Normal function and lack of fibronectin accumulation in kidneys of Clara cell secretory protein/uteroglobin deficient mice

Abstract

Clara cell secretory protein (CCSP), also known as uteroglobin (Ug), is a 16-kDa homodimeric protein of unknown function. Within rodent species, CCSP is expressed predominantly by nonciliated Clara cells that line conducting airways of the lung. To investigate in vivo functions for CCSP, we established mice homozygous for a null allele of the CCSP gene (CCSP-/-). We previously showed no overt phenotypic consequences associated with CCSP deficiency when CCSP-/- mice are maintained in the absence of environmental stress. However, CCSP-/- mice show an oxidant-sensitive phenotype that cannot be attributed to alterations in the inflammatory response when challenged by inhaled oxidant gases. The current study was undertaken to determine whether CCSP deficiency results in pathological changes to the kidney. This study was prompted by the recent description of severe systemic disease and kidney fibrosis/dysfunction in an independent line of CCSP-deficient mice, termed Ug-/- (Zhang et al, Science 276:1408-1412, 1997). CCSP-/- mice show normal growth and reproductive performance when maintained in two independent genetic backgrounds, inbred 129 and congenic C57BL/6. Strain 129 CCSP-/- mice have normal kidney function, as assessed by urinary glucose, lactate dehydrogenase, and glomerular filtration rate; they show no kidney fibrosis or abnormalities in fibronectin accumulation and no histological abnormalities in proximal convoluted tubules or glomeruli at either light or electron microscopic levels. CCSP deficiency is associated with mild proteinurea involving a modest increase in mouse major urinary protein-1. We conclude that CCSP (Ug) deficiency, per se, is not the cause of severe renal pathology and systemic disease reported for Ug-/- mice.