Vitamin D and calcium co-therapy mitigates pre-established cadmium nephropathy by regulating renal calcium homeostatic molecules and improving anti-oxidative and anti-inflammatory activities in rat

BACKGROUND

Cadmium (Cd) is a major environmental pollutant and chronic toxicity could induce nephropathy by increasing renal oxidative stress and inflammation. Although vitamin D (VD) and calcium (Ca) prophylactic treatments attenuated Cd-induced cell injury, none of the prior studies measure their renoprotective effects against pre-established Cd-nephropathy.

AIMS

To measure the alleviating effects of VD and/or Ca single and dual therapies against pre-established nephrotoxicity induced by chronic Cd toxicity prior to treatment initiation.

METHODS

Forty male adult rats were allocated into: negative controls (NC), positive controls (PC), Ca, VD and VC groups. The study lasted for eight weeks and all animals, except the NC, received CdCl₂ in drinking water (44 mg/L) throughout the study. Ca (100 mg/kg) and/or VD (350 IU/kg) were given (five times/week) during the last four weeks to the designated groups. Subsequently, the expression of transforming growth factor-β (TGF-β1), inducible nitric oxide synthase (iNOS), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), VD synthesising (Cyp27b1) and catabolizing (Cyp24a1) enzymes with VD receptor (VDR) and binding protein (VDBP) was measured in renal tissues. Similarly, renal expression of Ca voltage-dependent channels (Ca_V1.1/Ca_V3.1), store-operated channels (RyR1/ITPR1), and binding proteins (CAM/CAMKIIA/S100A1/S100B) were measured. Serum markers of renal function alongside several markers of oxidative stress (MDA/H₂O₂/GSH/GPx/CAT) and inflammation (IL-6/TNF-α/IL-10) together with renal cell apoptosis and expression of caspase-3 were also measured.

RESULTS

The PC group exhibited hypovitaminosis D, hypocalcaemia, hypercalciuria, proteinuria, reduced creatinine clearance, and increased renal apoptosis/necrosis with higher caspase-3 expression. Markers of renal tissue damage (TGF-β1/iNOS/NGAL/KIM-1), oxidative stress (MDA/H₂O₂), and inflammation (TNF-α/IL-1β/IL-6) increased, whilst the antioxidants (GSH/GPx/CAT) and IL-10 decreased, in the PC group. The PC renal tissues also showed abnormal expression of Cyp27b1, Cyp24a1, VDR, and VDBP, alongside Ca-membranous (Ca_V1.1/Ca_V3.1) and store-operated channels (RyR1/ITPR1) and cytosolic Ca-binding proteins (CAM/CAMKIIA/S100A1/S100B). Although VD was superior to Ca monotherapy, their combination revealed the best mitigation effects by attenuating serum and renal tissue Cd concentrations, inflammation and oxidative stress, alongside modulating the expression of VD/Ca-molecules.

CONCLUSIONS

This study is the first to show improved alleviations against Cd-nephropathy by co-supplementing VD and Ca, possibly by better regulation of Ca-dependent anti-oxidative and anti-inflammatory actions.

Ca2+ signalling system initiated by endoplasmic reticulum stress stimulates PERK activation

The accumulation of unfolded proteins within the Endoplasmic Reticulum (ER) activates a signal transduction pathway termed the unfolded protein response (UPR), which attempts to restore ER homoeostasis. If this cannot be done, UPR signalling ultimately induces apoptosis. Ca²⁺ depletion in the ER is a potent inducer of ER stress. Despite the ubiquity of Ca²⁺ as an intracellular messenger, the precise mechanism(s) by which Ca²⁺ release affects the UPR remains unknown. Tethering a genetically encoded Ca²⁺ indicator (GCamP6) to the ER membrane revealed novel Ca²⁺ signalling events initiated by Ca²⁺ microdomains in human astrocytes under ER stress, induced by tunicamycin (Tm), an N-glycosylation inhibitor, as well as in a cell model deficient in all three inositol triphosphate receptor isoforms. Pharmacological and molecular studies indicate that these local events are mediated by translocons and that the Ca²⁺ microdomains impact (PKR)-like-ER kinase (PERK), an UPR sensor, activation. These findings reveal the existence of a Ca²⁺ signal mechanism by which stressor-mediated Ca²⁺ release regulates ER stress.

Endoplasmic reticulum-mitochondria coupling attenuates vanadium-induced apoptosis via IP3R in duck renal tubular epithelial cells

Vanadium (V) is necessary for the health and growth of animals, but excessive V has harmful effects on the ecosystem health. Endoplasmic reticulum (ER)-mitochondria coupling as a membrane structure connects the mitochondrial outer membrane with the ER. The mitochondria-associated ER membrane (MAM) is a region of the ER-mitochondria coupling and is essential for normal cell function. Currently, the crosstalk between ER-mitochondrial coupling and apoptosis in the toxic mechanism of V on duck kidney is still unclear. In this study, duck renal tubular epithelial cells were incubated with different concentrations of sodium metavanadate (NaVO₃) and/or inositol triphosphate receptor (IP₃R) inhibitor 2-aminoethyl diphenyl borate (2-APB) for 24 h. The results showed that V could significantly increase lactate dehydrogenase (LDH) release, the mitochondrial calcium level and the numbers of the fluorescent signal points of IP₃R; shortened the length ER-mitochondria coupling and reduced its formation; markedly upregulate the mRNA levels of MAM-related genes and protein levels, causing MAM dysfunction. Additionally, V treatment appeared to upregulate pro-apoptotic genes and downregulate anti-apoptotic genes, followed by cell apoptosis. The V-induced changes were alleviated by treatment with IP₃R inhibitor. In summary, V could induce the dysfunction of ER-mitochondrial coupling and apoptosis, and inhibition of ER-mitochondrial coupling could attenuate V-induced apoptosis in duck renal tubular epithelial cells.

IP3 receptor blockade restores autophagy and mitochondrial function in skeletal muscle fibers of dystrophic mice

Duchenne muscular dystrophy (DMD) is characterized by a severe and progressive destruction of muscle fibers associated with altered Ca²⁺ homeostasis. We have previously shown that the IP₃ receptor (IP₃R) plays a role in elevating basal cytoplasmic Ca²⁺ and that pharmacological blockade of IP₃R restores muscle function. Moreover, we have shown that the IP₃R pathway negatively regulates autophagy by controlling mitochondrial Ca²⁺ levels. Nevertheless, it remains unclear whether IP₃R is involved in abnormal mitochondrial Ca²⁺ levels, mitochondrial dynamics, or autophagy and mitophagy observed in adult DMD skeletal muscle. Here, we show that the elevated basal autophagy and autophagic flux levels were normalized when IP₃R was downregulated in mdx fibers. Pharmacological blockade of IP₃R in mdx fibers restored both increased mitochondrial Ca²⁺ levels and mitochondrial membrane potential under resting conditions. Interestingly, mdx mitochondria changed from a fission to an elongated state after IP₃R knockdown, and the elevated mitophagy levels in mdx fibers were normalized. To our knowledge, this is the first study associating IP₃R1 activity with changes in autophagy, mitochondrial Ca²⁺ levels, mitochondrial membrane potential, mitochondrial dynamics, and mitophagy in adult mouse skeletal muscle. Moreover, these results suggest that increased IP₃R activity in mdx fibers plays an important role in the pathophysiology of DMD. Overall, these results lead us to propose the use of specific IP₃R blockers as a new pharmacological treatment for DMD, given their ability to restore both autophagy/mitophagy and mitochondrial function.

Genotype-specific alterations in vascular smooth muscle cell function in cystic fibrosis piglets

BACKGROUND

The most common CF-causing mutations interfere with CFTR trafficking from the endoplasmic reticulum (CFTR-F508del) or prematurely terminate transcription (CFTR-null). We suspected that genotype-specific patterns of CFTR expression would have differential effects on smooth muscle cell calcium signaling and hence vascular tone. We hypothesized that compared to wild-type or CFTR-null aorta, aorta from CFTR-F508del (dF) piglets will have reduced endoplasmic reticulum calcium mobilization and decreased vasoconstriction.

METHODS

Aortic reactivity was assessed by myography, and ratiometric calcium imaging was performed in isolated vascular smooth muscle cells.

RESULTS

Aorta from dF piglets had reduced myogenic tone (P<0.001) and decreased constriction to KCl (P<0.05). Combined inhibition of ryanodine and IP3 receptors decreased wild-type and CFTR-null responses to levels seen in dF aorta. Compared to wild-type cells, dF-expressing smooth muscle cells had reduced calcium transients, while CFTR-null cells had decreased baseline intracellular calcium concentrations.

CONCLUSIONS

Expression of CFTR-F508del interferes with smooth muscle cell calcium handling and decreases aortic responsiveness.

Actein induces calcium release in human breast cancer cells

BACKGROUND

The triterpene glycoside actein from the herb black cohosh preferentially inhibits the growth of breast cancer cells and activates the ER stress response. The ER IP3 receptor and Na,K-ATPase form a signaling microdomain. Since actein is lipophilic, its action may be limited by bioavailability.

PURPOSE

To develop actein to prevent and treat cancer, we examined the primary targets and combinations with chemotherapy agents, as well as the ability of nanoparticles to enhance the activity.

MATERIALS AND METHODS

To reveal signaling pathways, we treated human breast and colon cancer, as well as 293T and 293T (NF-κB), cells with actein, and measured effects using the MTT, luciferase promoter, Western blot and histology assays. To assess effects on calcium release, we preloaded cells with the calcium sensitive dye Fura-2. To enhance bioavailability, we conjugated actein to nanoparticle liposomes.

RESULTS

Actein strongly inhibited the growth of human breast cancer cells and induced a dose dependent release of calcium into the cytoplasm. The ER IP3 receptor antagonist heparin blocked this release, indicating that the receptor is required for activity. Heparin partially blocked the growth inhibitory effect, while the MEK inhibitor U0126 enhanced it. Consistent with this, actein synergized with the ER mobilizer thapsigargin. Further, actein preferentially inhibited the growth of 293T (NF-κB) cells. Nanoparticle liposomes increased the growth inhibitory activity of actein.

CONCLUSIONS

Actein alters the activity of the ER IP3 receptor and Na,K-ATPase, induces calcium release and modulates the NF-κB and MEK pathways and may be worthwhile to explore to prevent and treat breast cancer.