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Monocytes release pro-cathepsin D to drive blood-to-brain transcytosis in diabetes

ABSTRACT: Microvascular complications are the major outcome of type 2 diabetes mellitus progression and the underlying mechanism remains to be determined. To explore the contribution of circulating monocytes to the microvascular lesions, high-throughput RNA sequencing was conducted and we found high-level expression of cathepsin D (CTSD) in the monocytes of type 2 diabetes mellitus patients. The transgenic mice expressing human CTSD in the monocytes showed increased brain microvascular permeability resembling the diabetic microvascular phenotype, accompanied with cognitive deficit. Mechanistically, we found the monocytes release non-enzymatic pro-CTSD to upregulate caveolin expression in brain endothelium triggering caveolae-mediated transcytosis, without affecting the paracellular route of brain microvasculature. The circulating pro-CTSD activated the caveolae-mediated transcytosis in brain endothelial cells via its binding with low density lipoprotein receptor-related protein 1 (LRP1). Importantly, genetic ablation of CTSD in the monocytes exhibited protective effect against the diabetes-enhanced brain microvascular transcytosis and the diabetes-induced cognitive impairment. Our findings thus uncover the novel role of circulatory pro-CTSD from monocytes in the pathogenesis of cerebral microvascular lesions in diabetes. The circulatory pro-CTSD is thus a potential target for the intervention of microvascular complications in diabetes.

ORGANISM(S): Homo sapiens

PROVIDER: GSE253502 | GEO | 2024/01/23

REPOSITORIES: GEO

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Project description:Diabetes mellitus [DM], with its burden of premature morbidity and mortality, represents one of the major threats to human health in the 21st century (Zimmet 2001). Accelerated atherosclerosis affecting arteries that supply the heart, brain and lower extremities is responsible for an increased risk of acute ischemic events. DM is also associated with microvascular disease, which is a leading cause of blindness, renal failure and debilitating neuropathies. Endothelial dysfunction, increased vascular permeability and microvascular cell loss by apoptosis are all hallmarks of diabetic microangiopathy. Diabetic patients not only incur cardiovascular complications more frequently, but also experience worse outcomes due to attenuation of vascular repair mechanisms. This impairment includes quantitative and qualitative abnormalities of bone marrow [BM]-derived progenitor cells (Emanueli 2002&2004; Loomans 2004; Krankel 2005; Fadini 2006). The mechanisms underlying BM dysfunction remain however enigmatic, especially when considering the privileged location that protects stem cells [SC] and progenitor cells [PC] of the marrow from external insults (Kopp 2008 and Kiel 2008). BM endothelial cells [EC] are instead an obvious target of DM, because they are directly exposed to blood glucose and incapable to regulate glucose influx. Strangely enough, little is known about the impact of diabetes on BM microvasculature. We hypothesize that damage induced by DM might start at the microvascular level, in a similar fashion to microangiopathy, which occurs in kidney, retina, heart and brain. We also propose that enduring microvascular cell loss might result in marrow hypo-perfusion and destabilization of SC homeostasis. In order to test this hypothesis, we studied streptozotocin-induced (STZ) type-1 DM and age-matched non-DM mice (n=6 to 10 per group in each experiment). Histological examination of femurs, collected from STZ-mice at 28-30 weeks from induction of DM or controls, showed remarkable differences in bone density and marrow composition. Bone marrow cells from healthy and diabetic animals were next selected for endothelial progenitors and cultured for 10 days under endothelial cell growth conditions. Next RNA was isolated and analysed by Illumina Sentrix Beadarrays.

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Monocytes release pro-cathepsin D to drive blood-to-brain transcytosis in diabetes

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