Cellular prion protein targets amyloid-ß fibril ends via its C-terminal domain to prevent elongation.

Oligomeric forms of the amyloid-ß (Aß) peptide are thought to represent the primary synaptotoxic species underlying the neurodegenerative changes seen in Alzheimer's disease. It has been proposed that the cellular prion protein (PrPC) functions as a cell-surface receptor, which binds to Aß oligomers and transduces their toxic effects. However, the molecular details of the PrPC-Aß interaction remain uncertain. Here, we investigated the effect of PrPC on polymerization of Aß under rigorously controlled conditions in which Aß converts from a monomeric to a fibrillar state via a series of kinetically defined steps. We demonstrated that PrPC specifically inhibited elongation of Aß fibrils, most likely by binding to the ends of growing fibrils. Surprisingly, this inhibitory effect required the globular C-terminal domain of PrPC, which has not been previously implicated in interactions with Aß. Our results suggest that PrPC recognizes structural features common to both Aß oligomers and fibril ends and that this interaction could contribute to the neurotoxic effect of Aß aggregates. Additionally, our results identify the C terminus of PrPC as a new and potentially more druggable molecular target for treating Alzheimer's disease.

A C-terminal membrane anchor affects the interactions of prion proteins with lipid membranes.

Membrane attachment via a C-terminal glycosylphosphatidylinositol anchor is critical for conversion of PrP(C) into pathogenic PrP(Sc). Therefore the effects of the anchor on PrP structure and function need to be deciphered. Three PrP variants, including full-length PrP (residues 23-231, FL_PrP), N-terminally truncated PrP (residues 90-231, T_PrP), and PrP missing its central hydrophobic region (Δ105-125, ΔCR_PrP), were equipped with a C-terminal membrane anchor via a semisynthesis strategy. Analyses of the interactions of lipidated PrPs with phospholipid membranes demonstrated that C-terminal membrane attachment induces a different binding mode of PrP to membranes, distinct from that of non-lipidated PrPs, and influences the biochemical and conformational properties of PrPs. Additionally, fluorescence-based assays indicated pore formation by lipidated ΔCR_PrP, a variant that is known to be highly neurotoxic in transgenic mice. This finding was supported by using patch clamp electrophysiological measurements of cultured cells. These results provide new evidence for the role of the membrane anchor in PrP-lipid interactions, highlighting the importance of the N-terminal and the central hydrophobic domain in these interactions.

The neuroprotective effect of Klotho is mediated via regulation of members of the redox system.

Generation of reactive oxygen species (ROS), leading to oxidative damage and neuronal cell death, plays an important role in the pathogenesis of neurodegenerative disorders, including Alzheimer disease. The present study aimed to examine the mechanism by which the anti-aging protein Klotho exerts neuroprotective effects against neuronal damage associated with neurodegeneration and oxidative stress. Pretreatment of rat primary hippocampal neurons and mouse hippocampal neuronal cell line HT22 with recombinant Klotho protected these cells from glutamate and oligomeric amyloid ß (oAß)-induced cytotoxicity. In addition, primary hippocampal neurons obtained from Klotho-overexpressing mouse embryos were more resistant to both cytotoxic insults, glutamate and oAß, compared with neurons from wild-type littermates. An antioxidative stress array analysis of neurons treated with Klotho revealed that Klotho significantly enhances the expression of the thioredoxin/peroxiredoxin (Trx/Prx) system with the greatest effect on the induction of Prx-2, an antioxidant enzyme, whose increase was confirmed at the mRNA and protein levels. Klotho-induced phosphorylation of the PI3K/Akt pathway, a pathway important in apoptosis and longevity, was associated with sustained inhibitory phosphorylation of the transcription factor forkhead box O3a (FoxO3a) and was essential for the induction of Prx-2. Down-regulation of Prx-2 expression using a lentivirus harboring shRNA almost completely abolished the ability of Klotho to rescue neurons from glutamate-induced death and significantly, but not completely, inhibited cell death mediated by oAß, suggesting that Prx-2 is a key modulator of neuroprotection. Thus, our results demonstrate, for the first time, the neuroprotective role of Klotho and reveal a novel mechanism underlying this effect.

Continuous Subcutaneous Delivery of rhPTH(1-84) and rhPTH(1-34) by Pump in Adults With Hypoparathyroidism.

Context: Continuous subcutaneous infusion of recombinant parathyroid hormone (rhPTH) through a pump has been proposed as a therapeutic alternative for patients with chronic hypoparathyroidism who remain symptomatic or hypercalciuric on conventional treatment (calcium and active vitamin D) or daily injections of rhPTH(1-84) or rhPTH(1-34). However, the real-world evidence of the outcome of this novel therapy is limited. Case Descriptions: We report the clinical and biochemical outcomes of 12 adults with hypoparathyroidism (11 women, age 30-70 years, and 1 man, age 30 years) from 3 different clinical sites in the United States who were transitioned from conventional therapy to daily injections of rhPTH(1-84) or rhPTH(1-34) and then switched to continuous administration of rhPTH(1-84)/rhPTH(1-34) via pump therapy. In most patients, mean serum calcium concentrations increased while on PTH pump therapy compared with both conventional therapy (in 11 patients) and single/multiple daily rhPTH injections (in 8 patients). Despite this, 10 patients had lower median 24-hour urinary calcium levels while on PTH pump therapy compared with prior therapy (mean ± SD difference: -130 ± 222 mg/24 hours). All patients reported a qualitative decrease in hypocalcemic symptoms while receiving pump therapy. Three patients had pod failure at least once, and 1 patient developed an infusion site reaction. Conclusion: In this case series of 12 patients with chronic hypoparathyroidism treated with rhPTH(1-84)/rhPTH(1-34) administered via a pump, improvement in clinical and biochemical parameters were observed in the majority of the patients. Our observations indicate benefits of pump administration of rhPTH that warrant further investigation.

Hypocalcemic disorders.

Calcium is vital for life, and extracellular calcium concentrations must constantly be maintained within a precise concentration range. Low serum calcium (hypocalcemia) occurs in conjunction with multiple disorders and can be life-threatening if severe. Symptoms of acute hypocalcemia include neuromuscular irritability, tetany, and seizures, which are rapidly resolved with intravenous administration of calcium gluconate. However, disorders that lead to chronic hypocalcemia often have more subtle manifestations. Hypoparathyroidism, characterized by impaired secretion of parathyroid hormone (PTH), a key regulatory hormone for maintaining calcium homeostasis, is a classic cause of chronic hypocalcemia. Disorders that disrupt the metabolism of vitamin D can also lead to chronic hypocalcemia, as vitamin D is responsible for increasing the gut absorption of dietary calcium. Treatment and management options for chronic hypocalcemia vary depending on the underlying disorder. For example, in patients with hypoparathyroidism, calcium and vitamin D supplementation must be carefully titrated to avoid symptoms of hypocalcemia while keeping serum calcium in the low-normal range to minimize hypercalciuria, which can lead to renal dysfunction. Management of chronic hypocalcemia requires knowledge of the factors that influence the complex regulatory axes of calcium homeostasis in a given disorder. This chapter discusses common and rare disorders of hypocalcemia, symptoms and workup, and management options including replacement of PTH in hypoparathyroidism.