Progressive pulmonary fibrosis in a murine model of Hermansky-Pudlak syndrome.

BACKGROUND: HPS-1 is a genetic type of Hermansky-Pudlak syndrome (HPS) with highly penetrant pulmonary fibrosis (HPSPF), a restrictive lung disease that is similar to idiopathic pulmonary fibrosis (IPF). Hps1ep/ep (pale ear) is a naturally occurring HPS-1 mouse model that exhibits high sensitivity to bleomycin-induced pulmonary fibrosis (PF). Traditional methods of administering bleomycin as an intratracheal (IT) route to induce PF in this model often lead to severe acute lung injury and high mortality rates, complicating studies focusing on pathobiological mechanisms or exploration of therapeutic options for HPSPF. METHODS: To develop a murine model of HPSPF that closely mimics the progression of human pulmonary fibrosis, we investigated the pulmonary effects of systemic delivery of bleomycin in Hps1ep/ep mice using a subcutaneous minipump and compared results to oropharyngeal delivery of bleomycin. RESULTS: Our study revealed that systemic delivery of bleomycin induced limited, acute inflammation that resolved. The distinct inflammatory phase preceded a slow, gradually progressive fibrogenesis that was shown to be both time-dependent and dose-dependent. The fibrosis phase exhibited characteristics that better resembles human disease with focal regions of fibrosis that were predominantly found in peribronchovascular areas and in subpleural regions; central lung areas contained relatively less fibrosis. CONCLUSION: This model provides a preclinical tool that will allow researchers to study the mechanism of pulmonary fibrosis in HPS and provide a platform for the development of therapeutics to treat HPSPF. This method can be applied on studies of IPF or other monogenic disorders that lead to pulmonary fibrosis.

Neurologic involvement in patients with atypical Chediak-Higashi disease.

OBJECTIVE: To delineate the developmental and progressive neurodegenerative features in 9 young adults with the atypical form of Chediak-Higashi disease (CHD) enrolled in a natural history study. METHODS: Patients with atypical clinical features, but diagnostically confirmed CHD by standard evaluation of blood smears and molecular genotyping, underwent complete neurologic evaluation, MRI of the brain, electrophysiologic examination, and neuropsychological testing. Fibroblasts were collected to investigate the cellular phenotype and correlation with the clinical presentation. RESULTS: In 9 mildly affected patients with CHD, we documented learning and behavioral difficulties along with developmental structural abnormalities of the cerebellum and posterior fossa, which are apparent early in childhood. A range of progressive neurologic problems emerge in early adulthood, including cerebellar deficits, polyneuropathies, spasticity, cognitive decline, and parkinsonism. CONCLUSIONS: Patients with undiagnosed atypical CHD manifesting some of these wide-ranging yet nonspecific neurologic complaints may reside in general and specialty neurology clinics. The absence of the typical bleeding or infectious diathesis in mildly affected patients with CHD renders them difficult to diagnose. Identification of these individuals is important not only for close surveillance of potential CHD-related systemic complications but also for a full understanding of the natural history of CHD and the potential role of the disease-causing protein, LYST, to the pathophysiology of other neurodevelopmental and neurodegenerative disorders.

Neurologic involvement in patients with atypical Chediak-Higashi disease.

OBJECTIVE: To delineate the developmental and progressive neurodegenerative features in 9 young adults with the atypical form of Chediak-Higashi disease (CHD) enrolled in a natural history study. METHODS: Patients with atypical clinical features, but diagnostically confirmed CHD by standard evaluation of blood smears and molecular genotyping, underwent complete neurologic evaluation, MRI of the brain, electrophysiologic examination, and neuropsychological testing. Fibroblasts were collected to investigate the cellular phenotype and correlation with the clinical presentation. RESULTS: In 9 mildly affected patients with CHD, we documented learning and behavioral difficulties along with developmental structural abnormalities of the cerebellum and posterior fossa, which are apparent early in childhood. A range of progressive neurologic problems emerge in early adulthood, including cerebellar deficits, polyneuropathies, spasticity, cognitive decline, and parkinsonism. CONCLUSIONS: Patients with undiagnosed atypical CHD manifesting some of these wide-ranging yet nonspecific neurologic complaints may reside in general and specialty neurology clinics. The absence of the typical bleeding or infectious diathesis in mildly affected patients with CHD renders them difficult to diagnose. Identification of these individuals is important not only for close surveillance of potential CHD-related systemic complications but also for a full understanding of the natural history of CHD and the potential role of the disease-causing protein, LYST, to the pathophysiology of other neurodevelopmental and neurodegenerative disorders.

Oral monosaccharide therapies to reverse renal and muscle hyposialylation in a mouse model of GNE myopathy.

GNE myopathy, previously termed hereditary inclusion body myopathy (HIBM), is an adult-onset neuromuscular disorder characterized by progressive muscle weakness. The disorder results from biallelic mutations in GNE, encoding UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, the key enzyme of sialic acid synthesis. GNE myopathy, associated with impaired glycan sialylation, has no approved therapy. Here we test potential sialylation-increasing monosaccharides for their effectiveness in prophylaxis (at the embryonic and neonatal stages) and therapy (after the onset of symptoms) by evaluating renal and muscle hyposialylation in a knock-in mouse model (Gne p.M712T) of GNE myopathy. We demonstrate that oral mannosamine (ManN), but not sialic acid (Neu5Ac), mannose (Man), galactose (Gal), or glucosamine (GlcN), administered to pregnant female mice has a similar prophylactic effect on renal hyposialylation, pathology and neonatal survival of mutant offspring, as previously shown for N-acetylmannosamine (ManNAc) therapy. ManN may be converted to ManNAc by a direct, yet unknown, pathway, or may act through another mode of action. The other sugars (Man, Gal, GlcN) may either not cross the placental barrier (Neu5Ac) and/or may not be able to directly increase sialylation. Because GNE myopathy patients will likely require treatment in adulthood after onset of symptoms, we also administered ManNAc (1 or 2g/kg/day for 12 weeks), Neu5Ac (2 g/kg/day for 12 weeks), or ManN (2 g/kg/day for 6 weeks) in drinking water to 6 month old mutant Gne p.M712T mice. All three therapies markedly improved the muscle and renal hyposialylation, as evidenced by lectin histochemistry for overall sialylation status and immunoblotting of specific sialoproteins. These preclinical data strongly support further evaluation of oral ManNAc, Neu5Ac and ManN as therapy for GNE myopathy and conceivably for certain glomerular diseases with hyposialylation.

Exome sequencing identifies ACSF3 as a cause of combined malonic and methylmalonic aciduria.

We used exome sequencing to identify the genetic basis of combined malonic and methylmalonic aciduria (CMAMMA). We sequenced the exome of an individual with CMAMMA and followed up with sequencing of eight additional affected individuals (cases). This included one individual who was identified and diagnosed by searching an exome database. We identify mutations in ACSF3, encoding a putative methylmalonyl-CoA and malonyl-CoA synthetase as a cause of CMAMMA. We also examined a canine model of CMAMMA, which showed pathogenic mutations in a predicted ACSF3 ortholog. ACSF3 mutant alleles occur with a minor allele frequency of 0.0058 in ∼1,000 control individuals, predicting a CMAMMA population incidence of ∼1:30,000. ACSF3 deficiency is the first human disorder identified as caused by mutations in a gene encoding a member of the acyl-CoA synthetase family, a diverse group of evolutionarily conserved proteins, and may emerge as one of the more common human metabolic disorders.

Improper trafficking of melanocyte-specific proteins in Hermansky-Pudlak syndrome type-5.

Hermansky-Pudlak syndrome (HPS) is a disorder of lysosome-related organelle biogenesis resulting in melanosome dysfunction and absent platelet dense bodies. HPS patients have oculocutaneous albinism, bruising, and bleeding. HPS-5 results from deficiency of the HPS5 protein, a component of the biogenesis of lysosome-related organelles complex-2 (BLOC-2). HPS5 has an unknown function and lacks homology to known proteins. We performed ultrastructural studies of HPS-5 melanocytes revealing predominantly early-stage melanosomes with many small 3,4(OH)2-phenylalanine-positive vesicles throughout the cell body and dendrites. These findings resemble the distinct ultrastructural features of HPS-3 melanocytes; HPS3 is also a BLOC-2 component. Immunofluorescence and immunoEM studies showed decreased TYRP1 labeling in the dendrites of HPS-5 melanocytes, and the overall abundance of TYRP1 was reduced. No substantial differences were observed in the distribution or abundance of Pmel17 in HPS-5 melanocytes. In normal melanocytes, endogenous tyrosinase colocalized with Pmel17 and TYRP1 in the perinuclear area and dendritic tips; this was much reduced in HPS-5 melanocytes, particularly in the tips. We conclude that early stage melanosome formation and Pmel17 trafficking are preserved in HPS5-deficient cells. Tyrosinase and TYRP1 are mistrafficked, however, and fail to be efficiently delivered to melanosomes of HPS-5 melanocytes.