SummaryThe endothelium first forms in the blood islands in the extra-embryonic yolk sac and then throughout the embryo to establish circulatory networks that further acquire organ-specific properties during development to support diverse organ functions. Here, we investigated the properties of endothelial cells (ECs), isolated from four human major organs—the heart, lung, liver, and kidneys—in individual fetal tissues at three months' gestation, at gene expression, and at cellular function levels. We showed that organ-specific ECs have distinct expression patterns of gene clusters, which support their specific organ development and functions. These ECs displayed distinct barrier properties, angiogenic potential, and metabolic rate and support specific organ functions. Our findings showed the link between human EC heterogeneity and organ development and can be exploited therapeutically to contribute in organ regeneration, disease modeling, as well as guiding differentiation of tissue-specific ECs from human pluripotent stem cells.

Human kidney peritubular capillaries are particularly susceptible to injury, resulting in dysregulated angiogenesis, capillary rarefaction and regression, and progressive loss of kidney function. However, little is known about the structure and function of human kidney microvasculature. Here, we isolated, purified, and characterized human kidney peritubular microvascular endothelial cells (HKMECs) and reconstituted a three-dimensional human kidney microvasculature in a flow-directed microphysiologic system. By combining epithelial cell depletion and cell culture in media with high concentrations of vascular endothelial growth factor, we obtained HKMECs of high purity in large quantity. Unlike other endothelial cells, isolated HKMECs depended on high vascular endothelial growth factor concentration for survival and growth and exhibited high tubulogenic but low angiogenic potential. Furthermore, HKMECs had a different transcriptional profile. Under flow, HKMECs formed a thin fenestrated endothelium with a functional permeability barrier. In conclusion, this threedimensional HKMEC-specific microphysiologic system recapitulates human kidney microvascular structure and function and shows phenotypic characteristics different from those of other microvascular endothelial cells.

Autophagy is conserved in nature from lower eukaryotes to mammals and is an important self-cannibalizing, degradative process that contributes to the elimination of superfluous materials. Cardiac hypertrophy is primarily characterized by excess protein synthesis, increased cardiomyocyte size, and thickened ventricular walls and is a major risk factor that promotes arrhythmia and heart failure. In recent years, cardiomyocyte autophagy has been considered to play a role in controlling the hypertrophic response. However, the beneficial or aggravating role of cardiomyocyte autophagy in cardiac hypertrophy remains controversial. The exact mechanism of cardiomyocyte autophagy in cardiac hypertrophy requires further study. In this review, we summarize the controversies associated with autophagy in cardiac hypertrophy and provide insights into the role of autophagy in the development of cardiac hypertrophy. We conclude that future studies should emphasize the relationship between autophagy and the different stages of cardiac hypertrophy, as well as the autophagic flux and selective autophagy. Autophagy will be a potential therapeutic target for cardiac hypertrophy.

Aim: Homocysteine (Hcy) can elicit neuronal cell death, and hyperhomocysteinemia is a strong independent risk factor for Alzheimer's disease. The aim of this study was to examine the effects of hydrogen sulfide (H 2 S) on Hcy-induced endoplasmic reticulum (ER) stress and neuronal apoptosis in rat hippocampus. Methods: Adult male SD rats were intracerebroventricularly (icv) injected with Hcy (0.6 μmol/d) for 7 d. Before Hcy injection, the rats were treated with NaHS (30 or 100 μmol·kg -1 ·d -1 , ip) and/or k252a (1 μg/d, icv) for 2 d. The apoptotic neurons were detected in hippocampal coronal slices with TUNEL staining. The expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cleaved caspase-12, and BDNF in the hippocampus were examined using Western blotting assays. The generation of H 2 S in the hippocampus was measured with the NNDPD method. Results: Hcy markedly inhibited the production of endogenous H 2 S and increased apoptotic neurons in the hippocampus. Furthermore, Hcy induced ER stress responses in the hippocampus, as indicated by the upregulation of GRP78, CHOP, and cleaved caspase-12. Treatment with the H 2 S donor NaHS increased the endogenous H 2 S production and BDNF expression in a dosedependent manner, and significantly reduced Hcy-induced neuronal apoptosis and ER stress responses in the hippocampus. Treatment with k252a, a specific inhibitor of TrkB (the receptor of BDNF), abolished the protective effects of NaHS against Hcy-induced ER stress in the hippocampus. Conclusion: H 2 S attenuates ER stress and neuronal apoptosis in the hippocampus of Hcy-treated rats via upregulating the BDNF-TrkB pathway.

The kidney peritubular microvasculature is highly susceptible to injury from drugs and toxins, often resulting in acute kidney injury and progressive chronic kidney disease. Little is known about the process of injury and regeneration of human kidney microvasculature, resulting from the lack of appropriate kidney microvascular models that can incorporate the proper cells, extracellular matrices (ECMs), and architectures needed to understand the response and contribution of individual vascular components in these processes. In this study, we present methods to recreate the human kidney ECM (kECM) microenvironment by fabricating kECM hydrogels derived from decellularized human kidney cortex. The majority of native matrix proteins, such as collagen-IV, laminin, and heparan sulfate proteoglycan, and their isoforms were preserved in similar proportions as found in normal kidneys. Human kidney peritubular microvascular endothelial cells (HKMECs) became more quiescent when cultured on this kECM gel compared with culture on collagen-I-assessed using phenotypic, genotypic, and functional assays; whereas human umbilical vein endothelial cells became stimulated on kECM gels. We demonstrate for the first time that human kidney cortex can form a hydrogel suitable for use in flow-directed microphysiological systems. Our findings strongly suggest that selecting the proper ECM is a critical consideration in the development of vascularized organs on a chip and carries important implications for tissue engineering of all vascularized organs.

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Aberrant proliferation of vascular smooth muscle cells (VSMC) is a critical contributor to the pathogenesis of atherosclerosis (AS). Our previous studies have demonstrated that apelin‐13/APJ confers a proliferative response in VSMC, however, its underlying mechanism remains elusive. In this study, we aimed to investigate the role of mitophagy in apelin‐13‐induced VSMC proliferation and atherosclerotic lesions in apolipoprotein E knockout (ApoE‐/‐) mice. Apelin‐13 enhances human aortic VSMC proliferation and proliferative regulator proliferating cell nuclear antigen expression in dose and time‐dependent manner, while is abolished by APJ antagonist F13A. We observe the engulfment of damage mitochondria by autophagosomes (mitophagy) of human aortic VSMC in apelin‐13 stimulation. Mechanistically, apelin‐13 increases p‐AMPKα and promotes mitophagic activity such as the LC3I to LC3II ratio, the increase of Beclin‐1 level and the decrease of p62 level. Importantly, the expressions of PINK1, Parkin, VDAC1, and Tom20 are induced by apelin‐13. Conversely, blockade of APJ by F13A abolishes these stimulatory effects. Human aortic VSMC transfected with AMPKα, PINK1, or Parkin and subjected to apelin‐13 impairs mitophagy and prevents proliferation. Additional, apelin‐13 not only increases the expression of Drp1 but also reduces the expressions of Mfn1, Mfn2, and OPA1. Remarkably, the mitochondrial division inhibitor‐1(Mdivi‐1), the pharmacological inhibition of Drp1, attenuates human aortic VSMC proliferation. Treatment of ApoE‐/‐ mice with apelin‐13 accelerates atherosclerotic lesions, increases p‐AMPKα and mitophagy in aortic wall in vivo. Finally, PINK1‐/‐ mutant mice with apelin‐13 attenuates atherosclerotic lesions along with defective in mitophagy. PINK1/Parkin‐mediated mitophagy promotes apelin‐13‐evoked human aortic VSMC proliferation by activating p‐AMPKα and exacerbates the progression of atherosclerotic lesions.

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