Are Osteoclasts Mechanosensitive Cells?

Skeleton metabolism is a process in which osteoclasts constantly remove old bone and osteoblasts form new osteoid and induce mineralization; disruption of this balance may cause diseases. Osteoclasts play a key role in bone metabolism, as osteoclastogenesis marks the beginning of each bone remodeling cycle. As the only cell capable of bone resorption, osteoclasts are derived from the monocyte/macrophage hematopoietic precursors that terminally adhere to mineralized extracellular matrix, and they subsequently break down the extracellular compartment. Bone is generally considered the load-burdening tissue, bone homeostasis is critically affected by mechanical conductions, and the bone cells are mechanosensitive. The functions of various bone cells under mechanical forces such as chondrocytes and osteoblasts have been reported; however, the unique bone-resorbing osteoclasts are less studied. The oversuppression of osteoclasts in mechanical studies may be because of its complicated differentiation progress and flexible structure, which increases difficulty in targeting mechanical structures. This paper will focus on recent findings regarding osteoclasts and attempt to uncover proposed candidate mechanosensing structures in osteoclasts including podosome-associated complexes, gap junctions and transient receptor potential family (ion channels). We will additionally describe possible mechanotransduction signaling pathways including GTPase ras homologue family member A (RhoA), Yes-associated protein/transcriptional co-activator with PDZ-binding motif (TAZ), Ca2+ signaling and non-canonical Wnt signaling. According to numerous studies, evaluating the possible influence of various physical environments on osteoclastogenesis is conducive to the study of bone homeostasis.

Potassium Homeostasis

The average potassium intake in the United States population ranges from 90 to 120 mEq/day. About 98% of the total body\'s potassium is intracellular, and only 2% is present in the extracellular compartment. This distributional proportion is essential for cellular metabolic reactions and maintaining a gradient for resting membrane potential. A loss of this gradient results in hyper- or hypopolarization of the cell membrane, especially in cardiac muscles leading to life-threatening arrhythmias. Multiple mechanisms in human maintain homeostasis. Transient initial changes are due to transcellular shifts activating sodium-potassium ATPase pumps on the cell membrane. The kidneys essentially take part in excess potassium excretion, maintaining total body stores constant within normal range. Gastrointestinal secretion of potassium is insignificant in individuals with normal renal function, however plays an essential role in individuals with compromised renal function. So far, a classic feedback mechanism was thought to maintain potassium homeostasis; however, a recently recognized feedforward mechanism acting independently also helps preserve potassium homeostasis. Hence, potassium homeostasis is vital for humans to function at a normal level.

Finding appropriate signal peptides for secretory production of recombinant glucarpidase: an in silico method

Aims: Bioinformatics analysis of suitable signal peptide for recombinant glucarpidase. Background: Methotrexate (MTX) is a general chemotherapeutic agent utilized to treat a variety of malignancies., woefully, its high doses can cause nephrotoxicity and subsequent defect in the process of MTX excretion. The recombinant form of glucarpidase, is produced by engineered E. coli and is a confirmed choice to overcoming this problem. Objective: In the present study, in silico analyses were performed to select suitable SPs for the secretion of recombinant glucarpidase in E. coli. Methods: The signal peptide website and UniProt database were employed to collect the SPs and protein sequences. In the next step, SignalP-5.0 helped us to predict the SPs and the position of cleavage sites. Moreover, physicochemical properties and solubility were evaluated using ProtParam and Protein-sol online software, and finally, ProtCompB was used to predict the final sub-cellular localization. Results: Luckily, all SPs could form soluble fusion proteins. At last, it was found that PPB and TIBA could translocate the glucarpidase into the extracellular compartment. Conclusion: This study showed that there are only 2 applicable SPs for the extracellular translocation of glucarpidase. Although the findings were remarkable with high degrees of accuracy and precision based on the utilization of bioinformatics analyses, additional experimental assessments are required to confirm and validate it. Recent patents revealed several inventions related to the clinical aspects of vaccine peptide against human disorders.

A Methodological Approach Using rAAV Vectors Encoding Nanobody-Based Biologics to Evaluate ARTC2.2 and P2X7 In Vivo

On murine T cells, mono-ADP ribosyltransferase ARTC2.2 catalyzes ADP-ribosylation of various surface proteins when nicotinamide adenine dinucleotide (NAD+) is released into the extracellular compartment. Covalent ADP-ribosylation of the P2X7 receptor by ARTC2.2 thereby represents an additional mechanism of activation, complementary to its triggering by extracellular ATP. P2X7 is a multifaceted receptor that may represents a potential target in inflammatory, and neurodegenerative diseases, as well as in cancer. We present herein an experimental approach using intramuscular injection of recombinant AAV vectors (rAAV) encoding nanobody-based biologics targeting ARTC2.2 or P2X7. We demonstrate the ability of these in vivo generated biologics to potently and durably block P2X7 or ARTC2.2 activities in vivo, or in contrast, to potentiate NAD+- or ATP-induced activation of P2X7. We additionally demonstrate the ability of rAAV-encoded functional heavy chain antibodies to elicit long-term depletion of T cells expressing high levels of ARTC2.2 or P2X7. Our approach of using rAAV to generate functional nanobody-based biologics in vivo appears promising to evaluate the role of ARTC2.2 and P2X7 in murine acute as well as chronic disease models.

MOMC-2. Glioblastoma Metabolic Symbiosis: When Lactate Takes The Lead

Glioblastoma (GBM) is a common and devastating brain tumor, associated with a low median survival, despite standard therapeutic management. Among its major features, GBMs are highly angiogenic and exhibit paradoxically an elevated glycolysis. Most of differentiated cells convert glucose into pyruvate that enters into the Krebs cycle to maximize energy production in the presence of oxygen. For cancer cells, glucose uptake and catabolism are increased regardless of oxygen level. However, their energy needs are important – mainly for rapid growth – that it requires a much faster production flow. It is at this step that lactate dehydrogenase (LDH) are involved: LDHA converts efficiently pyruvate into lactate and generates NAD+ to maintain glycolysis. Thus, the lactate formed is exported into the extracellular compartment inducing an unfavourable acidification of the microenvironment. Moreover, LDHB, another LDH isoform, metabolizes lactate into pyruvate for generating energy in mitochondria. Though LDHA has already been studied in many cancers including GBM, the simultaneous role of LDH enzymes have not yet been investigated in GBM development. Hypoxia-driven LDHA expression and lactate production increased cell invasion. Infusing 13C-lactate in starved cells rescued TCA cycle. Then, we showed that, under hypoxia, double sgLDHA/B cell growth and invasion was dramatically decreased in comparison to control cells, mainly caused by an increase in apoptosis. Moreover, double impairment of LDHA and B significantly reduced tumor growth and cell invasion, and induces a massive increase in mouse survival. Tracing experiments with 13C-Glucose coupled with RNA sequencing revealed how metabolism adapts to these contraints, by modifying electron transport chain subunit expressions or by increasing lipid droplet formation. Considered for a long time as a metabolic waste, lactate is shown here to play a critical role in GBM cell symbiosis. This study highlighted GBM adaptability through the LDH isoforms and their involvement in GBM development.

Sensitivity analysis of solute kinetics in a four compartmental model for hemodialysis patients

Sensitivity Analysis of the most advanced four compartmental mathematical model explaining solute kinetic in the hemodialysis patients was performed on the basis of the data collected from six patients with different Body Mass Indices (BMIs). The toxin concentration in all compartments increases with the decrease in the BMIs of the patients. The clearance rate, kclear, and the volume of extracellular compartment, VE, are the most sensitive while the volume of the muscle tissue compartment, VMT, and the clearance rate, kMT, are the least sensitive parameters during dialytic interval. The production rate, G, and the volume of the extracellular compartment, VE, are the most sensitive while kclear and kE, AT are the least sensitive parameters of all parameters during the interdialytic interval. The overall production rate, G, remains more sensitive than the clearance rate, kclear during one complete cycle.

Approach to Hyponatremia

Hyponatremia is a common laboratory finding in numerous patients. It is defined as a serum sodium concentration <135 mmol/L and represents an excess of water in the extracellular compartment. The severity of this electrolyte abnormality ranges from asymptomatic to seizures, coma and death as a consequence of cerebral swelling. There are multiple medical conditions, medications and disease states that can cause hyponatremia. This article summarizes the important pathophysiological pathways involved in the development of hyponatremia, describes an approach to common causes and reviews the initial steps in management.

Intracellular Hydrogen Peroxide Produced by 6-Hydroxydopamine is a Trigger for Nigral Dopaminergic Degeneration Via Rapid Influx of Extracellular Zn2+

To elucidate the mechanism of 6-hydroxydopamine (6-OHDA)-induced Zn2+ toxicity, which is involved in neurodegeneration in the substantia nigra pars compacta (SNpc) of rats, we postulated that intracellular hydrogen peroxide (H2O2) produced by 6-OHDA is a trigger for intracellular Zn2+ dysregulation in the SNpc. Intracellular H2O2 level in the SNpc elevated by 6-OHDA was completely inhibited by co-injection of GBR 13069 dihydrochloride (GBR), a dopamine reuptake inhibitor, suggesting that 6-OHDA taken up through dopamine transporters produces H2O2 in the intercellular compartment of dopaminergic neurons. When the SNpc was perfused with H2O2, H2O2 accumulated glutamate in the extracellular compartment and the accumulation was inhibited in the presence of N-(p-amylcinnamoyl)anthranilic acid (ACA), a blocker of the transient receptor potential melastatin 2 (TRPM2) channels. In addition to 6-OHDA, H2O2 also induced intracellular Zn2+ dysregulation via AMPA receptor activation followed by nigral dopaminergic degeneration. Furthermore, 6-OHDA-induced nigral dopaminergic degeneration was completely inhibited by co-injection of HYDROP, an intracellular H2O2 scavenger or GBR into the SNpc. The present study indicates that H2O2 is produced by 6-OHDA taken up through dopamine transporters in the SNpc, is retrogradely transported to presynaptic glutamatergic terminals, activates TRPM2 channels, accumulates glutamate in the extracellular compartment, and induces intracellular Zn2+ dysregulation via AMPA receptor activation, resulting in nigral dopaminergic degeneration. It is likely that intracellular H2O2, but not extracellular H2O2, is a key trigger for nigral dopaminergic degeneration via intracellular Zn2+ dysregulation.

Evidence for the extracellular delivery of influenza NS1 protein

We constructed a reporter influenza A/Puerto Rico/8/1934 virus expressing truncated 124aa N-terminal NS1 protein fused to a luciferase reporter sequence (NanoLuc) without signal peptide. The reproduction activity of the vector correlated well with the luminescent activity in the lysates of infected cell cultures or mouse respiratory organ suspensions. Surprisingly, we found that luciferase enzymatic activity was present not only in the intracellular compartments but also in cell culture supernatants as well as in the sera or bronchiolar lavages of infected mice. This fact allowed us to formulate a working hypothesis about the extracellular delivery mechanism of the NS1 protein. To test this idea, we conducted co-transfection experiments in Vero cells with different combinations of plasmids encoding influenza genomic segments and chimeric NS1-NanoLuc encoding plasmid. We found that the emergence of the luciferase reporter in the extracellular compartment was promoted by the formation of the ribonucleoprotein complex (RNP) from the co-transfection of plasmids expressing PB1, PB2, PA, and NP proteins. Therefore, influenza NS1 protein may be delivered to the extracellular compartment together with the nascent RNP complexes during the maturation of virus particles.

Expression and protein sequence analyses of zebrafish impg2a and impg2b, two proteoglycans of the interphotoreceptor matrix

Photoreceptor outer segments projecting from the surface of the neural retina toward the retinal pigment epithelium (RPE) are surrounded by a carbohydrate-rich matrix, the interphotoreceptor matrix (IPM) [1,2]. This extracellular compartment is necessary for physiological retinal function. However, specific roles for molecules characterizing the IPM have not been clearly defined [3]. Recent studies have found the presence of nonsense mutations in the interphotoreceptor matrix proteoglycan 2 (IMPG2) gene in patients affected by autosomal recessive Retinitis Pigmentosa (arRP) [4,5] and autosomal dominant and recessive vitelliform macular dystrophy (VMD) [6,7]. The gene encodes for a proteoglycan synthesized by photoreceptors and secreted in the IPM. However, little is known about the function and structure of this protein. We used the teleost zebrafish (D.rerio) as a model to study IMPG2 expression both during development and in adulthood, as its retina is very similar in humans [8]. In zebrafish, there are two IMPG2 proteins, IMPG2a and IMPG2b. We generated a phylogenetic tree based on IMPG2 protein sequence similarity among different vertebrate species, showing a significant similarity despite the evolutionary distance between humans and teleosts. In fact, human IMPG2 and D.rerio IMPG2a and IMPG2b share conserved SEA and EGF-like domains. Homology models of these domains were obtained by using the iTasser server. Finally, expression analyses of impg2a and impg2b during development and in the adult fish showed expression of both mRNAs starting from 3 days post fertilization (dpf) in the outer nuclear layer of zebrafish retina that continues throughout adulthood. This data lays the groundwork for the generation of novel and most needed animal models for the study of IMPG2-related inherited retinal dystrophies.