The molecular mechanisms of chronic kidney disease induced hyperphosphatemia in cerebral microvasculature
Authors: Xu Jen , Chung Chih‐Ping , Lee Po‐Tsang , Ho Lilun , Lim Kenneth , Lu Tzongshi 
Published: June 2021

Introduction

Structural and functional impairments of cerebral small vessels (CSVs) result in white matter hypo‐perfusion and ischemia that are major cause of Cerebral small vessel disease (CSVD) or white matter disease is a variety of abnormalities in brain microvasculature. Recently, chronic kidney disease (CKD) has been identified as a significant risk factor for stroke as well as for subclinical vascular diseases such as CSVD. Endothelial cell dysfunction is a major contributor to CSVD in CKD. Interestingly, both kidney and cerebral microvasculature share similar anatomical and physiologic characteristics. The goal of this study was to elucidate the molecular mechanisms of hyperphosphatemia in cerebral microvasculature using human brain microvascular endothelial cells (HBMECs), human arteries, and CKD mice as our models.

Methods

CKD mice model was generated by 5/6 nephrectomy on 8‐week‐old C57BL/6 mice. Mice were sacrificed at four months after 5/6 nephrectomy. And, we performed transcriptome analysis by RNA sequencing in primary human brain microvascular endothelial cells (HBMECs) that were treated in calcification medium (CM: 5mM β‐glycerolphosphate and 5mM CaCl2) in time‐course experiments (0–48 hours), in vitro; and human arteries, ex vivo from healthy and CKD patients. Gene selections were performed by the combinations of fold‐changes on log 2 ratio, and p value < 0.05.

Results

Our results showed that CKD mice had decreased myelinated nerve fibers in the corpus callosum and cerebral cortex and loosening myelinated fibers in the corpus callosum. We found collagen IV accumulation in brain microvasculature, a pattern associated with aging. Serum phosphate levels were significant increased in CKD mice compared to control mice. In primary HBMECs treated with CM, we found that major transmembrane tight junction (TJ) protein Occludin was upregulated at 6 hours and peaked at 48 hours. Inflammation sensitive transmembrane TJ protein, Claudin‐5 increased at 1 hour followed by upregulation of downstream ZO‐1 at 6 hours. In human CKD arteries, we found that claudin‐5 was downregulated (Fold changes, FC, 2.16) while ZO‐1 was upregulated (FC=2.17). Furthermore, cell viability decreased and caspase‐3 mediated apoptosis increased in CM treated HBMEC. In addition, Collagen IV expression increased in a dose‐dependent manner at 72 hours after CM treated HBMECs.

Conclusion

Our data show for the first time that cerebral white matter and microvascular dysfunction occurs in uremic environments in CKD, in vitro and in vivo. In addition, our data indicates that TJ dysfunction in brain microvasculature is an important pathogenic process in the development of uremic‐related cardiovascular disease and CSVD. Our data provides a potential mechanism for the development of CSVD in CKD patients. It could benefit CKD patients to reduce the following CSVD and dementia through controlling blood phosphate levels and maintain TJ's function.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.