizations for Autoimmune Hepatitis Disproportionately Affect Black and Latino Americans.

OBJECTIVES: The healthcare burden of autoimmune hepatitis (AIH) in the United States has not been characterized. We previously showed that AIH disproportionately affects people of color in a single hospital system. The current study aimed to determine whether the same disparity occurs nationwide. METHODS: We analyzed hospitalizations with a primary discharge diagnosis corresponding to the ICD-9 code for AIH in the National Inpatient Sample between 2008 and 2012. For each racial/ethnic group, we calculated the AIH hospitalization rate per 100,000 population and per 100,000 all-cause hospitalizations, then calculated a risk ratio compared to the reference rate among whites. We used multivariable logistic regression models to assess for racial disparities and to identify predictors of in-hospital mortality during AIH hospitalizations. RESULTS: The national rate of AIH hospitalization was 0.73 hospitalizations per 100,000 population. Blacks and Latinos were hospitalized for AIH at a rate 69% (P<0.001) and 20% higher (P<0.001) than whites, respectively. After controlling for age, gender, payer, residence, zip code income, region, and cirrhosis, black race was a statistically significant predictor for mortality during AIH hospitalizations (odds ratio (OR) 2.81, 95% confidence interval (CI) 1.43, 5.47). CONCLUSIONS: Hospitalizations for AIH disproportionately affect black and Latino Americans. Black race is independently associated with higher odds of death during hospitalizations for AIH. This racial disparity may be related to biological, genetic, environmental, socioeconomic, and healthcare access and quality factors.

Low Yield of Clinically Significant Injury With Head-To-Pelvis Computed Tomography in Blunt Trauma Evaluation.

BACKGROUND: Many trauma centers have adopted routine head-to-pelvis computed tomography (CT) imaging for the evaluation of adults with blunt trauma. OBJECTIVE: We sought to determine the yields of detecting clinically significant injuries (CSIs) with CT in >1 anatomic region. METHODS: We conducted this observational cohort study of all trauma activation patients >14 years of age who received CT imaging during blunt trauma evaluation at a Level 1 trauma center from April to October 2014. Expert panels determined the clinical significance of head, neck, chest, abdomen, and pelvis injuries seen on CT. We calculated yields of CSI, defined as the number of patients with CSI divided by the total number of patients who underwent CT imaging. The 3 specified anatomic regions considered were head/neck, chest, and abdomen/pelvis. RESULTS: The median age of 1236 patients who had CT was 48 years; 69% were male; 51.2% were admitted; and hospital mortality was 4.4%. Yields of CSI with 95% confidence intervals (CIs) were: head/neck region injury 11.3% (9.6-13.3%); chest region injury only 7.9% (6.0-10.4%); abdomen/pelvis region injury only 5.1% (3.7-7.0%); both head/neck and chest CSI 2.8% (1.7-4.5%); both head/neck and abdomen/pelvis CSI 1.6% (0.9-2.9%); and both chest and abdomen/pelvis CSI 1.1% (0.5-2.4%). The yield of CSI in all 3 anatomic regions with head-to-pelvis CT was 0.6% (0.2-1.7%), and 76.7% (68.8-83.1%) of CSIs occurred in isolation. CONCLUSIONS: During multiple anatomic region CT imagng for adult blunt trauma evaluation, the yield for CSI in >1 region is low. In low-risk populations, selective CT imaging of anatomic regions (instead of reflexive head-to-pelvis CT imaging) may be more appropriate.

Ingression-type cell migration drives vegetal endoderm internalisation in the Xenopus gastrula.

During amphibian gastrulation, presumptive endoderm is internalised as part of vegetal rotation, a large-scale movement that encompasses the whole vegetal half of the embryo. It has been considered a gastrulation process unique to amphibians, but we show that at the cell level, endoderm internalisation exhibits characteristics reminiscent of bottle cell formation and ingression, known mechanisms of germ layer internalisation. During ingression proper, cells leave a single-layered epithelium. In vegetal rotation, the process occurs in a multilayered cell mass; we refer to it as ingression-type cell migration. Endoderm cells move by amoeboid shape changes, but in contrast to other instances of amoeboid migration, trailing edge retraction involves ephrinB1-dependent macropinocytosis and trans-endocytosis. Moreover, although cells are separated by wide gaps, they are connected by filiform protrusions, and their migration depends on C-cadherin and the matrix protein fibronectin. Cells move in the same direction but at different velocities, to rearrange by differential migration.

Molecular Targets of Ascochlorin and Its Derivatives for Cancer Therapy.

Cancer is an extremely complex disease comprising of a multitude of characteristic hallmarks that continue to evolve with time. At the genomic level, random mutations leading to deregulation of diverse oncogenic signal transduction cascades and polymorphisms coupled with environmental as well as life style-related factors are major causative agent contributing to chemoresistance and the failure of conventional therapies as well as molecular targeted agents. Hence, there is an urgent need to identify novel alternative therapies based on alternative medicines to combat this dreaded disease. Ascochlorin (ASC), an isoprenoid antibiotic isolated initially from the fermented broth of Ascochyta viciae, and its synthetic derivatives have recently demonstrated substantial antineoplastic effects in a variety of tumor cell lines and mouse models. The major focus of this review article is to briefly analyze the chemopreventive as well as therapeutic properties of ASC and its derivatives and to identify the multiple molecular targets modulated by this novel class of anticancer agent.

Excessive fatty acid oxidation induces muscle atrophy in cancer cachexia.

Cachexia is a devastating muscle-wasting syndrome that occurs in patients who have chronic diseases. It is most commonly observed in individuals with advanced cancer, presenting in 80% of these patients, and it is one of the primary causes of morbidity and mortality associated with cancer. Additionally, although many people with cachexia show hypermetabolism, the causative role of metabolism in muscle atrophy has been unclear. To understand the molecular basis of cachexia-associated muscle atrophy, it is necessary to develop accurate models of the condition. By using transcriptomics and cytokine profiling of human muscle stem cell-based models and human cancer-induced cachexia models in mice, we found that cachectic cancer cells secreted many inflammatory factors that rapidly led to high levels of fatty acid metabolism and to the activation of a p38 stress-response signature in skeletal muscles, before manifestation of cachectic muscle atrophy occurred. Metabolomics profiling revealed that factors secreted by cachectic cancer cells rapidly induce excessive fatty acid oxidation in human myotubes, which leads to oxidative stress, p38 activation and impaired muscle growth. Pharmacological blockade of fatty acid oxidation not only rescued human myotubes, but also improved muscle mass and body weight in cancer cachexia models in vivo. Therefore, fatty acid-induced oxidative stress could be targeted to prevent cancer-induced cachexia.

Stem cell mitochondria during aging.

Mitochondria are the central hubs of cellular metabolism, equipped with their own mitochondrial DNA (mtDNA) blueprints to direct part of the programming of mitochondrial oxidative metabolism and thus reactive oxygen species (ROS) levels. In stem cells, many stem cell factors governing the intricate balance between self-renewal and differentiation have been found to directly regulate mitochondrial processes to control stem cell behaviors during tissue regeneration and aging. Moreover, numerous nutrient-sensitive signaling pathways controlling organismal longevity in an evolutionarily conserved fashion also influence stem cell-mediated tissue homeostasis during aging via regulation of stem cell mitochondria. At the genomic level, it has been demonstrated that heritable mtDNA mutations and variants affect mammalian stem cell homeostasis and influence the risk for human degenerative diseases during aging. Because such a multitude of stem cell factors and signaling pathways ultimately converge on the mitochondria as the primary mechanism to modulate cellular and organismal longevity, it would be most efficacious to develop technologies to therapeutically target and direct mitochondrial repair in stem cells, as a unified strategy to combat aging-related degenerative diseases in the future.

PAPC mediates self/non-self-distinction during Snail1-dependent tissue separation.

Cleft-like boundaries represent a type of cell sorting boundary characterized by the presence of a physical gap between tissues. We studied the cleft-like ectoderm-mesoderm boundary in Xenopus laevis and zebrafish gastrulae. We identified the transcription factor Snail1 as being essential for tissue separation, showed that its expression in the mesoderm depends on noncanonical Wnt signaling, and demonstrated that it enables paraxial protocadherin (PAPC) to promote tissue separation through two novel functions. First, PAPC attenuates planar cell polarity signaling at the ectoderm-mesoderm boundary to lower cell adhesion and facilitate cleft formation. Second, PAPC controls formation of a distinct type of adhesive contact between mesoderm and ectoderm cells that shows properties of a cleft-like boundary at the single-cell level. It consists of short stretches of adherens junction-like contacts inserted between intermediate-sized contacts and large intercellular gaps. These roles of PAPC constitute a self/non-self-recognition mechanism that determines the site of boundary formation at the interface between PAPC-expressing and -nonexpressing cells.

Tissue cohesion and the mechanics of cell rearrangement.

Morphogenetic processes often involve the rapid rearrangement of cells held together by mutual adhesion. The dynamic nature of this adhesion endows tissues with liquid-like properties, such that large-scale shape changes appear as tissue flows. Generally, the resistance to flow (tissue viscosity) is expected to depend on the cohesion of a tissue (how strongly its cells adhere to each other), but the exact relationship between these parameters is not known. Here, we analyse the link between cohesion and viscosity to uncover basic mechanical principles of cell rearrangement. We show that for vertebrate and invertebrate tissues, viscosity varies in proportion to cohesion over a 200-fold range of values. We demonstrate that this proportionality is predicted by a cell-based model of tissue viscosity. To do so, we analyse cell adhesion in Xenopus embryonic tissues and determine a number of parameters, including tissue surface tension (as a measure of cohesion), cell contact fluctuation and cortical tension. In the tissues studied, the ratio of surface tension to viscosity, which has the dimension of a velocity, is 1.8 µm/min. This characteristic velocity reflects the rate of cell-cell boundary contraction during rearrangement, and sets a limit to rearrangement rates. Moreover, we propose that, in these tissues, cell movement is maximally efficient. Our approach to cell rearrangement mechanics links adhesion to the resistance of a tissue to plastic deformation, identifies the characteristic velocity of the process, and provides a basis for the comparison of tissues with mechanical properties that may vary by orders of magnitude.

EphA4-dependent Brachyury expression is required for dorsal mesoderm involution in the Xenopus gastrula.

Xenopus provides a well-studied model of vertebrate gastrulation, but a central feature, the movement of the mesoderm to the interior of the embryo, has received little attention. Here, we analyze mesoderm involution at the Xenopus dorsal blastopore lip. We show that a phase of rapid involution - peak involution - is intimately linked to an early stage of convergent extension, which involves differential cell migration in the prechordal mesoderm and a new movement of the chordamesoderm, radial convergence. The latter process depends on Xenopus Brachyury, the expression of which at the time of peak involution is controlled by signaling through the ephrin receptor, EphA4, its ligand ephrinB2 and its downstream effector p21-activated kinase. Our findings support a conserved role for Brachyury in blastopore morphogenesis.

Reactive oxygen species and Wnt signalling crosstalk patterns mouse extraembryonic endoderm.

Primitive endoderm formation from the inner cell mass is one of the earliest known cell fate decisions made in the mouse embryo. The mechanisms involved in orchestrating this process are not fully understood and are difficult to study in vivo. The F9 teratocarcinoma cell line is an in vitro model used to circumvent many technical problems surrounding the study of extraembryonic endoderm differentiation. F9 cells treated with retinoic acid differentiate to primitive endoderm and this is accompanied by the activation of canonical Wnt-ß-catenin signalling. Reactive oxygen species can modulate this signalling pathway, but whether they are sufficient to induce extraembryonic endoderm in vitro is not known. In the present study, a sustained increase in ROS levels was found in retinoic acid-treated F9 cells. An increase in Tcf-Lef transcriptional activity, a read out of Wnt-ß-catenin signalling, was also seen in response to exogenous H(2)O(2). Analysis from immunoblots, immunocytochemistry and real time PCR revealed the presence of markers of differentiation and a reduction in the expression of a marker of proliferation, confirming that H(2)O(2)-treated F9 cells developed into primitive endoderm. In contrast, exposing retinoic acid-treated cells to antioxidants impeded differentiation. Real time PCR was also used to identify candidates responsible for the observed elevation in ROS production. Results indicated that the NADPH oxidase 1, 2, 3 and 4 and Duox2 genes were RA responsive. Furthermore, the NADPH oxidase inhibitor, diphenyleneiodonium chloride was shown to attenuate primitive endoderm formation. Together, these results shed new light on how early mouse embryogenesis might be influenced by the crosstalk involving ROS and the Wnt-ß-catenin signalling pathway.

Persistent amyloidosis following suppression of Abeta production in a transgenic model of Alzheimer disease.

BACKGROUND: The proteases (secretases) that cleave amyloid-beta (Abeta) peptide from the amyloid precursor protein (APP) have been the focus of considerable investigation in the development of treatments for Alzheimer disease. The prediction has been that reducing Abeta production in the brain, even after the onset of clinical symptoms and the development of associated pathology, will facilitate the repair of damaged tissue and removal of amyloid lesions. However, no long-term studies using animal models of amyloid pathology have yet been performed to test this hypothesis. METHODS AND FINDINGS: We have generated a transgenic mouse model that genetically mimics the arrest of Abeta production expected from treatment with secretase inhibitors. These mice overexpress mutant APP from a vector that can be regulated by doxycycline. Under normal conditions, high-level expression of APP quickly induces fulminant amyloid pathology. We show that doxycycline administration inhibits transgenic APP expression by greater than 95% and reduces Abeta production to levels found in nontransgenic mice. Suppression of transgenic Abeta synthesis in this model abruptly halts the progression of amyloid pathology. However, formation and disaggregation of amyloid deposits appear to be in disequilibrium as the plaques require far longer to disperse than to assemble. Mice in which APP synthesis was suppressed for as long as 6 mo after the formation of Abeta deposits retain a considerable amyloid load, with little sign of active clearance. CONCLUSION: This study demonstrates that amyloid lesions in transgenic mice are highly stable structures in vivo that are slow to disaggregate. Our findings suggest that arresting Abeta production in patients with Alzheimer disease should halt the progression of pathology, but that early treatment may be imperative, as it appears that amyloid deposits, once formed, will require additional intervention to clear.