Molecular Mechanisms of Cardiac Amyloidosis

Cardiac involvement has a profound effect on the prognosis of patients with systemic amyloidosis. Therapeutic methods for suppressing the production of causative proteins have been developed for ATTR amyloidosis and AL amyloidosis, which show cardiac involvement, and the prognosis has been improved. However, a method for removing deposited amyloid has not been established. Methods for reducing cytotoxicity caused by amyloid deposition and amyloid precursor protein to protect cardiovascular cells are also needed. In this review, we outline the molecular mechanisms and treatments of cardiac amyloidosis.

PRIMARY AMYLOIDOSIS INVOLVONG THE HEART: CLINICAL OBSERVATION

Primary amyloidosis is a disease with a complex and not fully understood pathogenesis, which is characterized by a wide range of clinical manifestations. Light chain amyloidosis is the most common form of systemic amyloidosis. At this, the heart is the dominant target organ in systemic amyloidosis. Cardiac amyloidosis (amyloid cardiomyopathy) is most often manifested by diastolic heart failure resulting from restrictive cardiomyopathy. Therapy of amyloid cardiopathy includes optimal treatment of heart failure and chemotherapy. To reduce the symptoms of heart failure, diuretics are the main means, since other pathogenetic agents cannot be used due to hypotension and a possible decrease in cardiac output. With the introduction of new medicinal products into clinical practice, such as the proteosome inhibitor Bortezomib, the prognosis for patients has improved. However, amyloidosis remains a difficult disease to diagnose and treat.

Systemic amyloidosis derived from EFEMP1 in a captive Tsushima leopard cat

In animals, most cases of systemic amyloidosis are of amyloid A type, and the other types of systemic amyloidoses are rare. This study analyzed systemic amyloidosis in a 15-year-old female Tsushima leopard cat. Amyloid deposits strongly positive for Congo red staining were observed in the arterial walls as well as the interstitium in multiple organs. Mass spectrometry–based proteomic analysis with laser microdissection of amyloid deposits identified epidermal growth factor–containing fibulin-like extracellular matrix protein 1 (EFEMP1) as a prime amyloidogenic protein candidate. Immunohistochemistry showed that the amyloid deposits were positive for the N-terminal region of EFEMP1. From these results, the present case was diagnosed as EFEMP1-derived amyloidosis. It is the first such case in an animal. EFEMP1-derived amyloidosis in humans has recently been reported as a systemic amyloidosis, and it is known as an age-related venous amyloidosis. The present case showed different characteristics from human EFEMP1-derived amyloidosis, including the amyloid deposition sites and the amyloidogenic region of the EFEMP1 protein, suggesting a different pathogenesis between Tsushima leopard cat and human EFEMP1-derived amyloidosis.

Evaluation of peripheral amyloid neuropathy

Symptoms of peripheral nervous system (PNS) damage are common clinical manifestations of systemic amyloidosis. Peripheral amyloid neuropathy is characterized by a progressive course, leading to the disability of patients; however, the current possibilities of pathogenetic therapy make the early diagnosis of amyloid neuropathy particularly urgent.Objective: to evaluate the informative value of laser confocal microscopy (LCM) of the cornea in diagnosing small fiber neuropathy of peripheral nerves in patients with systemic amyloidosis.Patients and methods. The study included nine patients (three men and six women) with morphologically confirmed primary amyloidosis (ALamyloidosis) and 12 patients (three men and nine women) with hereditary transthyretin amyloidosis (TTR-amyloidosis) verified by genetic and morphological methods. At baseline, the mean age of patients with AL-amyloidosis was 60.6±10.7 years, with hereditary TTR-amyloidosis – 57.1±13.1 years. According to the history of the disease in AL-amyloidosis, the mean duration of clinical symptoms was 2.7±1.4 years, with TTR-amyloidosis – 5.5±3.6 years. 20 age- and sex-adjusted healthy volunteers were included in the control group. All patients underwent a clinical neurological examination with an assessment of the severity of neuropathy according to the Neuropathy Impairment Score (NIS); 21 patients with systemic amyloidosis and all volunteers of the control group underwent LCM of the corneal nerve fibers (CNF). The coefficients of anisotropy (КΔL) and orientation symmetry (Ksym) of the CNF were calculated to assess the severity of damage to the corneal nerves.Results and discussion. Clinical neurological examination in patients with AL-amyloidosis revealed polyneuropathic syndrome (45%), tunnel syndrome (22%), their combination (22%), and autonomic dysfunction in the form of orthostatic hypotension and impaired motility of the gastrointestinal tract (GI tract; 56%). Symptoms in patients with TTR-amyloidosis were characterized by a combination of tunnel neuropathy and sensory-motor polyneuropathy (50%), distal symmetric polyneuropathy (42%). Frequent symptoms of PNS damage in systemic amyloidosis include autonomic neuropathy (56% – in AL-amyloidosis, 92% – in TTR-amyloidosis) presenting with orthostatic hypotension, impaired gastrointestinal motility, hypohidrosis, and dysuria. The mean NIS score, which characterizes the severity of somatic neuropathy, was significantly higher in patients with TTR-amyloidosis than AL-amyloidosis (p<0.02). LCM of the cornea showed disturbances in the course and structure of the corneal nerve fibers in all examined patients with systemic amyloidosis. The mean anisotropy coefficient values were lower in patients with systemic amyloidosis than in the control group. There were no significant differences in the AL- and TTR-amyloidosis groups. An inverse correlation of average strength between the values of the anisotropy coefficient and NIS was revealed (r=-0.6; p=0.04) in the group of patients with TTR-amyloidosis.Conclusion. Clinical polymorphism of peripheral somatic and autonomic nervous systems lesions is typical for patients with systemic amyloidosis. LCM of the cornea is informative in the diagnosis of small fibers neuropathy of peripheral nerves in systemic amyloidosis; however, it cannot establish the nosology of neuropathy.

Global Proteotoxicity Caused by Human β2 Microglobulin Variants Impairs the Unfolded Protein Response in C. elegans

Aggregation of β2 microglobulin (β2m) into amyloid fibrils is associated with systemic amyloidosis, caused by the deposition of amyloid fibrils containing the wild-type protein and its truncated variant, ΔN6 β2m, in haemo-dialysed patients. A second form of familial systemic amyloidosis caused by the β2m variant, D76N, results in amyloid deposits in the viscera, without renal dysfunction. Although the folding and misfolding mechanisms of β2 microglobulin have been widely studied in vitro and in vivo, we lack a comparable understanding of the molecular mechanisms underlying toxicity in a cellular and organismal environment. Here, we established transgenic C. elegans lines expressing wild-type (WT) human β2m, or the two highly amyloidogenic naturally occurring variants, D76N β2m and ΔN6 β2m, in the C. elegans bodywall muscle. Nematodes expressing the D76N β2m and ΔN6 β2m variants exhibit increased age-dependent and cell nonautonomous proteotoxicity associated with reduced motility, delayed development and shortened lifespan. Both β2m variants cause widespread endogenous protein aggregation contributing to the increased toxicity in aged animals. We show that expression of β2m reduces the capacity of C. elegans to cope with heat and endoplasmic reticulum (ER) stress, correlating with a deficiency to upregulate BiP/hsp-4 transcripts in response to ER stress in young adult animals. Interestingly, protein secretion in all β2m variants is reduced, despite the presence of the natural signal sequence, suggesting a possible link between organismal β2m toxicity and a disrupted ER secretory metabolism.