On the age-associated presence of immunoglobulin and complement in the renal glomeruli of mice

Spontaneous hyaline glomerulopathy in a young Slc:ICR mouse

Hyaline glomerulopathy is a type of glomerular lesion that occurs in aging mice. Spontaneous hyaline glomerulopathy is rare in young mice. Here, we report spontaneous hyaline glomerulopathy in a young adult (15-week-old) ICR mouse. Necropsy revealed discoloration and roughness of the kidney surface. Microscopically, diffuse glomerular lesions were prominent. Amorphous, eosinophilic materials were deposited globally in the glomeruli. The mesangial region was expanded; however, the mesangial cells showed no proliferation. Thickening of the Bowman’s capsule with proliferation of parietal epithelial cells was observed. Glomerular deposits were strongly positive for anti-IgM, anti-IgG, and periodic acid-Schiff stain and were stained red by Masson’s trichrome stain. The deposits were negative for anti C3 and stained negatively with Congo red stain. Periodic acid methenamine silver and electron microscopy revealed glomerular deposits limited to intraglomerular capillaries. Based on the histological features, we diagnosed this lesion as hyaline glomerulopathy. This case could improve our understanding of spontaneous lesions in toxicological and pharmacological studies.

An electron microscopic study of glomerular lesions in hereditary nephrotic mice (ICGN strain)

Glomerular lesions in hereditary nephrotic mice (ICGN strain) were investigated by electron microscopy. The glomeruli of unaffected animals, which appeared normal by light microscopy, had developed an ultrastructural change in the glomerular capillary basement membrane (GCBM). There was a partial thickening of the GCBM with bilaminar splitting of the lamina densa and an electron-dense fibrillar material exhibiting cross-striations. In affected animals, light microscopy revealed a marked thickening of GCBM and an increase of mesangial matrix without cellular proliferation. By electron microscopy, multilaminar splitting of the lamina densa in the thickened GCBMs and fusion of the epithelial foot processes were observed. In some severely affected animals, immune complex deposition was found in GCBM, but little if any was observed in other animals. In the end, the glomeruli were globally sclerosed. Our findings suggest that initial structural abnormalities in GCBM may play an important role in the onset and development of the disease, though subsequent events such as immune complex deposition would modify the disease.

Age-associated changes in renal glomeruli of mice

To investigate age-associated changes in renal glomeruli of C57BL/6 female mice, we used a single radial immunodiffusion method to measure albumin excretion. Up to 100 mg/dl in urine samples was regarded as microalbuminuria. The mean amount of urinary albumin increased from 14.0 mg/dl at 6 months to 151.1 mg/dl at 24 months of age. Microalbuminuria occurred in 64.6% of tested mice by the time they were 24 months old, and 10% of the mice had marked albuminuria (more than 100 mg/dl) at that time. Parallel morphological study showed that renal mesangial changes were also age-dependent. Mesangial cell proliferation and spike lesions in glomerular capillary walls appeared in aged mice with microalbuminuria, and were then followed by diffuse glomerular sclerosis accompanied by marked albuminuria. Histological scores on damage in the renal mesangium with changes of glomerular basement membrane increased significantly with age from a mean score of 0 at 6 months to 3.24 at 24 months of age. Immunofluorescent study showed a marked deposition of IgG and IgM, but no complement component C3 in enlarged mesangium. Electron microscopic examination of diffuse sclerotic glomeruli in aged mice revealed amyloid substances. These results suggest that assays of albuminuria could be a useful method for early detection of age-associated renal deterioration.

Aging-associated increase in intestinal permeability to polyethylene glycol 900

Effect of aging on the intestinal permeability to medium size [3H]polyethylene glycol (PEG 900) was examined in vivo by gavage and in vitro in intestinal everted sacs of rats ranging in age from 5 to 102 weeks. Rats were gavaged with PEG 900 solution and urinary recovery of PEG 900 was measured for 6 hr in order to assess its absorption. Young rats, 5-15 weeks of age, absorbed 1-1.3% of administered PEG 900. In contrast, rats 35-102 weeks of age absorbed 1.8-2.4% of administered PEG 900 (P less than 0.05 vs younger animals). The increased absorption of PEG 900 with aging is due to changes in intestinal permeability since the total uptake (serosal appearance + tissue uptake) of PEG 900 by jejunum, ileum, and colonic everted sacs was significantly higher (P less than 0.05) in older rats (100 weeks) than young rats (9 1/2 weeks), while urinary excretion of PEG 900 following intravenous injection was the same in the two age groups. These studies indicate that aging rats have diminished capacity to exclude larger size molecules from penetrating the intestinal mucosa. The diminished barrier functions of the small intestine with aging may allow antigenic or mutagenic compounds to reach the systemic circulation.

Anatomic and physiologic age changes in the kidney

Cross-sectional studies of renal function in man indicate there is a progressive decline with age after the age of 40 years. The blood vessels, glomeruli, tubules and interstitium are all potential sites of primary involvement in the aging process as well as for renal disease. Regardless of the anatomic structure initially affected, most chronic renal conditions evolve with destruction of the entire nephron. Whether the observed decrease in renal function associated with aging is the result of intervening pathologic processes, e.g. ischemia (vascular obliteration) or infection, or is the result of a more insidious involutional process, it has generated much discussion but few answers. The purpose of this report is to review the descriptive studies documenting the changes in renal morphology and physiology with age and to focus on what is known about the mechanisms involved in these losses of renal substances and function.

Longitudinal studies on the rate of decline in renal function with age

Serial creatinine clearances (5 to 14 studies) were obtained for 446 normal volunteers in the Baltimore Longitudinal Study of Aging followed between 1958 and 1981. When those subjects with possible renal or urinary tract disease and subjects on diuretics and antihypertensives were removed from the study, leaving a group of 254 "normal" subjects, the mean decrease in creatinine clearance was 0.75 ml/min/year. The slopes of the creatinine clearance vs. time fell into a normal (Gaussian) distribution around this mean. One third of all subjects followed had no absolute decrease in renal function (positive slope of creatinine clearance vs. time) and there was a small group of patients who showed a statistically significant increase (P less than 0.05) in creatinine clearance with age.

Methodological aspects of immunofluorescence applied to nephrology

The influences of different conditions of specimens and conjugates, especially of pretreatments on the fluorescent patterns of kidneys with positive staining for immunoglobulins were examined. The nature of immunoglobulins might be differentiated by the proper combination of pretreatments. It was also found that fluorescent patterns of kidneys were remarkably changed by different methodological conditions.