Riou, G. | bioRxiv Science

bioRxiv2021

Impaired SorLA maturation and trafficking as a new mechanism for SORL1 missense variants in Alzheimer disease

The SorLA protein, encoded by the SORL1 gene, is a major player in Alzheimers disease (AD) pathophysiology. Functional and genetic studies demonstrated that SorLA deficiency results in increased production of A{beta} peptides, and thus a higher risk of AD. A large number of SORL1 missense variants have been identified in AD patients, but their functional consequences remain largely undefined. Here, we identified a new pathophysiological mechanism, by which rare SORL1 missense variants identified in AD patients result in altered maturation and trafficking of the SorLA protein. An initial screening, based on the overexpression of 71 SorLA variants in HEK293 cells, revealed that 15 of them (S114R, R332W, G543E, S564G, S577P, R654W, R729W, D806N, Y934C, D1535N, D1545E, P1654L, Y1816C, W1862C, P1914S) induced a maturation and trafficking-deficient phenotype. Three of these variations (R332W, S577P, and R654W) and two maturation-competent variations (S124R and N371T) were further studied in details in CRISPR/Cas9-modified hiPSCs. When expressed at endogenous levels, the R332W, S577P, and R654W SorLA variants also showed a maturation defective profile. We further demonstrated that these variants were largely retained in the endoplasmic reticulum, resulting in a reduction in the delivery of SorLA mature protein to the plasma membrane and to the endosomal system. Importantly, expression of the R332W and R654W variants in hiPSCs was associated with a clear increase of A{beta} secretion, demonstrating a loss-of-function effect of these SorLA variants regarding this ultimate readout, and a direct link with AD pathophysiology. Furthermore, structural analysis of the impact of missense variations on SorLA protein indicated that impaired cellular trafficking of SorLA protein could be due to subtle variations of the protein 3D structure resulting from changes in the interatomic interactions.

cell biology↗

bioRxiv2021

Regulation and impact of cardiac lymphangiogenesis in pressure-overload-induced heart failure

RationaleLymphatics are essential for cardiac health, and insufficient lymphatic expansion (lymphangiogenesis) contributes to development of heart failure (HF) after myocardial infarction. However, the regulation and impact of lymphatics in non-ischemic cardiomyopathy induced by pressure-overload remains to be determined. ObjectiveInvestigate cardiac lymphangiogenesis following transverse aortic constriction (TAC) in adult male or female C57Bl/6J or Balb/c mice, and in patients with end-stage HF. Methods & ResultCardiac function was evaluated by echocardiography, and cardiac hypertrophy, lymphatics, inflammation, edema, and fibrosis by immunohistochemistry, flow cytometry, microgravimetry, and gene expression analysis, respectively. Treatment with neutralizing anti-VEGFR3 antibodies was applied to inhibit cardiac lymphangiogenesis in mice. The gender- and strain-dependent mouse cardiac hypertrophic response to TAC, especially increased ventricular wall stress, led to lymphatic expansion in the heart. Our experimental findings that ventricular dilation triggered cardiac lymphangiogenesis was mirrored by observations in clinical HF samples, with increased lymphatic density found in patients with dilated cardiomyopathy. Surprisingly, the striking lymphangiogenesis observed post-TAC in Balb/c mice, linked to increased cardiac Vegfc, did not suffice to resolve myocardial edema, and animals progressed to dilated cardiomyopathy and HF. Conversely, selective inhibition of the essentially Vegfd-driven capillary lymphangiogenesis observed post-TAC in male C57Bl/6J mice did not significantly aggravate cardiac edema. However, cardiac immune cell levels were increased, notably myeloid cells at 3 weeks and T lymphocytes at 8 weeks. Moreover, while the TAC-triggered development of interstitial cardiac fibrosis was unaffected by anti-VEGFR3, inhibition of lymphangiogenesis increased perivascular fibrosis and accelerated the development of left ventricular dilation and cardiac dysfunction. ConclusionsWe demonstrate for the first time that endogenous cardiac lymphangiogenesis limits pressure-overload-induced cardiac inflammation and perivascular fibrosis, thus delaying HF development. While these findings remain to be confirmed in a larger study of HF patients, we propose that under settings of pressure-overload poor cardiac lymphangiogenesis may accelerate HF development.

physiology↗