Biogenesis Of Lysosome-related Organelles Research Articles

Evolutionary origins of the lysosome-related organelle sorting machinery reveal ancient homology in post-endosome trafficking pathways

The major organelles of the endomembrane system were in place by the time of the last eukaryotic common ancestor (LECA) (~1.5 billion years ago). Their acquisitions were defining milestones during eukaryogenesis. Comparative cell biology and evolutionary analyses show multiple instances of homology in the protein machinery controlling distinct interorganelle trafficking routes. Resolving these homologous relationships allows us to explore processes underlying the emergence of additional, distinct cellular compartments, infer ancestral states predating LECA, and explore the process of eukaryogenesis itself. Here, we undertake a molecular evolutionary analysis (including providing a transcriptome of the jakobid flagellate Reclinomonas americana), exploring the origins of the machinery responsible for the biogenesis of lysosome-related organelles (LROs), the Biogenesis of LRO Complexes (BLOCs 1,2, and 3). This pathway has been studied only in animals and is not considered a feature of the basic eukaryotic cell plan. We show that this machinery is present across the eukaryotic tree of life and was likely in place prior to LECA, making it an underappreciated facet of eukaryotic cellular organisation. Moreover, we resolve multiple points of ancient homology between all three BLOCs and other post-endosomal retrograde trafficking machinery (BORC, CCZ1 and MON1 proteins, and an unexpected relationship with the "homotypic fusion and vacuole protein sorting" (HOPS) and "Class C core vacuole/endosomal tethering" (CORVET) complexes), offering a mechanistic and evolutionary unification of these trafficking pathways. Overall, this study provides a comprehensive account of the rise of the LROs biogenesis machinery from before the LECA to current eukaryotic diversity, integrating it into the larger mechanistic framework describing endomembrane evolution.

Impairment of Renal Function in Hermansky-Pudlak Syndrome

Introduction: Hermansky-Pudlak syndrome (HPS) is a rare autosomal recessive disorder characterized by defective biogenesis of lysosome-related organelles. The genetic types of HPS are associated with a spectrum of multisystemic clinical manifestations. Phenotypic features of HPS type 1 (HPS-1) or HPS-4, which are associated with defects in biogenesis of lysosome-related organelles complex-3 (BLOC-3), are generally more severe than those of HPS-3, HPS-5, or HPS-6, which are associated with defects in BLOC-2. A paucity of information is available about renal impairment in HPS. The objective of this study is to expand the understanding of kidney disease in HPS. Methods: Medical records and clinical data of patients with HPS evaluated at the National Institutes of Health Clinical Center from 1995 to 2020 were retrospectively reviewed. For patients with more than one visit, the most recent renal function and urinalysis tests were analyzed. Estimated glomerular filtration rate (eGFR) was calculated using standard equations (i.e., Chronic Kidney Disease Epidemiology Collaboration, Modification of Diet in Renal Disease). Kidney tissue sections from 5 patients with HPS-1 and 1 patient with HPS-6 were examined. Results: Records from 205 adults and 52 children with HPS were reviewed. Calculated eGFR of adult patients with different HPS types differed significantly, and calculated eGFR of pediatric and adult patients with BLOC-3 disorders was significantly lower than that of patients with BLOC-2 disorders. Linear regression analysis showed that renal function progressively decreases with age in patients with BLOC-3 or BLOC-2 disorders, but the rate of decline was more rapid in patients with BLOC-3 disorders compared to patients with BLOC-2 disorders. In adult patients with HPS-1, glucosuria was found in 4%, proteinuria in 12%, hematuria in 15%, high levels of urinary β2MG in 24%, and elevated urinary albumin to creatinine ratios in 9%. Histological examination of kidney tissue showed accumulation of intracellular deposits of ceroid lipofuscin in proximal renal tubular epithelial cells in patients with HPS-1. There was no evidence of fibrosis, and glomeruli, distal renal tubular epithelial cells, and interstitial regions appeared histologically normal. Conclusion: Mild impairment of renal function is a feature of HPS. Kidneys of patients with HPS-1 contain proximal renal tubular intracellular deposits and no histologic evidence of fibrosis. Consistent with other manifestations of HPS, the phenotype of renal impairment is relatively more pronounced in patients with BLOC-3 disorders than in patients with BLOC-2 disorders. Strategies to avoid nephrotoxicity or renal tubular injury and to protect renal function should be considered for patients with HPS irrespective of age.

A new player in the biogenesis of lysosome-related organelles.

How are Rab GTPases regulated during lysosome-related organelle (LRO) biogenesis? Li et al. (https://doi.org/10.1083/jcb.202402016) identify LYSMD proteins as crucial activators of Rab32-family GTPases in LRO development, shedding light on the previously ambiguous mechanisms governing Rab functionality in this process.

LYSMD proteins promote activation of Rab32-family GTPases for lysosome-related organelle biogenesis.

Lysosome-related organelles (LROs) are specialized lysosomes with cell type-specific roles in organismal homeostasis. Dysregulation of LROs leads to many human disorders, but the mechanisms underlying their biogenesis are not fully understood. Here, we identify a group of LYSMD proteins as evolutionarily conserved regulators of LROs. In Caenorhabditis elegans, mutations of LMD-2, a LysM domain-containing protein, reduce the levels of the Rab32 GTPase ortholog GLO-1 on intestine-specific LROs, the gut granules, leading to their abnormal enlargement and defective biogenesis. LMD-2 interacts with GLO-3, a subunit of GLO-1 guanine nucleotide exchange factor (GEF), thereby promoting GLO-1 activation. Mammalian homologs of LMD-2, LYSMD1, and LYSMD2 can functionally replace LMD-2 in C. elegans. In mammals, LYSMD1/2 physically interact with the HPS1 subunit of BLOC-3, the GEF of Rab32/38, thus promoting Rab32 activation. Inactivation of both LYSMD1 and LYSMD2 reduces Rab32 activation, causing melanosome enlargement and decreased melanin production in mouse melanoma cells. These findings provide important mechanistic insights into LRO biogenesis and functions.

Bmpali, Bmb1 and Bmcap are necessary for uric acid granule formation in Bombyx mori

Uric acid is the end-product of nitrogen metabolism of the silkworm and other lepidopterans. The accumulation of uric acid particles in the epidermis causes the larval silkworm to appear white and opaque. However, the mechanism of uric acid granule formation is still unclear. Silkworm epidermis color is linked to the genes responsible for uric acid particle formation. We first identified two genes in the Bombyx mori genome that encode subunits of the Bloc-1 (Biogenesis of Lysosome-related Organelles Complex-1) by homology to these genes in other eukaryotes, Bmpali and Bmb1. Mutation in these genes caused a transparent phenotype in the silkworm larvae, and the loss of BmBloc-1 subunit gene Bmcap resulted in the same phenotype. These three genes are highly conserved between human and silkworm. We discovered that Bmpali, Bmcap, and Bmb1 localize in the cytoplasm of BmN cells. Yeast two-hybrid assays demonstrated that the Bmpali physically interacts with both Bmcap and Bmb1. Investigating the roles of Bmpali, Bmb1, and Bmcap is essential for uric acid granule formation understanding in Bombyx mori. These mutants present a valuable silkworm model for studying the biogenesis of lysosome-related organelles (LROs).

Hermansky-Pudlak Syndrome: A Comprehensive Review of Clinical Presentation, Pathogenesis, and Therapeutic Strategies

Hermansky-Pudlak Syndrome (HPS) is a rare, autosomal recessive disorder characterized by a complex clinical phenotype, including oculocutaneous albinism, bleeding diathesis, and a predisposition to pulmonary fibrosis. This article provides a comprehensive examination of HPS, encompassing its genetic underpinnings, molecular mechanisms, clinical manifestations, and emerging therapeutic interventions. HPS is primarily attributed to mutations in multiple genes, causing defects in the biogenesis of lysosome-related organelles, leading to platelet and granule abnormalities, which contribute to the bleeding diathesis. In addition, the oculocutaneous albinism associated with HPS is a result of impaired melanin synthesis. The article explores recent advancements in understanding HPS pathogenesis, such as aberrant platelet function and the dysregulation of various cellular pathways. Additionally, we discuss diagnostic challenges and the need for a multidisciplinary approach in managing patients with HPS. Furthermore, this review highlights the evolving landscape of therapeutic strategies, including experimental therapies targeting the underlying genetic defects, advances in supportive care for bleeding disorders, and novel approaches for managing pulmonary fibrosis. In conclusion, this article underscores the importance of ongoing research in HPS, emphasizing the potential for improved diagnosis and treatment outcomes in patients with this intriguing and complex syndrome.

Lysosome-related organelles promote stress and immune responses in C. elegans

Lysosome-related organelles (LROs) play diverse roles and their dysfunction causes immunodeficiency. However, their primordial functions remain unclear. Here, we report that C. elegans LROs (gut granules) promote organismal defenses against various stresses. We find that toxic benzaldehyde exposure induces LRO autofluorescence, stimulates the expression of LRO-specific genes and enhances LRO transport capacity as well as increases tolerance to benzaldehyde, heat and oxidative stresses, while these responses are impaired in glo-1/Rab32 and pgp-2 ABC transporter LRO biogenesis mutants. Benzaldehyde upregulates glo-1- and pgp-2-dependent expression of heat shock, detoxification and antimicrobial effector genes, which requires daf-16/FOXO and/or pmk-1/p38MAPK. Finally, benzaldehyde preconditioning increases resistance against Pseudomonas aeruginosa PA14 in a glo-1- and pgp-2-dependent manner, and PA14 infection leads to the deposition of fluorescent metabolites in LROs and induction of LRO genes. Our study suggests that LROs may play a role in systemic responses to stresses and in pathogen resistance.

Characterization of Rab32- and Rab38-positive lysosome-related organelles in osteoclasts and macrophages

Both the biogenesis and functions of osteoclasts and macrophages involves dynamic membrane traffic. We screened transcript levels for Rab family small GTPases related to osteoclasts and identified Rab38. Rab38 expression is upregulated during osteoclast differentiation and maturation. In osteoclasts, both Rab38 and its paralog, Rab32, colocalize to lysosome-related organelles (LROs). In macrophages, Rab32 is also found in LROs. LROs are part of the endocytic pathway but are distinct from lysosomes. After receptor activator of NF-κB ligand stimulation, LROs contain cathepsin K and tartrate-resistant acid phosphatase inside and help both proteins to accumulate around bone resorption pits. After osteoclast maturation, these enzymes are hardly found within LROs. In macrophages derived from Rab32 and Rab38 double knockout mice, both acidification and V-ATPase a3 localization were severely compromised. Both the double knockout macrophage and bafilomycin-treated wildtype macrophage show an increase in Lamp1-positive organelles, implying that biogenesis of lysosomes and LROs are related. These results indicate that Rab32 and Rab38 both play a crucial role in LRO biogenesis in macrophages and in osteoclasts.

Functional characterization of Bmcap in uric acid metabolism in the silkworm.

After a millennium of domestication, numerous silkworm mutants have emerged that exhibit transparent epidermis, which is caused by abnormally low levels of uric acid. We identified the Bombyx mori gene Bmcap (BMSK0003832) as the homolog of cappuccino, a subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1) that has been extensively characterized in human, mouse, and insect species, by analyzing the amino acid sequences of putative purine metabolism genes. Using the clustered regularly interspaced palindromic repeats (CRISPR) / CRISPR-associated protein 9 system, we disrupted Bmcap, resulting in decreased uric acid levels in the silkworm epidermis and a translucent skin phenotype. In the Bmcap mutant, the purine metabolism, nitrogen metabolism, pyrimidine metabolism, and membrane system were altered compared to the wild type. Biogenesis of lysosome-related organelle complex genes play a role in the pigmentation and biogenesis of lysosome-related organelles (LROs) in platelets, melanocytes, and megakaryocytes. LROs exhibit unique morphologies and functions in various tissues and cells. Investigation of the Bmcap mutant will enhance our understanding of the uric acid metabolic pathway in silkworms, and this mutant offers a valuable silkworm model for LRO studies.

Overlapping Machinery in Lysosome-Related Organelle Trafficking: A Lesson from Rare Multisystem Disorders.

Lysosome-related organelles (LROs) are a group of functionally diverse, cell type-specific compartments. LROs include melanosomes, alpha and dense granules, lytic granules, lamellar bodies and other compartments with distinct morphologies and functions allowing specialised and unique functions of their host cells. The formation, maturation and secretion of specific LROs are compromised in a number of hereditary rare multisystem disorders, including Hermansky-Pudlak syndromes, Griscelli syndrome and the Arthrogryposis, Renal dysfunction and Cholestasis syndrome. Each of these disorders impacts the function of several LROs, resulting in a variety of clinical features affecting systems such as immunity, neurophysiology and pigmentation. This has demonstrated the close relationship between LROs and led to the identification of conserved components required for LRO biogenesis and function. Here, we discuss aspects of this conserved machinery among LROs in relation to the heritable multisystem disorders they associate with, and present our current understanding of how dysfunctions in the proteins affected in the disease impact the formation, motility and ultimate secretion of LROs. Moreover, we have analysed the expression of the members of the CHEVI complex affected in Arthrogryposis, Renal dysfunction and Cholestasis syndrome, in different cell types, by collecting single cell RNA expression data from the human protein atlas. We propose a hypothesis describing how transcriptional regulation could constitute a mechanism that regulates the pleiotropic functions of proteins and their interacting partners in different LROs.

Dysregulated myosin in Hermansky-Pudlak syndrome lung fibroblasts is associated with increased cell motility

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by improper biogenesis of lysosome-related organelles (LROs). Lung fibrosis is the leading cause of death among adults with HPS-1 and HPS-4 genetic types, which are associated with defects in the biogenesis of lysosome-related organelles complex-3 (BLOC-3), a guanine exchange factor (GEF) for a small GTPase, Rab32. LROs are not ubiquitously present in all cell types, and specific cells utilize LROs to accomplish dedicated functions. Fibroblasts are not known to contain LROs, and the function of BLOC-3 in fibroblasts is unclear. Here, we report that lung fibroblasts isolated from patients with HPS-1 have increased migration capacity. Silencing HPS-1 in normal lung fibroblasts similarly leads to increased migration. We also show that the increased migration is driven by elevated levels of Myosin IIB. Silencing HPS1 or RAB32 in normal lung fibroblasts leads to increased MYOSIN IIB levels. MYOSIN IIB is downstream of p38-MAPK, which is a known target of angiotensin receptor signaling. Treatment with losartan, an angiotensin receptor inhibitor, decreases MYOSIN IIB levels and impedes HPS lung fibroblast migration in vitro. Furthermore, pharmacologic inhibition of angiotensin receptor with losartan seemed to decrease migration of HPS lung fibroblasts in vivo in a zebrafish xenotransplantation model. Taken together, we demonstrate that BLOC-3 plays an important role in MYOSIN IIB regulation within lung fibroblasts and contributes to fibroblast migration.

HPS6 Regulates the Biogenesis of Weibel-Palade Body in Endothelial Cells Through Trafficking v-ATPase to Its Limiting Membrane.

The Weibel–Palade body (WPB) is one of the lysosome-related organelles (LROs) in endothelial cells, whose main content is von Willebrand factor (vWF). The biogenesis of LROs is regulated by the Hermansky–Pudlak syndrome (HPS) protein-associated complexes through transporting cargo proteins to WPBs. Our previous studies have shown that HPS6, a subunit of BLOC-2 complex, is likely involved in the maturation of WPBs. However, the underlying mechanism remains unknown. In this study, we found that the knockdown of HPS6 in human umbilical vein endothelial cells (HUVECs) resulted in misshaped WPBs, decreased WPB number, and impaired vWF tubulation, which are similar to the characteristics of HPS6-deficient mouse endothelial cells. We observed similar morphological changes of WPBs in HUVECs after the knockdown of ATP6V0D1 (a subunit of v-ATPase). Furthermore, we found that HPS6 interacted with ATP6V0D1, suggesting that HPS6 transports ATP6V0D1 to the WPB limiting membrane for the assembly of the v-ATPase complex to maintain its acidic luminal pH, which is critical for the formation of vWF tubules during WPB maturation. In conclusion, HPS6 likely regulates the biogenesis of WPBs by participating in the trafficking of v-ATPase to the WPB membrane.

New insights into the pathogenesis of Hermansky–Pudlak syndrome

Hermansky-Pudlak syndrome (HPS) is characterized by defects of multiple tissue-specific lysosome-related organelles (LROs), typically manifesting with oculocutaneous albinism or ocular albinism, bleeding tendency, and in some cases with pulmonary fibrosis, inflammatory bowel disease or immunodeficiency, neuropsychological disorders. Eleven HPS subtypes in humans and at least 15subtypes in mice have been molecularly identified. Current understanding of the underlying mechanisms of HPS is focusing on the defective biogenesis of LROs. Compelling evidences have shown that HPS protein-associated complexes (HPACs) function in cargo transport, cargo recycling, and cargo removal to maintain LRO homeostasis. Further investigation on the molecular and cellular mechanism of LRO biogenesis and secretion will be helpful for better understanding of its pathogenesis and for the precise intervention of HPS.

P360 Aggressive Inflammatory Bowel Disease is associated to Hermansky-Pudlak Syndrome: Characterization of a Puerto Rican Cohort

Abstract Background Hermansky-Pudlak Syndrome (HPS), a rare autosomal recessive disorder, is the most common single-gene disorder in Puerto Rico. It is characterized by an aberrant biogenesis of lysosome-related organelles inducing oculocutaneous albinism, bleeding diathesis, and damage to other organs. Around 30% of patients with HPS develop granulomatous enterocolitis, a Crohn’s-like inflammatory bowel disease (IBD). The mutant HPS1 gene is associated with a more severe Early Onset IBD (EO-IBD). We wish to describe a group of patients with HPS-associated IBD. Methods Puerto Ricans with HPS and concomitant IBD were recruited in our IBD clinic for a prospective cohort study. After informed consent, demographic and medical data were collected from the patient and the medical record. Variables included sex, HPS genotype, age at the time of IBD diagnosis, IBD location and behavior according to Montreal and Paris Classification, surgical interventions, medications, and extra-intestinal manifestations (EIM). Descriptive analysis was performed calculating mean and standard deviations. This study is approved by the MSC IRB. Results 13 patients with HPS and IBD, 9 with confirmed genotype 1, were identified: 8 males and 5 females. The mean age at the time of IBD diagnosis was 22 ± 11 years. 6 were diagnosed at ≤ 16 y/o (A1), 6 were diagnosed between 17-40 years (A2) and 1 patient was in the range of EO-IBD (7 y/o). 9 patients had advanced penetrating behavior (B3) of which 7 had concomitant perianal involvement. Most patients (9) had a surgical intervention; 8 have an ostomy. The majority (10) are using biologics (4 with concurrent immunomodulators). The most frequent EIM was peripheral arthropathy seen in 45%. Conclusion HPS patients had a severe course of IBD, as shown by age at diagnosis, phenotype, the prevalence of perianal disease, surgery and use of biologics. In comparison to a database of 836 Puerto Ricans with non HPS Crohn’s Disease, those with HPS were more likely to have surgeries (69% vs 55%, P=.303) and use biologics (77% vs 43%, P=.015). Gastrointestinal symptoms including bleeding may be overlooked by the primary physician. Proactive vigilance in patients with HPS to make an early diagnosis of IBD and aggressive medical treatment may result in better outcomes for these patients.

Hermansky-Pudlak syndrome pulmonary fibrosis: a rare inherited interstitial lung disease.

Pulmonary fibrosis is a progressive interstitial lung disease of unknown aetiology with a poor prognosis. Studying genetic diseases associated with pulmonary fibrosis provides insights into the pathogenesis of the disease. Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterised by abnormal biogenesis of lysosome-related organelles, manifests with oculocutaneous albinism and excessive bleeding of variable severity. Pulmonary fibrosis is highly prevalent in three out of 10 genetic types of HPS (HPS-1, HPS-2 and HPS-4). Thus, genotyping of individuals with HPS is clinically relevant. HPS-1 tends to affect Puerto Rican individuals due to a genetic founder effect. HPS pulmonary fibrosis shares some clinical features with idiopathic pulmonary fibrosis (IPF), including dyspnoea, cough, restrictive lung physiology and computed tomography (CT) findings of fibrosis. In contrast to IPF, HPS pulmonary fibrosis generally affects children (HPS-2) or middle-aged adults (HPS-1 or HPS-4) and may be associated with ground-glass opacification in CT scans. Histopathology of HPS pulmonary fibrosis, and not IPF, shows vacuolated hyperplastic type II cells with enlarged lamellar bodies and alveolar macrophages with lipofuscin-like deposits. Antifibrotic drugs approved as treatment for IPF are not approved for HPS pulmonary fibrosis. However, lung transplantation has been performed in patients with severe HPS pulmonary fibrosis. HPS pulmonary fibrosis serves as a model for studying fibrotic lung disease and fibrosis in general.

A zinc transporter, transmembrane protein 163, is critical for the biogenesis of platelet dense granules

Lysosome-related organelles (LROs) are a category of secretory organelles enriched with ions such as calcium, which are maintained by ion transporters or channels. Homeostasis of these ions is important for LRO biogenesis and secretion. Hermansky-Pudlak syndrome (HPS) is a recessive disorder with defects in multiple LROs, typically platelet dense granules (DGs) and melanosomes. However, the underlying mechanism of DG deficiency is largely unknown. Using quantitative proteomics, we identified a previously unreported platelet zinc transporter, transmembrane protein 163 (TMEM163), which was significantly reduced in BLOC-1 (Dtnbp1sdy and Pldnpa)–, BLOC-2 (Hps6ru)–, or AP-3 (Ap3b1pe)–deficient mice and HPS patients (HPS2, HPS3, HPS5, HPS6, or HPS9). We observed similar platelet DG defects and higher intracellular zinc accumulation in platelets of mice deficient in either TMEM163 or dysbindin (a BLOC-1 subunit). In addition, we discovered that BLOC-1 was required for the trafficking of TMEM163 to perinuclear DG and late endosome marker–positive compartments (likely DG precursors) in MEG-01 cells. Our results suggest that TMEM163 is critical for DG biogenesis and that BLOC-1 is required for the trafficking of TMEM163 to putative DG precursors. These new findings suggest that loss of TMEM163 function results in disruption of intracellular zinc homeostasis and provide insights into the pathogenesis of HPS or platelet storage pool deficiency.

Inflammatory bowel disease in Hermansky-Pudlak syndrome: a retrospective single-centre cohort study.

Knowledge about inflammatory bowel disease (IBD) in patients with Hermansky-Pudlak syndrome (HPS), a rare autosomal recessive disorder characterized by defective biogenesis of lysosome-related organelles, could provide insights into IBD in general. To expand the understanding of IBD in patients with HPS. Retrospective review of records from patients with HPS evaluated at the National Institutes of Health Clinical Center from 1995 to 2019 was conducted. Clinical features of IBD, genotyping results and histologic findings of colectomy specimens were analysed. IBD affected 37 (14.2%; 12 male, 25 female) of 261 patients with HPS. Median age of onset was 17years; range was 1 to 52years. The most common symptoms of HPS IBD were hematochezia, abdominal pain and loose stools. Fistulae or extra-intestinal manifestations developed in 30% or 22%, respectively. Genotyping showed that patients with biallelic variants in HPS1, HPS3, HPS4 or HPS6 were diagnosed with IBD. Six children had very early-onset IBD. Patients with HPS-3 had mild manifestations of IBD. Medical therapy and bowel resection were utilized to treat 73% and 35% of patients with HPS IBD, respectively; 7 of 13 patients receiving anti-tumor necrosis factor alpha therapy had prolonged clinical responses. Active cryptitis, chronic inflammatory changes, granulomas and ceroid lipofuscinosis were histopathologic findings in three colectomy specimens. IBD resembling Crohn's disease affects some patients with HPS; genetic heterogeneity is a feature of HPS IBD. HPS3 is a new gene associated with human IBD. Very early-onset IBD can develop in HPS.

Periodic albinism of a widely used albino mutant of Xenopus laevis caused by deletion of two exons in the Hermansky-Pudlak syndrome type 4 gene.

The periodic albino mutant of Xenopus laevis is a recessive mutant, in which reduced amounts of melanin appear in the retinal pigment epithelium (RPE) and in melanophores at the late embryonic stage, after which both RPE and melanophores gradually depigment. Three types of pigment cells (melanophores, iridophores and xanthophores) have been reported to be affected in this albino. However, the causative gene of the periodic albinism remains unknown. Hermansky–Pudlak syndrome (HPS) is an autosomal recessive disorder that affects humans and mice, which is caused by defective biogenesis of lysosome‐related organelles (LROs). Two subgenomes (L and S) are present in the allotetraploid frog X. laevis. Comparison of genes between the chromosomes 1L and 1S revealed that the HPS type 4 (hps4) gene was present only in chromosome 1L. In the albino mutant, a 1.9 kb genomic deletion in the hps4.L gene including exons 7 and 8 caused a premature stop codon to create a truncated Hps4 protein. Injection of wild‐type hps4.L mRNA into mutant embryos rescued the albino phenotype. These findings indicate that hps4 is a causative gene for the periodic albinism in X. laevis. The phenotype of this mutant should be reassessed from the perspective of LRO biogenesis.

HPS1 Regulates the Maturation of Large Dense Core Vesicles and Lysozyme Secretion in Paneth Cells.

HPS1, a BLOC-3 subunit that acts as a guanine nucleotide exchange factor of Rab32/38, may play a role in the removal of VAMP7 during the maturation of large dense core vesicles of Paneth cells. Loss of HPS1 impairs lysozyme secretion and alters the composition of intestinal microbiota, which may explain the susceptibility of HPS-associated inflammatory bowel disease. Hermansky-Pudlak syndrome (HPS) is characterized by oculocutaneous albinism, bleeding tendency, and other chronic organ lesions due to defects in tissue-specific lysosome-related organelles (LROs). For some HPS subtypes, such as HPS-1, it is common to have symptoms of HPS-associated inflammatory bowel disease (IBD). However, its underlying mechanism is largely unknown. HPS1 is a subunit of the BLOC-3 complex which functions in the biogenesis of LROs. Large dense core vesicles (LDCVs) in Paneth cells of the intestine are a type of LROs. We here first report the abnormal LDCV morphology (increased number and enlarged size) in HPS1-deficient pale ear (ep) mice. Similar to its role in melanosome maturation, HPS1 plays an important function in the removal of VAMP7 from LDCVs to promote the maturation of LDCVs. The immature LDCVs in ep mice are defective in regulated secretion of lysozyme, a key anti-microbial peptide in the intestine. We observed changes in the composition of intestinal microbiota in both HPS-1 patients and ep mice. These findings provide insights into the underlying mechanism of HPS-associated IBD development, which may be implicated in possible therapeutic intervention of this devastating condition.

S3215 Hermansky-Pudlak-Associated IBD: Is It the Same? Description of a Puerto Rican Cohort

INTRODUCTION: Hermansky-Pudlak Syndrome (HPS) is the most common single gene disorder in Puerto Rico. It is a rare autosomal recessive disorder due to aberrant biogenesis of lysosome-related organelles leading to oculocutaneous albinism, bleeding diathesis, and involvement in other organs. About 30% of patients with HPS develop a form of Crohn’s-like inflammatory bowel disease (IBD), granulomatous enterocolitis. Whether this is a manifestation of HPS or true IBD is still in debate. We wish to describe a group of patients with HPS-associated IBD. METHODS: This is a prospective cohort study in which phenotypically identified patients with HPS and concomitant IBD are recruited. After informed consent, a questionnaire with demographic and medical data is administered through patient interview and record review is performed. The variables collected are sex, HPS genotype, age at the time of IBD diagnosis, comorbidities, IBD location and behavior according to Montreal Classification, surgical interventions, medications, and extra-intestinal manifestations (EIM). This study is approved by the IRB. RESULTS: Ten patients with HPS and concomitant IBD were identified in our clinics - 5 males and 5 females. HPS genotype in 9 showed 8 were HPS-1 and 1 was HPS-3. The mean age at the time of IBD diagnosis was 22 ± 10 years. Six were diagnosed between ages 17 and 40 years and 4 patients were diagnosed at ≤16 y/o. Seven patients had colonic involvement, 3 had ileocolonic involvement. Sixty percent of patients had an advanced penetrating behavior and 50% had perianal involvement. Six patients had some type of surgical intervention. Three patients were on both a biologic and an immunomodulator (IMM), 5 were on a biologic alone, 1 on IMM alone, and 1 without maintenance treatment. The most frequent EIM was anemia in 40% of patients. CONCLUSION: HPS patients had a severe course of IBD, as shown by phenotype, surgery, and use of biologics. A younger age at diagnosis and a higher than usual prevalence of perianal disease also predict a complicated course. Further studies are necessary to determine if HPS-associated IBD is related to the genetic defect and if this may result in a different clinical course than idiopathic IBD.