II. Characterization and development of the regional- and cellular-specific abnormalities in the epididymis of mice with beta-hexosaminidase A deficiency
Hi. Adamali et al., II. Characterization and development of the regional- and cellular-specific abnormalities in the epididymis of mice with beta-hexosaminidase A deficiency, J ANDROLOGY, 20(6), 1999, pp. 803-824
beta-Hexosaminidase (Hex) is a lysosomal enzyme that exists as two isoenzym
es: Hex A (subunit structure alpha beta) and Hex B (beta beta) Its presence
in the testis and epididymis suggests important roles for Hex and its subs
trates in male fertility and reproductive functions. Disruption of the Hexa
gene encoding the alpha-subunit of Hex has led to the generation of a mild
ly affected mouse model of human Tay-Sachs disease, allowing us the opportu
nity to analyze the effects of isolated Hex A deficiency on epithelial cell
ular morphology of the male reproductive tract. At 5 weeks and at 3, 5, and
12 months, the testes, efferent ducts and epididymides of Hex A-deficient
(Hexa -/-) and wild-type (Hexa +/+) mice were perfuse fixed and analyzed by
routine light and electron microscopy as well as with immunocytochemistry
employing antibodies to lysosomal enzymes. In the testis, the seminiferous
epithelium of Hexa -/- mice appeared comparable to that of wild-type mice i
n appearance and topographical arrangement of its cell types at all ages ex
amined. Also, no differences were noted for the efferent ducts. In contrast
, there were striking abnormalities in the epididymides of the mutant mice;
however, the abnormalities were mainly restricted to the initial segment a
nd intermediate zone. Principal cells of these regions at 5 weeks showed a
dramatic increase in the number of lysosomes as compared with those from wi
ld-type animals, and this progressed with increasing age. Furthermore, unli
ke the few small lysosomes present in wild-type mice, those of Hexa -/- mic
e were at times enlarged and often filled the supranuclear and basal region
s of these cells. In the light microscope, large, dense cellular aggregates
were noted at the base of the epithelium in the proximal initial segment t
hat corresponded in the electron microscope to two different cell types, bo
th of which increased in size with age. One aggregate was considered to bel
ong to narrow cells on the basis of the presence of numerous cup-shaped ves
icles characteristic of these cells; they appeared to be dislocated from th
e upper half of the epithelium. In the distal initial segment and intermedi
ate zone, narrow cells were readily identified, but rather than being slend
er as in the control animals, they were greatly enlarged and filled with pa
le lysosomes in mutant mice. The second type of cellular aggregate noted in
the proximal initial segment corresponded to halo cells. They contained nu
merous small and large lysosomes and small, Golgi-related, dense, core gran
ules characteristic of halo cells. On the basis of the large size of these
cells, they appeared to be actively internalizing substances from the inter
cellular space. In contrast, principal and clear cells of the caput, corpus
, and cauda regions did not appear to show a significant increase in number
or size of lysosomes as compared with those of wild-type animals. All stru
ctures identified as lysosomes in the various cell types were immunoreactiv
e for cathepsin D. The present data thus reveal that isolated Hex A deficie
ncy results in region- and cell-specific abnormalities in the epididymis bu
t in no apparent abnormalities in the testis or efferent ducts. Specific ro
les for Hex A that cannot be compensated for by other isozymes of Hex appea
r to exist within lysosomes of epithelial cells predominantly of the initia
l segment and intermediate zone. Taken together, the results also suggest t
hat the inability to degrade endocytosed substrates normally acted upon by
Hex A in lysosomes of principal and narrow cells leads to their accumulatio
n, eventual fusion, and increased size.