Combining single-cell RNA sequencing and population-based studies reveals hand osteoarthritis-associated chondrocyte subpopulations and pathways

Hand osteoarthritis is a common heterogeneous joint disorder with unclear molecular mechanisms and no disease-modifying drugs. In this study, we performed single-cell RNA sequencing analysis to compare the cellular composition and subpopulation-specific gene expression between cartilage with macroscopically confirmed osteoarthritis (n = 5) and cartilage without osteoarthritis (n = 5) from the interphalangeal joints of five donors. Of 105 142 cells, we identified 13 subpopulations, including a novel subpopulation with inflammation-modulating potential annotated as inflammatory chondrocytes. Fibrocartilage chondrocytes exhibited extensive alteration of gene expression patterns in osteoarthritic cartilage compared with nonosteoarthritic cartilage. Both inflammatory chondrocytes and fibrocartilage chondrocytes showed a trend toward increased numbers in osteoarthritic cartilage. In these two subpopulations from osteoarthritic cartilage, the ferroptosis pathway was enriched, and expression of iron overload-related genes, e.g., FTH1, was elevated. To verify these findings, we conducted a Mendelian randomization study using UK Biobank and a population-based cross-sectional study using data collected from Xiangya Osteoarthritis Study. Genetic predisposition toward higher expression of FTH1 mRNA significantly increased the risk of hand osteoarthritis (odds ratio = 1.07, 95% confidence interval: 1.02-1.11) among participants (n = 332 668) in UK Biobank. High levels of serum ferritin (encoded by FTH1), a biomarker of body iron overload, were significantly associated with a high prevalence of hand osteoarthritis among participants (n = 1 241) of Xiangya Osteoarthritis Study (P-for-trend = 0.037). In conclusion, our findings indicate that inflammatory and fibrocartilage chondrocytes are key subpopulations and that ferroptosis may be a key pathway in hand osteoarthritis, providing new insights into the pathophysiology and potential therapeutic targets of hand osteoarthritis.

Lupus autoantibodies act as positive allosteric modulators at GluN2A-containing NMDA receptors and impair spatial memory

Patients with Systemic lupus erythematosus (SLE) experience various peripheral and central nervous system manifestations including spatial memory impairment. A subset of autoantibodies (DNRAbs) cross-react with the GluN2A and GluN2B subunits of the NMDA receptor (NMDAR). We find that these DNRAbs act as positive allosteric modulators on NMDARs with GluN2A-containing NMDARs, even those containing a single GluN2A subunit, exhibiting a much greater sensitivity to DNRAbs than those with exclusively GluN2B. Accordingly, GluN2A-specific antagonists provide greater protection from DNRAb-mediated neuronal cell death than GluN2B antagonists. Using transgenic mice to perturb expression of either GluN2A or GluN2B in vivo, we find that DNRAb-mediated disruption of spatial memory characterized by early neuronal cell death and subsequent microglia-dependent pathologies requires GluN2A-containing NMDARs. Our results indicate that GluN2A-specific antagonists or negative allosteric modulators are strong candidates to treat SLE patients with nervous system dysfunction.

Systemic lupus erythematosus (SLE) is an autoimmune disorder which can have neurological manifestations, including autoantibody targeting of the NMDA receptor. In this study, the authors GluN2A subunit is a target of SLE autoantibodies, using sample derived from patient.

Treatment of atypical pulmonary carcinoid with combination ipilimumab and nivolumab

Atypical pulmonary carcinoid (APC) is a lung neuroendocrine neoplasm (NEN), whose treatment draws from management of gastrointestinal NENs and small-cell lung carcinoma. We present a patient with recurrent metastatic APC and persistent mediastinal lymphadenopathy refractory to cisplatin and etoposide. After pursuing alternative treatments, he returned with significant progression, including diffuse subcutaneous nodules, weight loss and worsening cough. New biopsy analysis demonstrated APC with low mutational burden, low Ki-67 and Programmed Death-Ligand 1 (PD-L1), and without microsatellite instability. We pursued combination nivolumab and ipilimumab treatment based on success of CheckMate 032 in small-cell lung cancer. The patient's symptoms dramatically responded within a month, with almost complete resolution of lymphadenopathy following four cycles. He has been successfully maintained on nivolumab for the last 18 months. This suggests combination immunotherapy may be beneficial in the treatment of metastatic APC, and that PD-L1 and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors may be valuable in treating tumours lacking traditional biomarkers.

Lupus antibodies induce behavioral changes mediated by microglia and blocked by ACE inhibitors

Nestor et al. examine how lupus antibodies that enter the brain cause neuronal dysfunction and cognitive impairment. The results show that activated microglia are critical for neuronal damage and that inhibiting them can preserve neuronal function and cognition.

Cognitive impairment occurs in 40–90% of patients with systemic lupus erythematosus (SLE), which is characterized by autoantibodies to nuclear antigens, especially DNA. We discovered that a subset of anti-DNA antibodies, termed DNRAbs, cross reacts with the N-methyl-d-aspartate receptor (NMDAR) and enhances NMDAR signaling. In patients, DNRAb presence associates with spatial memory impairment. In a mouse model, DNRAb-mediated brain pathology proceeds through an acute phase of excitotoxic neuron loss, followed by persistent alteration in neuronal integrity and spatial memory impairment. The latter pathology becomes evident only after DNRAbs are no longer detectable in the brain. Here we investigate the mechanism of long-term neuronal dysfunction mediated by transient exposure to antibody. We show that activated microglia and C1q are critical mediators of neuronal damage. We further show that centrally acting inhibitors of angiotensin-converting enzyme (ACE) can prevent microglial activation and preserve neuronal function and cognitive performance. Thus, ACE inhibition represents a strong candidate for clinical trials aimed at mitigating cognitive dysfunction.

Immune-mediated brain pathology: from autoantibodies to microglia

Cells and molecules of the immune system contribute to brain pathology as well as to brain homeostasis. We suggest that there are numerous anti-brain antibodies that can cause acute neuronal dysfunction if they penetrate brain parenchyma. Many of these acute immune-mediated insults may alter the homeostatic mechanisms in the brain and initiate pathologic events that no longer depend on the presence of the inciting antibody, but rather on microglial cell activation. This paradigm, if correct, suggests that there may be two potential moments of therapeutic intervention. The first moment is when antibody contacts cells of the central nervous system and the second is when microglia become activated and impair normal neuronal functions. In this review, we discuss data that support this model for immune-mediated pathology in both the adult brain and the developing fetal brain.

Activation of distinct protein kinase C isozymes by phorbol esters: correlation with induction of interleukin 1 beta gene expression

Treatment of human promyelocytic leukemia cells U937 with phorbol 12-myristate 13-acetate (TPA) induces them to differentiate into monocytic cells [Harris, P., & Ralph, P. (1985) J. Leukocyte Biol. 37, 407-422]. Here we investigated the effects of TPA on interleukin 1 gene expression and the possible role of protein kinase C (PKC) in this process. Addition of TPA to serum-starved U937 cells induced the expression of the interleukin 1 beta (IL-1 beta) gene. This effect was apparent as early as 2 h and peaked at 24 h in the presence of 5 X 10(-8) M TPA. Higher concentrations of TPA, which partially or totally depleted protein kinase C levels in the cells (10(-9)-2 X 10(-5) M), had an inhibitory effect on IL-1 beta mRNA expression. Cell-permeable 1,2-dioctanoyl-sn-glycerol (diC8), a diacylglycerol that activates PKC in intact cells and cell-free systems, did not mimic the effect of TPA on the IL-1 beta mRNA induction. To determine the protein kinase C isozymes present in the control and TPA- (5 X 10(-8) M) treated U937 cells, we prepared antipeptide antibodies that specifically recognize the alpha, beta, and gamma isoforms of protein kinase C in rat brain cytosol and U937 cell extracts. In "control" U937 cells, 30% of PKC alpha was particulate, and PKC beta was cytosolic, while there was no detectable PKC gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Human perioral directional sensitivity

The capacity of 41 neurologically healthy young adults to distinguish opposing directions of brush motion across the skin innervated by the mental nerve was determined. The velocity and orientation and the length and width of skin traversed by the moving tactile stimuli were carefully controlled. Directional sensitivity, d', was found to vary curvilinearly with velocity over the range 0.5 to 32 cm/s. Because the data from most subjects were well described by a generalized gamma function, it was possible to characterize this velocity dependency quantitatively. Specifically, indices derived from these functions were found to describe the subject's peak (i.e., maximal) sensitivity, the velocity which resulted in peak sensitivity (i.e., the optimal velocity), and the degree to which stimulus velocity influenced the ability to recognize direction of motion (i.e., the velocity-tuning of d'). Peak sensitivity, optimal velocity, and the degree of global velocity-tuning were found to differ between males and females. Confidence limits (the lower and upper 2.5% points) for the normative data were determined to enable detection and characterization of deficits in orofacial tactile motion sensitivity in individuals with damaged mandibular nerves.

In vitro synthesis of the tryptophan operon leader peptides of Escherichia coli, Serratia marcescens, and Salmonella typhimurium

We used an in vitro DNA-dependent protein-synthesizing system to demonstrate de novo synthesis of the leader peptide specified by the tryptophan (trp) operons of several bacterial species. Peptide synthesis was directed by self-ligated short restriction fragments containing the trp promoter and leader regions. Synthesis of leader peptides was established by demonstrating that they were labeled in vitro only by those amino acids predicted to be present in the peptides. Leader peptide synthesis was abolished by the addition of the Escherichia coli trp repressor. The E. coli trp leader peptide was found to be extremely labile in vitro; it had a half-life of 3-4 min. In a highly purified DNA-dependent peptide-synthesizing system, synthesis of the di- and tripeptides predicted from the Salmonella typhimurium trp operon leader sequence, fMet-Ala and fMet-Ala-Ala, also was observed. Using this dipeptide synthesis system, we demonstrated that translation initiation at the ribosome binding site used for trp leader peptide synthesis was reduced 10-fold when the transcript contained a segment complementary to the ribosome binding site.

Coherent anti-Stokes Raman scattering (CARS) spectra, with resonance enhancement, of cytochrome c and vitamin B12 in dilute aqueous solution

Coherent anti-Stokes Raman scattering (CARS) spectra have been obtained for ferrocytochrome c and cyano cobalamin in aqueous solution at millimolar concentrations, using a pair of tunable dye lasers pumped by a pulsed nitrogen laser. Resonance enhancement was obtained by tuning the omega1 laser to the visible absorption bands of the samples. The spectral features correspond to those observed in the conventional resonance Raman spectra. It appears that CARS spectroscopy, with its advantageous fluorescence rejection, can be usefully applied to biological samples by exploiting resonance enhancement. While the background scattering from water is 10 times higher than that of benzene and other aromatic solvents, it is actually at the low end of the scale for most liquids. The anomalously low background of aromatic liquids is thought to result from competition by the unusually efficient stimulated Raman scattering which they display. Off-resonance spectra for both cobalamin and cytochrome c contain negative peaks, i.e., absorption bands in the background. These are interpreted as inverse Raman processes induced by the omega1 photons in the presence of the continuum provided by the background scattering. While both CARS and the inverse Raman effect are subject to resonance enhancement, the wavelength dependence of CARS is evidently steeper.