Incomplete autophagy: Trouble is a friend

Incomplete autophagy is an impaired self-eating process of intracellular macromolecules and organelles in which accumulated autophagosomes do not fuse with lysosomes for degradation, resulting in the blockage of autophagic flux. In this review, we summarized the literature over the past decade describing incomplete autophagy, and found that different from the double-edged sword effect of general autophagy on promoting cell survival or death, incomplete autophagy plays a crucial role in disrupting cellular homeostasis, and promotes only cell death. What matters is that incomplete autophagy is closely relevant to the pathogenesis and progression of various human diseases, which, meanwhile, intimately linking to the pharmacologic and toxicologic effects of several compounds. Here, we comprehensively reviewed the latest progress of incomplete autophagy on molecular mechanisms and signaling pathways. Moreover, implications of incomplete autophagy for pharmacotherapy are also discussed, which has great relevance for our understanding of the distinctive role of incomplete autophagy in cellular physiology and disease. Consequently, targeting incomplete autophagy may contribute to the development of novel generation therapeutic agents for diverse human diseases.

Curcumin promotes functional recovery and inhibits neuronal apoptosis after spinal cord injury through the modulation of autophagy

Objective: The study was aimed to investigate whether the neuroprotective role of curcumin is associated with regulation of autophagy.Methods: Rat spinal cord injury (SCI) models were established according to Allen's weight-drop trauma method. Curcumin was administered 30 min after the contusion and continued weekly. At 3, 7, 14, 21, and 28 days after SCI, functional recovery was evaluated using the Basso, Beattie and Bresnahan (BBB) scoring and the oblique plate test, following which, spinal cord tissues were obtained. Histological changes and apoptosis were then measured with H&E staining and TUNEL assay. Glia activation, inflammatory infiltration, inflammatory factor release, and myelination were observed through immunohistochemical (IHC) staining and ELISA. Autophagy and Akt activation were detected by western blotting. After autophagy was inhibited by injection of chloroquine, TUNEL, inflammatory factor release, myelin basic protein (MBP) IHC staining and functional recovery evaluation were performed again.Results: Curcumin treatment promoted functional recovery after SCI and reduced neuron apoptosis, improved spinal cord integrity, recovery, and re-myelination, and suppressed the inflammatory response. Autophagy was enhanced and Akt/mTOR pathway was inhibited by curcumin. Autophagy inhibition partially eliminated the protective effect of curcumin on SCI.Conclusion: Curcumin may exert its therapeutic effect on SCI through the enhancement of autophagy, in which, inhibition of the Akt/mTOR signaling pathway may be also involved.

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T₄). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

A Proteomic Atlas of Cardiac Amyloid Plaques

Background

In vivo mechanisms of amyloid clearance and cardiac tissue damage in cardiac amyloidosis are not well understood.

Objectives

We aimed to define and quantify the amyloid plaque proteome in cardiac transthyretin amyloidosis (ATTR) and light chain amyloidosis (AL) and identify associations with patient characteristics and outcomes.

Methods

A proteomics approach was used to identify all proteins in cardiac amyloid plaques, and to compare both normal and diseased controls. All proteins identified within amyloid plaques were defined as the expanded proteome; only proteins that were enriched in comparison to normal and disease controls were defined as the amyloid-specific proteome.

Results

Proteomic data from 292 patients with ATTR and 139 patients with AL cardiac amyloidosis were included; 160 and 161 unique proteins were identified in the expanded proteomes, respectively. In the amyloid-specific proteomes, we identified 28 proteins in ATTR, 19 in AL amyloidosis, with 13 proteins overlapping between ATTR and AL. ATTR was characterized by a higher abundance of complement and contractile proteins and AL by a higher abundance of keratins. We found that the proteome of kappa AL had higher levels of clusterin, a protective chaperone, and lower levels of light chains than lambda despite higher levels of circulating light chains. Hierarchical clustering identified a group of patients with worse survival in ATTR, characterized by high levels of PIK3C3, a protein with a central role in autophagy.

Conclusions

Cardiac AL and ATTR have both common and distinct pathogenetic mechanisms of tissue damage. Our findings suggest that autophagy represents a pathway that may be impaired in ATTR and should be further studied.

Amyloid Proteins and Peripheral Neuropathy

Painful peripheral neuropathy affects millions of people worldwide. Peripheral neuropathy develops in patients with various diseases, including rare familial or acquired amyloid polyneuropathies, as well as some common diseases, including type 2 diabetes mellitus and several chronic inflammatory diseases. Intriguingly, these diseases share a histopathological feature-deposits of amyloid-forming proteins in tissues. Amyloid-forming proteins may cause tissue dysregulation and damage, including damage to nerves, and may be a common cause of neuropathy in these, and potentially other, diseases. Here, we will discuss how amyloid proteins contribute to peripheral neuropathy by reviewing the current understanding of pathogenic mechanisms in known inherited and acquired (usually rare) amyloid neuropathies. In addition, we will discuss the potential role of amyloid proteins in peripheral neuropathy in some common diseases, which are not (yet) considered as amyloid neuropathies. We conclude that there are many similarities in the molecular and cell biological defects caused by aggregation of the various amyloid proteins in these different diseases and propose a common pathogenic pathway for "peripheral amyloid neuropathies".

Uncovering the Neuroprotective Mechanisms of Curcumin on Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses (ATTR amyloidosis) are diseases associated with transthyretin (TTR) misfolding, aggregation and extracellular deposition in tissues as amyloid. Clinical manifestations of the disease are variable and include mainly polyneuropathy and/or cardiomyopathy. The reasons why TTR forms aggregates and amyloid are related with amino acid substitutions in the protein due to mutations, or with environmental alterations associated with aging, that make the protein more unstable and prone to aggregation. According to this model, several therapeutic approaches have been proposed for the diseases that range from stabilization of TTR, using chemical chaperones, to clearance of the aggregated protein deposited in tissues in the form of oligomers or small aggregates, by the action of disruptors or by activation of the immune system. Interestingly, different studies revealed that curcumin presents anti-amyloid properties, targeting multiple steps in the ATTR amyloidogenic cascade. The effects of curcumin on ATTR amyloidosis will be reviewed and discussed in the current work in order to contribute to knowledge of the molecular mechanisms involved in TTR amyloidosis and propose more efficient drugs for therapy.

Emerging therapeutic targets currently under investigation for the treatment of systemic amyloidosis

INTRODUCTION

Systemic amyloidosis occurs when one of a growing list of circulating proteins acquires an abnormal fold, aggregates and gives rise to extracellular amyloid deposits in different body sites, leading to organ dysfunction and eventually death. Current approaches are mainly aimed at lowering the supply of the amyloidogenic precursor or at stabilizing it in a non-amyloidogenic state, thus interfering with the initial phases of amyloid formation and toxicity. Areas covered: Improved understanding of the pathophysiology is indicating novel steps and molecules that could be therapeutically targeted. Here, we will review emerging molecular targets and therapeutic approaches against the main forms of systemic amyloidosis at the early preclinical level. Expert opinion: Conspicuous efforts in drug design and drug discovery have provided an unprecedented list of potential new drugs or therapeutic strategies, from gene-based therapies to small molecules and peptides, from novel monoclonal antibodies to engineered cell-based therapies. The challenge will now be to validate and optimize the most promising candidates, cross the bridge from the preclinical phase to the clinics and identify, through innovative trials design, the safest and most effective combination therapies, striving for a better care, possibly a definitive cure for these diseases.

Autophagy: The spotlight for cellular stress responses

Autophagy is an essential cellular mechanism which plays "housekeeping" role in normal physiological processes including removing of long lived, aggregated and misfolded proteins, clearing damaged organelles, growth regulation and aging. Autophagy is also involved in a variety of biological functions like development, cellular differentiation, defense against pathogens and nutritional starvation. The integration of autophagy into these biological functions and other stress responses is determined by the transcriptional factors that undertake the regulatory mechanism. This review discusses the machinery of autophagy, the molecular web that connects autophagy to various stress responses like inflammation, hypoxia, ER stress, and various other pathologic conditions. Defects in autophagy regulation play a central role in number of diseases, including neurodegenerative diseases, cancer, pathogen infection and metabolic diseases. Similarly, inhibiting autophagy would contribute in the treatment of cancer. However, understanding the biology of autophagy regulation requires pharmacologically active compounds which modulate the autophagy process. Inducers of autophagy are currently receiving considerable attention as autophagy upregulation may be a therapeutic benefit for certain neurodegenerative diseases (via removal of protein aggregates) while the inhibitors are being investigated for the treatment of cancers. Both induction and inhibition of autophagy have been proven to be beneficial in the treatment of cancer. This dual role of autophagy in cancers is now getting uncovered by the advancement in the research findings and development of effective autophagy modulators.

Transthyretin amyloidosis: an under-recognized neuropathy and cardiomyopathy

Transthyretin (TTR) amyloidosis (ATTR amyloidosis) is an underdiagnosed and important type of cardiomyopathy and/or polyneuropathy that requires increased awareness within the medical community. Raising awareness among clinicians about this type of neuropathy and lethal form of heart disease is critical for improving earlier diagnosis and the identification of patients for treatment. The following review summarizes current criteria used to diagnose both hereditary and wild-type ATTR (ATTRwt) amyloidosis, tools available to clinicians to improve diagnostic accuracy, available and newly developing therapeutics, as well as a brief biochemical and biophysical background of TTR amyloidogenesis.

Differential expression of Cathepsin E in transthyretin amyloidosis: from neuropathology to the immune system

Background

Increasing evidence supports a key role for inflammation in the neurodegenerative process of familial amyloidotic polyneuropathy (FAP). While there seems to be an overactivation of the neuronal interleukin-1 signaling pathway, the immune response is apparently compromised in FAP. Accordingly, little immune cell infiltration is observed around pre-fibrillar or fibrillar amyloid deposits, with the underlying mechanism for this phenomenon remaining poorly understood. Cathepsin E (CtsE) is an important intermediate for antigen presentation and chemotaxis, but its role in the pathogenesis of FAP disease remains unknown.

Methods

In this study, we used both mouse primary macrophages and in vivo studies based on transgenic models of FAP and human samples to characterize CtsE expression in different physiological systems.

Results

We show that CtsE is critically decreased in bone marrow-derived macrophages from a FAP mouse model, possibly contributing for cell function impairment. Compromised levels of CtsE were also found in injured nerves of transgenic mice and, most importantly, in naïve peripheral nerves, sensory ganglia, murine stomach, and sural nerve biopsies derived from FAP patients. Expression of CtsE in tissues was associated with transthyretin (TTR) deposition and differentially regulated accordingly with the physiological system under study. Preventing deposition with a TTR small interfering RNA rescued CtsE in the peripheral nervous system (PNS). In contrast, the expression of CtsE increased in splenic cells (mainly monocytes) or peritoneal macrophages, indicating a differential macrophage phenotype.

Conclusion

Altogether, our data highlights the potential of CtsE as a novel FAP biomarker and a possible modulator for innate immune cell chemotaxis to the disease most affected tissues—the peripheral nerve and the gastrointestinal tract.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0891-9) contains supplementary material, which is available to authorized users.