Congenital Disorders of Glycosylation: CDG-I, CDG-II, and beyond

The Congenital Disorders of Glycosylation (CDG) are a collection of over 20 inherited diseases that impair protein N-glycosylation. The clinical appearance of CDG patients is quite diverse making it difficult for physicians to recognize them. A simple blood test of transferrin glycosylation status signals a glycosylation abnormality, but not the specific defect. An abnormal trasferrin glycosylation pattern suggests that the defect is in either genes that synthesize and add the precursor glycan (Glc(3)Man(9)GlcNAc(2)) to proteins (Type I) or genes that process the protein-bound N-glycans (Type II). Type I defects create unoccupied glycosylation sites, while Type II defects give fully occupied sites with abnormally processed glycans. These types are expected to be mutually exclusive, but a group of patients is now emerging who have variable coagulopathy and hypoglycemia together with a combination of Type I and Type II transferrin features. This surprising finding makes identifying their defects more challenging, but the defects and associated clinical manifestations of these patients suggest that the N-glycosylation pathway has some secrets left to share.     

Deficiency of Dol-P-Man Synthase Subunit DPM3 Bridges the Congenital Disorders of Glycosylation with the Dystroglycanopathies

Alpha-dystroglycanopathies such as Walker Warburg syndrome represent an important subgroup of the muscular dystrophies that have been related to defective O-mannosylation of alpha-dystroglycan. In many patients, the underlying genetic etiology remains unsolved. Isolated muscular dystrophy has not been described in the congenital disorders of glycosylation (CDG) caused by N-linked protein glycosylation defects. Here, we present a genetic N-glycosylation disorder with muscular dystrophy in the group of CDG type I. Extensive biochemical investigations revealed a strongly reduced dolichol-phosphate-mannose (Dol-P-Man) synthase activity. Sequencing of the three DPM subunits and complementation of DPM3-deficient CHO2.38 cells showed a pathogenic p.L85S missense mutation in the strongly conserved coiled-coil domain of DPM3 that tethers catalytic DPM1 to the ER membrane. Cotransfection experiments in CHO cells showed a reduced binding capacity of DPM3(L85S) for DPM1. Investigation of the four Dol-P-Man-dependent glycosylation pathways in the ER revealed strongly reduced O-mannosylation of alpha-dystroglycan in a muscle biopsy, thereby explaining the clinical phenotype of muscular dystrophy. This mild Dol-P-Man biosynthesis defect due to DPM3 mutations is a cause for alpha-dystroglycanopathy, thereby bridging the congenital disorders of glycosylation with the dystroglycanopathies.     

Mannose supplementation corrects GDP-mannose deficiency in cultured fibroblasts from some patients with Congenital Disorders of Glycosylation (CDG)

Congenital Disorders of Glycosylation (CDG) are human deficiencies in glycoprotein biosynthesis. Previous studies showed that 1 mM mannose corrects defective protein N-glycosylation in cultured fibroblasts from some CDG patients. We hypothesized that these CDG cells have limited GDP-mannose (GDP-Man) and that exogenous mannose increases the GDP-Man levels. Using a well established method to measure GDP-Man, we found that normal fibroblasts had an average of 23.5 pmol GDP-Man/10(6) cells, whereas phosphomannomutase (PMM)-deficient fibroblasts had only 2.3-2.7 pmol/10(6) cells. Adding 1 mM mannose to the culture medium increased the GDP-Man level in PMM-deficient cells to approximately 15.5 pmol/10(6) cells, but had no significant effect on GDP-Man levels in normal fibroblasts. Similarly, mannose supplementation increased GDP-Man from 4.6 pmol/10(6) cells to 24.6 pmol/10(6) cells in phosphomannose isomerase (PMI)-deficient fibroblasts. Based on the specific activity of the GDP-[(3)H]Man pool present in [2-(3)H]mannose labeled cells, mannose supplementation also partially corrected the impaired synthesis of mannosylphosphoryldolichol (Man-P-Dol) and Glc(0)(-)(3)Man(9)GlcNAc(2)-P-P-Dol. These results confirm directly that deficiencies in PMM and PMI result in lowered cellular GDP-Man levels that are corrected by the addition of mannose. In contrast to these results, GDP-Man levels in fibroblasts from a CDG-Ie patient, who is deficient in Man-P-Dol synthase, were normal and unaffected by mannose supplementation even though mannose addition was found to correct abnormal lipid intermediate synthesis in another study (Kim et al. [2000] J. Clin. Invest., 105, 191-198). The mechanism by which mannose supplementation corrects abnormal protein N-glycosylation in Man-P-Dol synthase deficient cells is unknown, but this observation suggests that the regulation of Man-P-Dol synthesis and utilization may be more complex than is currently understood.     

Glycosylation control technologies for recombinant therapeutic proteins

Protein glycosylation is a very important quality attribute of any biopharmaceutical product as it affects the efficacy, serum half-life, and antigenicity of a molecule. The present expression hosts commercially utilized for a recombinant glycoprotein production generally cannot produce a desired and uniform glycan composition and generally exhibit non-human glycans that can lead to unwanted side effects. The authors provide a comprehensive review of various approaches which can be implemented to minimize the glycan heterogeneity for the production of the desired protein with improved glycoforms. The authors also describe that the industry standard expression systems such as mammalian, insect, and yeast are glycoengineered to produce human-like glycan composition of a recombinant product. This review summarizes the recent technologies used for the improvement of the glycan composition of the biotherapeutics, focusing largely on the selection of an appropriate expression host, glycoengineering, and upstream process optimization to control protein glycosylation and thus enhanced biological activity with fewer side effects. Here, we also suggest various approaches such as host and clone selection to achieve expected glycosylation in a recombinant protein. The cell culture, biochemical, and physical process parameters play a key role in the manufacturing of the desired glycoform of a therapeutic protein. Hence, these components are to be considered very carefully while developing such glycoproteins. Also, glycoengineering of production host to modulate the protein glycosylation is also recommended in the present review.

     

Understanding Human Glycosylation Disorders: Biochemistry Leads the Charge

Nearly 70 inherited human glycosylation disorders span a breathtaking clinical spectrum, impacting nearly every organ system and launching a family-driven diagnostic odyssey. Advances in genetics, especially next generation sequencing, propelled discovery of many glycosylation disorders in single and multiple pathways. Interpretation of whole exome sequencing results, insights into pathological mechanisms, and possible therapies will hinge on biochemical analysis of patient-derived materials and animal models. Biochemical diagnostic markers and readouts offer a physiological context to confirm candidate genes. Recent discoveries suggest novel perspectives for textbook biochemistry and novel research opportunities. Basic science and patients are the immediate beneficiaries of this bidirectional collaboration.     

Mindfulness-Based Therapies in the Treatment of Somatization Disorders: A Systematic Review and Meta-Analysis

Background

Mindfulness-based therapy (MBT) has been used effectively to treat a variety of physical and psychological disorders, including depression, anxiety, and chronic pain. Recently, several lines of research have explored the potential for mindfulness-therapy in treating somatization disorders, including fibromyalgia, chronic fatigue syndrome, and irritable bowel syndrome.

Methods

Thirteen studies were identified as fulfilling the present criteria of employing randomized controlled trials to determine the efficacy of any form of MBT in treating somatization disorders. A meta-analysis of the effects of mindfulness-based therapy on pain, symptom severity, quality of life, depression, and anxiety was performed to determine the potential of this form of treatment.

Findings

While limited in power, the meta-analysis indicated a small to moderate positive effect of MBT (compared to wait-list or support group controls) in reducing pain (SMD  = −0.21, 95% CI: −0.37, −0.03; p<0.05), symptom severity (SMD  = −0.40, 95% CI: −0.54, −0.26; p<0.001), depression (SMD  = −0.23, 95% CI: −0.40, −0.07, p<0.01), and anxiety (SMD  = −0.20, 95% CI: −0.42, 0.02, p = 0.07) associated with somatization disorders, and improving quality of life (SMD  = 0.39, 95% CI: 0.19, 0.59; p<0.001) in patients with this disorder. Subgroup analyses indicated that the efficacy of MBT was most consistent for irritable bowel syndrome (p<0.001 for pain, symptom severity, and quality of life), and that mindfulness-based stress reduction (MBSR) and mindfulness-based cognitive therapy (MCBT) were more effective than eclectic/unspecified MBT.

Conclusions

Preliminary evidence suggests that MBT may be effective in treating at least some aspects of somatization disorders. Further research is warranted.     

ErbB-targeted therapeutic approaches in human cancer

The overexpression and aberrant function of the epidermal growth factor receptor (EGFR, erbB1, HER1) and its ligands and coreceptors in a wide spectrum of epithelial cancers have provided a rationale for targeting this signaling network with novel treatment approaches. Several antireceptor therapeutic strategies have been pursued, but two stand ahead in their clinical development. One approach has been the generation of small molecules that compete with adenosine triphosphate (ATP) for binding to the receptor's kinase pocket, thus blocking receptor activation and the transduction of postreceptor signals. The second approach utilizes humanized monoclonal antibodies generated against the receptor's ligand-binding extracellular domain. These antibodies block binding of receptor-activating ligands and, in some cases, can induce receptor endocytosis and downregulation. Clinical studies already suggest that both of these approaches, either alone or in combination with standard anticancer therapies, are well tolerated and can induce clinical responses and tumor stabilization in a variety of common carcinomas.     

Modern therapeutic approaches in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder of the brain and typically presents with a disorder of movement. The core pathological event underlying the condition is the loss of the dopaminergic nigrostriatal pathway with the formation of alpha-synuclein-positive Lewy bodies. As a result, drugs that target the degenerating dopaminergic network within the brain work well, at least in the early stages of the disease. Unfortunately, with time, these therapies fail and produce their own unique side-effect profile and this, coupled with the more-diffuse pathological and clinical findings in advancing disease, has led to the search for more-effective therapies. In this review, we discuss the emerging new therapies in PD in terms of neuroprotective agents, drugs designed to control symptoms more effectively, and finally curative cell therapies.     

Protein-misfolding diseases and chaperone-based therapeutic approaches

A large number of neurodegenerative diseases in humans result from protein misfolding and aggregation. Protein misfolding is believed to be the primary cause of Alzheimer's disease, Parkinson's disease, Huntington's disease, Creutzfeldt-Jakob disease, cystic fibrosis, Gaucher's disease and many other degenerative and neurodegenerative disorders. Cellular molecular chaperones, which are ubiquitous, stress-induced proteins, and newly found chemical and pharmacological chaperones have been found to be effective in preventing misfolding of different disease-causing proteins, essentially reducing the severity of several neurodegenerative disorders and many other protein-misfolding diseases. In this review, we discuss the probable mechanisms of several protein-misfolding diseases in humans, as well as therapeutic approaches for countering them. The role of molecular, chemical and pharmacological chaperones in suppressing the effect of protein misfolding-induced consequences in humans is explained in detail. Functional aspects of the different types of chaperones suggest their uses as potential therapeutic agents against different types of degenerative diseases, including neurodegenerative disorders.     

Glycosylation: impact,control and improvement during therapeutic protein production

Abstract

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.     

Animal models of polyglutamine diseases and therapeutic approaches

The dominant gain-of-function polyglutamine repeat diseases, in which the initiating mutation is known, allow development of models that recapitulate many aspects of human disease. To the extent that pathology is a consequence of disrupted fundamental cellular activities, one can effectively study strategies to ameliorate or protect against these cellular insults. Model organisms allow one to identify pathways that affect disease onset and progression, to test and screen for pharmacological agents that affect pathogenic processes, and to validate potential targets genetically as well as pharmacologically. Here, we describe polyglutamine repeat diseases that have been modeled in a variety of organisms, including worms, flies, mice, and non-human primates, and discuss examples of how they have broadened the therapeutic landscape.     

PGM3 Mutations Cause a Congenital Disorder of Glycosylation with Severe Immunodeficiency and Skeletal Dysplasia

Human phosphoglucomutase 3 (PGM3) catalyzes the conversion of N-acetyl-glucosamine (GlcNAc)-6-phosphate into GlcNAc-1-phosphate during the synthesis of uridine diphosphate (UDP)-GlcNAc, a sugar nucleotide critical to multiple glycosylation pathways. We identified three unrelated children with recurrent infections, congenital leukopenia including neutropenia, B and T cell lymphopenia, and progression to bone marrow failure. Whole-exome sequencing demonstrated deleterious mutations in PGM3 in all three subjects, delineating their disease to be due to an unsuspected congenital disorder of glycosylation (CDG). Functional studies of the disease-associated PGM3 variants in E. coli cells demonstrated reduced PGM3 activity for all mutants tested. Two of the three children had skeletal anomalies resembling Desbuquois dysplasia: short stature, brachydactyly, dysmorphic facial features, and intellectual disability. However, these additional features were absent in the third child, showing the clinical variability of the disease. Two children received hematopoietic stem cell transplantation of cord blood and bone marrow from matched related donors; both had successful engraftment and correction of neutropenia and lymphopenia. We define PGM3-CDG as a treatable immunodeficiency, document the power of whole-exome sequencing in gene discoveries for rare disorders, and illustrate the utility of genomic analyses in studying combined and variable phenotypes.     

Protein-based therapeutic approaches targeting death receptors

Death receptors (DRs) are a growing family of transmembrane proteins that can detect the presence of specific extracellular death signals and rapidly trigger cellular destruction by apoptosis. Eight human DRs (Fas, TNF-R1, TRAMP, TRAIL-R1, TRAIL-R2, DR-6, EDA-R and NGF-R) have been identified. The best studied to date is Fas (CD95). Expression and signaling by Fas and its ligand (FasL, CD95L) is a tightly regulated process essential for key physiological functions in a variety of organs, including the maintenance of immune homeostasis. Recently, strong evidence has shown that dysregulation of Fas expression and/or signaling contributes to the pathogenesis of tissue destructive diseases such as graft-versus-host disease, toxic epidermal necrolysis, multiple sclerosis and stroke. With these new developments, strategies for modulating the function of Fas signaling have emerged and provided novel protein-based therapeutic possibilities that will be discussed herein. Selective triggering of DR-mediated apoptosis in cancer cells is an emerging approach that is being intensely investigated as a mode of cancer therapy. Local administration of Fas agonists, and more promisingly, systemic use of soluble recombinant forms of TRAIL have shown efficacy in preclinical models of the disease. Developments in this field that may have important clinical implications for the treatment of cancer are reviewed.     

Emerging therapeutic approaches for osteogenesis imperfecta

Osteogenesis imperfecta (OI) is an incurable genetic brittle-bone disease. Although drug therapy, surgery and physiotherapy represent current treatments for OI, the search is ongoing for effective and innovative new therapies targeting the underlying causes of the disease. In this regard, recent advances in the fields of gene and stem-cell therapies have been considerable. In spite of the many challenges that remain, potential new therapies for OI, which have been tested in cell culture systems, animal models and patients, offer hope for the future development of successful therapies. Recent progress in the field is reviewed here.     

Molecular pathogenesis of hepatic fibrosis and current therapeutic approaches

The pathogenesis of hepatic fibrosis involves significant deposition of fibrilar collagen and other extracellular matrix proteins. It is a rather dynamic process of wound healing in response to a variety of persistent liver injury caused by factors such as ethanol intake, viral infection, drugs, toxins, cholestasis, and metabolic disorders. Liver fibrosis distorts the hepatic architecture, decreases the number of endothelial cell fenestrations and causes portal hypertension. Key events are the activation and transformation of quiescent hepatic stellate cells into myofibroblast-like cells with the subsequent up-regulation of proteins such as α-smooth muscle actin, interstitial collagens, matrix metalloproteinases, tissue inhibitor of metalloproteinases, and proteoglycans. Oxidative stress is a major contributing factor to the onset of liver fibrosis and it is typically associated with a decrease in the antioxidant defense. Currently, there is no effective therapy for advanced liver fibrosis. In its early stages, liver fibrosis is reversible upon cessation of the causative agent. In this review, we discuss some aspects on the etiology of liver fibrosis, the cells involved, the molecular pathogenesis, and the current therapeutic approaches.     

Copy-Number Disorders Are a Common Cause of Congenital Kidney Malformations

We examined the burden of large, rare, copy-number variants (CNVs) in 192 individuals with renal hypodysplasia (RHD) and replicated findings in 330 RHD cases from two independent cohorts. CNV distribution was significantly skewed toward larger gene-disrupting events in RHD cases compared to 4,733 ethnicity-matched controls (p = 4.8 × 10⁻¹¹). This excess was attributable to known and novel (i.e., not present in any database or in the literature) genomic disorders. All together, 55/522 (10.5%) RHD cases harbored 34 distinct known genomic disorders, which were detected in only 0.2% of 13,839 population controls (p = 1.2 × 10⁻⁵⁸). Another 32 (6.1%) RHD cases harbored large gene-disrupting CNVs that were absent from or extremely rare in the 13,839 population controls, identifying 38 potential novel or rare genomic disorders for this trait. Deletions at the HNF1B locus and the DiGeorge/velocardiofacial locus were most frequent. However, the majority of disorders were detected in a single individual. Genomic disorders were detected in 22.5% of individuals with multiple malformations and 14.5% of individuals with isolated urinary-tract defects; 14 individuals harbored two or more diagnostic or rare CNVs. Strikingly, the majority of the known CNV disorders detected in the RHD cohort have previous associations with developmental delay or neuropsychiatric diseases. Up to 16.6% of individuals with kidney malformations had a molecular diagnosis attributable to a copy-number disorder, suggesting kidney malformations as a sentinel manifestation of pathogenic genomic imbalances. A search for pathogenic CNVs should be considered in this population for the diagnosis of their specific genomic disorders and for the evaluation of the potential for developmental delay.