Truncation of the constant domain drives amyloid formation by immunoglobulin light chains

AL amyloidosis is a life-threatening disease caused by deposition of immunoglobulin light chains. While the mechanisms underlying light chains amyloidogenesis in vivo remain unclear, several studies have highlighted the role that tissue environment and structural amyloidogenicity of individual light chains have in the disease pathogenesis. AL natural deposits contain both full-length light chains and fragments encompassing the variable domain (VL) as well as different length segments of the constant region (CL), thus highlighting the relevance that proteolysis may have in the fibrillogenesis pathway. Here, we investigate the role of major truncated species of the disease-associated AL55 light chain that were previously identified in natural deposits. Specifically, we study structure, molecular dynamics, thermal stability, and capacity to form fibrils of a fragment containing both the VL and part of the CL (133-AL55), in comparison with the full-length protein and its variable domain alone, under shear stress and physiological conditions. Whereas the full-length light chain forms exclusively amorphous aggregates, both fragments generate fibrils, although, with different kinetics, aggregate structure, and interplay with the unfragmented protein. More specifically, the VL-CL 133-AL55 fragment entirely converts into amyloid fibrils microscopically and spectroscopically similar to their ex vivo counterpart and increases the amorphous aggregation of full-length AL55. Overall, our data support the idea that light chain structure and proteolysis are both relevant for amyloidogenesis in vivo and provide a novel biocompatible model of light chain fibrillogenesis suitable for future mechanistic studies

Obstructive intramural coronary amyloidosis: a distinct phenotype of cardiac amyloidosis that can cause acute heart failure.

66-year-old man was admitted to a cardiology unit with diagnosis of congestive heart failure, having complained of worsening asthenia and myalgia for several months before referral. Family history was aspecific. Echocardiography showed a moderately dilated and uniformly hypokinetic left ventricle (end-diastolic diameter 68 mm; ejection fraction 35%); wall thickness was normal. Coronary angiography showed normal epicardial arteries. After temporary improvement during treatment with beta-blockers and ACE-inhibitors, heart failure became severe and left ventricular ejection fraction fell to 20%. Suspected myocarditis prompted a right ventricular endomyocardial biopsy (Panel A), which excluded inflammation but identified amyloid infiltration of small intramural vessels without interstitial involvement. A left ventricular assist device was urgently implanted: histopathological examination of the excised left ventricular apex confirmed obstructive intramural coronary amyloidosis without interstitial deposits and with foci of coagulative necrosis. The patient died a few days later because of gastroenteric haemorrhage (autopsy was not performed) (Panels B–D). This case documents the existence of isolated intramural coronary obstruction as a peculiar phenotype of cardiac amyloidosis (distinct from the more common amyloidotic cardiomyopathy) (Panels E–I). This rare type of amyloidotic cardiac involvement—which in this patient led to a mistaken clinical diagnosis of myocarditis—must be recognized as one of the possible causes of acute or rapidly progressive heart failure

Involvement of dermal microvascular basement membrane in senile purpura: quantitative immunohistochemical study

Senile purpura (SP), characterized by purpuric macules and patches on photoaged skin of the extremities, belongs to the earliest stage of dermatoporosis, a progressive condition of the elderly resulting in skin fragility and subsequent bleeding, ulceration, delayed wound healing and deep dissecting hematomas that may require hospitalization and surgical treatment. The haemorrhage observed in SP has been related to impaired mechanical protection by the dermal extracellular matrix, leading to vessel rupture after minor traumas. Despite microvasculature changes in photoaged skin are recognized, these have not been investigated in SP. We quantitatively assessed dermal microvasculature density and thickness of dermal microvascular basement membrane (MBM) collagen IV, in consecutive SP patients

Electron and immuno-electron microscopy of abdominal fat identifies and characterizes amyloid fibrils in suspected cardiac amyloidosis

We evaluated the role of electron microscopy and immuno-electron microscopy studies on abdominal fat fine-needle biopsy samples in diagnosis and characterization of cardiac amyloidosis. The series consists of 15 patients with echocardiographic evidence of "restrictive cardiomyopathy" suspected to be due to amyloidosis. Patients underwent: clinical examination, electrocardiography, 2-D and Doppler echocardiography, immunofixation of serum and urine for detection of monoclonal immunoglobulins, and abdominalfat biopsies that were investigated with polarized light (Congo red), electron and immuno-electron microscopy using specific antibodies to kappa and lambda light chains, apolipoprotein A1, serum amyloid A (SAA), and transthyretin (TTR). Ultrastructural study of abdominal fat samples identified amyloid deposits in 15/15 cases. Immuno-electron microscopy specifically stained amyloid fibrils with antibodies anti-lambda (n = 8), -kappa (n = 2), -apolipoprotein A1 (n = 2) and -TTR (n = 3). Immuno-electron microscopy revealed TTR immuno-labelling in 2 patients with accidental monoclonal components, and a A reaction in I patient without monoclonal components. TTR and apolipoprotein A1 positive cases carried missense mutations in the corresponding genes. Our results demonstrate that amyloid deposits are present in the abdominalfat of patients suspected to have cardiac amyloidosis and that immuno-electron microscopy was able to characterize the amyloid protein in all cases

A novel mutation of the glomulin gene in an Italian family with autosomal dominant cutaneous glomuvenous malformations.

Glomuvenous malformations (GVM) are hamartomas characterized histologically by glomus cells, which should be distinguished from glomus tumors. Familial GVM are rare, often present as multiple lesions, and exhibit familial aggregation, with autosomal dominant transmission. GVM are caused by mutations of the glomulin (GLMN) gene on chromosome 1p21-p22. Their development is thought to follow the 'two-hit' hypothesis, with a somatic mutation required in addition to the inherited germline mutation. We describe a novel GLMN mutation in an Italian family with GVM in which some members present with the less commonly observed phenotype of solitary lesions. A second somatic 'hit' mutation in GLMN was not discovered in our family. We further provide histological, immunohistochemical and electron microscopic data exhibiting the classic features of GVM. The diagnosis of GVM is critical because of distinction from venous malformations and blue rubber bleb nevus syndrome, which may demonstrate clinical similarities but require different treatment