Gender Differences in the Acute Kidney Injury to Chronic Kidney Disease Transition

Abstract

This study evaluated if there is a sexual dimorphism in the acute kidney injury (AKI) to chronic kidney disease (CKD) transition and the time-course of the potential mechanisms involved in the dimorphic response. Female and male rats were divided into sham-operated or underwent 45-min renal ischemia (F + IR, and M + IR). All groups were studied at 24-h and 1, 2, 3, or 4-months post-ischemia. Additionally, oophorectomized rats were divided into sham or IR groups. After 24-h, AKI extent was simllar in females and males, but female rats exhibited less oxidative stress and increased renal GSH content. After 4-months and despite similar AKI, the M + IR group developed CKD characterized by proteinuria, tubulointerstitial fibrosis, glomerular hypertrophy, increased oxidative stress and a reduction in HIF1α and VEGF from the 1^st-month and persisting throughout the time-course studied. Interestingly, the F + IR group did not develop CKD due to lesser oxidative stress and increased eNOS, TGFβ and HIF1α mRNA levels from the 1^st-month after IR. Whereas, oophorectomized rats did develop CKD. We found a sexual dimorphic response in the AKI to CKD transition. Early antioxidant defense and higher TGFβ, HIF1α and eNOS were among the renoprotective mechanisms that the F + IR group demonstrated.

Figure 1

Renal injury induced by ischemia/reperfusion after 24-h in both female and male rats. (A) Creatinine clearance, (B) renal blood flow, (C) proteinuria, (D) Urinary H₂O₂ excretion, (E) Urinary Hsp72 levels by Western blot (n = 4–5 per group). (F) Densitometric analysis of Hsp72 levels, (G) a representative image of a periodic acid–Schiff (PAS) stained kidney slides from a female rat underwent IR (left), and an IR male rat (right), (H) percentage of injured tubules. Female groups are in a gray background in which sham female is represented by white bars and IR female group in black bars. Following by sham male in white bars and IR male group in gray bars. Control groups were formed at least n = 5, and IR Female or Male = at least 6. Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. sham male group, and ^çp < 0.05 vs. F + IR group.

Figure 2

The IR renal injury induced a dimorphic GSH and GSSG kidney content response. (A) Cortex GSH levels, (B) Medulla GSH levels, (C) Cortex GSSG levels, (D) Medulla GSSG levels. Female groups are in a gray background in which Sham female is represented by white bars and IR female group in black bars. Following by sham male in white bars and IR male group in gray bars. The GSH and GSSG kidney content was evaluated 24-h post-ischemia. Control groups were formed by n = 4, whereas F + IR and M + IR groups included n = 6. Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. sham male group, and ^çp < 0.05 vs. F + IR group.

Figure 3

The AKI to CKD transition is prevented in female rats. Every 30-days (A) Urinary protein excretion, (B) creatinine clearance and (C) Urinary H₂O₂ excretion were measured. White triangles represent Sham female (n = at least 7), black triangles represent IR female (n = at least 10), white circles represent Sham male (n = at least 4) and gray circles represent IR male group (n = at least 4). After 4 months, (D) body weight, (E) mean arterial pressure, and (F) renal blood flow were recorded. Sham Female or Male (n = at least 4) and IR Female or Male groups (n = at least 7). Female groups are in a gray background in which sham is represented by white bars and F + IR group in black bars, following by Sham male in white bars and M + IR group in gray bars. Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. Sham male group, and ^çp < 0.05 vs. F + IR group.

Figure 4

CKD induced by an AKI episode was associated with glomerular and tubulointerstitial injury in males but prevented in females. Representative light microphotographs of kidney slides stained with Sirius red from (A) female IR rat an (B) male IR rat after 4-months of IR injury (Magnification ×100). Temporal course of tubulointerstitial fibrosis in (C) female (white bar represents sham and black bars IR groups) and in (D) male groups (white bar represents sham and gray bars IR groups). Temporal course of tubular dilation (μm) in (E) female and in (F) male groups. Temporal course of Glomerular area (μm²) in (G) female and in (H) male groups. All parameters were determined at 1, 2, 3 and 4-months in both F + IR and M + IR groups and at 4-months in female and male sham groups in at least 4 rats per group. Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. sham male group, and ^çp < 0.05 vs. F + IR group.

Figure 5

The depletion of estrogens is associated with AKI to CKD transition in female rats. (A) Estradiol levels before oophorectomy (Pre-Op) is represented in white bars (n = 24) and 1-month after oophorectomy (Post-Op) in black bars (n = 24). Then, oophrorectomized rats (Oop) were underwent to sham surgery or bilateral renal ischemia of 45 min (Oop + IR) and studied 24-h or 1 to 4-months. In (B) proteinuria, (C) creatinine clearance, and (D) renal blood flow evaluated 24-h post-ischemia. Both female groups without oophorectomy are in a gray background in which sham (S) is represented by white bars and IR female group (IR) in black bars, following by the sham oophorectomized group (Op) in white bars and the ophrorectomized underwent IR group (Oop + IR) in pattern bars. For the long-time experiment, (E) urinary protein excretion, and (F) Urinary H₂O₂ excretion were measured every 30 days during the follow-up. Black triangles represent IR female (n = at least 8), black squares represent IR + Oop (n = at least 4). Data are shown as mean ± SE. *p < 0.05 vs. sham female group, ⁺ p < 0.05 vs. Op, ^çp < 0.05 vs. F + IR group.

Figure 6

Dimorphic response of some mediators involved in the AKI to CKD transition. (A) eNOS mRNA levels, (B) catalase mRNA levels, (C) HIF1α mRNA levels, (D) VEGF mRNA levels, (E) Representative autoradioghraphies of VEGF and β-actin Western Blot analysis, and (F) VEGF protein levels. Female groups are in a gray background, in which sham is represented by white bars and F + IR group in black bars, following by sham male in white bars and M + IR group in gray bars. The mRNA levels were determined at least by duplicate (n = at least 4 per group). Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. sham male group, and ^çp < 0.05 vs. F + IR group.

Figure 7

Anti-inflammatory and vasoactive pathways mRNA levels in the dimorphism found in the progression of CKD induced by AKI. (A) TGF-β mRNA levels, (B) Interleukin 10 mRNA levels, (C) ET_A receptor mRNA levels, (D) ET_B receptor mRNA levels, (E) AT₁ receptor mRNA levels, (F) AT₂ receptor mRNA levels. Female groups are in a gray background, in which sham is represented by white bars and F + IR group in black bars, following by sham male in white bars and M + IR group in gray bars. Groups included at least 4 rats per group. Data are shown as mean ± SE. *p < 0.05 vs, Sham female group, ⁺p < 0.05 vs. sham male group, and ^çp < 0.05 vs. F + IR group.