Glucagon is a 29-amino-acid peptide released from the α-cells of the islet of Langerhans, which has a key role in glucose homeostasis. Glucagon action is transduced by the class B G-protein-coupled ...glucagon receptor (GCGR), which is located on liver, kidney, intestinal smooth muscle, brain, adipose tissue, heart and pancreas cells, and this receptor has been considered an important drug target in the treatment of diabetes. Administration of recently identified small-molecule GCGR antagonists in patients with type 2 diabetes results in a substantial reduction of fasting and postprandial glucose concentrations. Although an X-ray structure of the transmembrane domain of the GCGR has previously been solved, the ligand (NNC0640) was not resolved. Here we report the 2.5 Å structure of human GCGR in complex with the antagonist MK-0893 (ref. 4), which is found to bind to an allosteric site outside the seven transmembrane (7TM) helical bundle in a position between TM6 and TM7 extending into the lipid bilayer. Mutagenesis of key residues identified in the X-ray structure confirms their role in the binding of MK-0893 to the receptor. The unexpected position of the binding site for MK-0893, which is structurally similar to other GCGR antagonists, suggests that glucagon activation of the receptor is prevented by restriction of the outward helical movement of TM6 required for G-protein coupling. Structural knowledge of class B receptors is limited, with only one other ligand-binding site defined--for the corticotropin-releasing hormone receptor 1 (CRF1R)--which was located deep within the 7TM bundle. We describe a completely novel allosteric binding site for class B receptors, providing an opportunity for structure-based drug design for this receptor class and furthering our understanding of the mechanisms of activation of these receptors.
Genetics of Amyotrophic Lateral Sclerosis Ghasemi, Mehdi; Brown, Jr, Robert H
Cold Spring Harbor perspectives in medicine,
05/2018, Letnik:
8, Številka:
5
Journal Article
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Amyotrophic lateral sclerosis (ALS) is a devastating, uniformly lethal degenerative disorder of motor neurons that overlaps clinically with frontotemporal dementia (FTD). Investigations of the 10% of ...ALS cases that are transmitted as dominant traits have revealed numerous gene mutations and variants that either cause these disorders or influence their clinical phenotype. The evolving understanding of the genetic architecture of ALS has illuminated broad themes in the molecular pathophysiology of both familial and sporadic ALS and FTD. These central themes encompass disturbances of protein homeostasis, alterations in the biology of RNA binding proteins, and defects in cytoskeletal dynamics, as well as numerous downstream pathophysiological events. Together, these findings from ALS genetics provide new insight into therapies that target genetically distinct subsets of ALS and FTD.
Adult-onset neurodegenerative diseases (AONDs) comprise a heterogeneous group of neurological disorders characterized by a progressive, age-dependent decline in neuronal function and loss of selected ...neuronal populations. Alterations in synaptic function and axonal connectivity represent early and critical pathogenic events in AONDs, but molecular mechanisms underlying these defects remain elusive. The large size and complex subcellular architecture of neurons render them uniquely vulnerable to alterations in axonal transport (AT). Accordingly, deficits in AT have been documented in most AONDs, suggesting a common defect acquired through different pathogenic pathways. These observations suggest that many AONDs can be categorized as dysferopathies, diseases in which alterations in AT represent a critical component in pathogenesis. Topics here address various molecular mechanisms underlying alterations in AT in several AONDs. Illumination of such mechanisms provides a framework for the development of novel therapeutic strategies aimed to prevent axonal and synaptic dysfunction in several major AONDs.
The most common form of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting adult motor neurons, is caused by dominant mutations in the ubiquitously expressed Cu-Zn Superoxide ...dismutase (SOD1). In chimeric mice that are mixtures of normal and SOD1 mutant-expressing cells, toxicity to motor neurons is shown to require damage from mutant SOD1 acting within nonneuronal cells. Normal motor neurons in SOD1 mutant chimeras develop aspects of ALS pathology. Most important, nonneuronal cells that do not express mutant SOD1 delay degeneration and significantly extend survival of mutant-expressing motor neurons.
Amyotrophic lateral sclerosis (ALS) is an adult-onset, lethal, paralytic disorder caused by the degeneration of motor neurons. Our understanding of this disease has been greatly facilitated by ...studies of familial ALS caused by mutations in the gene encoding superoxide dismutase 1 (SOD1). Evidence indicates that misfolded wild-type SOD1 may also be pathogenic in sporadic ALS. Mutant SOD1 is neurotoxic through multiple mechanisms. Because the pathogenicity of mutant SOD1 is proportional to the dose of the toxic protein, a rational approach to treating SOD1-related ALS is to reduce levels of the toxic SOD1 species. An advantage of this strategy is that it potentially obviates intervening in multiple, downstream pathological cascades. In recent years, several strategies to silence gene expression have been developed. The most clinically promising are predicated on approaches that enhance degradation of RNA, such as anti-sense oligonucleotides (ASO) and RNA interference (RNAi); the latter include small inhibitory RNA (siRNA), short hairpin RNA (shRNA) and microRNA (miR). Agents such as shRNA and either native or synthetic miR are capable of permeating the central nervous system (CNS) and efficiently silencing genes in the brain and spinal cord. Here we review recent progress in silencing SOD1, focusing on studies using artificial shRNA or miRNA in combination with potent viral vector delivery systems to mediate SOD1 silencing within the CNS in transgenic SOD1G93A mice and non-human primates.
Cardiac surgery is associated with cognitive decline and postoperative delirium. The relationship between postoperative delirium and cognitive decline after cardiac surgery is unclear
The development ...of postoperative delirium is associated with a greater degree of cognitive decline 1 month after cardiac surgery. The development of postoperative delirium is not a predictor of cognitive decline 1 yr after cardiac surgery.
Delirium is common after cardiac surgery and has been associated with morbidity, mortality, and cognitive decline. However, there are conflicting reports on the magnitude, trajectory, and domains of cognitive change that might be affected. The authors hypothesized that patients with delirium would experience greater cognitive decline at 1 month and 1 yr after cardiac surgery compared to those without delirium.
Patients who underwent coronary artery bypass and/or valve surgery with cardiopulmonary bypass were eligible for this cohort study. Delirium was assessed with the Confusion Assessment Method. A neuropsychologic battery was administered before surgery, at 1 month, and at 1 yr later. Linear regression was used to examine the association between delirium and change in composite cognitive Z score from baseline to 1 month (primary outcome). Secondary outcomes were domain-specific changes at 1 month and composite and domain-specific changes at 1 yr.
The incidence of delirium in 142 patients was 53.5%. Patients with delirium had greater decline in composite cognitive Z score at 1 month (greater decline by -0.29; 95% CI, -0.54 to -0.05; P = 0.020) and in the domains of visuoconstruction and processing speed. From baseline to 1 yr, there was no difference between delirious and nondelirious patients with respect to change in composite cognitive Z score, although greater decline in processing speed persisted among the delirious patients.
Patients who developed delirium had greater decline in a composite measure of cognition and in visuoconstruction and processing speed domains at 1 month. The differences in cognitive change by delirium were not significant at 1 yr, with the exception of processing speed.
Axonal and synaptic degeneration is a hallmark of peripheral neuropathy, brain injury, and neurodegenerative disease. Axonal degeneration has been proposed to be mediated by an active autodestruction ...program, akin to apoptotic cell death; however, loss-of-function mutations capable of potently blocking axon self-destruction have not been described. Here, we show that loss of the Drosophila Toll receptor adaptor dSarm (sterile α/Armadillo/Toll-Interleukin receptor homology domain protein) cell-autonomously suppresses Wallerian degeneration for weeks after axotomy. Severed mouse Sarm1 null axons exhibit remarkable long-term survival both in vivo and in vitro, indicating that Sarm1 prodegenerative signaling is conserved in mammals. Our results provide direct evidence that axons actively promote their own destruction after injury and identify dSarm/Sarm1 as a member of an ancient axon death signaling pathway.
HSAN1 is an inherited neuropathy found to be associated with several missense mutations in the SPTLC1 subunit of serine palmitoyltransferase (SPT). SPT catalyzes the condensation of serine and ...palmitoyl-CoA, the initial step in the de novo synthesis of sphingolipids. Here we show that the HSAN1 mutations induce a shift in the substrate specificity of SPT, which leads to the formation of the two atypical deoxy-sphingoid bases (DSBs) 1-deoxy-sphinganine and 1-deoxymethyl-sphinganine. Both metabolites lack the C1 hydroxyl group of sphinganine and can therefore neither be converted to complex sphingolipids nor degraded. Consequently, they accumulate in the cell, as demonstrated in HEK293 cells overexpressing mutant SPTLC1 and lymphoblasts of HSAN1 patients. Elevated DSB levels were also found in the plasma of HSAN1 patients and confirmed in three groups of HSAN1 patients with different SPTLC1mutations. The DSBs show pronounced neurotoxic effects on neurite formation in cultured sensory neurons. The neurotoxicity co-occurs with a disturbed neurofilament structure in neurites when cultured in the presence of DSBs. Based on these observations, we conclude that HSAN1 is caused by a gain of function mutation, which results in the formation of two atypical and neurotoxic sphingolipid metabolites.
The Gram-negative opportunistic bacterium
is a significant cause of hospital-borne infections worldwide. Alarmingly, the rapid development of antimicrobial resistance coupled with the remarkable ...ability of isolates to persist on surfaces for extended periods of time has led to infiltration of
into our healthcare environments. A major virulence determinant of
is the presence of a capsule that surrounds the bacterial surface. This capsule is comprised of tightly packed repeating polysaccharide units which forms a barrier around the bacterial cell wall, providing protection from environmental pressures including desiccation and disinfection regimes as well as host immune responses such as serum complement. Additionally, capsule has been shown to confer resistance to a range of clinically relevant antimicrobial compounds. Distressingly, treatment options for
infections are becoming increasingly limited, and the urgency to develop effective infection control strategies and therapies to combat infections is apparent. An increased understanding of the contribution of capsule to the pathobiology of
is required to determine its feasibility as a target for new strategies to combat drug resistant infections. Significant variation in capsular polysaccharide structures between
isolates has been identified, with over 100 distinct capsule types, incorporating a vast variety of sugars. This review examines the studies undertaken to elucidate capsule diversity and advance our understanding of the role of capsule in
pathogenesis.
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