Although osteoarthritis (OA) was historically referred to as the non-inflammatory arthritis, it is now considered a condition involving persistent low-grade inflammation and activation of innate ...inflammatory pathways. Synovitis increases the risk of OA onset and progression and involves the recruitment of monocytes, lymphocytes, and other leukocytes. In particular, macrophages are important mediators of synovial inflammatory activity and pathologic cartilage and bone responses that are characteristic of OA. Advances in understanding how damage-associated molecular patterns (DAMPs) trigger monocyte/macrophage recruitment and activation in joints provide opportunities for disease-modifying therapies. However, the complexity and plasticity of macrophage phenotypes that exist
in vivo
have thus far prevented the successful development of macrophage-targeted treatments. Current studies show that synovial macrophages are derived from distinct cellular lineages, which correspond to unique functional roles for maintaining joint homeostasis. An improved understanding of the etiology of synovial inflammation in specific OA-subtypes, such as with obesity or genetic risk, is a potential strategy for developing patient selection criteria for future precision therapies.
Colon mucus segregates the intestinal microbiota from host tissues, but how it organizes to function throughout the colon is unclear. In mice, we found that colon mucus consists of two distinct ...O-glycosylated entities of Muc2: a major form produced by the proximal colon, which encapsulates the fecal material including the microbiota, and a minor form derived from the distal colon, which adheres to the major form. The microbiota directs its own encapsulation by inducing Muc2 production from proximal colon goblet cells. In turn, O-glycans on proximal colon-derived Muc2 modulate the structure and function of the microbiota as well as transcription in the colon mucosa. Our work shows how proximal colon control of mucin production is an important element in the regulation of host-microbiota symbiosis.
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•We review the current state and future of high frequency dynamic nuclear polarization.•Polarizing agents tailored for experiments at high spinning frequencies are ...essential.•Microwave sources on the horizon are diodes, klystrons, tunable gyrotrons and amplifiers.•Helium recirculation will enable higher spinning frequencies and lower temperature operation.•High frequency gyroamplifiers will enable pulsed DNP experiments.
Objective
To quantify functional age‐related changes in the cartilage antioxidant network in order to discover novel mediators of cartilage oxidative stress and osteoarthritis (OA) pathophysiology.
...Methods
We evaluated histopathologic changes of knee OA in 10‐, 20‐, and 30‐month‐old male F344BN rats and analyzed cartilage oxidation according to the ratio of reduced to oxidized glutathione. Antioxidant gene expression and protein abundance were analyzed by quantitative reverse transcription–polymerase chain reaction and selected reaction–monitoring mass spectrometry, respectively. Superoxide dismutase 2 (SOD2) activity and acetylation were analyzed by colorimetric enzyme assays and Western blotting, respectively. We examined human OA cartilage to evaluate the clinical relevance of SOD2 acetylation, and we tested age‐related changes in the mitochondrial deacetylase sirtuin 3 (SIRT‐3) in rats and mice.
Results
Cartilage oxidation and OA severity in F344BN rats increased with age and were associated with an increase in SOD2 expression and protein abundance. However, SOD2‐specific activity decreased with age due to elevated posttranslational lysine acetylation. Consistent with these findings, SIRT‐3 levels decreased substantially with age, and treatment with SIRT‐3 increased SOD2 activity in an age‐dependent manner. SOD2 was also acetylated in human OA cartilage, and activity was increased with SIRT‐3 treatment. Moreover, in C57BL/6J mice, cartilage SIRT‐3 expression decreased with age, and whole‐body deletion of SIRT‐3 accelerated the development of knee OA.
Conclusion
Our results show that SIRT‐3 mediates age‐related changes in cartilage redox regulation and protects against early‐stage OA. These findings suggest that mitochondrial acetylation promotes OA and that restoration of SIRT‐3 in aging cartilage may improve cartilage resistance to oxidative stress by rescuing acetylation‐dependent inhibition of SOD2 activity.
During the three decades 1980–2010, magic angle spinning (MAS) NMR developed into the method of choice to examine many chemical, physical, and biological problems. In particular, a variety of dipolar ...recoupling methods to measure distances and torsion angles can now constrain molecular structures to high resolution. However, applications are often limited by the low sensitivity of the experiments, due in large part to the necessity of observing spectra of low-γ nuclei such as the I = 1/2 species 13C or 15N. The difficulty is still greater when quadrupolar nuclei, such as 17O or 27Al, are involved. This problem has stimulated efforts to increase the sensitivity of MAS experiments. A particularly powerful approach is dynamic nuclear polarization (DNP) which takes advantage of the higher equilibrium polarization of electrons (which conventionally manifests in the great sensitivity advantage of EPR over NMR). In DNP, the sample is doped with a stable paramagnetic polarizing agent and irradiated with microwaves to transfer the high polarization in the electron spin reservoir to the nuclei of interest. The idea was first explored by Overhauser and Slichter in 1953. However, these experiments were carried out on static samples, at magnetic fields that are low by current standards. To be implemented in contemporary MAS NMR experiments, DNP requires microwave sources operating in the subterahertz regime, roughly 150–660 GHz, and cryogenic MAS probes. In addition, improvements were required in the polarizing agents, because the high concentrations of conventional radicals that are required to produce significant enhancements compromise spectral resolution. In the last two decades, scientific and technical advances have addressed these problems and brought DNP to the point where it is achieving wide applicability. These advances include the development of high frequency gyrotron microwave sources operating in the subterahertz frequency range. In addition, low temperature MAS probes were developed that permit in situ microwave irradiation of the samples. And, finally, biradical polarizing agents were developed that increased the efficiency of DNP experiments by factors of ∼4 at considerably lower paramagnet concentrations. Collectively, these developments have made it possible to apply DNP on a routine basis to a number of different scientific endeavors, most prominently in the biological and material sciences. This Account reviews these developments, including the primary mechanisms used to transfer polarization in high frequency DNP, and the current choice of microwave sources and biradical polarizing agents. In addition, we illustrate the utility of the technique with a description of applications to membrane and amyloid proteins that emphasizes the unique structural information that is available in these two cases.
Frequency‐Swept Integrated Solid Effect Can, Thach V.; Weber, Ralph T.; Walish, Joseph J. ...
Angewandte Chemie (International ed.),
June 6, 2017, Letnik:
56, Številka:
24
Journal Article
Recenzirano
Odprti dostop
The efficiency of continuous wave dynamic nuclear polarization (DNP) experiments decreases at the high magnetic fields used in contemporary high‐resolution NMR applications. To recover the expected ...signal enhancements from DNP, we explored time domain experiments such as NOVEL which matches the electron Rabi frequency to the nuclear Larmor frequency to mediate polarization transfer. However, satisfying this matching condition at high frequencies is technically demanding. As an alternative we report here frequency‐swept integrated solid effect (FS‐ISE) experiments that allow low power sweeps of the exciting microwave frequencies to constructively integrate the negative and positive polarizations of the solid effect, thereby producing a polarization efficiency comparable to (±10 % difference) NOVEL. Finally, the microwave frequency modulation results in field profiles that exhibit new features that we coin the “stretched” solid effect.
Expanding the repertoire: Frequency‐swept integrated solid effect (FS‐ISE) is introduced as a strategy for time domain dynamic nuclear polarization (DNP). In contrast to the original implementation of the ISE that employs sweeps of B0, the new pulse sequence is suitable for high‐resolution NMR applications.
Innate Immune Responses and Osteoarthritis Kalaitzoglou, Evangelia; Griffin, Timothy M.; Humphrey, Mary Beth
Current rheumatology reports,
08/2017, Letnik:
19, Številka:
8
Journal Article
Recenzirano
Purpose of the Review
Osteoarthritis (OA) is a chronic, painful joint disease that affects approximately 40% of adults over 70 year. Age is the strongest predictor of OA, while obesity is considered ...the primary preventable risk factor for OA. Both conditions are associated with abnormal innate immune inflammatory responses that contribute to OA progression and are the focus of this review.
Recent Findings
Recent studies have identified risk factors for OA progression including increased innate immune responses secondary to aging-associated myeloid skewing, obesity-related myeloid activation, and synovial tissue hyperplasia with activated macrophage infiltration. Toll-like receptor (TLR)4-induced catabolic responses also play a significant role in OA.
Summary
The complex interplay between obesity and aging-associated macrophage activation, pro-inflammatory cytokine production from TLR-driven responses, and adipokines leads to a vicious cycle of synovial hyperplasia, macrophage activation, cartilage catabolism, infrapatellar fat pad fibrosis, and joint destruction.
Caseinolytic peptidase P (ClpP) is a mammalian quality control protease that is proposed to play an important role in the initiation of the mitochondrial unfolded protein response (UPRmt), a ...retrograde signaling response that helps to maintain mitochondrial protein homeostasis. Mitochondrial dysfunction is associated with the development of metabolic disorders, and to understand the effect of a defective UPRmt on metabolism, ClpP knockout (ClpP−/−) mice were analyzed. ClpP−/− mice fed ad libitum have reduced adiposity and paradoxically improved insulin sensitivity. Absence of ClpP increased whole‐body energy expenditure and markers of mitochondrial biogenesis are selectively up‐regulated in the white adipose tissue (WAT) of ClpP−/− mice. When challenged with a metabolic stress such as high‐fat diet, despite similar caloric intake, ClpP−/− mice are protected from diet‐induced obesity, glucose intolerance, insulin resistance, and hepatic steatosis. Our results show that absence of ClpP triggers compensatory responses in mice and suggest that ClpP might be dispensable for mammalian UPRmt initiation. Thus, we made an unexpected finding that deficiency of ClpP in mice is metabolically beneficial.
Synopsis
Mitochondrial matrix protease ClpP is proposed to play an important role in the initiation of mammalian mitochondrial unfolded protein response (UPRmt). This study reveals that ClpP deficiency in mice has paradoxical beneficial effects on metabolism and ClpP might be dispensable for mammalian UPRmt initiation.
ClpP−/− mice have reduced adiposity and improved insulin sensitivity.
Mitochondrial biogenesis markers and respiration are selectively up‐regulated in white adipose tissue of ClpP−/− mice.
ClpP−/− mice are protected from diet‐induced obesity, glucose intolerance, and insulin resistance.
Mitochondrial matrix protease ClpP is proposed to play an important role in the initiation of mammalian mitochondrial unfolded protein response (UPRmt). This study reveals that ClpP deficiency in mice has paradoxical beneficial effects on metabolism and ClpP might be dispensable for mammalian UPRmt initiation.
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