MyD88 Is Dispensable for Cerebral Amyloidosis and Neuroinflammation in APP/PS1 Transgenic Mice

Activated microglia are associated with amyloid plaques in transgenic mouse models of cerebral amyloidosis and in human Alzheimer disease; yet, their implication in Alzheimer disease pathogenesis remains unclear. It has been suggested that microglia play dual roles depending on the context of activation, contributing negatively to disease pathogenesis by secreting proinflammatory innate cytokines or performing a beneficial role via phagocytosis of amyloid beta (Aβ) deposits. Toll-like receptors, most of which signal through the adaptor protein myeloid differentiation factor 88 (MyD88), have been suggested as candidate Aβ innate pattern recognition receptors. It was recently reported that MyD88 deficiency reduced brain amyloid pathology and microglial activation. To assess a putative role of MyD88 in cerebral amyloidosis and glial activation in APPswe/PS1ΔE9 (APP/PS1) mice, we crossed MyD88-deficient (MyD88^−/−) mice with APP/PS1 mice, interbred first filial offspring, and studied APP/PS1 MyD88^+/+, APP/PS1 MyD88^+/−, and APP/PS1 MyD88^−/− cohorts. Biochemical analysis of detergent-soluble and detergent-insoluble Aβ_1-40 or Aβ_1-42 in brain homogenates did not reveal significant between-group differences. Furthermore, no significant differences were observed on amyloid plaque load or soluble fibrillar Aβ by quantitative immunohistochemical analysis. In addition, neither activated microglia nor astrocytes differed among the three groups. These data suggest that MyD88 signaling is dispensable for Aβ-induced glial activation and does not significantly affect the nature or extent of cerebral β-amyloidosis in APP/PS1 mice.Alzheimer disease (AD) is an insidious public health threat characterized by deposition of β-amyloid as senile plaques, formation of neurofibrillary tangles, and large-scale cortical neuronal loss leading to dementia. In addition to these pathognomonic features of the disease, AD patients exhibit low-level chronic neuroinflammation. This is hallmarked by the spatial and temporal occurrence of activated microglia with amyloid beta (Aβ) deposits. Yet, the mechanisms by which microglia recognize and respond to Aβ accumulation remain unclear. Current evidence suggests that there are varied forms of activated microglia in AD, some of which are detrimental and others beneficial.¹ Because microglial activation is a complex continuum of varied responses,² it stands to reason that a wide array of immune molecules may orchestrate microglial responses to Aβ. Ultimately, a clearer understanding of the pathways leading to beneficial microglial responses and clearance of misfolded proteins could open new avenues for AD treatment.Numerous recent studies have proposed that Toll-like receptors (TLRs) play a role in the microglial response to Aβ and, more specifically, that aggregated Aβ can activate microglia via TLRs.^3–11 Most TLRs (except TLR3) signal through the adaptor protein myeloid differentiation factor 88 (MyD88), suggesting that it may play an important role in microglial activation in response to cerebral amyloid accumulation. To test this possibility, two recent studies crossed MyD88 knockout mice with APP/PS1 mouse models of cerebral amyloid deposition and examined effects on cognitive deficits and AD-like pathology. In one study, it was reported that MyD88 deficiency of the doubly transgenic APPswe/PS1dE9 mouse reduced cerebral amyloid pathology and microglial activation and decreased expression of CX3CR1 in 10-month-old animals.¹² Lim and coworkers¹² suggested that inhibiting MyD88-associated TLR signaling would alter the microglial activation state, and they reported less cerebral amyloid deposition in this cross. However, their findings were perplexing given previous reports showing that activation of TLRs leads to decreased amyloid load and increased Aβ phagocytosis, leading to the hypothesis that MyD88 deficiency would either cause buildup of amyloid or have no effect on amyloid levels in APP/PS1 mice.^{4,6,11,13–15} Another recent study published findings more consistent with this hypothesis, demonstrating that APPswe/PS1A246E mice heterozygous for MyD88 had accelerated spatial learning and memory deficits and increased levels of soluble Aβ oligomers. These results led the authors to conclude that MyD88-mediated activation of microglia was protective in the context of cerebral amyloid deposition.¹⁶ In an attempt to clarify the uncertainty surrounding this critical question, we crossed APPswe/PS1dE9 (APP/PS1) mice with MyD88 knockout (MyD88^−/−) mice (both on a C57BL/6 background) and analyzed APP/PS1 MyD88^+/+, APP/PS1 MyD88^+/−, and APP/PS1 MyD88^−/− cohorts for Alzheimer-like pathology at 15 months of age.     

N-methylation of anthracyclines modulates their cytotoxicity and pharmacokinetic in wild type and multidrug resistant cells.

Anthracyclines are the most commonly used classes of anticancer agents in chemotherapy. Development of resistance to these molecules is one of the major reasons for treatment failure. The overexpression of the membrane transporter P-glycoprotein (P-gp) is among the principal mechanisms involved in this phenomenon. This pump, which is responsible for the multidrug resistance (MDR) phenotype, decreases the toxicity of a wide range of unrelated anticancer drugs by increasing their cellular efflux. Structure-activity relationship experiments have shown that the positively charged amino group of the anthracyclines could be responsible for their transport by P-gp. Here, we used three new anthracyclines that shared the same chromophore but differed by the degree of N-methylation of their sugar moiety. Oxaunomycin (OXN) possessed a non-methylated amino group, while LB-1 was monomethylated and beta-clamycin T (BCT) was dimethylated. In sensitive cells (FLC), reduced cytotoxicity was related to the level of N-methylation; whereas in resistant cells (DOX-RFLC(1) and DOX-RFLC(2)) overexpressing different levels of P-gp, increased N-methylation enhanced anthracycline cytotoxicity. Decreased resistance in DOX-RFLCs was associated with an increased drug accumulation due to a reduced cellular efflux. As expected, the MDR modulator verapamil decreased resistance to these anthracyclines by increasing the cellular accumulation. These results suggest that N-methylation of anthracyclines circumvents resistance by diminishing drug transport by P-gp in MDR-positive cells. These observations could be the consequence of the steric hindrance created by the methyl group(s) which may impair the interaction between the positively charged amino group and the active site of P-gp.     

Deformational posterior plagiocephaly: diagnosis and treatment.

OBJECTIVE: This study was designed to evaluate the effectiveness of helmet therapy (DOC band) in the correction of patients with moderate to severe posterior deformational plagiocephaly. DESIGN: In this prospective study, the infants were evaluated using 18 anthropometric measurements. PATIENTS: The charts of 248 patients seen between August 1, 1995, and July 31, 1999, were reviewed, and 125 met the criteria for inclusion in the study. All the patients had posterior deformational plagiocephaly with no other craniofacial deformities or medical conditions. Treatment was instituted prior to 1 year of age, and all patients were compliant with DOC band usage and had complete anthropometric measurements. RESULTS: The study recorded a 41.56% (p < .001) reduction in cranial vault asymmetry and a 40.23% (p <.001) reduction in cranial base asymmetry. Orbitotragial asymmetry was improved 18.72% (p = .0738). The age at which treatment was begun was not a significant factor in predicting treatment outcomes.     

Comparison of the Efficacies of Three Fluoroquinolone Antimicrobial Agents, Given as Continuous or Pulsed-Water Medication, against Escherichia coli Infection in Chickens

This study compared the efficacy of continuous or pulsed-water medication with enrofloxacin, danofloxacin, and sarafloxacin in eight groups of 90 chicks each by using an infectious bronchitis virus-Escherichia coli model of colisepticemia. The model produced lesions of typical those occurring in birds with severe colisepticemia; for the infected, nonmedicated birds the mortality was 43.5% and the morbidity was 89%, 17.8% of birds had severe lesions, and the birds had a mean air sac lesion score of 2.58. This experiment showed that continuous dosing and pulsed dosing are clinically equivalent. However, for all fluoroquinolones studied, there was a trend for the continuously mediated birds to have lower mortality and less severe disease than birds receiving pulsed doses. Compared with infected, nonmedicated controls, only birds continuously medicated with enrofloxacin had a significantly lower morbidity (32%), and only birds medicated with enrofloxacin and danofloxacin (continuous and pulsed treatments) had significantly lower mortality (6.7 and 11.0% and 16.8 and 19.2% for continuous and pulsed treatments with enrofloxacin and danofloxacin, respectively). A significantly lower proportion of birds only in the groups medicated with enrofloxacin had severe lesions (for birds receiving continuous and pulsed treatments, 2.2 and 6.7%, respectively). Birds medicated with any of the three fluoroquinolones (continuous and pulsed treatments) except pulsed-water treatment with sarafloxacin had significantly reduced mean air sac lesion scores compared with the scores for nonmedicated birds (air sac lesion scores, 0.60 and 0.83, 1.38 and 1.63, and 1.80 and 2.05 for birds receiving continuous and pulsed treatments with enrofloxacin, danofloxacin, and sarafloxacin, respectively). The performance of the birds that survived the challenge or that recovered after receiving medication was not compromised compared to the performance of noninfected birds. Enrofloxacin was more efficacious than either danofloxacin or sarafloxacin for the treatment of colisepticemia in chickens by medication in drinking water. Similarly, danofloxacin appeared to be more effective than sarafloxacin in treating colisepticemia.     

The metabolic fate of the amido-N group of glutamine in the tissues of the gastrointestinal tract in 24 h-fasted sheep

Whole-body and gastrointestinal tract (GIT) metabolism of [5-(15)N]glutamine were monitored in lambs (33 kg live weight) fasted for 24 h. Animals were previously prepared with vascular catheters across the mesenteric-(MDV) and portal-drained viscera (PDV) to permit quantification of mass and isotopic transfers of metabolites by arterio-venous difference. Continuous infusions of [5-(15)N]glutamine into the jugular vein were conducted for 10 h and integrated blood samples withdrawn over 75 min intervals for the last 5 h of infusion. The lambs were then killed and portions from various tissues of the digestive tract and other body organs removed for determination of 15N enrichment in RNA, DNA and protein (the latter obtained by difference using total acid-precipitable N). Whole-body glutamine flux was 108 mumol/min of which 23 and 47% could be attributed to MDV and PDV metabolism (P < 0.001) respectively. There was a small net production of glutamine across the MDV. GIT blood-flows and NH3 production were partitioned 3:2 between MDV and non-MDV components. Less than 5% of the NH3 produced was derived from the amido-N of glutamine, while across the small intestine (MDV) 26% of the glutamine flux was converted to NH3, compared with 18% for non-MDV transfers. The 15N enrichments in protein were of the order jejunum > duodenum > ileum with mucosal cells more labelled than serosal (P < 0.001). Lesser enrichments were observed for other GIT tissues (abomasum > caecum > rumen) while liver and lymph were comparable with the abomasum; kidney, spleen and muscle were lower still (P < 0.05). Enrichments of RNA were similar to that of protein and followed the same pattern, except for higher relative values for liver, spleen and lymphoid tissue. The lowest enrichments were observed for DNA, but again the pattern order was similar except for increased label in lymph, caecum and the spleen. For the MDV there was reasonable agreement between 15N-disappearance as glutamine and appearance in NH3 (24%), protein (81%), RNA (3.6%) and DNA (2.1%). For the total PDV there was a shortfall (-12%), however, which may be due to losses in lumen components. These results show the importance of the GIT as a contributor to total glutamine plasma flux, but indicate a lesser reliance on glutamine metabolism by the digestive tract of the ruminant compared with observations from non-ruminants.     

CNS Infiltration of Peripheral Immune Cells: D-Day for Neurodegenerative Disease?

While the central nervous system (CNS) was once thought to be excluded from surveillance by immune cells, a concept known as “immune privilege,” it is now clear that immune responses do occur in the CNS—giving rise to the field of neuroimmunology. These CNS immune responses can be driven by endogenous (glial) and/or exogenous (peripheral leukocyte) sources and can serve either productive or pathological roles. Recent evidence from mouse models supports the notion that infiltration of peripheral monocytes/macrophages limits progression of Alzheimer's disease pathology and militates against West Nile virus encephalitis. In addition, infiltrating T lymphocytes may help spare neuronal loss in models of amyotrophic lateral sclerosis. On the other hand, CNS leukocyte penetration drives experimental autoimmune encephalomyelitis (a mouse model for the human demyelinating disease multiple sclerosis) and may also be pathological in both Parkinson's disease and human immunodeficiency virus encephalitis. A critical understanding of the cellular and molecular mechanisms responsible for trafficking of immune cells from the periphery into the diseased CNS will be key to target these cells for therapeutic intervention in neurodegenerative diseases, thereby allowing neuroregenerative processes to ensue.     

Macrophages in Alzheimer’s disease: the blood-borne identity

Alzheimer’s disease (AD) is a progressive and incurable neurodegenerative disorder clinically characterized by cognitive decline involving loss of memory, reasoning and linguistic ability. The amyloid cascade hypothesis holds that mismetabolism and aggregation of neurotoxic amyloid-β (Aβ) peptides, which are deposited as amyloid plaques, are the central etiological events in AD. Recent evidence from AD mouse models suggests that blood-borne mononuclear phagocytes are capable of infiltrating the brain and restricting β-amyloid plaques, thereby limiting disease progression. These observations raise at least three key questions: (1) what is the cell of origin for macrophages in the AD brain, (2) do blood-borne macrophages impact the pathophysiology of AD and (3) could these enigmatic cells be therapeutically targeted to curb cerebral amyloidosis and thereby slow disease progression? This review begins with a historical perspective of peripheral mononuclear phagocytes in AD, and moves on to critically consider the controversy surrounding their identity as distinct from brain-resident microglia and their potential impact on AD pathology.