Tissue remodeling after interference RNA mediated knockdown of transthyretin in a familial amyloidotic polyneuropathy mouse model

SERPINA1 modulates expression of amyloidogenic transthyretin

Hereditary transthyretin amyloidosis (ATTR) is caused by amyloid deposition of misfolded transthyretin (TTR) in various tissues. Recently, reduction of circulating serum TTR, achieved via silencing oligonucleotides, was introduced as therapy of ATTR amyloidosis. We explored the impact of Serpin Family A Member 1 (SERPINA1) on TTR mRNA and protein expression. Oncostatin M (OSM) induced SERPINA1 in hepatoma cells and mice, while concomitantly TTR expression was significantly reduced. SERPINA1 knockdown resulted in specific elevated TTR expression in hepatoma cells; however other genes belonging to the group of acute phase proteins were unaffected. In mice, serum TTR was elevated after mSERPINA1 knockdown throughout antisense treatment. Following SERPINA1 knockdown, TTR deposition in several tissues, including dorsal root ganglia and intestine, was found to be increased, however numbers did not exceed significance levels. The data suggest that SERPINA1 is a co-factor of TTR expression. Our findings provide novel insight in the regulation of TTR and reveal a role of SERPINA1 in the pathogenesis of ATTR amyloidosis.

Schwann cell p75 neurotrophin receptor modulates small fiber degeneration in diabetic neuropathy

Diabetic neuropathy has an incidence as high as 50% of diabetic patients and is characterized by damage to neurons, Schwann cells and blood vessels within the peripheral nervous system. The low-affinity neurotrophin receptor p75 (p75^NTR ), particularly expressed by the Schwann cells in the peripheral nerve, has previously been reported to play a role in developmental myelination and cell survival/death. Increased levels of p75^NTR , in the endoneurium and plasma from diabetic patients and rodent models of disease, have been observed, proposing that this receptor might be involved in the pathogenesis of diabetic neuropathy. Therefore, in this study, we addressed this hypothesis by utilizing a mouse model of selective nerve growth factor receptor (Ngfr) deletion in Schwann cells (SC-p75^NTR -KO). Electron microscopy of sciatic nerves from mice with high fat diet induced obesity demonstrated how loss of Schwann cell-p75^NTR aggravated axonal atrophy and loss of C-fibers. RNA sequencing disclosed several pre-clinical signaling alterations in the diabetic peripheral nerves, dependent on Schwann cell p75^NTR signaling, specially related with lysosome, phagosome, and immune pathways. Morphological and biochemical analyses identified abundant lysosomes and autophagosomes in the C-fiber axoplasm of the diabetic SC-p75^NTR -KO nerves, which together with increased Cathepsin B protein levels corroborates gene upregulation from the phagolysosomal pathways. Altogether, this study demonstrates that Schwann cell p75^NTR deficiency amplifies diabetic neuropathy disease by triggering overactivation of immune-related pathways and increased lysosomal stress.

Localised foot and ankle amyloid deposition

BACKGROUND

Localised (transthyretin-associated) amyloid is commonly seen in articular/periarticular tissues of elderly individuals. Whether age-associated, amyloid deposition occurs in foot and ankle (F&A) tissues has not previously been investigated. In this study we assessed the nature and frequency of F&A amyloid deposition and determined whether it is associated with age and/or specific articular/periarticular F&A lesions.

METHODS

Histological sections of twenty five normal F&A articular/periarticular tissues (16-71 years) and a range of F&A lesions were stained by Congo Red. The amyloid protein was identified by immunohistochemistry and type of matrix glycosaminoglycans determined by Alcian Blue (critical electrolyte concentration) histochemistry.

RESULTS

Amyloid deposits were found in the joint cartilage and capsule of 3/25 normal specimens (57, 62 and 78 years). Amyloid deposits were small, contained transthyretin, and found in areas of matrix degeneration associated with the presence of highly sulphated glycosaminoglycans. In patients older than 47 years, small amyloid deposits were noted in some F&A lesions, including osteoarthritis, Charcot arthropathy, bursa, ganglion, chondrocalcinosis, gout, calcific tendonitis and Achilles tendonitis.

CONCLUSION

Small localised amyloid deposits in F&A tissues contain transthyretin and occur in areas of matrix degeneration associated with the presence of highly sulphated glycosaminoglycans; these deposits are age-associated and, although seen more commonly in some F&A lesions, are small and unlikely to be of pathogenic significance.

MMP-14 overexpression correlates with the neurodegenerative process in familial amyloidotic polyneuropathy

Levels of matrix metalloproteases (MMPs) can be differentially regulated in response to injury or neurological diseases. For instance, it is known that selective and short-term inhibition of MMP-14, a membrane-type 1 MMP, accelerates axon regeneration. Because axon growth and regeneration is impaired in familial amyloidotic polyneuropathy (FAP), a neurodegenerative disorder characterized by misfolding and deposition of mutant transthyretin (TTR) in the peripheral nervous system (PNS), we presently investigated the expression levels and the potential role for MMP-14 in this condition. By using cell culture studies, a mouse model of disease and human clinical samples, we observed that MMP-14: (i) is overexpressed in FAP nerves, correlating with TTR deposition; (ii) is upregulated in sciatic nerves from a preclinical transgenic mouse model, increasing with TTR deposition; (iii) levels in the PNS and plasma are rescued upon treatment of mice with anakinra or TTR siRNA, drugs acting over the IL-1 signaling pathway or TTR liver synthesis, respectively; (iv) increases in Schwann cells upon incubation with amyloid-like aggregates; and, finally, (v) is increased in plasma of FAP patients, correlating with disease progression. These results highlight the relevance of MMP-14 in the pathophysiology of FAP, suggesting not only a potential role for this molecule as a novel biomarker for therapy follow up, but also as a new potential therapeutic target.

Summary: MMP-14 overexpression correlates with familial amyloidotic polyneuropathy disease and progression, as determined using mouse models and human samples. TTR gene silencing in the preclinical model decreases MMP-14 plasma levels.

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.