Distinct patterns of kidney and liver cyst growth in pkd2(WS25/-) mice

Abstract

Background: Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease that results in the development of cystic kidneys and liver. Pkd2(WS25/-) mice are a key genetic mouse model of human ADPKD that recapitulate the 'molecular recessive' nature of human ADPKD. Providing the foundation for future long-term studies, the present work documents distinct patterns of long-term cyst growth in the kidneys and liver of male and female pkd2(WS25/-) mice.

Methods: Gravimetric measurements documented the progression of kidney and liver growth in male and female pkd2(WS25/-) mice over 12 months. A fast imaging with steady-state precision-magnetic resonance imaging (FISP-MRI) technique to measure kidney and liver organ and cyst volumes was optimized and validated. Longitudinal FISP-MRI analyses of changes in cyst volumes were performed in pkd2(WS25/-) mice over 15 months.

Results: Male and female pkd2(WS25/-) mice had significant increases in kidney weights after 4 months of age. The progression of kidney growth was minimal after 4 months of age. Liver cyst growth in male pkd2(WS25/-) mice was minimal after 4 months of age but showed an accelerated rate of growth after 8 months of age. Female pkd2(WS25/-) mice also showed accelerated growth but this was delayed in time when compared with male pkd2(WS25/-) mice.

Conclusions: Pkd2(WS25/-) mice are a genetic mouse model that recapitulates the early phenotypic characteristics of human ADPKD kidney cystogenesis. Male pkd2(WS25/-) mice consistently display a late progression in liver growth that is seen in clinically impacted livers of human ADPKD patients.

Fig. 1

Characteristics of FISP-MRI of kidney and liver cysts. Images from axially oriented H&E (A) and FISP-MRI (B) sections through a cystic kidney from a 6-month-old male pkd2(WS25/−) mouse show the comparative capacity of the two techniques to image cysts. While not perfectly matched in orientation, the images have several cysts in common (arrowheads; bar = 5 mm). Axial imaging of liver (C) shows a relatively homogeneous signal density (bar = 5 mm). The stomach (asterisk) and portal vein/vena cava (arrows) are also observed. The gall bladder is not seen in this section. Within the body of the liver, liver cysts of various sizes are observed (arrowheads). A contrast-adjusted image of the smallest cyst (inset bar = 0.3 mm) highlights the resolution of FISP-MRI detection.

Fig. 2

Longitudinal FISP-MRI imaging of cysts in pkd2(WS25/−) mice. FISP-MRI images displayed the ability to discern kidney and liver cyst growth longitudinally within the same animal. Coronal mid-organ images of the right kidney in a female pkd2(WS25/−) mouse after (A) 5, (B) 6 and (C) 7 months of age are shown (bar = 5 mm). Arrowheads point to cysts. Axial mid-organ images of the liver in a female pkd2(WS25/−) mouse after (D) 7 and (E) 13 months of age are shown. Arrowheads point to cysts; the stomach (asterisk) and portal vein/vena cava (arrows) are also observed. The gall bladder is not seen in these sections. The liver hilum appears as a diffuse white area in the mid-liver region at this level.

Fig. 3

Validation of FISP-MRI organ volume measurements. Using both pkd2(+/+) (n = 6) and pkd2(WS25/−) (n = 3) mice, (A) linear regression analysis showed that MRI-calculated kidney volumes were highly correlated with gravimetric kidney weights (r²=0.975) and (B) MRI-calculated liver volumes were strongly correlated with gravimetric liver weights (r²=0.932).

Fig. 4

Left versus right kidney weights in pkd2(WS25/−) mice. Measurements were made in mice at 4, 8 and 12 months of age. Left and right kidney weights from male pkd2(+/+) mice (open circles) were relatively consistent (r²= 0.70; regression line is shown). In contrast, left and right kidney weights in male pkd2(WS25/−) mice (closed circles) varied significantly (r² = 0.19; line not shown). This variation did not appear to have a left or right preference.

Fig. 5

Temporal changes in kidneys in pkd2(WS25/−) mice. (A) Kidney weights in male pkd2(WS25/−) mice (closed circles) were significantly greater than kidney weights in pkd2(+/+) mice (closed squares) after 4 months. The comparative difference in pkd2(WS25/−) mice versus pkd2(+/+) mice remained constant after 8 and 12 months of age. (B) Kidney weights in female pkd2(WS25/−) mice (open circles) were significantly greater than kidney weights in pkd2(+/+) mice (open squares) at 4 months of age. This comparative difference remained relatively constant at 12 months of age. (C) FISP-MRI-determined kidney cyst volumes in a male pkd2(WS25/−) mouse (closed circle) were progressively increased between 5 and 15 months of age. Kidney cyst volumes in female pkd2(WS25/−) mice (open symbols) were measurable, but minimal, with little increase in volume in four of five mice. One female pkd2(WS25/−) mouse (open circles) had large cyst volumes at 5 months of age and showed marked rates of increase between 5 and 11 months of age in both kidneys.

Fig. 6

Temporal changes in livers in pkd2(WS25/−) mice. (A) At 4 months of age, liver weights in male pkd2(WS25/−) mice (closed circles) were not significantly different than those from pkd2(+/+) mice (closed squares). At 8 months of age, there was a significant increase in liver weights in male pkd2(WS25/−) mice and an even more dramatic increase after 12 months of age. (B) At 4 months of age, liver weights in female pkd2(WS25/−) mice (open circles) were significantly but minimally greater than liver weights in pkd2(+/+) mice (open squares). There was little increase in female pkd2(WS25/−) liver weights between 4 and 12 months of age. (C) The liver cyst volume in the male pkd2(WS25/−) mouse (closed circles) was modest up through 7 months of age but underwent progressive increases in volume between 9 and 15 months of age. Female pkd2(WS25/−) mice (open symbols) had modest liver cyst volumes during the initial 9 months of life but then also began to display progressive increases in cyst volumes.

Fig. 7

Longitudinal assessment of parenchymal volumes in pkd2(WS25/−) mice. Kidneys and livers in male pkd2(+/+) mice (closed squares) and female pkd2(+/+) mice (open squares) increased in mass between 4 and 12 months of age. (A) MRI-determined kidney parenchymal volumes (grey circles; one male, three to four females) appeared relatively constant but variable between 5, 7, 9 and 11 months of age. (B) MRI-determined liver parenchymal volumes (grey circles; one male, three to four females) appeared to increase at a rate similar to the rate of liver mass increase seen in wild-type mice.