Golgi maturation-dependent glycoenzyme recycling controls glycosphingolipid biosynthesis and cell growth via GOLPH3.

Glycosphingolipids are important components of the plasma membrane where they modulate the activities of membrane proteins including signalling receptors. Glycosphingolipid synthesis relies on competing reactions catalysed by Golgi-resident enzymes during the passage of substrates through the Golgi cisternae. The glycosphingolipid metabolic output is determined by the position and levels of the enzymes within the Golgi stack, but the mechanisms that coordinate the intra-Golgi localisation of the enzymes are poorly understood. Here, we show that a group of sequentially-acting enzymes operating at the branchpoint among glycosphingolipid synthetic pathways binds the Golgi-localised oncoprotein GOLPH3. GOLPH3 sorts these enzymes into vesicles for intra-Golgi retro-transport, acting as a component of the cisternal maturation mechanism. Through these effects, GOLPH3 controls the sub-Golgi localisation and the lysosomal degradation rate of specific enzymes. Increased GOLPH3 levels, as those observed in tumours, alter glycosphingolipid synthesis and plasma membrane composition thereby promoting mitogenic signalling and cell proliferation. These data have medical implications as they outline a novel oncogenic mechanism of action for GOLPH3 based on glycosphingolipid metabolism.

Higher Level of Dickkopf-1 is Associated with Low Bone Mineral Density and Higher Prevalence of Vertebral Fractures in Patients with Ankylosing Spondylitis.

Patients with ankylosing spondylitis (AS) have an increased risk of bone loss and vertebral fractures. In this study, we explored the hypothesis that the excess bone loss and vertebral fractures might be related with the activity of the Wingless signaling pathway, and in particular with the serum levels of its circulating inhibitors, Sclerostin and Dickkopf-1 (DKK1). We recruited 71 patients diagnosed with AS. Lateral radiographs of the total spine were analyzed to detect the presence of vertebral fractures, and bone mineral density (BMD) was assessed in all patients using dual X-ray absorptiometry at lumbar spine and proximal femoral site. Blood samples were obtained and levels of C-reactive protein (CRP), DKK1, and Sclerostin were measured. Blood samples from 71 healthy sex- and age-matched volunteers were collected to be used as controls. Vertebral fractures were detected more commonly among men than in women (29 vs 8 %, respectively). DKK1, but not Sclerostin serum levels, were inversely correlated to lumbar spine Z-score BMD. Patients with one or more prevalent vertebral fractures had significantly higher DKK1 levels, without significant difference in Sclerostin serum levels. A significant positive correlation was found between DKK1 serum levels and CRP (r = 0.240, p = 0.043). The association we found between serum DKK1 levels and BMD values and vertebral fracture prevalence suggests that DKK1 might contribute to the severity of osteoporosis in AS.

CERT1 mutations perturb human development by disrupting sphingolipid homeostasis.

Neural differentiation, synaptic transmission, and action potential propagation depend on membrane sphingolipids, whose metabolism is tightly regulated. Mutations in the ceramide transporter CERT (CERT1), which is involved in sphingolipid biosynthesis, are associated with intellectual disability, but the pathogenic mechanism remains obscure. Here, we characterize 31 individuals with de novo missense variants in CERT1. Several variants fall into a previously uncharacterized dimeric helical domain that enables CERT homeostatic inactivation, without which sphingolipid production goes unchecked. The clinical severity reflects the degree to which CERT autoregulation is disrupted, and inhibiting CERT pharmacologically corrects morphological and motor abnormalities in a Drosophila model of the disease, which we call ceramide transporter (CerTra) syndrome. These findings uncover a central role for CERT autoregulation in the control of sphingolipid biosynthetic flux, provide unexpected insight into the structural organization of CERT, and suggest a possible therapeutic approach for patients with CerTra syndrome.

Modifying effects of δ-Aminolevulinate dehydratase polymorphism on blood lead levels and ALAD activity.

Lead is an environmental hazard with great public health concern and has been known to inhibit delta-aminolevulinate dehydratase (ALAD) activity involved in the heme biosynthetic pathway. The study aimed to investigate the influence of ALAD polymorphism (G177C) on retention of Pb-B levels and ALAD activity on occupationally exposed lead workers. In the present study, we enrolled 561 lead exposed and 317 non-occupationally exposed subjects and performed a comprehensive analysis of Pb-B levels along with ALAD activity and genotyping. The frequency of ALAD variants observed in the total subjects (n = 878) was 70.04% for ALAD 1-1, 27.44% for heterozygous ALAD 1-2 and 2.5% for homozygous mutant ALAD 2-2. Our study revealed that ALAD 1-2 carriers presented higher Pb-B levels compared to wild type ALAD 1-1 carriers. Further, a significant difference was observed in the activity of ALAD between ALAD 1-2/ 2-2 and ALAD 1-1 carriers of non-occupationally exposed group indicating that the polymorphic nature of the enzyme may contribute to altered activity of ALAD irrespective of lead exposure. Hence, ALAD 2 allele might contribute to increased susceptibility to high Pb-B retention, and genotyping of ALAD in lead exposed subjects might be used as a prediction marker to impede tissue/organ damage due to lead toxicity.

CD14++ CD16- monocytes are the main source of 11ß-HSD type 1 after IL-4 stimulation.

The anti-inflammatory actions of IL-4 are well established through earlier findings. However, the exact mechanism it uses to downregulate the pro-inflammatory cytokine production through monocytes and macrophages is poorly understood. In this study, we examined the effect of IL-4 in the induction of 11ß-HSD1 in the two main classes of monocytes, CD14++ CD16- (CD14) and CD14+ CD16+ (CD16). Peripheral Blood Mononuclear Cells (PBMCs) were isolated from 17 healthy donors and were sorted into CD14 and CD16 subpopulations using cell sorting. Effect of IL-4 on 11ß-HSD1-enzyme activity was measured in sorted and unsorted monocytes using Homogeneous Time-Resolved Fluorescence (HTRF) and M1/M2 polarization analysis was performed by flow cytometry. Our results indicate that CD14 cells are the major source of 11ß-HSD1 enzyme after IL-4 stimulation and that M2 phenotype is not a pre-requisite for its synthesis.

Distinct effect of zoledronate and clodronate on circulating levels of DKK1 and sclerostin in women with postmenopausal osteoporosis.

The coupling of bone formation to bone resorption during treatment of postmenopausal osteoporosis with antiresorbers might be related to changes in Wnt/b-catenin signaling. We compared the effects of two bisphosphonate treatments on two Wnt-inhibitors Sclerostin (SOST) and Dickkopf-related protein 1 (DKK1). The study population included 74 women with postmenopausal osteoporosis participating simultaneously in two multicenter, placebo controlled trials. The patients were randomized to: intramuscular clodronate 100mg/week (CLO) (N=36), and yearly intravenous therapy with 5mg zoledronate (ZOL) (N=18) and placebo (N=20). Bone turnover markers (intact N-propeptide of type I collagen [P1NP], C-terminal telopeptide of type I collagen [CTX]) remained unchanged in the placebo group while they significantly decreased during treatment with the two bisphosphonates, versus both placebo and baseline. In CLO treated patients serum DKK1 remained stable over the entire period of observation while serum SOST levels increased significantly after 12months of treatment both versus placebo group (p<0,005), baseline (p<0,001) and ZOL treated group. In the ZOL group, DKK1 levels increased significantly within one month and for the following 6months and it fell back to baseline values at 12months. The second ZOL infusion was again associated with an increase in DKK1 a month later, although to a lesser extent. In conclusion, in this study we have found that the treatment of postmenopausal osteoporosis with intermittent yearly ZOL is associated with transient and declining increases in DKK1 while continuous treatment with CLO, results in a late increase in serum SOST. These preliminary results and further ad hoc studies might contribute to shed light on our understanding of the bone coupling effects taking place during treatment of osteoporosis with different anti-resorbers or with different treatment regimens.

Osteoporosis treatment: why ibandronic acid?

INTRODUCTION: In this article, we have summarized the specific evidence on ibandronic acid (or ibandronate) efficacy, tolerability, and feasibility acquired from trials and clinical use. AREAS COVERED: This critical review focuses on evidence from randomized controlled clinical trials, meta-analyses, surrogate markers, bridging trials, long-term extension studies, observational studies, clinical experiences in osteoporosis in addition to postmenopausal treatment adherence in clinical practice, and safety profile of ibandronic acid. EXPERT OPINION: Pivotal studies on ibandronic acid efficacy in terms of antifracture effects on nonvertebral fractures had some intrinsic limitations. However, a large body of indirect evidence suggests that ibandronate has significantly sustained vertebral and nonvertebral antifracture efficacies in women with postmenopausal osteoporosis, in comparison to those observed with other nitrogen-containing bisphosphonates. Discrepancies in efficacy between the available bisphosphonate regimens appear to be a function of dose rather than to inherent differences in their respective therapeutic potential. Drugs or treatment regimens that minimize the risk of osteoporotic fractures and make the treatment of osteoporosis more convenient and suitable for patients are preferred: ibandronic acid marketed at oral doses of 150 mg once monthly and 3 mg quarterly as intravenous injection has these characteristics. The safety profile of ibandronic acid treatment appears to be good overall and in some cases better than that of other nitrogen-containing bisphosphonates.