Mario Nuvolone

Prion protein and Aβ-related synaptic toxicity impairment

Alzheimers disease (AD), the most common neurodegenerative disorder, goes along with extracellular amyloid‐β (Aβ) deposits. The cognitive decline observed during AD progression correlates with damaged spines, dendrites and synapses in hippocampus and cortex. Numerous studies have shown that Aβ oligomers, both synthetic and derived from cultures and AD brains, potently impair synaptic structure and functions. The cellular prion protein (PrPC) was proposed to mediate this effect. We report that ablation or overexpression of PrPC had no effect on the impairment of hippocampal synaptic plasticity in a transgenic model of AD. These findings challenge the role of PrPC as a mediator of Aβ toxicity.

Identification of Amyloidogenic Light Chains Requires the Combination of Serum-Free Light Chain Assay with Immunofixation of Serum and Urine

BACKGROUND The diagnosis of systemic immunoglobulin light-chain (AL) amyloidosis requires demonstration of amyloid deposits in a tissue biopsy and amyloidogenic monoclonal light chains. The optimal strategy to identify the amyloidogenic clone has not been established. We prospectively assessed the diagnostic sensitivity of the serum free light chain (FLC) kappa/lambda ratio, a commercial serum and urine agarose gel electrophoresis immunofixation (IFE), and the high-resolution agarose gel electrophoresis immunofixation (HR-IFE) developed at our referral center in patients with AL amyloidosis, in whom the amyloidogenic light chain was unequivocally identified in the amyloid deposits. METHODS The amyloidogenic light chain was identified in 121 consecutive patients with AL amyloidosis by immunoelectron microscopy analysis of abdominal fat aspirates and/or organ biopsies. We characterized the monoclonal light chain by using IFE and HR-IFE in serum and urine and the FLC kappa/lambda ratio in serum. We then compared the diagnostic sensitivities of the 3 assays. RESULTS The HR-IFE of serum and urine identified the amyloidogenic light chain in all 115 patients with a monoclonal gammopathy. Six patients with a biclonal gammopathy were omitted from the statistical analysis. The diagnostic sensitivity of commercial serum and urine IFE was greater than that of the FLC kappa/lambda ratio (96% vs 76%). The combination of serum IFE and the FLC assay detected the amyloidogenic light chain in 96% of patients. The combination of IFE of both serum and urine with the FLC kappa/lambda ratio had a 100% sensitivity. CONCLUSIONS The identification of amyloidogenic light chains cannot rely on a single test and requires the combination of a commercially available FLC assay with immunofixation of both serum and urine.

Oral melphalan and dexamethasone grants extended survival with minimal toxicity in AL amyloidosis: long-term results of a risk-adapted approach

The combination of oral melphalan and dexamethasone is considered standard therapy for patients with light-chain amyloidosis ineligible for autologous stem cell transplantation. However, previous trials reported different rates of response and survival, mainly because of the different proportions of high-risk patients. In the present study, including a total of 259 subjects, we treated 119 patients with full-dose melphalan and dexamethasone (dexamethasone 40 mg days 1–4), and 140 patients with advanced cardiac disease with an attenuated dexamethasone schedule (20 mg). Hematologic response rates were 76% in the full-dose group and 51% in the patients receiving the attenuated schedule; the corresponding complete response rates were 31% and 12%, respectively. The median survival was 7.4 years in the full-dose group and 20 months in the attenuated-dose group. Use of high-dose dexamethasone, amino-terminal pro-natriuretic peptide type-B >1800 ng/L, a difference between involved and uninvolved free light chains of >180 mg/L, troponin I >0.07 ng/mL, and response to therapy were independent prognostic determinants. In relapsed/refractory subjects bortezomib combinations granted high hematologic response rates (79% and 63%, respectively), proving the most effective rescue treatment after melphalan and dexamethasone. In summary, melphalan plus dexamethasone was highly effective with minimal toxicity, confirming its central role in the treatment of AL amyloidosis. Future randomized trials will clarify whether bortezomib is best used in frontline combination with melphalan and dexamethasone or as rescue treatment.

The immunobiology of prion diseases

Individuals infected with prions succumb to brain damage, and prion infections continue to be inexorably lethal. However, many crucial steps in prion pathogenesis occur in lymphatic organs and precede invasion of the central nervous system. In the past two decades, a great deal has been learnt concerning the cellular and molecular mechanisms of prion lymphoinvasion. These properties are diagnostically useful and have, for example, facilitated preclinical diagnosis of variant Creutzfeldt–Jakob disease in the tonsils. Moreover, the early colonization of lymphoid organs can be exploited for post-exposure prophylaxis of prion infections. As stromal cells of lymphoid organs are crucial for peripheral prion infection, the dedifferentiation of these cells offers a powerful means of hindering prion spread in infected individuals. In this Review, we discuss the current knowledge of the immunobiology of prions with an emphasis on how basic discoveries might enable translational strategies.

Melphalan and dexamethasone with or without bortezomib in newly diagnosed AL amyloidosis: a matched case-control study on 174 patients.

Oral melphalan and dexamethasone (MDex) is a standard treatment for patients with AL amyloidosis who are not eligible for stem cell transplantation at many referral centers. However, following encouraging reports on the activity of bortezomib combined with alkylators and dexamethasone, these combinations are being moved to frontline therapy. We compared the outcome of 87 patients treated with bortezomib plus MDex (BMDex) with that of 87 controls treated with MDex. Patients and controls were matched for age, cardiac and renal function and free light chain burden. A higher rate of complete responses was observed with BMDex (42 vs 19%), but this did not result in a survival improvement in the overall population. However, a significant survival advantage for BMDex was observed in patients without severe (New York Heart Association class III or IV) heart failure and with N-terminal pro-natriuretic peptide type-B <8500 ng/l. Patients treated with full-dose dexamethasone had similar response rates and survival whether they received bortezomib or not. Intermediate-risk patients who are not fit enough to receive high-dose dexamethasone are likely to take the greatest advantage from the addition of bortezomib to MDex.

The prion protein is an agonistic ligand of the G protein-coupled receptor Adgrg6

Ablation of the cellular prion protein PrPC leads to a chronic demyelinating polyneuropathy affecting Schwann cells. Neuron-restricted expression of PrPC prevents the disease, suggesting that PrPC acts in trans through an unidentified Schwann cell receptor. Here we show that the cAMP concentration in sciatic nerves from PrPC-deficient mice is reduced, suggesting that PrPC acts via a G protein-coupled receptor (GPCR). The amino-terminal flexible tail (residues 23–120) of PrPC triggered a concentration-dependent increase in cAMP in primary Schwann cells, in the Schwann cell line SW10, and in HEK293T cells overexpressing the GPCR Adgrg6 (also known as Gpr126). By contrast, naive HEK293T cells and HEK293T cells expressing several other GPCRs did not react to the flexible tail, and ablation of Gpr126 from SW10 cells abolished the flexible tail-induced cAMP response. The flexible tail contains a polycationic cluster (KKRPKPG) similar to the GPRGKPG motif of the Gpr126 agonist type-IV collagen. A KKRPKPG-containing PrPC-derived peptide (FT23–50) sufficed to induce a Gpr126-dependent cAMP response in cells and mice, and improved myelination in hypomorphic gpr126 mutant zebrafish (Danio rerio). Substitution of the cationic residues with alanines abolished the biological activity of both FT23–50 and the equivalent type-IV collagen peptide. We conclude that PrPC promotes myelin homeostasis through flexible tail-mediated Gpr126 agonism. As well as clarifying the physiological role of PrPC, these observations are relevant to the pathogenesis of demyelinating polyneuropathies—common debilitating diseases for which there are limited therapeutic options.

The workings of the amyloid diseases

The amyloidoses constitute a large group of diseases caused by an alteration in the conformation and metabolism of several globular proteins which, under particular conditions, deposit in tissues as insoluble fibrillar aggregates. To date, at least 24 different proteins have been recognized as causative agents of amyloid diseases. Despite a high heterogeneity in amino acid sequence, three‐dimensional structure, and biological function, all amyloidogenic proteins share a reduced folding stability, a strong propensity to acquire more than one conformation, and the capacity to form almost indistinguishable amyloid fibrils. In some cases, the generation of an aggregation‐prone state can be triggered or enhanced by the occurrence of mutations, a proteolytic cleavage, or a seeding process. The interaction between the amyloidogenic precursor, some common components of amyloid deposits, and the extra‐cellular environment also plays a role in fibrillogenesis and in particular in the organ tropism of amyloid deposition. The process of amyloid fibril formation exerts a cytotoxic effect, resulting in tissue damage and organ dysfunction. Prefibrillar aggregates are thought to have an active part in this process. Due to the pathogenic complexity of amyloid diseases, the integration of several therapeutic interventions involving different critical levels of the amyloidogenic cascade is envisaged.

A phase II trial of cyclophosphamide, lenalidomide and dexamethasone in previously treated patients with AL amyloidosis

Immune-modulatory drugs are active in immunoglobulin light-chain amyloidosis and the addition of alkylating agents can potentiate their action. In this phase II prospective trial we used cyclophosphamide, lenalidomide and dexamethasone in the treatment of 21 patients who were refractory (n=13, 62%) or relapsed (n=8, 38%) after prior treatment including melphalan in all cases, bortezomib in 4 and thalidomide in 6. Median number of cycles administered was 4 (range 2–9 cycles). Severe adverse events were observed in 57% of patients, most common being neutropenia (29%). The hematologic response rate was 62%, with one complete response and 5 very good partial responses. Overall median survival was three years. The achievement of CR/VGPR was associated with a significant survival advantage. The combination of cyclophosphamide, lenalidomide and dexamethasone is an effective treatment for relapsed/refractory AL amyloidosis, and good quality hematologic response should be the aim of treatment in this setting. (clinicaltrials.gov identifier: NCT00607581)

Structure-based drug design identifies polythiophenes as antiprion compounds

The targeted chemical design of luminescent conjugated polythiophenes may yield new therapeutic compounds for treating prion diseases. Putting prions in their place In a mouse model of prion disease, Herrmann et al. evaluated the therapeutic efficacy of luminescent conjugated polythiophenes (LCPs), which are molecules with a high affinity for ordered protein aggregates. Intracerebral administration of LCPs into prion-infected mice using osmotic pumps increased survival. Solid-state nuclear magnetic resonance and in silico binding studies of LCPs to simplified model fibrils allowed the authors to define structural rules, which they then used for the design of LCPs with superior prophylactic and therapeutic potency. The new work demonstrates the feasibility of rational drug design for developing therapeutics to treat prion diseases. Prions cause transmissible spongiform encephalopathies for which no treatment exists. Prions consist of PrPSc, a misfolded and aggregated form of the cellular prion protein (PrPC). We explore the antiprion properties of luminescent conjugated polythiophenes (LCPs) that bind and stabilize ordered protein aggregates. By administering a library of structurally diverse LCPs to the brains of prion-infected mice via osmotic minipumps, we found that antiprion activity required a minimum of five thiophene rings bearing regularly spaced carboxyl side groups. Solid-state nuclear magnetic resonance analyses and molecular dynamics simulations revealed that anionic side chains interacted with complementary, regularly spaced cationic amyloid residues of model prions. These findings allowed us to extract structural rules governing the interaction between LCPs and protein aggregates, which we then used to design a new set of LCPs with optimized binding. The new set of LCPs showed robust prophylactic and therapeutic potency in prion-infected mice, with the lead compound extending survival by >80% and showing activity against both mouse and hamster prions as well as efficacy upon intraperitoneal administration into mice. These results demonstrate the feasibility of targeted chemical design of compounds that may be useful for treating diseases of aberrant protein aggregation such as prion disease.

SIRPα polymorphisms, but not the prion protein, control phagocytosis of apoptotic cells

The regulation of phagocytosis previously ascribed to prion protein PrPC is found to be controlled by the linked locus encoding SIRPα.