Comparative pathology of murine mucolipidosis types II and IIIC

Abstract

UDP-GlcNAc: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-1-phosphotransferase) is an alpha(2)beta(2)gamma(2) hexameric enzyme that catalyzes the first step in the synthesis of the mannose 6-phosphate targeting signal on lysosomal hydrolases. In humans, mutations in the gene encoding the alpha/beta subunit precursor give rise to mucolipidosis II (MLII), whereas mutations in the gene encoding the gamma subunit cause the less severe mucolipidosis IIIC (MLIIIC). In this study we describe the phenotypic, histologic, and serum lysosomal enzyme abnormalities in knockout mice lacking the gamma subunit and compare these findings to those of mice lacking the alpha/beta subunits and humans with MLII and MLIIIC. We found that both lines of mutant mice had elevated levels of serum lysosomal enzymes and cytoplasmic alterations in secretory cells of several exocrine glands; however, lesions in gamma-subunit deficient (Gnptg(-/-)) mice were milder and more restricted in distribution than in alpha/beta-subunit deficient (Gnptab(-/-)) mice. We found that onset, extent, and severity of lesions that developed in these two different knockouts correlated with measured lysosomal enzyme activity; with a more rapid, widespread, and severe storage disease phenotype developing in Gnptab(-/-) mice. In contrast to mice deficient in the alpha/beta subunits, the mice lacking the gamma subunits were of normal size, lacked cartilage defects, and did not develop retinal degeneration. The milder disease in the gamma-subunit deficient mice correlated with residual synthesis of the mannose 6-phosphate recognition marker. Of significance, neither strain of mutant mice developed cytoplasmic vacuolar inclusions in fibrocytes or mesenchymal cells (I-cells), the characteristic lesion associated with the prominent skeletal and connective tissue abnormalities in humans with MLII and MLIII. Instead, the predominant lesions in both lines of mice were found in the secretory epithelial cells of several exocrine glands, including the pancreas, and the parotid, submandibular salivary, nasal, lacrimal, bulbourethral, and gastric glands. The absence of retinal and chondrocyte lesions in Gnptg(-/-) mice might be attributed to residual beta-glucuronidase activity. We conclude that mice lacking either alpha/beta or gamma subunits displayed clinical and pathologic features that differed substantially from those reported in humans having mutations in orthologous genes.

Fig. 1

Pancreas; wild-type control mouse. Normal acinar cells have a pyramidal shape, with the round basal nucleus being surrounded by basophilic cytoplasm that transitions sharply to eosinophilic secretory granules that pack the apical zone. HE.

Fig. 2

Pancreas; 14-week-old Gnptg^−/− mouse. Acinar cells are moderately enlarged and contain a zone of pale foamy cytoplasm between the basal nuclear region of the cell and the apical secretory granules. HE.

Fig. 3

Pancreas; 14-week-old Gnptab^−/− mouse. Acinar cells are distorted by large cytoplasmic microvacuoles that compress basal nuclei and apical cytoplasm. HE.

Fig. 4

Pancreas; 2-year-old Gnptg^−/− mouse. In older mice, there is disorganization of the acinar architecture and diffuse marked cytoplasmic alteration and cytomegaly of acinar cells. The ballooning vacuolar inclusions efface the basal perinuclear basophilia and are associated with decreased size and number of apical zymogen granules. The pancreatic interstitium was expanded multifocally by clusters of large round-to-polygonal pale histiocytic cells. HE.

Fig. 5

Pancreas; 2-year-old Gnptg^−/− mouse. By periodic acid-Schiff (PAS)-stain reaction, cytoplasmic granules in acinar cells and filling interstitial histiocytes stain crimson red. PAS.

Fig. 6

Pancreas; 2-year-old Gnptg^−/− mouse. The blue cytoplasmic granules filling interstitial histiocytes are also AB positive. Alcian Blue stain (AB).

Fig. 7

Pancreas; 2-year-old Gnptg^−/− mouse. The clusters of pale interstitial cells are identified as macrophages by positive labeling for F4/80 antigen. Immunohistochemical staining: avidin-biotin complex methods, Mayer's hematoxylin counterstain.

Fig. 8

Parotid salivary gland; 2-year-old Gnptg^−/− mouse. There is marked disruption of normal cellular and tissue structure by large ballooning vacuoles. HE.

Fig. 9

Submandibular salivary gland; 2-year-old Gnptg^−/− mouse. The mucus acinar cells of the submandibular salivary gland were enlarged by myriad cytoplasmic microvacuoles. HE.

Fig. 10

Maxillary sinus; wild-type control mouse. The intense crimson PAS staining of the maxillary gland on the right side is clearly differentiated from the pale lateral nasal (Steno) glands on the left side. PAS.

Fig. 11

Maxillary sinus; 14-week-old Gnptg^−/− mouse. Vacuolization is more severe in the secretory cells of the maxillary glands (right side) than in lateral nasal (Steno) glands (left side). PAS.

Fig. 12

Stomach, gastric glands; wild-type control mouse. The chief cells in gastric glands of normal mice typically show basal nuclei with apical secretory granules. HE.

Fig. 13

Stomach, gastric glands; 14-week-old Gnptab^−/− mouse. Chief cells are distended by cytoplasmic microvacuolization and ill-defined secretory granules. HE.

Fig. 14

Stomach, gastric glands; 2-year-old Gnptg^−/− mouse. Chief cells are essentially normal even in aged mice.

Fig. 15

Sternum, cartilage; wild-type control mouse. Normal chondrocytes typically contain a single, large, clear vacuole, and their cytoplasm typically only partially fills the lacunar space. AB.

Fig. 16

Sternum, cartilage; Gnptab^−/− mouse. Chondrocytes are hypertrophic and distended by myriad cytoplasmic vacuoles to completely fill the enlarged cartilage lacunae. AB.

Fig. 17

Sternum, cartilage; Gnptab^−/− mouse. Chondrocytes appear to be completely normal in the Gnptg^−/− mice. AB.

Fig. 18

(upper panel). Retina; Gnptab^−/− mouse. There is a severe reduction in the thickness of both the inner and outer segments of the photoreceptors as well as the outer nuclear layer. HE. (lower panel). Retina; 2-year-old Gnptg^−/− mouse. In marked contrast, there is no evidence of retinal degeneration in aged Gnptg^−/− mice. HE.