Functional Study of Splicing Xbp-1 in the Kidney Injury by Using Tet-On System in Vitro and in Vivo = 利用Tet-on系統於細胞及基因轉殖鼠模型研究剪接型XBP-1於腎臟損傷之功能

Chronic kidney disease has emerged as a global public health burden. The prevalence of end-stage renal disease (ESRD) in Taiwan stands at the highest ranking in the world. Acute kidney injury (AKI), AKI to chronic kidney disease (CKD) continuum and CKD all will lead to ESRD as a common ending of kidney diseases. However, pathological analysis of biopsy samples from patients with ESRD commonly reveals impaired glomeruli and tubulointerstitial fibrosis. Accumulating evidence has emphasized the important role of chronic hypoxia in the tubulointerstitium in the final common pathway that leads to development of ESRD. Chronic hypoxia triggers cellular stresses, including endoplasmic reticulum (ER) stress, oxidative stress and mitochondrial stress. In parallel, energy loss owing to aberrant oxygen metabolism decreases ER and mitochondrial function. The ER is a key cellular organelle for protein maturation, and approximately one-third of all cellular proteins (including secretory, lumenal, and membrane proteins) are translocated into the lumen of the ER, where they are modified to form their proper tertiary structure by ER-resident enzymes and chaperones. Protein homeostasis, or proteostasis, is conducted via sophisticated networks of mechanisms that act to maintain the quality of proteins and the evolutionary diversity of the biological functions of proteins. Therefore, proteostasis exerts substantial influence on cell homeostasis or, in other words, on cell fate. Insufficient proteostasis has been suggested to have a pathophysiological role in various diseases, such as Parkinson disease and Alzheimer disease. Recently, renal pathogenic factors that include proteinuria, uraemic toxins and metabolic derangement act in association with renal cell dysfunction to disrupt proteostasis. Thus, normalization of ER proteostasis might, therefore, be effective and novel for cell maintenance, and protect against kidney pathologies. Splicing X-Box binding protein-1 (sXBP-1) catalyzes the unconventional processing of the mRNA, plays the central roles to activate the ER proteostasis. sXBP1 involved in different processes including (a) Metabolic and redox, (b) Apoptosis, (c) Autophagy, (d) ER-associated degradation (ERAD), (e) chaperones and foldases and (f) vesicle trafficking. Regardless of etiology, all patients with chronic renal disease show a progressive decline in renal function with time. Chronic inflammation and diabetes are associated with renal fibrosis, is a key factor of this pathophysiologic changes. Our recent publication demonstrated the down-regulation of ER proteostasis in the ischemia/ reperfusion AKI and chronic unilateral ureteral obstruction CKD model. We believe that selective activation of splicing XBP1 pathway might play a role in overcoming the kidney insult. By using Tet-on splicing XBP1 transgene in vitro and in vivo, we can explore the salvage mechanisms in AKI and chronic renal fibrosis. We will further explore the potential targets via metabolomics and transcriptomics within the 3 years’ project. In the first year, we will study the rescue ability of Tet-on splicing XBP1 gene in cellular models of acute and chronic kidney injury. In the second year, we will generate kidney-specific Tet-on splicing XBP1 transgenic mice, and study the consequences of the splicing XBP1 overexpression by passing the traditional adaptive ER proteostasis in acute and chronic kidney and metabolic stress mice model. In the third year, we will investigate the metabolomics and transcriptomics profiles of Tet-on splicing XBP-1 systems in vitro and in vivo. Using these available tools will help us to develop a novel approach in ER proteostasis, which might be a new convincing treatment approach in kidney diseases.