Advances in proteomic phenotyping of microglia in neurodegeneration

Microglia are dynamic resident immune cells of the central nervous system (CNS) that sense, survey, and respond to changes in their environment. In disease states, microglia transform from homeostatic to diverse molecular phenotypic states that play complex and causal roles in neurologic disease pathogenesis, as evidenced by the identification of microglial genes as genetic risk factors for neurodegenerative disease. While advances in transcriptomic profiling of microglia from the CNS of humans and animal models have provided transformative insights, the transcriptome is only modestly reflective of the proteome. Proteomic profiling of microglia is therefore more likely to provide functionally and therapeutically relevant targets. In this review, we discuss molecular insights gained from transcriptomic studies of microglia in the context of Alzheimer's disease as a prototypic neurodegenerative disease, and highlight existing and emerging approaches for proteomic profiling of microglia derived from in vivo model systems and human brain.

Cellular Proteomic Profiling Using Proximity Labeling by TurboID-NES in Microglial and Neuronal Cell Lines

Different brain cell types play distinct roles in brain development and disease. Molecular characterization of cell-specific mechanisms using cell type-specific approaches at the protein (proteomic) level can provide biological and therapeutic insights. To overcome the barriers of conventional isolation-based methods for cell type-specific proteomics, in vivo proteomic labeling with proximity-dependent biotinylation of cytosolic proteins using biotin ligase TurboID, coupled with mass spectrometry (MS) of labeled proteins, emerged as a powerful strategy for cell type-specific proteomics in the native state of cells without the need for cellular isolation. To complement in vivo proximity labeling approaches, in vitro studies are needed to ensure that cellular proteomes using the TurboID approach are representative of the whole-cell proteome and capture cellular responses to stimuli without disruption of cellular processes. To address this, we generated murine neuroblastoma (N2A) and microglial (BV2) lines stably expressing cytosolic TurboID to biotinylate the cellular proteome for downstream purification and analysis using MS. TurboID-mediated biotinylation captured 59% of BV2 and 65% of N2A proteomes under homeostatic conditions. TurboID labeled endolysosome, translation, vesicle, and signaling proteins in BV2 microglia and synaptic, neuron projection, and microtubule proteins in N2A neurons. TurboID expression and biotinylation minimally impacted homeostatic cellular proteomes of BV2 and N2A cells and did not affect lipopolysaccharide-mediated cytokine production or resting cellular respiration in BV2 cells. MS analysis of the microglial biotin-labeled proteins captured the impact of lipopolysaccharide treatment (>500 differentially abundant proteins) including increased canonical proinflammatory proteins (Il1a, Irg1, and Oasl1) and decreased anti-inflammatory proteins (Arg1 and Mgl2).

Cell type-specific biotin labeling in vivo resolves regional neuronal and astrocyte proteomic differences in mouse brain

Proteomic profiling of brain cell types using isolation-based strategies pose limitations in resolving cellular phenotypes representative of their native state. We describe a mouse line for cell type-specific expression of biotin ligase TurboID, for in vivo biotinylation of proteins. Using adenoviral and transgenic approaches to label neurons, we show robust protein biotinylation in neuronal soma and axons throughout the brain, allowing quantitation of over 2000 neuron-derived proteins spanning synaptic proteins, transporters, ion channels and disease-relevant druggable targets. Next, we contrast Camk2a-neuron and Aldh1l1-astrocyte proteomes and identify brain region-specific proteomic differences within both cell types, some of which might potentially underlie the selective vulnerability to neurological diseases. Leveraging the cellular specificity of proteomic labeling, we apply an antibody-based approach to uncover differences in neuron and astrocyte-derived signaling phospho-proteins and cytokines. This approach will facilitate the characterization of cell-type specific proteomes in a diverse number of tissues under both physiological and pathological states.

Enkephalin analogues with N-phenyl-N-(piperidin-2-ylmethyl)propionamide derivatives: Synthesis and biological evaluations

N-Phenyl-N-(piperidin-2-ylmethyl)propionamide based bivalent ligands are unexplored for the design of opioid based ligands. Two series of hybrid molecules bearing N-phenyl-N-(piperidin-2-ylmethyl)propionamide derived small molecules conjugated with an enkephalin analogues with and without a linker (β-alanine) were designed and synthesized. Both bivalent ligand series exhibited remarkable binding affinities from nanomolar to subnanomolar range at both μ and δ opioid receptors and displayed potent agonist activities as well. The replacement of Tyr with Dmt and introduction of a linker between the small molecule and enkephalin analogue resulted in highly potent ligands. Both series of ligands showed excellent binding affinities at both μ (0.6-0.9nM) and δ (0.2-1.2nM) opioid receptors respectively. Similarly, these bivalent ligands exhibited potent agonist activities in both MVD and GPI assays. Ligand 17 was evaluated for in vivo antinociceptive activity in non-injured rats following spinal administration. Ligand 17 was not significantly effective in alleviating acute pain. The most likely explanations for this low intrinsic efficacy in vivo despite high in vitro binding affinity, moderate in vitro activity are (i) low potency suggesting that higher doses are needed; (ii) differences in experimental design (i.e. non-neuronal, high receptor density for in vitro preparations versus CNS site of action in vitro); (iii) pharmacodynamics (i.e. engaging signalling pathways); (iv) pharmacokinetics (i.e. metabolic stability). In summary, our data suggest that further optimisation of this compound 17 is required to enhance intrinsic antinociceptive efficacy.

Effect of sandblasting on the retention of orthodontic brackets: a controlled clinical trial

OBJECTIVE

To study the effect of chairside sandblasting of the bases upon the retention of mesh backed orthodontic brackets.

DESIGN

Prospective controlled clinical trial.

METHODS

Brackets were bonded to 60 successive patients who were treated at an orthodontic practice in Amman, Jordan. Using a crossover system of allocation, quadrants were bonded using either sandblasted or non-sandblasted brackets respectively. Rely-A-Bond adhesive was used throughout. Bond failures were monitored over one year.

RESULTS

1112 brackets were assessed. The overall failure rate was 4.0% and the failure rates for non-sandblasted and sandblasted brackets were 4.7 and 3.4% respectively. The odds ratio for at least one bracket failure within the control quadrant compared with the experimental quadrant was 0.50 (95% CI 0.185 to 1.238), which was not statistically significant.

CONCLUSION

Sandblasting did not significantly improve the retention of mesh based orthodontic brackets in this study.

An ex vivo investigation into the bond strength of orthodontic brackets and adhesive systems

The aim of this study was to compare the shear bond strength of Adhesive Precoated Brackets (APC) with that of two types of uncoated bracket bases, Straight-Wire and Dyna-Lock. Two types of orthodontic adhesives were used, Transbond XT and Right-On. Three different curing times were evaluated with the APC brackets in order to find the best. Adhesive remnants on the enamel surface following debond were evaluated using the Adhesive Remnant Index (Artun and Bergland, 1984). Bond strengths ranged from 11.00 to 22.08 MPa. For both types of brackets Transbond produced a significant increase in bond strength compared to Right-On. The Dyna-Lock/Right-On combination produced the poorest results. APC brackets cured for 40 s had similar bond strengths to uncoated brackets fixed by means of Transbond. Overall, 79 per cent of specimens had less than half the tooth surface covered with adhesive following debond. Significantly more adhesive remained on tooth surfaces following debond of the Straight-Wire/Right-On group than any other bracket/adhesive combination. Bond strengths were higher with light-cured Transbond than with chemically-cured Right-On. When Transbond is used in association with APC brackets a 40-second cure time is recommended.

Clinical performance of orthodontic brackets and adhesive systems: a randomized clinical trial

The aim of the study was to evaluate and compare the clinical performance of adhesive precoated brackets (APC) with that of two types of uncoated bracket bases, Straight-Wire and Dyna-Lock, bonded using two types of orthodontic adhesives, Transbond XT, and Right-On. Forty consecutive orthodontic patients entered the trial and 607 brackets were bonded. The incidence and site of first time bond failures were recorded over a period of 1 year. The time required for bonding was also recorded. The overall bond failure rate was 6.6 per cent. There were no significant differences between the failure rates of the five groups, or between the upper and lower arch. However, significantly more brackets failed on the left side than on the right. Premolar brackets were lost most often, whilst incisor brackets failed least. No association was found between bond failure and time elapsed since bonding. Bonding time was least with Right-On adhesive. There were no significant differences between bonding times using APC or Transbond. Results of the present study conflict with those of a previous ex vivo study by the authors, using the same materials and bonding technique. Suggested reasons for this are discussed.