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Background: Osteoarthritis (OA) is a significant social problem as it is the most common disease of the joints. OA is a multifactorial disease in which great attention is paid to hereditary factors. Recently, a number of studies have demonstrated the contribution of a number of genes to the subjective assessment of pain in OA, which is the main symptom of this disease. The association of P2X7, TRPV1 and TACR1 genes and some others with pain sensitivity has been shown. One of the risk factors of pain among many others, is the increased weight. Abdominal adipose tissue is a source of release of pro-inflammatory adipokines that cause systemic inflammation associated with damage to many tissues, including subchondral bone, synovial membrane. Leptin is an endogenous hormone from the adipokine family encoded by the obesity gene leptin (LEP) and which is synthesized primarily in adipocytes.Aims: To investigate the possible association of rs2167270 (A19G) polymorphism of the LEP gene with pain intensity in ­patients with knee OA.Materials and methods: The study was conducted among women diagnosed with OA. Using the VAS scale (Visual analog scale), patients with mild knee pain — group 1 (VAS ≤ 40 mm) and patients with moderate or severe pain — group 2 (VAS>40 mm) were selected for pain assessment. Genetic variants of A19G leptin gene polymorphism were studied by polymerase chain reaction followed by restriction fragment length analysis (PCR-RFLP) method.Results: In the group of patients with moderate or severe pain intensity (group 2, n=61), a statistically significant association was shown with a higher body mass index (p=0.006) and an increased frequency of carriers of the 19GG genotype (p=0,051) compared to group 1 (n=36). Carriers of the 19GG genotype statistically significantly had a higher rate of knee pain and an early age of OA debut compared to carriers of the 19AA genotype (p=0,035 and p=0,015, respectively).Conclusions: The findings open up new possibilities for predicting pain symptoms in patients with knee OA by genetic testing of A19G polymorphic variants of the leptin gene.

Background ― A number of studies confirmed a crucial role of type 1 interferon in pathophysiology of connective tissue diseases. Interferon regulatory factors (IRF) coordinate an expression of type 1 interferon, while interferon regulatory factor 5 (IRF5) gene was recently identified as causing predisposition to systemic lupus erythematosus and Sjögren syndrome. The objective of our study was to identify possible association of IRF5 rs2004640 (G/T) single nucleotide polymorphism with systemic sclerosis (SSc). Material and Methods―The study involved 236 individuals, including 105 patients with SSc diagnosis and 131 control individuals from Moscow region. The latter were healthy, unrelated to each other, their genders and ages were matched to those of SSc patients. Allele-specific real-time polymerase chain reaction (PCR) was used to study IFR5 rs2004640 polymorphism. Results ― We detected significantly higher percentage of IRF5 T-allele carriers in all patients (59.5%), those with diffuse cutaneous SSc (67.3%), patients with interstitial lung lesions (62.3%), and those with positive titers of anti-topoisomerase I antibodies (66.3%), compared with control group (46.2%). The odds ratios (OR) were: 1.71 (р=0.00), 2.40 (р=0.0004), 1.93 (р=0.002), and 2.30 (р=0.0008), correspondingly. Conclusion ― The replacement of nucleotide G by T in the IRF5 rs2004640 gene polymorphism was associated with a predisposition to SSc. Our data implied an existence of a novel SSc pathogenetic pathway associated with important role of type 1 interferon in pathophysiology of connective tissue diseases.

Abstract The origin of the friction between sliding bodies establishes an outstanding scientific problem. In this article, we demonstrate that the energy loss in each microscopic slip event between the bodies readily follows from the dephasing of phonons that are generated in the slip process. The dephasing mechanism directly links the typical timescales of the lattice vibrations with those of the experienced energy ‘dissipation’ and manifests itself as if the slip-induced motion were close to critically damped. Graphical abstract

We are grateful to Dr. B.N.J. Persson for his prompt attention to our work (Hu et al. in Tribol Lett, 10.1007/s11249-019-1247-7, 2020). In his Comment, he remarks (i) that near-critical damping of motion in/on solids, one of our main results, is well known for atoms and molecules at surfaces and (ii) that this result may be invalid for real practical cases (Persson in Tribol Lett, this issue). We fully agree with both statements. However, some discussion is justified.

It has been shown that, in spite of the success achieved in describing atomic-scale friction, serious problems concerning friction force microscopy remain unsolved. The traditional theoretical approach, which, on default, ignores possible effects of nonlocality and memory, leads to a number of contradictions. Proceeding from the general concepts of nonequilibrium statistical mechanics, rigorous analysis, and simple atomistic simulation, it has been shown that the phonon mechanism of energy dissipation upon friction is essentially nonlocal with the prevalence of memory effects.

In this paper, we use a set of rate equations to describe the thermal activation of a tip moving along a one-dimensional lattice, including the possibility of multiple back and forth jumps between neighboring potential wells. This description of an atomic-scale friction experiment is used to investigate how temperature acts as a lubricant, an effect that we refer to as thermolubricity. We discuss the detailed theoretical aspects of the model, which explains many aspects of the variation in atomic friction over a wide range of temperatures, velocities, and surface corrugations. We conclude that friction at low velocities and low surface corrugations is much lower than the weak logarithmic velocity dependence predicted before. Another consequence of the model is the trivial result that friction is zero in the zero-velocity limit. We confront numerical results from our theoretical model with experiments, in which the surface corrugation was controlled by use of geometrical effects, to demonstrate the experimental existence of thermolubricity. Although the calculations produce excellent fits to our data, the values of the fitting parameters clearly indicate that the underlying single-spring model suffers from an intrinsic flaw, which we ascribe to either the absence of flexibility of the tip or the restriction to a one-dimensional sliding geometry.

This paper summarizes and extends results from a series of recent investigations of atomic scale friction, in which an ultra-low effective mass and a corresponding thermal delocalization of the contact play a dominant role. A rich variety of physically different regimes of friction concerned with the contact delocalization are analyzed in a systematic way and visualized by advanced numerical calculations. The results shed an essentially new light on what is actually measured in friction force microscopy and suggest the necessity to reinterpret many seemingly standard experiments. Even more importantly, our results can possibly be extended to the asperities that establish the contact between two sliding bodies thus predicting a much more pronounced role of thermally driven dynamics in macroscopic sliding than has ever been imagined. The paper is supplied with a detailed introduction to the subject, aimed at a general physical audience.

Shortly after the invention of the atomic force microscope (AFM) this instrument has been applied [1 ]a s a friction force microscope (FFM). This seemingly trivial extension of the AFM to the lateral direction has enjoyed great interest [2], since it is believed to provide direct atomic-scale access to the phenomenon of friction. Experiments with atomic resolution typically show periodic, sawtoothlike behavior of the lateral force known as stick-slip. The FFM tip is thought to be held periodically in lattice positions of the surface, which is easily modeled using a quasistatic approach, first proposed by Prandtl [3] and often referred to as the Tomlinson model [4 –6]. An object (the tip) is considered to move in a periodic potential field formed by the substrate lattice, while being dragged along the surface by an external spring (the cantilever), which is at the same time used to measure the lateral force experienced. Generalizations of the model, from dynamical modeling to nonequilibrium statistical mechanics [7], have advanced our understanding of atomic-scale friction, e.g., its velocity dependence, transitions from stick-slip to other regimes, and the role of thermal effects [4,8–10].