Practical pathology of aging mice

Pettan-Brewer, Christina; Treuting, Piper M.

Renal lesions are common in older mice and include chronic nephropathy, glomerular amyloidosis (42), glomerulonephropathies (43) , and obstructive uropathy (44) . Kidneys with chronic nephropathy and or glomerular amyloid (if severe) appear pale and pitted and the size may be altered. Cysts, infarcts, and hydronephrosis all may impact kidney size and shape. Obstructive uropathy is common in male mice and is due to blockage of the lower urinary tract from multiple causes (44) . Retention of urine may result in or from inflammation of the urogenital tract or accessory sex glands and pressure may cause hydronephrosis (Fig. 4E) . Histologically, chronic nephropathy is characterized by early tubular lesions and progresses to include glomerular changes and interstitial inflammation (Fig. 6C,D) . There is a large reserve capacity of the kidney to maintain function even in the face of nephron loss thus, for nephropathy alone to cause significant morbidity, it would have to be moderate to severe or accompanied by other lesions affecting the kidney such as hydronephrosis or neoplasia. However, subclinical or mild nephropathy with associated diminished renal reserve would increase susceptibility to additional insults and homeostatic imbalance (45) . Glo-merular amyloidosis and membranous glomerulonephropathy may appear histologically similar and can be differentiated by use of Congo Red for amyloid and PAS for increased mesangial matrix (31) . Arteritis Segmental arteritis with variable components including fibrinoid necrosis, smooth muscle proliferation, and mixed inflammation occurs in small to medium arteries of various organs (Fig. 6I,J) (31) . Commonly affected tissues in these studies included the mesentery, tongue heart, reproductive tracts, and kidney. An immune mediate pathogenesis has been proposed (27, 46) . In humans with a similar disease processes, polyarteritis nodosa, clinical signs are related to affected organ dysfunction (47) . In mice, the most overt clinical sign associated with arteritis is vestibular syndrome (head tilts and/or circling) as describe above (31) .