The biology of caveolae: lessons from caveolin knockout mice and implications for human disease

Altered expression of caveolin 2 and 3 in smooth muscle of rat urinary bladder by 17β-estradiol

Background

The purpose of this study was to investigate the effect of estrogen alteration on the expression of caveolin 2 and 3 in rat smooth muscle of urinary bladder.

Methods

Female Sprague–Dawley rats were divided into three groups: control, bilateral ovariectomy (Ovx), and bilateral ovariectomy followed by subcutaneous injections of 17β-estradiol (Ovx?+?Est). After 4 weeks, urodynamic measurements were taken to ascertain the contraction interval and contraction pressure. The expression and cellular localization of caveolin 2 and 3 were determined by Western blot and immunohistochemistry in rat urinary bladder smooth muscle.

Results

In cystometrograms, the contraction interval (min) was significantly lower in the Ovx group (3.1?±?1.5) than in the control group (5.6?±?1.2), but was increased after estrogen treatment (9.3?±?1.0). Conversely, the average contraction pressure (mmHg) was higher in the Ovx group (26.2?±?2.3) than in the control group (21.9?±?3.1), and was decreased after estrogen treatment (23.8?±?3.5). Caveolin 2 and 3 expression was localized in the cell membrane of the smooth muscle. The protein expression of both caveolin 2 and 3 was significantly lower after ovariectomy and was restored to the control levels after 17β-estradiol treatment.

Conclusions

Hormonal alteration causes a significant change in the expression of caveolin 2 and 3 in smooth muscle of rat urinary bladder. These findings suggest that these molecules might have functional roles in the detrusor overactivity that occurs in association with hormonal alteration.

Caveolae-dependent internalization and homologous desensitization of VIP/PACAP receptor, VPAC₂, in gastrointestinal smooth muscle

The main membrane proteins of caveolae (caveolin-1, -2 and -3) oligomerize within lipid rich domains to form regular invaginations of smooth muscle plasma membrane and participate in receptor internalization and desensitization independent of clathrin-coated vesicle endocytosis. We have previously shown that Gs-coupled VIP/PACAP receptors, VPAC2, predominantly expressed in smooth muscle cells of the gut, are exclusively phosphorylated by GRK2 leading to receptor internalization and desensitization. Herein, we characterized the role of caveolin-1 in VPAC2 receptor internalization and desensitization in gastric smooth muscle using three approaches: (i) methyl β-cyclodextrin (MβCD) to deplete cholesterol and disrupt caveolae in dispersed muscle cells, (ii) caveolin-1 siRNA to suppress caveolin-1 expression in cultured muscle cells, and (iii) caveolin-1 knockout mice (caveolin-1(-/-)). Pretreatment of gastric muscle cells with VIP stimulated tyrosine phosphorylation of caveolin-1, and induced VPAC2 receptor internalization (measured as decrease in (125)I-VIP binding after pretreatment) and desensitization (measured as decrease in VIP-induced cAMP formation after pretreatment). Caveolin-1 phosphorylation, and VPAC2 receptor internalization and desensitization were blocked by disruption of caveolae with MβCD, suppression of caveolin-1 with caveolin-1 siRNA or inhibition of Src kinase activity by PP2. Pretreatment with VIP significantly inhibited adenylyl cyclase activity and muscle relaxation in response to subsequent addition of VIP in freshly dispersed muscle cells and in muscle strips isolated from wild type and caveolin-1(-/-) mice; however, the inhibition was significantly attenuated in caveolin-1(-/-) mice. These results suggest that caveolin-1 plays an important role in VPAC2 receptor internalization and desensitization.

Palmitate diet-induced loss of cardiac caveolin-3: a novel mechanism for lipid-induced contractile dysfunction

Obesity is associated with an increased risk of cardiomyopathy, and mechanisms linking the underlying risk and dietary factors are not well understood. We tested the hypothesis that dietary intake of saturated fat increases the levels of sphingolipids, namely ceramide and sphingomyelin in cardiac cell membranes that disrupt caveolae, specialized membrane micro-domains and important for cellular signaling. C57BL/6 mice were fed two high-fat diets: palmitate diet (21% total fat, 47% is palmitate), and MCT diet (21% medium-chain triglycerides, no palmitate). We established that high-palmitate feeding for 12 weeks leads to 40% and 50% increases in ceramide and sphingomyelin, respectively, in cellular membranes. Concomitant with sphingolipid accumulation, we observed a 40% reduction in systolic contractile performance. To explore the relationship of increased sphingolipids with caveolins, we analyzed caveolin protein levels and intracellular localization in isolated cardiomyocytes. In normal cardiomyocytes, caveolin-1 and caveolin-3 co-localize at the plasma membrane and the T-tubule system. However, mice maintained on palmitate lost 80% of caveolin-3, mainly from the T-tubule system. Mice maintained on MCT diet had a 90% reduction in caveolin-1. These data show that caveolin isoforms are sensitive to the lipid environment. These data are further supported by similar findings in human cardiac tissue samples from non-obese, obese, non-obese cardiomyopathic, and obese cardiomyopathic patients. To further elucidate the contractile dysfunction associated with the loss of caveolin-3, we determined the localization of the ryanodine receptor and found lower expression and loss of the striated appearance of this protein. We suggest that palmitate-induced loss of caveolin-3 results in cardiac contractile dysfunction via a defect in calcium-induced calcium release.

Direct renin inhibition modulates insulin resistance in caveolin-1-deficient mice

OBJECTIVE

To test the hypothesis that aliskiren improves the metabolic phenotype in a genetic mouse model of the metabolic syndrome (the caveolin-1 (cav-1) knock out (KO) mouse).

MATERIALS/METHODS

Eleven-week-old cav-1 KO and genetically matched wild-type (WT) mice were randomized to three treatment groups: placebo (n=8/group), amlodipine (6 mg/kg/day, n=18/ group), and aliskiren (50 mg/kg/day, n=18/ group). After three weeks of treatment, all treatment groups were assessed for several measures of insulin resistance (fasting insulin and glucose, HOMA-IR, and the response to an intraperitoneal glucose tolerance test (ipGTT)) as well as for triglyceride levels and the blood pressure response to treatment.

RESULTS

Treatment with aliskiren did not affect the ipGTT response but significantly lowered the HOMA-IR and insulin levels in cav-1 KO mice. However, treatment with amlodipine significantly degraded the ipGTT response, as well as the HOMA-IR and insulin levels in the cav-1 KO mice. Aliskiren also significantly lowered triglyceride levels in the cav-1 KO but not in the WT mice. Moreover, aliskiren treatment had a significantly greater effect on blood pressure readings in the cav-1 KO vs. WT mice, and was marginally more effective than amlodipine.

CONCLUSIONS

Our results support the hypothesis that aliskiren reduces insulin resistance as indicated by improved HOMA-IR in cav-1 KO mice whereas amlodipine treatment resulted in changes consistent with increased insulin resistance. In addition, aliskiren was substantially more effective in lowering blood pressure in the cav-1 KO mouse model than in WT mice and marginally more effective than amlodipine.

Overexpression of caveolin-1 in cancer-associated fibroblasts predicts good outcome in breast cancer

BACKGROUND

The aim of this study was to investigate the expression of caveolin-1 (Cav-1) in cancer-associated fibroblasts (CAFs) and to explore its correlation with clinicopathologic parameters and prognosis.

MATERIALS AND METHODS

Cav-1 expression was detected in the stroma of 143 patients with breast cancer, 10 patients with ductal carcinoma in situ (DCIS), and 10 normal breast tissue samples.

RESULTS

Overexpression of stromal Cav-1 in breast cancer was associated with histological type, low histological grade, estrogen receptor (ER) negativity, and molecular subtypes. The expression rate of stromal Cav-1 in breast cancer (65.7%, 94/143) was significantly higher than that of DCIS (0%, 0/10) and normal breast tissue (0%, 0/10) (p = 0.000). A positive correlation was found between stromal Cav-1 and ER (p = 0.046, rs = 0.218). Stromal Cav-1 expression in luminal B was significantly higher than in basal-like type (p = 0.048). Furthermore, stromal expression of Cav-1 was significantly correlated with the 5-year survival rate (p = 0.029), and it was an independent prognostic factor (p = 0.009).

CONCLUSION

Cav-1 expression in CAFs was correlated with histological type, histological grade, ER status, and molecular subtypes in breast cancer. Stromal Cav-1 expression was an independent prognostic factor, and the absence or reduction of Cav-1 expression in stromal CAFs of invasive breast cancer predicts poor prognostic outcome.

Impaired contractility and detrusor hypertrophy in cavin-1-deficient mice

Caveolae are membrane invaginations present in a variety of cell types. Formation of caveolae depends on caveolins and on the more recently discovered family of proteins known as the cavins. Genetic ablation of caveolin-1 was previously shown to give rise to a number of urogenital alterations, but the effects of cavin-1 deletion on urogenital function remain unknown. Here we characterised detrusor contractility and structure in cavin-1-deficient mice. Electron microscopy demonstrated essentially complete lack of caveolae in the knock-out detrusor, and immunoblotting disclosed reduced levels of cavin-3 and of all caveolin proteins. Bladder weight was increased in male knock-out mice, and length-tension relationships demonstrated a reduction in depolarisation-induced contraction. Contractility in response to muscarinic receptor activation was similarly reduced. Despite these functional changes, micturition patterns were similar in conscious and freely moving animals and diuresis was unchanged. Our breeding additionally disclosed that the number of knock-out mice generated in heterozygous crosses was lower than expected, suggesting embryonic/perinatal lethality. In conclusion, this is the first study to show that cavin-1 is critical for detrusor caveolae and for the overall contractility and structure of the urinary bladder.

Clinical and functional significance of loss of caveolin-1 expression in breast cancer-associated fibroblasts

Loss of caveolin-1 (Cav-1) expression in breast cancer-associated fibroblasts (CAFs) is predictive of poor prognosis in breast cancer, but its function has not been established. Our study tested the hypotheses that loss of Cav-1 expression in breast fibroblasts was associated with poor prognosis in breast cancer, through promotion of breast cancer cell invasion. Cav-1 stromal expression was immunohistochemically assessed in 358 breast cancers. Cav-1 expression in primary breast fibroblasts was analysed by western blot. Modified Boyden chamber assays determined fibroblast ability to promote invasion of breast cancer cells. The impact of siRNA silencing of Cav-1 in fibroblasts was evaluated using invasion assays and 3D co-culture assays. Loss of Cav-1 expression in breast stroma was significantly associated with decreased breast cancer-specific and disease-free survival (p = 0.01). Mean survival was 72 months (Cav-1(+) group) versus 29.5 months (Cav-1(-) group). This was confirmed in multivariate analysis. Cav-1 expression was significantly decreased in CAFs compared to normal fibroblasts (p = 0.01) and was associated with increased invasion-promoting capacity. Cav-1 siRNA-treated fibroblasts promoted significantly increased invasion of MDA-MB-468 and T47D breast cancer cells from 27% (control) to 67% (p = 0.006) and from 37% to 56%, respectively (p = 0.01). 3D co-cultures of MDA-MB-468 cells with myoepithelial cells led to the formation of organized cohesive structures when cultured with conditioned media from fibroblasts but resulted in a disorganized appearance in the presence of conditioned media from Cav-1 siRNA-treated fibroblasts, accompanied by loss of E-cadherin expression in tumour cells. Our data confirm that loss of stromal Cav-1 in breast cancer predicts poor outcome. At a functional level, Cav-1-deficient CAFs are capable of significantly increasing the invasive capacity of breast cancer cells.

Diabetes-related alterations in the enteric nervous system and its microenvironment

Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.

Caveolae and propofol effects on airway smooth muscle

BACKGROUND

The i.v. anaesthetic propofol produces bronchodilatation. Airway relaxation involves reduced intracellular Ca(2+) ([Ca(2+)](i)) in airway smooth muscle (ASM) and lipid rafts (caveolae), and constitutional caveolin proteins regulate [Ca(2+)](i). We postulated that propofol-induced bronchodilatation involves caveolar disruption.

METHODS

Caveolar fractions of human ASM cells were tested for propofol content. [Ca(2+)](i) responses of ASM cells loaded with fura-2 were performed in the presence of 10 µM histamine with and without clinically relevant concentrations of propofol (10 and 30 μM and intralipid control). Effects on sarcoplasmic reticulum (SR) Ca(2+) release were evaluated in zero extracellular Ca(2+) using the blockers Xestospongin C and ryanodine. Store-operated Ca(2+) entry (SOCE) after SR depletion was evaluated using established techniques. The role of caveolin-1 in the effect of propofol was tested using small interference RNA (siRNA) suppression. Changes in intracellular signalling cascades relevant to [Ca(2+)](i) and force regulation were also evaluated.

RESULTS

Propofol was present in ASM caveolar fractions in substantial concentrations. Exposure to 10 or 30 µM propofol form decreased [Ca(2+)](i) peak (but not plateau) responses to histamine by ~40%, an effect persistent in zero extracellular Ca(2+). Propofol effects were absent in caveolin-1 siRNA-transfected cells. Inhibition of ryanodine receptors prevented propofol effects on [Ca(2+)](i), while propofol blunted [Ca(2+)](i) responses to caffeine. Propofol reduced SOCE, an effect also prevented by caveolin-1 siRNA. Propofol effects were associated with decreased caveolin-1 expression and extracellular signal-regulated kinase phosphorylation.

CONCLUSIONS

These novel data suggest a role for caveolae (specifically caveolin-1) in propofol-induced bronchodilatation. Due to its lipid nature, propofol may transiently disrupt caveolar regulation, thus altering ASM [Ca(2+)](i).

Caveolins in rhabdomyosarcoma

Caveolins are scaffolding proteins that play a pivotal role in numerous processes, including caveolae biogenesis, vesicular transport, cholesterol homeostasis and regulation of signal transduction. There are three different isoforms (Cav-1, -2 and -3) that form homo- and hetero-aggregates at the plasma membrane and modulate the activity of a number of intracellular binding proteins. Cav-1 and Cav-3, in particular, are respectively expressed in the reserve elements (e.g. satellite cells) and in mature myofibres of skeletal muscle and their expression interplay characterizes the switch from muscle precursors to differentiated elements. Recent findings have shown that caveolins are also expressed in rhabdomyosarcoma, a group of heterogeneous childhood soft-tissue sarcomas in which the cancer cells seem to derive from progenitors that resemble myogenic cells. In this review, we will focus on the role of caveolins in rhabdomyosarcomas and on their potential use as markers of the degree of differentiation in these paediatric tumours. Given that the function of Cav-1 as tumour conditional gene in cancer has been well-established, we will also discuss the relationship between Cav-1 and the progression of rhabdomyosarcoma.

An evolving web of signaling networks regulated by Cripto-1

Over the past few decades, our understanding of the embryonic gene Cripto-1 has considerably advanced through biochemical, cell biology, and animal studies. Cripto-1 performs key functions during embryonic development, while it dramatically disappears in adult tissues, except possibly in adult tissue stem cells. Cripto-1 is re-expressed in human tumors promoting cell proliferation, migration, invasion, epithelial to mesenchymal transition, and tumor angiogenesis. This diversity of biological effects is dependent upon interaction of Cripto-1 with an extensive array of signaling molecules. In fact, Cripto-1 modulates signaling of transforming growth factor-β family members, including Nodal, GDF-1/-3, Activin, and TGF-β1, activates c-src/MAPK/Protein Kinase B (AKT) pathway in a Glypican-1 and GRP78-dependent manner, and cross-talks with erbB4, Wnt/β-catenin, Notch, Caveolin-1, and Apelin/putative receptor protein related to Angiotensin-type I receptor (APJ) pathways. This article provides an updated survey of the various signaling pathways modulated by Cripto-1 with a focus on mechanistic insights in our understanding of the biological function of Cripto-1 in eukaryotic cells.

Caveolins and heart diseases

Caveolins serve as a platform in plasma membrane associated caveolae to orchestrate various signaling molecules to effectively communicate extracellular signals into the interior of cell. All three types of caveolin, Cav-1, Cav-2 and Cav-3 are expressed throughout the cardiovascular system especially by the major cell types involved including endothelial cells, cardiac myocytes, smooth muscle cells and fibroblasts. The functional significance of caveolins in the cardiovascular system is evidenced by the fact that caveolin loss leads to the development of severe cardiac pathology. Caveolin gene mutations are associated with altered expression of caveolin protein and inherited arrhythmias. Altered levels of caveolins and related downstream signaling molecules in cardiomyopathies validate the integral participation of caveolin in normal cardiac physiology. This chapter will provide an overview of the role caveolins play in cardiovascular disease. Furthering our understanding of the role for caveolins in cardiovascular pathophysiology has the potential to lead to the manipulation of caveolins as novel therapeutic targets.

Lipid rafts and redox regulation of cellular signaling in cholesterol induced atherosclerosis

Redox mediated signaling mechanisms play crucial roles in the pathogenesis of several cardiovascular diseases. Atherosclerosis is one of the most important disorders induced mainly by hypercholesterolemia. Oxidation products and related signaling mechanisms are found within the characteristic biomarkers of atherosclerosis. Several studies have shown that redox signaling via lipid rafts play a significant role in the regulation of pathogenesis of many diseases including atherosclerosis. This review attempts to summarize redox signaling and lipid rafts in hypercholesterolemia induced atherosclerosis.

Stromal caveolin-1 expression in breast carcinoma. Correlation with early tumor recurrence and clinical outcome

Caveolin- (cav-1) has been linked to tumor progression and clinical outcome in breast cancer, but its role as a prognostic marker is still unclear. We evaluated stromal and tumor caveolin-1 expression in 91 breast carcinomas, and assessed the association between their expression and clinicopathologic variables as well as patient outcome and early tumor recurrence. Absence of stromal caveolin-1 expression was detected in 18.7% of cases, while 25.3% of cases revealed tumor epithelial caveolin-1 expression. Combined stromal and tumor caveolin-1 immunopositivity was seen in 24.2% of cases. Absence of stromal cav-1 associated with larger tumor size, higher grade, higher nodal stage, higher number of positive nodes, higher TNM stage, positive HER2 status, higher recurrence rate, and shorter mean progression free survival (PFS). Stromal cav-1 status was a significant predictor of PFS in ER+, PR +, and HER2 + tumors. In tamoxifen-treated patients, absence of stromal Cav-1 was a significant predictor of poor clinical outcome, suggestive of tamoxifen resistance. Conversely, tumor epithelial and combined caveolin-1 expression, didnot associate with patient outcome. In multivariate analysis, only TNM stage independently associated with survival. Loss of stromal caveolin-1 is a novel breast cancer biomarker that can predict early tumor recurrence, short PFS, and tamoxifen- resistance. Thus, its use as a predictive biomarker, especially in lower grade, lower stage, ER+, PR+, HER2+, and tamoxifen treated patients may allow for early interventions with more aggressive therapies. Thus, stromal marker expression and epithelial-stromal cross talk may be critical for tumor progression and metastasis.

Altered arachidonate distribution in macrophages from caveolin-1 null mice leading to reduced eicosanoid synthesis

In this work we have studied the effect of caveolin-1 deficiency on the mechanisms that regulate free arachidonic acid (AA) availability. The results presented here demonstrate that macrophages from caveolin-1-deficient mice exhibit elevated fatty acid incorporation and remodeling and a constitutively increased CoA-independent transacylase activity. Mass spectrometry-based lipidomic analyses reveal stable alterations in the profile of AA distribution among phospholipids, manifested by reduced levels of AA in choline glycerophospholipids but elevated levels in ethanolamine glycerophospholipids and phosphatidylinositol. Furthermore, macrophages from caveolin-1 null mice show decreased AA mobilization and prostaglandin E(2) and LTB(4) production upon cell stimulation. Collectively, these results provide insight into the role of caveolin-1 in AA homeostasis and suggest an important role for this protein in the eicosanoid biosynthetic response.

Variants of the caveolin-1 gene: a translational investigation linking insulin resistance and hypertension

CONTEXT

The co-occurrence of insulin resistance (IR) and hypertension is a heritable condition leading to cardiovascular complications. Caveolin-1 (CAV1), a gene previously associated with metabolic dysfunction in animal and cellular models, may be a marker for these conditions in humans.

OBJECTIVE

The objective of the study was to examine the relationship between CAV1 variants and IR in two hypertensive cohorts and to corroborate the findings in a CAV1 knockout mouse.

DESIGN, SETTING, AND PARTICIPANTS

A candidate gene association study was conducted in two hypertensive cohorts: 1) Caucasian and 2) Hispanic. Multivariate associations between individual variants and insulin-resistant phenotypes were analyzed, accounting for age, gender, body mass index, and sibling relatedness. Intraperitoneal glucose tolerance tests were conducted in wild-type and CAV1 knockout mice.

RESULTS

In the Caucasian hypertensive cohort, minor allele carriers of two CAV1 single-nucleotide polymorphisms (rs926198, rs3807989) had significantly higher fasting insulin levels (P = 0.005, P = 0.007), increased homeostatic assessment model for insulin resistance (HOMA-IR) (P =0.005, P = 0.008), and decreased M value during hyperinsulinemic, euglycemic clamp procedure (P = 0.004, P = 0.05) than major allele homozygotes. Findings were replicated in the Hispanic hypertensive cohort cohort for fasting insulin levels (P = 0.005, P = 0.02) and HOMA-IR (P = 0.008 and P = 0.02). Meta-analysis demonstrated significant associations of both single-nucleotide polymorphisms with fasting insulin levels (P = 0.00008, P = 0.0004) and HOMA-IR (P = 0.0001, P = 0.0004). As compared with wild type, CAV1 knockout mice displayed higher blood pressure levels and higher fasting glucose, insulin, and HOMA-IR levels and an exaggerated glycemic response to a glucose challenge.

CONCLUSION

Variations in the CAV1 gene are associated with IR and hypertension. CAV1 gene polymorphisms may be a biomarker for IR and hypertension, enabling earlier detection and improved treatment strategies.

Caveolin-1 deficiency decreases atherosclerosis by hampering leukocyte influx into the arterial wall and generating a regulatory T-cell response

Caveolin-1 plays a crucial role in atherosclerosis, which is mainly attributed to its effects on low-density-lipoprotein (LDL) transcytosis. However, caveolin-1 has also been implicated in the regulation of inflammation. We investigated the effects of caveolin-1 deficiency in atherosclerosis with its accompanying changes in plaque- and lymphoid-related immunology and inflammation. Cav1(-/-)Apoe(-/-) mice exhibited a 15-fold reduction in plaque size with plaques containing fewer macrophages, T cells, and neutrophils. Intravital microscopy revealed 83% less leukocyte adhesion to the vessel wall in Cav1(-/-)Apoe(-/-) mice, which could be attributed to reduced endothelial chemokine ligand-2 (CCL-2/MCP-1) and vascular cell adhesion molecule-1 (VCAM-1) expression. Caveolin-1 deficiency resulted in a 57% increase in regulatory T cells and a 4% decrease in CD4(+) effector T cells in lymphoid organs. Bone marrow transplantations revealed that Cav1(-/-)Apoe(-/-) mice receiving Cav1(+/+)Apoe(-/-) or Cav1(-/-)Apoe(-/-) bone marrow presented 4- to 4.5-fold smaller plaques with no additional phenotypic changes. In contrast, atherosclerosis was not affected in Cav1(+/+) Apoe(-/-) recipients receiving Cav1(-/-)Apoe(-/-) or Cav1(+/+) Apoe(-/-) bone marrow. However, the presence of Cav1(-/-) Apoe(-/-) bone marrow was associated with an anti-inflammatory T-cell profile. Our study reveals that nonhematopoietic caveolin-1 determines plaque size, whereas hematopoietic caveolin-1 regulates lymphoid immune-modulation. However, both are required for phenotypic modulation of plaques.

NFBD1/MDC1 regulates Cav1 and Cav2 independently of DNA damage and p53

NFBD1/MDC1 is involved in DNA damage checkpoint signaling and DNA repair. NFBD1 binds to the chromatin component γH2AX at sites of DNA damage, causing amplification of ataxia telangiectasia-mutated gene (ATM) pathway signaling and recruitment of DNA repair factors. Residues 508-995 of NFBD1 possess transactivation activity, suggesting a possible role of NFBD1 in transcription. Furthermore, NFBD1 influences p53-mediated transcription in response to adriamycin. We sought to determine the role of NFBD1 in ionizing radiation (IR)-responsive transcription and if NFBD1 influences transcription independently of p53. Using microarray analysis, we identified genes altered upon NFBD1 knockdown. Surprisingly, most NFBD1 regulated genes are regulated in both the absence and presence of IR, thus pointing toward a novel function for NFBD1 outside of the DNA damage response. Furthermore, NFBD1 knockdown regulated genes mostly independent of p53 knockdown. These genes are involved in pathways including focal adhesion signaling, carbohydrate metabolism, and insulin signaling. We found that CAV1 and CAV2 mRNA and protein levels are reduced by both NFBD1 knockdown and knockout independently of IR and p53. NFBD1-depleted cells exhibit some similar phenotypes to Cav1-depleted cells. Furthermore, like Cav1-depletion, NFBD1 shRNA increases Erk phosphorylation. Thus, Cav1 could act as a mediator of the DNA-damage independent effects of NFBD1 in mitogenic signaling.

Caveolin-1 and force regulation in porcine airway smooth muscle

Caveolae are specialized membrane microdomains expressing the scaffolding protein caveolin-1. We recently demonstrated the presence of caveolae in human airway smooth muscle (ASM) and the contribution of caveolin-1 to intracellular calcium ([Ca(2+)](i)) regulation. In the present study, we tested the hypothesis that caveolin-1 regulates ASM contractility. We examined the role of caveolins in force regulation of porcine ASM under control conditions as well as TNF-α-induced airway inflammation. In porcine ASM strips, exposure to 10 mM methyl-β-cyclodextrin (CD) or 5 μM of the caveolin-1 specific scaffolding domain inhibitor peptide (CSD) resulted in time-dependent decrease in force responses to 1 μM ACh. Overnight exposure to the cytokine TNF-α (50 ng/ml) accelerated and increased caveolin-1 expression and enhanced force responses to ACh. Suppression of caveolin-1 with small interfering RNA mimicked the effects of CD or CSD. Regarding mechanisms by which caveolae contribute to contractile changes, inhibition of MAP kinase with 10 μM PD98059 did not alter control or TNF-α-induced increases in force responses to ACh. However, inhibiting RhoA with 100 μM fasudil or 10 μM Y27632 resulted in significant decreases in force responses, with lesser effects in TNF-α exposed samples. Furthermore, Ca(2+) sensitivity for force generation was substantially reduced by fasudil or Y27632, an effect even more enhanced in the absence of caveolin-1 signaling. Overall, these results indicate that caveolin-1 is a critical player in enhanced ASM contractility with airway inflammation.

The role of caveolae in endothelial cell dysfunction with a focus on nutrition and environmental toxicants

Complications of vascular diseases, including atherosclerosis, are the number one cause of death in Western societies. Dysfunction of endothelial cells is a critical underlying cause of the pathology of atherosclerosis. Lipid rafts, and especially caveolae, are enriched in endothelial cells, and down-regulation of the caveolin-1 gene may provide protection against the development of atherosclerosis. There is substantial evidence that exposure to environmental pollution is linked to cardiovascular mortality, and that persistent organic pollutants can markedly contribute to endothelial cell dysfunction and an increase in vascular inflammation. Nutrition can modulate the toxicity of environmental pollutants, and evidence suggests that these affect health and disease outcome associated with chemical insults. Because caveolae can provide a regulatory platform for pro-inflammatory signalling associated with vascular diseases such as atherosclerosis, we suggest a link between atherogenic risk and functional changes of caveolae by environmental factors such as dietary lipids and organic pollutants. For example, we have evidence that endothelial caveolae play a role in uptake of persistent organic pollutants, an event associated with subsequent production of inflammatory mediators. Functional properties of caveolae can be modulated by nutrition, such as dietary lipids (e.g. fatty acids) and plant-derived polyphenols (e.g. flavonoids), which change activation of caveolae-associated signalling proteins. The following review will focus on caveolae providing a platform for pro-inflammatory signalling, and the role of caveolae in endothelial cell functional changes associated with environmental mediators such as nutrients and toxicants, which are known to modulate the pathology of vascular diseases.

Alterations of excitation-contraction coupling and excitation coupled Ca(2+) entry in human myotubes carrying CAV3 mutations linked to rippling muscle

Rippling muscle disease is caused by mutations in the gene encoding caveolin-3 (CAV3), the muscle-specific isoform of the scaffolding protein caveolin, a protein involved in the formation of caveolae. In healthy muscle, caveolin-3 is responsible for the formation of caveolae, which are highly organized sarcolemmal clusters influencing early muscle differentiation, signalling and Ca²⁺ homeostasis. In the present study we examined Ca²⁺ homeostasis and excitation–contraction (E-C) coupling in cultured myotubes derived from two patients with Rippling muscle disease with severe reduction in caveolin-3 expression; one patient harboured the heterozygous c.84C>A mutation while the other patient harbored a homozygous splice-site mutation (c.102+ 2T>C) affecting the splice donor site of intron 1 of the CAV3 gene. Our results show that cells from control and rippling muscle disease patients had similar resting [Ca²⁺]_i and 4-chloro-m-cresol-induced Ca²⁺ release but reduced KCl-induced Ca²⁺ influx. Detailed analysis of the voltage-dependence of Ca²⁺ transients revealed a significant shift of Ca²⁺ release activation to higher depolarization levels in CAV3 mutated cells. High resolution immunofluorescence analysis by Total Internal Fluorescence microscopy supports the hypothesis that loss of caveolin-3 leads to microscopic disarrays in the colocalization of the voltage-sensing dihydropyridine receptor and the ryanodine receptor, thereby reducing the efficiency of excitation–contraction coupling. Hum Mutat 32:309–317, 2011. © 2011 Wiley-Liss, Inc.

Caveolinopathies: translational implications of caveolin-3 in skeletal and cardiac muscle disorders

Caveolae are specialized lipid rafts localized on the cytoplasmic surface of the sarcolemmal membrane. Caveolae contribute to the maintenance of plasma membrane integrity, constitute specific macromolecular complexes that provide highly localized regulation of ion channels, and regulate vesicular trafficking and signal transduction. In skeletal muscle, the main structural assembly of caveolae is mediated by caveolin-3. Another family of adapter proteins, the cavins, is involved in the regulation of caveolae function and in the trafficking of caveolin-derived structures. Caveolin-3 defects lead to four distinct skeletal muscle disease phenotypes: limb-girdle muscular dystrophy, rippling muscle disease, distal myopathy, and hyperCKemia. Many patients show an overlap of these symptoms, and the same mutation can be linked to different clinical phenotypes. An ever-growing interest is also focused on the association between caveolin-3 mutations and heart disorders. Indeed, caveolin-3 mutants have been described in a patient with hypertrophic cardiomyopathy and two patients with dilated cardiomyopathy, and mutations in the caveolin-3 gene (CAV3) have been identified in patients affected by congenital long QT syndrome. Although caveolin-3 deficiency represents the primary event, multiple secondary molecular mechanisms lead to muscle tissue damage. Among these, sarcolemmal membrane alterations, disorganization of skeletal muscle T-tubule network, and disruption of distinct cell signaling pathways have been determined.

Knockdown of caveolin-1 decreases activity of breast cancer resistance protein (BCRP/ABCG2) and increases chemotherapeutic sensitivity

The ATP-binding cassette transporter breast cancer resistance protein (BCRP/ABCG2) is supposed to be a major determinant of the multidrug resistance phenotype of tumors by extruding chemically diverse cytostatic drugs out of tumor cells. BCRP physically and possibly also functionally interacts with caveolin-1 (CAV1, encoded by Cav1), an integral membrane protein of lipid rafts important for signal transduction and membrane trafficking. Moreover, Cav1 is linked to an aggressive phenotype of cancer cells in various tumors. We therefore investigated whether Cav1 plays a functional role in the regulation of BCRP transport activity and in the resistance against chemotherapeutics that are BCRP substrates. As a cell model, we used the BCRP overexpressing cell line MDCKII-BCRP and the corresponding parental cell line MDCKII as a control. Cav1 expression was down-regulated using retrovirus-mediated RNA interference technology. BCRP activity was assessed by pheophorbide A efflux assay and the resistance towards cytostatic drugs was measured by proliferation assays. Efficient knockdown of Cav1 reduced Cav1 expression by 85-95% and BCRP activity by 35%. Concurrently, it reduced resistance towards the BCRP substrate mitoxantrone but not towards vincristine, a chemotherapeutic that is not extruded by BCRP. Western blot analysis of gradient ultracentrifugation fractions and immunofluorescence demonstrates that BCRP localization within the plasma membrane was largely unaltered in Cav1-deficient cells compared to controls. The diminished BCRP function after Cav1 knockdown is, thus, likely mediated by alterations in protein-protein interactions and suggests a positive regulation of BCRP function by CAV1.

Macrophages, reactive nitrogen species, and lung injury

Evidence has accumulated over the past several years demonstrating that lung injury following inhalation of irritants like ozone is due, not only to direct effects of the chemical, but also indirectly to the actions of inflammatory mediators released by infiltrating macrophages. Among the mediators involved in the cytotoxic process, reactive nitrogen species (RNS) are of particular interest because of their well-documented cytotoxic potential. Findings that macrophage suppression blocks RNS production and ozone-induced toxicity provide strong support for a role of these cells and inflammatory mediators in lung injury. Recent investigations have focused on understanding pathways by which macrophages become activated to release RNS. One protein that has attracted considerable attention is caveolin-1, a membrane scaffolding molecule that functions to negatively regulate cell signaling. The fact that expression of caveolin-1 is down-regulated in macrophages after ozone inhalation suggests a mechanism controlling the release of cytotoxic mediators by these inflammatory cells.

Common variants near CAV1 and CAV2 are associated with primary open-angle glaucoma

We conducted a genome-wide association study for primary open-angle glaucoma (POAG) in 1,263 affected individuals (cases) and 34,877 controls from Iceland. We identified a common sequence variant at 7q31 (rs4236601[A], odds ratio (OR) = 1.36, P = 5.0 × 10⁻¹⁰). We then replicated the association in sample sets of 2,175 POAG cases and 2,064 controls from Sweden, the UK and Australia (combined OR = 1.18, P = 0.0015) and in 299 POAG cases and 580 unaffected controls from Hong Kong and Shantou, China (combined OR = 5.42, P = 0.0021). The risk variant identified here is located close to CAV1 and CAV2, both of which are expressed in the trabecular meshwork and retinal ganglion cells that are involved in the pathogenesis of POAG.

Targeted delivery for breast cancer therapy: the history of nanoparticle-albumin-bound paclitaxel

IMPORTANCE OF THE FIELD

Taxanes are agents for the treatment of breast cancer. Paclitaxel is hydrophobic, and available formulations require polyoxyethylated castor oil, Cremphor EL (CrEL) and an ethanol vehicle to allow parental administration. Nanoparticle albumin-bound paclitaxel (nab-P) is a CrEL-free formulation of paclitaxel. The human albumin-stabilized paclitaxel particles have a size of approximately 130 nm, which allows intravenous infusion without capillary blockage.

AREAS COVERED IN THIS REVIEW

Efficacy and safety of nab-P in breast cancer has been compared with paclitaxel and docetaxel in large Phase III and II trials. Additionally, the efficacy and safety of nab-P have been investigated in other single-arm clinical trials, in early and advanced disease.

WHAT THE READER WILL GAIN

Preclinical and clinical development of the drug across all clinical trials published so far, the approved clinical indications, the benefits of this taxane formulation and a look into the future with emphasis on the application in specific subtypes of breast cancer.

TAKE HOME MESSAGE

nab-P has been approved for the treatment of metastatic breast cancer in patients who have failed first-line treatment for metastatic disease and for whom standard, anthracycline-containing therapy is not indicated and represents one of most authoritative and sophisticated applications of nanotechnology in cancer treatment so far.

Caveolin-1 ablation reduces the adverse cardiovascular effects of N-omega-nitro-L-arginine methyl ester and angiotensin II

Caveolae are the major cellular membrane structure through which extracellular mediators transmit information to intracellular signaling pathways. In vascular tissue (but not ventricular myocardium), caveolin-1 (cav-1) is the main component of caveolae; cav-1 modulates enzymes and receptors, such as the endothelial nitric oxide synthase and the angiotensin II (AngII) type 1 receptor. Evidence suggests that AngII and aldosterone (ALDO) are important mediators of ventricular injury. We have described a model of biventricular damage in rodents that relies on treatment with N-omega-nitro-l-arginine methyl ester (L-NAME (nitric oxide synthase inhibitor)) and AngII. This damage initiated at the vascular level and was observed only in the presence of ALDO and an activated mineralocorticoid receptor (MR). We hypothesize that cav-1 modulates the adverse cardiac effects mediated by ALDO in this animal model. To test this hypothesis, we assessed the ventricular damage and measures of inflammation, in wild-type (WT) and cav-1 knockout (KO) mice randomized to either placebo or L-NAME/AngII treatment. Despite displaying cardiac hypertrophy at baseline and higher blood pressure responses to L-NAME/AngII, cav-1 KO mice displayed, as compared with WT, decreased treatment-induced biventricular damage as well as decreased transcript levels of the proinflammatory marker plasminogen activator inhibitor-1. Additionally, L-NAME/AngII induced an increase in cardiac MR levels in WT but not cav-1-ablated mice. Moreover and despite similar circulating ALDO levels in both genotypes, the myocardial damage (as determined histologically and by plasminogen activator inhibitor-1 mRNA levels) was less sensitive to ALDO levels in cav-1 KO vs. WT mice, consistent with decreased MR signaling in the cav-1 KO. Thus, we conclude that the L-NAME/AngII-induced biventricular damage is mediated by a mechanism partially dependent on cav-1 and signaling via MR/ALDO.

FAT/CD36 is localized in sarcolemma and in vesicle-like structures in subsarcolemma regions but not in mitochondria

The primary aim of the present study was to investigate in which cellular compartments fatty acid trans-locase CD36 (FAT/CD36) is localized. Intact and fully functional skeletal muscle mitochondria were isolated from lean and obese female Zucker rats and from 10 healthy male individuals. FAT/CD36 could not be detected in the isolated mitochondria, whereas the mitochondrial marker F(1)ATPase-beta was clearly detected using immunoblotting. Lack of markers for other membrane structures indicated that the mitochondria were not contaminated with membranes known to contain FAT/CD36. In addition, fluorescence immunocytochemistry was performed on single muscle fibers dissected from soleus muscle of lean and obese Zucker rats and from the vastus lateralis muscle from humans. Costaining against FAT/CD36 and MitoNEET clearly show that FAT/CD36 is highly present in sarcolemma and it also associates with some vesicle-like intracellular compartments. However, FAT/CD36 protein was not detected in mitochondrial membranes, supporting the biochemical findings. Based on the presented data, FAT/CD36 seems to be abundantly expressed in sarcolemma and in vesicle-like structures throughout the muscle cell. However, FAT/CD36 is not present in mitochondria in rat or human skeletal muscle. Thus, the functional role of FAT/CD36 in lipid transport seems primarily to be allocated to the plasma membrane in skeletal muscle.

Alterations in caveolin expression and ultrastructure after bladder smooth muscle hypertrophy

PURPOSE

Partial bladder outlet obstruction in male rabbits causes detrusor smooth muscle hypertrophy and voiding dysfunction similar to that observed in men with benign prostate hyperplasia. Using this model, we analyzed the protein expression and ultrastructure of caveolae and the intermediate size filament in detrusor smooth muscle following partial bladder outlet obstruction induced hypertrophy.

MATERIALS AND METHODS

Detrusor smooth muscle sections from bladder body were processed for immunofluorescence and electron microscopy. Western analysis was performed to determine the expression of caveolin isoform-1, 2 and 3, and intermediate size filament proteins.

RESULTS

Detrusor smooth muscle cells from both normal and hypertrophied bladders contain orderly arrays of thick and thin myofilaments, interspersed with dense bodies. In addition, there was an increase in intermediate size filaments in the hypertrophic detrusor smooth muscle cells. The dense plaques in the inner membrane of hypertrophied detrusor smooth muscle were longer than those of the control. Detrusor smooth muscle from hypertrophied bladder revealed a decreased number of caveolae and a lack of their orderly distribution at the plasma membrane. Western blotting showed decreased expression of caveolin-1, 2 and 3 in hypertrophied detrusor smooth muscle.

CONCLUSIONS

Caveolae serve as platforms for proteins and receptors that have a role in signal transduction. The decreased number of caveolae and caveolin protein expression in hypertrophied detrusor smooth muscle might contribute to alterations in signal transduction pathways that regulate the downstream effects of agonist induced contraction, including calcium sensitization, observed in obstructed bladder. In addition, the increased number of intermediate size filaments in the hypertrophied detrusor smooth muscle is likely to alter the cytoskeletal structure and affect the cellular transmission of passive and/or active force.

Nitrative and oxidative stress in toxicology and disease

Persistent inflammation and the generation of reactive oxygen and nitrogen species play pivotal roles in tissue injury during disease pathogenesis and as a reaction to toxicant exposures. The associated oxidative and nitrative stress promote diverse pathologic reactions including neurodegenerative disorders, atherosclerosis, chronic inflammation, cancer, and premature labor and stillbirth. These effects occur via sustained inflammation, cellular proliferation and cytotoxicity and via induction of a proangiogenic environment. For example, exposure to the ubiquitous air pollutant ozone leads to generation of reactive oxygen and nitrogen species in lung macrophages that play a key role in subsequent tissue damage. Similarly, studies indicate that genes involved in regulating oxidative stress are altered by anesthetic treatment resulting in brain injury, most notable during development. In addition to a role in tissue injury in the brain, inflammation, and oxidative stress are implicated in Parkinson's disease, a neurodegenerative disease characterized by the loss of dopamine neurons. Recent data suggest a mechanistic link between oxidative stress and elevated levels of 3,4-dihydroxyphenylacetaldehyde, a neurotoxin endogenous to dopamine neurons. These findings have significant implications for development of therapeutics and identification of novel biomarkers for Parkinson's disease pathogenesis. Oxidative and nitrative stress is also thought to play a role in creating the proinflammatory microenvironment associated with the aggressive phenotype of inflammatory breast cancer. An understanding of fundamental concepts of oxidative and nitrative stress can underpin a rational plan of treatment for diseases and toxicities associated with excessive production of reactive oxygen and nitrogen species.

Role of caveolin-1 in thyroid phenotype, cell homeostasis, and hormone synthesis: in vivo study of caveolin-1 knockout mice

In human thyroid, caveolin-1 is localized at the apex of thyrocytes, but its role there remains unknown. Using immunohistochemistry, (127)I imaging, transmission electron microscopy, immunogold electron microscopy, and quantification of H(2)O(2), we found that in caveolin-1 knockout mice thyroid cell homeostasis was disrupted, with evidence of oxidative stress, cell damage, and apoptosis. An even more striking phenotype was the absence of thyroglobulin and iodine in one-half of the follicular lumina and their presence in the cytosol, suggesting that the iodide organification and binding to thyroglobulin were intracellular rather than at the apical membrane/extracellular colloid interface. The latter abnormality may be secondary to the observed mislocalization of the thyroid hormone synthesis machinery (dual oxidases, thyroperoxidase) in the cytosol. Nevertheless, the overall uptake of radioiodide, its organification, and secretion as thyroid hormones were comparable to those of wild-type mice, suggesting adequate compensation by the normal TSH retrocontrol. Accordingly, the levels of free thyroxine and TSH were normal. Only the levels of free triiodothyronine showed a slight decrease in caveolin-1 knockout mice. However, when TSH levels were increased through low-iodine chow and sodium perchlorate, the induced goiter was more prominent in caveolin-1 knockout mice. We conclude that caveolin-1 plays a role in proper thyroid hormone synthesis as well as in cell number homeostasis. Our study demonstrates for the first time a physiological function of caveolin-1 in the thyroid gland. Because the expression and subcellular localization of caveolin-1 were similar between normal human and murine thyroids, our findings in caveolin-1 knockout mice may have direct relevance to the human counterpart.

Kappa and delta opioid receptor signaling is augmented in the failing heart

The opioidergic system, an endogenous stress pathway, modulates cardiac function. Furthermore, opioid peptide and receptor expression is altered in a number of cardiac pathologies. However, whether the response of myocardial opioid receptor signaling is altered in heart failure progression is currently unknown. Elucidating possible alterations in and effects of opioidergic signaling in the failing myocardium is of critical importance as opioids are commonly used for pain management, including in patients at risk for cardiovascular disease. A hamster model of cardiomyopathy and heart failure (Bio14.6) was used to investigate cardiac opioidergic signaling in heart failure development. This study found an augmented negative inotropic and lusitropic response to administration of agonists selective for the kappa opioid receptor and delta opioid receptor in the failing heart that was mediated by a pertussis toxin-sensitive G-protein. The augmented decrease in cardiac function was manifested by increased inhibition of cAMP accumulation and the amplitude of the systolic Ca(2+) transient. Furthermore, increased depression of cardiac function and of two important second messengers, cAMP and intracellular Ca(2+), were independent of changes in cardiac opioid peptide or receptor expression. Thus, the cardiomyopathy-induced failing heart experiences increased cardiac depressant effects following opioid receptor stimulation which could exacerbate diminished cardiac function in end-stage heart failure. As cardiac function is already depressed in heart failure patients, administration of opioids could exacerbate the degree of cardiac dysfunction and worsen disease progression.

Quis custodiet ipsos custodies: who watches the watchmen?

This Commentary highlights two articles in this issue of the American Journal of Pathology, discussing the implications of stromal expression of caveolin-1 in breast cancer.

Lipid rafts and caveolae and their role in compartmentation of redox signaling

Membrane (lipid) rafts and caveolae, a subset of rafts, are cellular domains that concentrate plasma membrane proteins and lipids involved in the regulation of cell function. In addition to providing signaling platforms for G-protein-coupled receptors and certain tyrosine kinase receptors, rafts/caveolae can influence redox signaling. This review discusses molecular characteristics of and methods to study rafts/caveolae, determinants that contribute to the localization of molecules in these entities, an overview of signaling molecules that show such localization, and the contribution of rafts/caveolae to redox signaling. Of particular note is the evidence that endothelial nitric oxide synthase (eNOS), NADPH oxygenase, and heme oxygenase, along with other less well-studied redox systems, localize in rafts and caveolae. The precise basis for this localization and the contribution of raft/caveolae-localized redox components to physiology and disease are important issues for future studies.

An absence of stromal caveolin-1 expression predicts early tumor recurrence and poor clinical outcome in human breast cancers

Previously, we showed that caveolin-1 (Cav-1) expression is down-regulated in human breast cancer-associated fibroblasts. However, it remains unknown whether loss of Cav-1 occurs in the breast tumor stroma in vivo. Here, we immunostained a well-annotated breast cancer tissue microarray with antibodies against Cav-1 and scored its stromal expression. An absence of stromal Cav-1 was associated with early disease recurrence, advanced tumor stage, and lymph node metastasis, resulting in a 3.6-fold reduction in progression-free survival. When tamoxifen-treated patients were selected, an absence of stromal Cav-1 was a strong predictor of poor clinical outcome, suggestive of tamoxifen resistance. Interestingly, in lymph node-positive patients, an absence of stromal Cav-1 predicted an 11.5-fold reduction in 5-year progression-free survival. Clinical outcomes among patients positive for HER2, and patients triple-negative for estrogen receptor, progesterone receptor and HER2, were also strictly dependent on stromal Cav-1 levels. When our results were adjusted for tumor and nodal staging, an absence of stromal Cav-1 remained an independent predictor of poor outcome. Thus, stromal Cav-1 expression can be used to stratify human breast cancer patients into low-risk and high-risk groups, and to predict their risk of early disease recurrence at diagnosis. Based on related mechanistic studies, we suggest that breast cancer patients lacking stromal Cav-1 might benefit from anti-angiogenic therapy in addition to standard regimens. We conclude that Cav-1 functions as a tumor suppressor in the stromal microenvironment.

Immunohistochemical evidence of caveolin-1 expression in the human fetal and neonatal striated muscle and absence in the adult's

BACKGROUND

Caveolin-1 (Cav-1) is a 22-kd protein, which exerts essential roles in the regulation of cell proliferation and in transmembrane transport processes. It is mainly expressed in adipocytes, smooth muscle, fibroblasts, and endothelial cells. Its expression in striated muscle fibers is controversial. Indeed, most authors have attributed Cav-1 detection in striated muscle to endothelial cells, adipocytes, and fibroblasts secretion. Nonetheless, recent in vitro studies have shown that Cav-1 is expressed in L6 myoblasts and maintained during the differentiation process. In view of this, and, because only one study has heretofore explored Cav-1 expression in human striated muscle, the aim of the present study was to evaluate and to compare Cav-1 immunohistochemical expression in the human striated muscles of fetus, newborn, and adult.

DESIGN

Samples of skeletal muscles of different sites and of myocardium were taken at autopsy from 13 fetuses and 4 newborns and submitted to the immunohistochemical analysis for Cav-1 together with 10 samples of adult skeletal muscle.

RESULTS

Myocardial fibers displayed a weak immunoreaction in all samples, from both the newborns and the fetuses, independently of the week of gestation. Conversely, skeletal muscle fibers were only labeled in specimens from fetuses at late gestation and from the newborns, whereas no immunoreaction was evidenced in muscles taken from fetuses at mid-gestation and in the adult samples.

CONCLUSIONS

This novel and unexpected pattern of Cav-1 expression in human skeletal muscle suggests a role for Cav-1 in terminal differentiation processes, which need to be clarified by further studies.

Abnormal bradykinin signalling in fibroblasts deficient in the PIP(2) 5-phosphatase, ocrl1

The oculocerebrorenal syndrome of Lowe (Lowe syndrome) is an X-linked disorder of phosphatidylinositol metabolism characterized by congenital cataracts, renal proximal tubulopathy and neurological deficits. The disorder is due to the deficiency of the phosphatidylinositol 4,5-bisphosphate (PIP(2)) 5-phosphatase, ocrl1. PIP(2) is critical for numerous cellular processes, including cell signalling, actin reorganization and protein trafficking, and is chronically elevated in patients with Lowe syndrome. The elevation of PIP(2) cells of patients with Lowe syndrome provides the unique opportunity to investigate the roles of this phospholipid in fundamental cellular processes. We previously demonstrated that ocrl1 deficiency causes alterations in the actin cytoskeleton. Since actin remodelling is strongly activated by [Ca(+2)], which increases in response to IP(3) production, we hypothesized that altered calcium signalling might contribute to the observed abnormalities in actin organization. Here we report a specific increase in bradykinin-induced Ca(+2) mobilization in Lowe fibroblasts. We show that the abnormal bradykinin signalling occurs in spite of normal total cellular receptor content. These data point to a novel role for ocrl1 in agonist-induced calcium release.

The role of caveolae and caveolin 1 in calcium handling in pacing and contraction of mouse intestine

In mouse intestine, caveolae and caveolin-1 (Cav-1) are present in smooth muscle (responsible for executing contractions) and in interstitial cells of Cajal (ICC; responsible for pacing contractions). We found that a number of calcium handling/dependent molecules are associated with caveolae, including L-type Ca(2+) channels, Na(+)-Ca(2+) exchanger type 1 (NCX1), plasma membrane Ca(2+) pumps and neural nitric oxide synthase (nNOS), and that caveolae are close to the peripheral endo-sarcoplasmic reticulum (ER-SR). Also we found that this assemblage may account for recycling of calcium from caveolar domains to SR through L-type Ca (+) channels to sustain pacing and contractions. Here we test this hypothesis further comparing pacing and contractions under various conditions in longitudinal muscle of Cav-1 knockout mice (lacking caveolae) and in their genetic controls. We used a procedure in which pacing frequencies (indicative of functioning of ICC) and contraction amplitudes (indicative of functioning of smooth muscle) were studied in calcium-free media with 100 mM ethylene glycol tetra-acetic acid (EGTA). The absence of caveolae in ICC inhibited the ability of ICC to maintain frequencies of contraction in the calcium-free medium by reducing recycling of calcium from caveolar plasma membrane to SR when the calcium stores were initially full. This recycling to ICC involved primarily L-type Ca(2+) channels; i.e. pacing frequencies were enhanced by opening and inhibited by closing these channels. However, when these stores were depleted by block of the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) pump or calcium release was activated by carbachol, the absence of Cav-1 or caveolae had little or no effect. The absence of caveolae had little impact on contraction amplitudes, indicative of recycling of calcium to SR in smooth muscle. However, the absence of caveolae slowed the rate of loss of calcium from SR under some conditions in both ICC and smooth muscle, which may reflect the loss of proximity to store operated Ca channels. We found evidence that these channels were associated with Cav-1. These changes were all consistent with the hypothesis that a reduction of the extracellular calcium associated with caveolae in ICC of the myenteric plexus, the state of L-type Ca(2+) channels or an increase in the distance between caveolae and SR affected calcium handling.