Lifelong challenge of calcium homeostasis in male mice lacking TRPV5 leads to changes in bone and calcium metabolism

Decreased calcium permeability caused by biallelic TRPV5 mutation leads to autosomal recessive renal calcium-wasting hypercalciuria

Hypercalciuria is the most common metabolic risk factor in people with kidney stone disease. Its etiology is mostly multifactorial, although monogenetic causes of hypercalciuria have also been described. Despite the increased availability of genetic diagnostic tests, the vast majority of individuals with familial hypercalciuria remain unsolved. In this study, we investigated a consanguineous pedigree with idiopathic hypercalciuria. The proband additionally exhibited severe skeletal deformities and hyperparathyroidism. Whole-exome sequencing of the proband revealed a homozygous ultra-rare variant in TRPV5 (NM_019841.7:c.1792G>A; p.(Val598Met)), which encodes for a renal Ca2+-selective ion channel. The variant segregates with the three individuals with hypercalciuria. The skeletal phenotype unique to the proband was due to an additional pathogenic somatic mutation in GNAS (NM_000516.7:c.601C>T; p.(Arg201Cys)), which leads to polyostotic fibrous dysplasia. The variant in TRPV5 is located in the TRP helix, a characteristic amphipathic helix that is indispensable for the gating movements of TRP channels. Biochemical characterization of the TRPV5 p.(Val598Met) channel revealed a complete loss of Ca2+ transport capability. This defect is caused by reduced expression of the mutant channel, due to misfolding and preferential targeting to the proteasome for degradation. Based on these findings, we conclude that biallelic loss of TRPV5 function causes a novel form of monogenic autosomal recessive hypercalciuria, which we name renal Ca2+-wasting hypercalciuria (RCWH). The recessive inheritance pattern explains the rarity of RCWH and underscores the potential prevalence of RCWH in highly consanguineous populations, emphasizing the importance of exploration of this disorder within such communities.

Preliminary study of the role of nanobacteria in the formation of renal stones in experimental rats and its mechanism

Introduction

The aim of the study was to study the role of nanobacteria in the formation of renal calculi and the underlying mechanism.

Material and methods

A total of 90 clean Wistar male rats were randomly divided into a negative control group, an experimental group, and an interference group. From the end of the first week of modelling, 10 consecutive times once a week, 3 rats in each group were randomly selected to measure the biochemical blood markers and urine metabolism. After sacrifice, the formation of kidney stones was assessed by observing the ultrastructure of the kidney by electron microscopy and pathohistology. Finally, the expression of calcium-sensitive receptor (CaSR) and claudin-14 protein in the kidney tissue was examined by western blotting.

Results

Compared with the control group, the gross structure of the kidney was changed in the model group. At the fourth week of modelling, the rats in the nanobacteria group had significantly enlarged kidneys and increased kidney-to-body ratio, and the difference had statistical significance (p < 0.05). The colour of the kidney profile was dark, the structure of the skin pulp was less clear, and the accumulation of yellowish particles was observed at the junction of the cortical pulp. The creatinine, uric acid, urea nitrogen, and urinary calcium of the rats in the nanobacteria group began to increase at the third week, and the difference between the third and eighth week had statistical significance (p < 0.05). However, the difference between the 3 groups had no statistical significance after the eighth week. At the fourth week, we observed the formation of calculi, which were mainly distributed in the renal tubules and surrounding tissues. The kidney stone formation rate was 52.4% in the nanobacteria group and 27.8% in the interference group, and the difference had statistical significance (p < 0.05). Ultrastructure observations revealed that from the fourth week, the renal tissues in the nanobacteria group showed expanded renal tubules, swollen renal tubular epithelium, granular degeneration, shedding and lymphocyte infiltration of renal tubular epithelial cells, and a small amount of calcium salt crystals in renal tubules. At the third week, the expression of CaSR and Claudin-14 protein in the nanobacteria group increased, and the difference had statistical significance (p < 0.05). The expression of CaSR and Claudin-14 was positively correlated with urinary calcium (p < 0.05).

Conclusions

The formation of renal calculi began in the fourth week after the model was established, and the crystals were mostly located in the renal tubules. During the formation of renal calculi, the renal tubular epithelial cells were damaged, showing granular degeneration and small amounts of calcium salt crystals, accompanied by a few renal tubules beginning to expand and epithelial swelling, granular degeneration, necrosis and shedding of renal tubular epithelial cells, lymphocyte infiltration in the renal interstitium, and small amounts of calcium salt crystals in the renal tubules, which aggravated with time. The serum creatinine, serum uric acid, urea nitrogen, and urinary calcium levels increased with time from the third week and returned to normal after the eighth week. The expression of CaSR and Claudin-14 protein was upregulated and positively correlated with the 24-h urinary calcium excretion value.

Alterations in the microenvironment and the effects produced of TRPV5 in osteoporosis

The pathogenesis of osteoporosis involves multiple factors, among which alterations in the bone microenvironment play a crucial role in disrupting normal bone metabolic balance. Transient receptor potential vanilloid 5 (TRPV5), a member of the TRPV family, is an essential determinant of the bone microenvironment, acting at multiple levels to influence its properties. TRPV5 exerts a pivotal influence on bone through the regulation of calcium reabsorption and transportation while also responding to steroid hormones and agonists. Although the metabolic consequences of osteoporosis, such as loss of bone calcium, reduced mineralization capacity, and active osteoclasts, have received significant attention, this review focuses on the changes in the osteoporotic microenvironment and the specific effects of TRPV5 at various levels.

Calcium-Permeable Channels Cooperation for Rheumatoid Arthritis: Therapeutic Opportunities

Rheumatoid arthritis is a common autoimmune disease that results from the deposition of antibodies–autoantigens in the joints, leading to long-lasting inflammation. The main features of RA include cartilage damage, synovial invasion and flare-ups of intra-articular inflammation, and these pathological processes significantly reduce patients’ quality of life. To date, there is still no drug target that can act in rheumatoid arthritis. Therefore, the search for novel drug targets has become urgent. Due to their unique physicochemical properties, calcium ions play an important role in all cellular activities and the body has evolved a rigorous calcium signaling system. Calcium-permeable channels, as the main operators of calcium signaling, are widely distributed in cell membranes, endoplasmic reticulum membranes and mitochondrial membranes, and mediate the efflux and entry of Ca2+. Over the last century, more and more calcium-permeable channels have been identified in human cells, and the role of this large family of calcium-permeable channels in rheumatoid arthritis has gradually become clear. In this review, we briefly introduce the major calcium-permeable channels involved in the pathogenesis of RA (e.g., acid-sensitive ion channel (ASIC), transient receptor potential (TRP) channel and P2X receptor) and explain the specific roles and mechanisms of these calcium-permeable channels in the pathogenesis of RA, providing more comprehensive ideas and targets for the treatment of RA.

Molecular mechanisms, physiological roles, and therapeutic implications of ion fluxes in bone cells: Emphasis on the cation-Cl- cotransporters

Bone turnover diseases are exceptionally prevalent in human and come with a high burden on physical health. While these diseases are associated with a variety of risk factors and causes, they are all characterized by common denominators, that is, abnormalities in the function or number of osteoblasts, osteoclasts, and/or osteocytes. As such, much effort has been deployed in the recent years to understand the signaling mechanisms of bone cell proliferation and differentiation with the objectives of exploiting the intermediates involved as therapeutic preys. Ion transport systems at the external and in the intracellular membranes of osteoblasts and osteoclasts also play an important role in bone turnover by coordinating the movement of Ca²⁺ , PO₄ ^2- , and H⁺ ions in and out of the osseous matrix. Even if they sustain the terminal steps of osteoformation and osteoresorption, they have been the object of very little attention in the last several years. Members of the cation-Cl^- cotransporter (CCC) family are among the systems at work as they are expressed in bone cells, are known to affect the activity of Ca²⁺ -, PO₄ ^2- -, and H⁺ -dependent transport systems and have been linked to bone mass density variation in human. In this review, the roles played by the CCCs in bone remodeling will be discussed in light of recent developments and their potential relevance in the treatment of skeletal disorders.

Effects and mechanisms of microenvironmental acidosis on osteoclast biology

Due to continuous bone remodeling, the bone tissue is dynamic and constantly being updated. Bone remodeling is precisely regulated by the balance between osteoblast-induced bone formation and osteoclast-induced bone resorption. As a giant multinucleated cell, formation and activities of osteoclasts are regulated by macrophage colony-stimulating factor (M-CSF), receptor activator of nuclear factor-kappaB ligand (RANKL), and by pathological destabilization of the extracellular microenvironment. Microenvironmental acidosis, as the prime candidate, is a driving force of multiple biological activities of osteoclast precursor and osteoclasts. The mechanisms involved in these processes, especially acid-sensitive receptors/channels, are of great precision and complicated. Recently, remarkable progress has been achieved in the field of acid-sensitive mechanisms of osteoclasts. It is important to elucidate the relationship between microenvironmental acidosis and excessive osteoclasts activity, which will help in understanding the pathophysiology of diseases that are associated with excess bone resorption. This review summarizes physiological consequences and in particular, potential mechanisms of osteoclast precursor or osteoclasts in the context of acidosis microenvironments.