Changes in skeletal muscle expression of AQP1 and AQP4 in dystrophinopathy and dysferlinopathy patients

Non-coding RNAs and Aquaporin 4: Their Role in the Pathogenesis of Neurological Disorders

Neurological disorders are a major group of non-communicable diseases affecting quality of life. Non-Coding RNAs (ncRNAs) have an important role in the etiology of neurological disorders. In studies on the genesis of neurological diseases, aquaporin 4 (AQP4) expression and activity have both been linked to ncRNAs. The upregulation or downregulation of several ncRNAs leads to neurological disorder progression by targeting AQP4. The role of ncRNAs and AQP4 in neurological disorders is discussed in this review.

Renal dysfunction in AQP4 NMOSD and MS; a potential predictor of relapse and prognosis

OBJECTIVE

This study aimed to explore the association between kidney function and the risk of relapse as well as prognosis in patients with aquaporin-4 (AQP4)-immunoglobulin G (IgG)-seropositive neuromyelitis optica spectrum disorder (NMOSD).

METHODS

We focused on patients experiencing their first onset of AQP4-IgG-seropositive NMOSD. Data on demographics, disease characteristics, and kidney function were collected, with the primary assessment utilizing the estimated glomerular filtration rate (eGFR). Associations between eGFR and relapse risk were examined using multivariate Cox proportional hazards regression models. Additionally, logistic regression models were employed to evaluate the impact of eGFR on clinical prognosis.

RESULTS

Our analysis revealed glomerular hyperfiltration and impaired urine concentrating ability in patients with AQP4-IgG-seropositive NMOSD. Multivariate Cox proportional hazards regression demonstrated a positive correlation between eGFR and the risk of relapse. Logistic regression analysis further identified higher eGFR as an independent predictor of disease relapse and prognosis in AQP4-IgG-seropositive NMOSD patients.

CONCLUSIONS

The eGFR of patients with AQP4-IgG-seropositive NMOSD emerges as a potential diagnostic biomarker for this condition, indicating its significance in predicting both relapse risk and clinical prognosis.

Characterization and comparative transcriptomic analysis of skeletal muscle in female Pekin duck and Hanzhong Ma duck during different growth stages using RNA-seq

Duck is an economically important poultry, and there is currently a major focus on improving its meat quality through breeding. There are wide variations in the growth regulation mechanisms of different duck breeds, that fundamental research on skeletal muscle growth is essential for understanding the regulation of unknown genes. The study aimed to broaden the understanding the duck skeletal muscle development and thereby to improve the performance of domestic ducks. In this study, RNA-seq data from skeletal muscles (breast muscle and leg muscle) of Pekin duck and Hanzhong Ma duck sampled at d 17, 21, and 27 of embryo (E17d, E21d, and E27d), as well as at 6-mo-old following birth (M6), to investigate and compare the mRNA temporal expression profiles and associated pathways that regulate skeletal myogenesis of different duck breeds. There were 331 to 1,440 annotated differentially expressed genes (DEGs) in breast muscle and 380 to 1,790 annotated DEGs in leg muscle from different databases between 2 duck breeds. Gene ontology (GO) enrichment in skeletal muscles indicated that these DEGs were mainly involved in biosynthetic process, developmental process, regulation of protein metabolic process and regulation of gene expression. KEGG analysis in skeletal muscles showed that a total of 41 DEGs were mapped to 7 KEGG pathways, including ECM-receptor interaction, focal adhesion, carbon metabolism, regulation of actin cytoskeleton, calcium signaling pathway, biosynthesis of amino acids and PPAR signaling pathway. The differential expression of 8 selected DEGs was verified by qRT-PCR, and the results were consistent with RNA-seq data. The identified DEGs, such as SDC, SPP1, PAK1, MYL9, PGK1, NOS1, PHGDH, TNNT2, FN1, and AQP4, were specially highlighted, indicating their associations with muscle development in the Pekin duck and Hanzhong Ma duck. This study provides a basis for revealing the differences in skeletal muscle development between Pekin duck and Hanzhong Ma duck.

Changes in aquaporins expression due to acute water restriction in naturally aging mice

Aquaporins (AQPs) are water channels in the cell membrane that regulate osmosis in response to rapid changes in intracellular and extracellular fluid concentration caused by extrinsic factors. While there are so many studies on the association of AQPs with muscular atrophy, sarcopenia, and Duchenne muscular dystrophy (DMD), the expression of AQP has not been verified in naturally aging mice or humans. Notably, due to the characteristics of AQPs, the difference in function cannot be evaluated without extrinsic factors such as acute water restriction. The purpose of this study was to investigate the changes in AQPs expression and function due to natural aging under acute water restriction conditions in aging mice. The expression of AQP4 was shown to decrease with aging similar to previous studies. However, for the first time, this study results confirmed that AQP1 expression increased in aging mice. In addition, the expression of Aqp1 decreased in the acute water restricted group compared to the control group after acute water restriction in aging mice. These results suggest that although the expression of AQP1 increases with aging, its function is reduced. We also confirmed that overexpression of Aqp1 can inhibit myotube differentiation and that knockdown can promote myotube differentiation through in vitro experiments. In conclusion, based on our results, we suggest that the AQP1 is an important factor in sarcopenia caused by natural aging accompanied by chronic dehydration.

Assessing the Role of Aquaporin 4 in Skeletal Muscle Function

Water transport across the biological membranes is mediated by aquaporins (AQPs). AQP4 and AQP1 are the predominantly expressed AQPs in the skeletal muscle. Since the discovery of AQP4, several studies have highlighted reduced AQP4 levels in Duchenne muscular dystrophy (DMD) patients and mouse models, and other neuromuscular disorders (NMDs) such as sarcoglycanopathies and dysferlinopathies. AQP4 loss is attributed to the destabilizing dystrophin-associated protein complex (DAPC) in DMD leading to compromised water permeability in the skeletal muscle fibers. However, AQP4 knockout (KO) mice appear phenotypically normal. AQP4 ablation does not impair physical activity in mice but limits them from achieving the performance demonstrated by wild-type mice. AQP1 levels were found to be upregulated in DMD models and are thought to compensate for AQP4 loss. Several groups investigated the expression of other AQPs in the skeletal muscle; however, these findings remain controversial. In this review, we summarize the role of AQP4 with respect to skeletal muscle function and findings in NMDs as well as the implications from a clinical perspective.

Signaling Mechanisms and Pharmacological Modulators Governing Diverse Aquaporin Functions in Human Health and Disease

The aquaporins (AQPs) are a family of small integral membrane proteins that facilitate the bidirectional transport of water across biological membranes in response to osmotic pressure gradients as well as enable the transmembrane diffusion of small neutral solutes (such as urea, glycerol, and hydrogen peroxide) and ions. AQPs are expressed throughout the human body. Here, we review their key roles in fluid homeostasis, glandular secretions, signal transduction and sensation, barrier function, immunity and inflammation, cell migration, and angiogenesis. Evidence from a wide variety of studies now supports a view of the functions of AQPs being much more complex than simply mediating the passive flow of water across biological membranes. The discovery and development of small-molecule AQP inhibitors for research use and therapeutic development will lead to new insights into the basic biology of and novel treatments for the wide range of AQP-associated disorders.

Increased oxidative stress and cancer biomarkers in the ventral prostate of older rats submitted to maternal malnutrition

The concept of Developmental Origins of Health and Disease (DOHaD) states that exposure to malnutrition early in life increase the incidence of non-communicable chronic diseases throughout the lifespan. In this study, a reduction in serum testosterone and an increase in estrogen levels were shown in older rats born to protein malnourished dams (6% protein in the diet) during gestation and lactation. Intraprostatic levels of reduced glutathione were decreased, while tissue expression of glutathione S-transferase pi and sulfiredoxin-1 were increased in these animals. Strong immunostaining for alfametilacil CoA racemase (AMACR), vascular endothelial growth factor-A (VEGF-A), and aquaporin-1 (AQP1) was also observed. In silico analysis confirmed commonly deregulated proteins in the ventral prostate of old rats and patients with prostate cancer. In conclusion, the increase in oxidative stress associated with an imbalance of sex hormones may contribute to prostate carcinogenesis in offspring, highlighting early-life malnutrition as a key risk factor for this malignance.

Recurrent HyperCKemia with Immunological Involvement of the Endomysial Capillaries in Neuromyelitis Optica

A 55-year-old woman with neuromyelitis optica (NMO) had recurrent myalgias with hyperCKemia. A muscle biopsy suggested nonspecific myopathic changes. Regarding immunohistochemistry, the expression of both major histocompatibility complex class I and myxovirus resistance protein A was observed in the endomysial capillaries, suggesting immunological involvement of these capillaries, whereas both C5b9 (membrane attack complex) and aquaporin 4 immunofluorescence stainings were normal. The present findings led us to conclude that one possible mechanism for hyperCKemia in NMO underlying the immunological involvement of the endomysial capillaries was an as-yet-unidentified factor that triggered damage to the integrity of the sarcolemma and thereby cause CK leakage into the serum.

The expression of aquaporin-4 is regulated based on innervation in skeletal muscles

Aquaporin-4 (AQP4) is a selective water channel, which expresses on the plasma membrane of myofibers and regulates the osmotic pressure, energy metabolism and morphological changes in myofibers by modulating water transport across sarcolemma in skeletal muscles. Although the physiological roles of AQP4 have been gradually clarified in skeletal muscles, the regulatory mechanisms of AQP4 expression have been poorly understood in skeletal muscles. Recently, it was reported that the expression of AQP4 decreased in atrophied skeletal muscles following sciatic nerve transection, but not tail-suspension. Therefore, expecting that the nerve supply to myofibers would be one of the major regulatory factors regulating AQP4 expression in skeletal muscles, we investigated whether the expression patterns of AQP4 were changed in skeletal muscles by denervation and subsequent reinnervation. As a result, while the APQ4 expression levels were significantly decreased by sciatic nerve freezing-induced denervation, subsequently the expression levels of AQP4 were fully restored during reinnervation in skeletal muscles (p < 0.05, respectively). On the other hand, the expression levels of α1-syntrophin and AQP1, which are respectively structural and functional related AQP4 factors, were stably maintained during the denervation and subsequent reinnervation. Therefore, the present study demonstrated that the expression of AQP4 may be regulated depending on the innervation to skeletal muscles. Moreover, AQP4 regulatory mechanisms may be fundamentally different to those of AQP1 in skeletal muscles.

Aquaporin 4 expression in human skeletal muscle fiber types

INTRODUCTION

Aquaporins (AQPs) are a family of transmembrane proteins involved in the maintenance of osmotic gradients. AQP4 is abundant in skeletal muscle, where it seems to be associated with glycolytic metabolism. We investigated the pattern of expression of AQP4 in normal human myofibers relative to the main forms of myosin heavy chain (MHC).

METHODS

Six normal human muscle biopsies were analyzed by double immunofluorescence for co-expression of AQP4 and slow or fast MHC.

RESULTS

A high percentage (64-99%) of MHC-fast positive fibers showed immunoreaction for AQP4. Immunoreactivity for AQP4 was also present in MHC-slow positive fibers, but with a higher variability (5-72%) among biopsies.

DISCUSSION

The expression pattern of AQP4 in human myofibers is highly variable among different patients and cannot be predicted for single fibers depending on MHC type expression. Other factors, possibly related to muscle activity, may modulate AQP4 expression. Muscle Nerve 57: 856-859, 2018.

Impairment of microvascular angiogenesis is associated with delay in prostatic development in rat offspring of maternal protein malnutrition

Experimental data demonstrated the negative impact of maternal protein malnutrition (MPM) on rat prostate development, but the mechanism behind the impairment of prostate growth has not been well understood. Male Sprague Dawley rats, borned to dams fed a normal protein diet (CTR group, 17% protein diet), were compared with those borned from dams fed a low protein diet (6% protein diet) during gestation (GLP group) or gestation and lactation (GLLP). The ventral prostate lobes (VP) were removed at post-natal day (PND) 10 and 21, and analyzed via different methods. The main findings were low birth weight, a reduction in ano-genital distance (AGD, a testosterone-dependent parameter), and an impairment of prostate development. A delay in prostate morphogenesis was associated with a reduced testosterone levels and angiogenic process through downregulation of aquaporin-1 (AQP-1), insulin/IGF-1 axis and VEGF signaling pathway. Depletion of the microvascular network, which occurs in parallel to the impairment of proliferation and differentiation of the epithelial cells, affects the bidirectional flux between blood vessels impacting prostatic development. In conclusion, our data support the hypothesis that a reduction in microvascular angiogenesis, especially in the subepithelial compartment, is associated to the impairment of prostate morphogenesis in the offspring of MPM dams.

Investigation of the effects of aging on the expression of aquaporin 1 and aquaporin 4 protein in heart tissue

Objective:

Aquaporin (AQP) 1 and AQP 4 are expressed in human heart and several studies have been focused on these two aquaporins. For this purpose, the present study is aimed to research the effects of aging on AQP 1 and AQP 4 in heart tissue.

Methods:

In this study, 14 Balb/C type white mice were used. Animals were divided into two equal groups. Group I consisted of 2-month-old young animals (n=7), and group II consisted of 18-month-old animals (n=7). To determine the AQP1 and AQP4 expression in the myocardium, the heart tissue was removed to perform western blotting and immunohistochemical and histopathological evaluations.

Results:

Muscle fibers of the heart in aged animals were more irregular and loosely organized in hematoxylin–eosin (H&E) stained sections. H-score analysis revealed that AQP1 and AQP4 immunoreactivity significantly increased in heart tissues of old mice compared with those of young mice (p<0.001). In addition, AQP1 and AQP4 protein expressions in the tissues of old animals were increased significantly according to western blot analysis (p=0.018 and p<0.001 for AQP1 and AQP4, respectively).

Conclusion:

Increased AQP1 and AQP4 levels in the heart tissue may be correlated with the maintenance of water and electrolytes balance, which decreases with aging. In this context, it might be the result of a compensatory response to decreased AQP4 functions. In addition, this increase with aging as demonstrated in our study might be one of the factors that increases the tendency of ischemia in elder people.

Aquaporin-4 expression in distal myopathy with rimmed vacuoles

Background

Distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy is clinically characterized by the early involvement of distal leg muscles. The striking pathological features of the myopathy are muscle fibers with rimmed vacuoles. To date, the role of aquaporin-4 water channel in distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy has not been studied.

Case presentation

Here, we studied the expression of aquaporin-4 in muscle fibers of a patient with distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy. Immunohistochemical and immunofluorescence analyses showed that sarcolemmal aquaporin-4 immunoreactivity was reduced in many muscle fibers of the patient. However, the intensity of aquaporin-4 staining was markedly increased at rimmed vacuoles or its surrounding areas and in some muscle fibers. The fast-twitch type 2 fibers were predominantly involved with the strong aquaporin-4-positive rimmed vacuoles and TAR-DNA-binding protein-43 aggregations. Rimmed vacuoles with strong aquaporin-4 expression seen in the distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy patient were not found in control muscles without evidence of neuromuscular disorders and the other disease-controls.

Conclusions

Aquaporin-4 might be crucial in determining the survival or degeneration of fast-twitch type 2 fibers in distal myopathy with rimmed vacuoles/hereditary inclusion body myopathy.

Development of a Novel Ligand, [C]TGN-020, for Aquaporin 4 Positron Emission Tomography Imaging

Aquaporin 4 (AQP4), the most abundant isozyme of the water specific membrane transporter aquaporin family, has now been implicated to play a significant role in the pathogenesis of various disease processes of the nervous system from epilepsy to Alzheimer’s disease. Considering its clinical relevance, it is highly desirable to develop a noninvasive method for the quantitative analysis of AQP distribution in humans under clinical settings. Currently, the method of choice for such diagnostic examinations continues to be positron emission tomography (PET). Here, we report the successful development of a PET ligand for AQP4 imaging based on TGN-020, a potent AQP4 inhibitor developed previously in our laboratory. Utilizing [¹¹C]-TGN-020, PET images were successfully generated in wild type and AQP4 null mice, providing a basis for future evaluation regarding its suitability for clinical studies.

Aquaporin 4 Expression in the mdx Mouse Diaphragm

Expression of aquaporin (AQP) 4 in the surface membranes of skeletal myofibers is well established; however, its functional significance is still unknown. The alterations of AQP4 expressions in dystrophic muscles at RNA and protein levels have been reported in various dystrophic muscles such as dystrophinopathy, dysferlinopathy, and sarcoglycanopathy. We are interested in the relationship between the severity of dystrophic muscle degeneration and the expression of AQP4. Here we compared the AQP4 expression of the limb muscles with that of diaphragms in both mdx and control mice. The dystrophic muscle degeneration, such as rounding profile of cross sectional myofiber shape, dense eosin staining, central nuclei, and endomysial fibrosis in mdx mice, were more marked in diaphragms than in limb muscles. The decrease of AQP4 expression at protein level was more marked in diaphragms than in the limb muscles of mdx mice. However, the expression of AQP4 mRNA in the diaphragms of mdx mice was not reduced in comparison with limb muscles of mdx mice. The present study revealed that AQP4 expression at protein level was correlated with the severity of dystrophic changes in muscle tissues of mdx mice.

Structure and functions of aquaporin-4-based orthogonal arrays of particles

Orthogonal arrays or assemblies of intramembranous particles (OAPs) are structures in the membrane of diverse cells which were initially discovered by means of the freeze-fracturing technique. This technique, developed in the 1960s, was important for the acceptance of the fluid mosaic model of the biological membrane. OAPs were first described in liver cells, and then in parietal cells of the stomach, and most importantly, in the astrocytes of the brain. Since the discovery of the structure of OAPs and the identification of OAPs as the morphological equivalent of the water channel protein aquaporin-4 (AQP4) in the 1990s, a plethora of morphological work on OAPs in different cells was published. Now, we feel a need to balance new and old data on OAPs and AQP4 to elucidate the interrelationship of both structures and molecules. In this review, the identity of OAPs as AQP4-based structures in a diversity of cells will be described. At the same time, arguments are offered that under pathological or experimental circumstances, AQP4 can also be expressed in a non-OAP form. Thus, we attempt to project classical work on OAPs onto the molecular biology of AQP4. In particular, astrocytes and glioma cells will play the major part in this review, not only due to our own work but also due to the fact that most studies on structure and function of AQP4 were done in the nervous system.

Aquaporin expression in normal and pathological skeletal muscles: a brief review with focus on AQP4

Freeze-fracture electron microscopy enabled us to observe the molecular architecture of the biological membranes. We were studying the myofiber plasma membranes of health and disease by using this technique and were interested in the special assembly called orthogonal arrays (OAs). OAs were present in normal myofiber plasma membranes and were especially numerous in fast twitch type 2 myofibers; while OAs were lost from sarcolemmal plasma membranes of severely affected muscles with dystrophinopathy and dysferlinopathy but not with caveolinopathy. In the mid nineties of the last century, the OAs turned out to be a water channel named aquaporin 4 (AQP4). Since this discovery, several groups of investigators have been studying AQP4 expression in diseased muscles. This review summarizes the papers which describe the expression of OAs, AQP4, and other AQPs at the sarcolemma of healthy and diseased muscle and discusses the possible role of AQPs, especially that of AQP4, in normal and pathological skeletal muscles.