Biomedical subjects

Renate Lüllmann-Rauch

Publications and source records attributed to Renate Lüllmann-Rauch.

7 recordsLinked to original sources

PubMed2006

Deafness in LIMP2-deficient mice due to early loss of the potassium channel KCNQ1/KCNE1 in marginal cells of the stria vascularis.

Our previous studies revealed a critical role of the lysosomal membrane protein LIMP2 in the regulation of membrane transport processes in the endocytic pathway. Here we show that LIMP2-deficient mice display a progressive high-frequency hearing loss and decreased otoacoustic emissions as early as 4 weeks of age. In temporal overlap to hearing impairment, fluorescence immunohistochemical studies revealed that the potassium channel KCNQ1 and its beta-subunit KCNE1 were almost completely lost in the luminal part of marginal cells in the stria vascularis, affecting first higher and later also lower frequency processing cochlear turns. Concomitant with this, the expression of megalin, a multiligand endocytic receptor, was reduced in luminal surfaces of marginal cells within the stria vascularis. KCNQ1/KCNE1 and megalin were also lost in the dark cells of the vestibular system. Although LIMP2 is normally expressed in all cells of the stria vascularis, in the organ of Corti and cochlear neurons, the lack of LIMP2 preferentially caused a loss of KCNQ1/KCNE1 and megalin, and structural changes were only seen months later, indicating that these proteins are highly sensitive to disturbances in the lysosomal pathway. The spatio-temporal correlation of the loss of KCNQ1/KCNE1 surface expression and loss of hearing thresholds supports the notion that the decline of functional KCNQ1/KCNE1 is likely to be the primary cause of the hearing loss. Our findings suggest an important role for LIMP2 in the control of the localization and the level of apically expressed membrane proteins such as KCNQ1, KCNE1 and megalin in the stria vascularis.

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PubMed2006

LAMP-2 deficient mice show depressed cardiac contractile function without significant changes in calcium handling.

OBJECTIVE: Mutations in the highly glycosylated lysosome associated membrane protein-2 (LAMP-2) cause, as recently shown, familial Danon disease with mental retardation, mild myopathy and fatal cardiomyopathy. Extent and basis of the contractile dysfunction is not completely understood. METHODS: In LAMP-2 deficient mice, we investigated cardiac function in vivo using Doppler-echocardiography and contractile function in vitro in isolated myocardial trabeculae. RESULTS: LAMP-2 deficient mice displayed reduced ejection fraction (EF) (58.9+/-3.4 vs. 80.7+/-5.1%, P<0.05) and reduced cardiac output (8.3+/-3.1 vs. 14.7+/-3.6 ml/min, P<0.05) as compared to wild-type controls. Isolated multicellular muscle preparations from LAMP-2 deficient mice confirmed depressed force development (3.2+/-0.6 vs. 8.4+/-0.9 mN/mm2, P<0.01). All groups showed similar force-frequency behaviour when normalised to baseline force. Post-rest potentiation was significantly depressed at intervals>15 s in LAMP-2 deficient mice (P<0.05). Although attenuated in absolute force development, the normalised inotropic response to increased calcium and beta-adrenoreceptor stimulation was unaltered. Electron microscopic analysis revealed autophagic vacuoles in LAMP-2 deficient cardiomyocytes. Protein analysis showed unaltered levels of SERCA2a, calsequestrin and phospholamban. CONCLUSIONS: Cardiac contractile function in LAMP-2 deficient mice as a model for Danon disease is significantly attenuated. The occurrence of autophagic vacuoles in LAMP-2 deficient myocytes is likely to be causal for the depressed contractile function resulting in an attenuated cardiac pump reserve.

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PubMed2005

Neurocognitive and psychotiform behavioral alterations and enhanced hippocampal long-term potentiation in transgenic mice displaying neuropathological features of human alpha-mannosidosis.

Mice with alpha-mannosidase gene inactivation provide an experimental model for alpha-mannosidosis, a lysosomal storage disease with severe neuropsychological and psychopathological complications. Neurohistological alterations in these mice were similar to those in patients and included vacuolations and axonal spheroids in the CNS and peripheral nervous system. Vacuolation was most prominent and evenly distributed in neuronal perikarya of the hippocampal CA2 and CA3 regions, whereas CA1 and dentate gyrus were weakly or not affected. Field potential recordings from CA1 region in hippocampal slices showed enhanced theta burst-induced long-term potentiation (LTP) in alpha-mannosidase-deficient mice. Longitudinal assessment in age-matched alpha-mannosidase-deficient and wild-type littermates, using an extended test battery, demonstrated a neurocognitive and psychotiform profile that may relate to the psychopathological alterations in clinical alpha-mannosidosis. Brainstem auditory-evoked potentials and basic neuromotor abilities were not impaired and did not deteriorate with age. Exploratory and conflict tests revealed consistent decreases in exploratory activity and emotional blunting in the knock-out group. alpha-Mannosidosis mice were also impaired in aversively motivated learning and acquisition of signal-shock associations. Acquisition and reversal learning in the water maze task, passive avoidance learning in the step-through procedure, as well as emotional response conditioning in an operant procedure were all impaired. Acquisition or shaping of an appetitive instrumental conditioning task was unchanged. Appetitive odor discrimination learning was only marginally impaired during shaping, whereas both the discrimination and reversal subtasks were normal. We propose that prominent storage and enhanced LTP in hippocampus have contributed to these specific behavioral alterations in alpha-mannosidase-deficient mice.

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PubMed2005

Enzyme replacement improves nervous system pathology and function in a mouse model for metachromatic leukodystrophy.

A deficiency of arylsulfatase A (ASA) causes the lysosomal storage disease metachromatic leukodystrophy, which is characterized by accumulation of the sphingolipid 3-O-sulfogalactosylceramide (sulfatide). Sphingolipid storage results in progressive demyelination and severe neurologic symptoms. The disease is lethal, and curative therapy is not available. To assess the therapeutic potential of enzyme replacement therapy (ERT), ASA knockout mice were treated by intravenous injection of recombinant human ASA. Plasma levels of ASA declined with a half-time of approximately 40 min, and enzyme was detectable in tissues within minutes after injection. The uptake of injected enzyme was high into liver, moderate into peripheral nervous system (PNS) and kidney and very low into brain. The apparent half-life of endocytosed enzyme was approximately 4 days. A single injection led to a time- and dose-dependent decline of the excess sulfatide in PNS and kidney by up to 70%, but no reduction was seen in brain. Four weekly injections with 20 mg/kg body weight not only reduced storage in peripheral tissues progressively, but also were surprisingly effective in reducing sulfatide storage in brain and spinal cord. The histopathology of kidney and central nervous system was ameliorated. Improved neuromotor coordination capabilities and normalized peripheral compound motor action potential demonstrate the benefits of ERT on the nervous system function. Enzyme replacement may therefore be a promising therapeutic option in this devastating disease.

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PubMed2004

Efficacy of enzyme replacement therapy in alpha-mannosidosis mice: a preclinical animal study.

Alpha-mannosidosis is a lysosomal storage disorder which manifests itself in the excessive storage of mannose-containing oligosaccharides in the lysosomes of multiple peripheral tissues and in the brain. Here we report on the correction of storage in a mouse model of alpha-mannosidosis after intravenous administration of lysosomal acid alpha-mannosidase (LAMAN) from bovine kidney, and human and mouse recombinant LAMAN. The bovine and the human enzyme were barely phosphorylated, whereas the bulk of the mouse LAMAN contained mannose 6-phosphate recognition markers. The clearance decreased from bovine to human to mouse LAMAN with plasma half-times of 4, 8 and 12 min, respectively. The apparent half-life of the internalized enzyme was dependent on the enzyme source as well as tissue type and varied between 3 and 16 h. The corrective effect on the storage of neutral oligosaccharides was time-, tissue- and dose-dependent, and the effects were observed to be transient. After a single dose of LAMAN the maximum corrective effect was observed between 2 and 6 days after injection. In general the corrective effect of the human LAMAN was higher than that of the mouse LAMAN and lowest for the bovine LAMAN. Injection of 250 mU human LAMAN/g body weight followed by a subsequent injection 3.5 days later was sufficient to clear liver, kidney and heart from neutral oligosaccharides. Surprisingly a decrease in mannose containing oligosaccharides was also observed in the brain, with storage levels reported at <30% than that found in controls. These data clearly underline the efficacy of enzyme replacement therapy for the correction of storage in alpha-mannosidosis and suggest that this treatment can substantially decrease storage in the brain.

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PubMed2004

Disturbed cholesterol traffic but normal proteolytic function in LAMP-1/LAMP-2 double-deficient fibroblasts.

Mice double deficient in LAMP-1 and -2 were generated. The embryos died between embryonic days 14.5 and 16.5. An accumulation of autophagic vacuoles was detected in many tissues including endothelial cells and Schwann cells. Fibroblast cell lines derived from the double-deficient embryos accumulated autophagic vacuoles and the autophagy protein LC3II after amino acid starvation. Lysosomal vesicles were larger and more peripherally distributed and showed a lower specific density in Percoll gradients in double deficient when compared with control cells. Lysosomal enzyme activities, cathepsin D processing and mannose-6-phosphate receptor expression levels were not affected by the deficiency of both LAMPs. Surprisingly, LAMP-1 and -2 deficiencies did not affect long-lived protein degradation rates, including proteolysis due to chaperone-mediated autophagy. The LAMP-1/2 double-deficient cells and, to a lesser extent, LAMP-2 single-deficient cells showed an accumulation of unesterified cholesterol in endo/lysosomal, rab7, and NPC1 positive compartments as well as reduced amounts of lipid droplets. The cholesterol accumulation in LAMP-1/2 double-deficient cells could be rescued by overexpression of murine LAMP-2a, but not by LAMP-1, highlighting the more prominent role of LAMP-2. Taken together these findings indicate partially overlapping functions for LAMP-1 and -2 in lysosome biogenesis, autophagy, and cholesterol homeostasis.

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PubMed2003

LIMP-2/LGP85 deficiency causes ureteric pelvic junction obstruction, deafness and peripheral neuropathy in mice.

In previous overexpression studies we revealed a role for the lysosomal membrane protein LIMP-2/LGP85 in lysosomal biogenesis. LIMP-2-deficient mice show an increased postnatal mortality which is associated with a development of a uni- or bilateral hydronephrosis caused by an obstruction of the ureteropelvic junction. An accumulation of lysosomes in epithelial cells of the ureter adjacent to the ureteral lumen and a disturbed apical expression of uroplakin was observed, suggesting an impairment of membrane transport processes. Serious hearing impairment in LIMP-2-deficient animals was indicated by deficits in acoustic startle responses, in brainstem evoked auditory potentials and a reduced endochondral potential. LIMP-2-deficient mice suffer from a massive decline of spiral ganglia in the cochlea concomitant with that of the inner and outer hair cells. These pathological changes begin at the age of 3 months and are probably secondary to a degeneration of the stria vascularis. LIMP-2-deficient mice are also characterized by a peripheral demyelinating neuropathy. Demyelinization was found to be associated with a massive loss of peripheral myelin proteins and an increased activity and expression of lysosomal proteins highlighting a hitherto unknown role of the lysosomal compartment in the development of this myelination disorder. The phenotype of LIMP-2-deficient mice stimulates the search for mutations in human disorders associated with degeneration of the stria vascularis and/or demyelinization of peripheral nerves.

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