Pathological Characteristics Of Renal Lipid Disorders Associated With Renin-Angiotensin System Activation

Objective: Lipid is pivotal for maintaining normal structures and functions of organs and tissues.Kidney impairment and lipid dysmetabolism are mutually correlated in the development and progression of multiple cardiovascular and cerebrovascular diseases.Here,we used autopsy kidney samples of type 2 diabetes mellitus(T2DM)to explore the pathological characteristics of renal lipid deposition.Moreover,we established a uninephrectomy(UNX)rat model to exlore the changes of lipid metanolism in the remanant kidney.We aim to unveil the pathological characteristics of renal lipid deposition and its associations with Renin-Angiotensin System(RAS).Methods:(1)In the first part,kidney tissues of paraffin blocks from T2 DM autopsy cases were collected and stained with Haematoxylin-eosin(HE),Periodic acid-Schiff(PAS),Periodic-acid silver methenamine(PASM)and Masson.Immunohistochemical staining with antibodies of CD68,α-smooth muscle actin(α-SMA),AngiotensinⅡ(ANG Ⅱ),Angiotensin Ⅱ type 1 receptor(AT1R)and hydroxy-3-methyl glutary coenzyme A reductase(HMGCR)were performed as well as the transmission electron microscope were conducted to demonstrated renal lipid associated pathological changes.Correlations were analyzed between renal lipid deposition and RAS components.(2)In the second part,adult Sprague-Dawley rats were assigned into Sham group(sham operated control rats,n=16),Unilateral nephrectomy(UNX)group(untreated UNX model rats,n=16)and RAS inhibitors treated group(ACEI—lisinopril treated UNX rats,n=16).Basic biochemical parameters and blood glucose were measured regularly post operation.Lipid profiles,blood glucese and renal function parameters were measured when the rats were sacrificed at the 3th,6th,10 th months post operation.The per-renal fat,remnant kidney,liver,pancreas,heart,spleen and adrenal glands were stained with HE and PAS to demonstrate changes of the fat and lipid metabolism.Immunofluorescence or western blot were used to reflect expressions of RAS components(Renin,ANG,AT1 R,AT2R)and HMGCR in the remnant kidney.At the 6th and 10 th post operation,we detected differential gene expressions and identified relevant key molecules and pathways of the peri-renal fat using next generation sequencing and biotechonology analysis.Results:(1)In the autopsy study,184 autopsy cases(94 males)with T2 DM were included.Average age was 70.4 ±11.2 years,the mean durations was 135.5 ± 82.4 months,end-stage renal disease accounted for21.7% of the total cases.A spectrum of lipid associated pathological changes were observed in the diabetic kidney,including:(1)Foamy cells infiltrated in the renal interstitial;(2)Extensive vacuolar degeneration and CD68 protein overexpression of renal tubular epithelial cells;(3)Foamy cells infiltrated and atherosclerosis plaques formatted in kidney arteries;(4)Foamy cells infiltrateted in glomerulus;(5)Lipid droplets deposited in the podocyte,mesangial cells,endothelial cells and mesangial matrix;(6)Peri-renal fat inflammation.These renal associated lipid deposition usually coexisted with renal dysfunction and pathological changes.Higher tubular CD68 expression and worse interstitial foam cell deposition usually coexisted severer renal damage and glomerulosclerosis.Lipid dysmetabolism in the kidney may be ascribed to dyslipidemia and overexpressions of HMGCR or ANGⅡprotein.(2)In the animal study,UNX could elevated blood glucose,lipid profiles and insulin resistance as well as decreased kidney functions.Additionally,UNX derived glomerulosclerosis,interstitial inflammatory infiltration and interstitial fibrosis were also frequently observed in the remnant kidney.Lipid dysmetabolism in the UNX rats were as followed:(1)Dyslipidemia;(2)Remarkable transformation of unilocular adipocytes into multilocular cells in the peri-renal fat;(3)Lipodystrophy with decressed weight of the peri-renal fat;(4)Ectopic fat accumulation in the glomeruli and renal interstitial as well as steatosis of renal tubular epithelial cells;(5)Lipofuscin deposits in multiple organs;(6)Over expressions of HMGCR in the renal tubular epithelial cells;(7)Adipogenesis in the remnant kidney;(8)Gene differentially expressions of peri-renal fat.UNX could elevate the expressions of RAS components in the remnant kidney.Inhibiting RAS pathway by ACEI could alleviate renal damage and lipid dysmetabolism.Results from the next generation sequencing and biotechonology analysis showed that morpoogical changes of peri-renal fat may be related to differentially expressed genes(DEG).The number of DEG rises with longer survival time after operation.Key genes or pathways included the Jun or Fos and the PI3K-Akt or MAPK pathway.Conclusions: This study shed light on a spectrum of lipid associated pathological changes in the kidney of T2 DM.UNX could induce renal impairment,pathological changes and various kinds of lipid depositions in rats.The renal lipid depositions and RAS overactivation were closely correlated.Blocking RAS pathway may be benefit for kidney dependent lipid deposition and renal function.