The Sec1-Munc18 protein VPS33B forms a uniquely bidirectional complex with VPS16B.

Loss-of-function variants of vacuolar protein sorting proteins VPS33B and VPS16B (VIPAS39) are causative for arthrogryposis, renal dysfunction, and cholestasis syndrome, where early lethality of patients indicates that VPS33B and VPS16B play essential cellular roles. VPS33B is a member of the Sec1-Munc18 protein family and thought to facilitate vesicular fusion via interaction with soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complexes, like its paralog VPS33A in the homotypic fusion and vacuole sorting complex. VPS33B and VPS16B are known to associate, but little is known about the composition, structure, or function of the VPS33B-VPS16B complex. We show here that human VPS33B-VPS16B is a high molecular weight complex, which we expressed in yeast to perform structural, composition, and stability analysis. Circular dichroism data indicate VPS33B-VPS16B has a well-folded α-helical secondary structure, and size-exclusion chromatography-multiangle light scattering revealed a molecular weight of ∼315 kDa. Quantitative immunoblotting indicated a VPS33B:VPS16B ratio of 2:3. Expression of arthrogryposis, renal dysfunction, and cholestasis syndrome-causing VPS33B missense variants showed L30P disrupts complex formation but not S243F or H344D. Truncated VPS16B (amino acids 143 to 316) was sufficient to form a complex with VPS33B. Small-angle X-ray scattering and negative-staining EM revealed a two-lobed shape for VPS33B-VPS16B. Avidin tagging indicated that each lobe contains a VPS33B molecule, and they are oriented in opposite directions. We propose a structure for VPS33B-VPS16B that allows the VPS33B at each end to interact with separate SNARE bundles and/or SNAREpins, plus associated membrane components. These observations reveal the only known potentially bidirectional Sec1-Munc18 protein complex.

Rosacea: Pathogenesis and Therapeutic Correlates.

Rosacea is a chronic inflammatory condition of which there is no cure. The pathogenesis of rosacea is likely multifactorial, involving genetic and environmental contributions. Current understanding suggests that pro-inflammatory pathways involving cathelicidins and inflammasome complexes are central to rosacea pathogenesis. Common rosacea triggers modulate these pathways in a complex manner, which may contribute to the varying severity and clinical presentations of rosacea. Established and emerging rosacea treatments may owe their efficacy to their ability to target different players in these pro-inflammatory pathways. Improving our molecular understanding of rosacea will guide the development of new therapies and the use of combination therapies.

Efficacy of Treatments in Reducing Inflammatory Lesion Count in Rosacea: A Systematic Review.

INTRODUCTION: Rosacea is a chronic inflammatory skin condition affecting approximately 5.5% of the global population. Patients present heterogeneously with a mix of features in the central facial region, of which papules and pustules are considered to be a major feature. The identification of effective treatments for reducing inflammatory lesions in rosacea can alleviate the psychosocial burden that many rosacea patients experience, including reduced self-esteem, anxiety, and social withdrawal. The objective of this systematic review is to determine the effectiveness of topical and systemic therapies in reducing lesion count in rosacea patients. METHODS/RESULTS: Medline, Embase, and Cochrane CENTRAL databases were searched, resulting in the inclusion of 43 clinical trials reporting on a total of 18,347 rosacea patients. The most well-studied treatments include ivermectin, metronidazole, azelaic acid, minocycline, and doxycycline. Oral isotretinoin was the most effective treatment in reducing inflammatory lesions and may be recommended for severe recalcitrant cases of rosacea. CONCLUSIONS: Several topical and systemic therapies have demonstrated efficacy in reducing inflammatory lesion count in rosacea patients, with mechanisms of action centred around suppressing inflammation and killing Demodex folliculorum mites. Additional research is required to determine effective combination therapies in rosacea.

Atopic Dermatitis: Clinical Aspects and Treatments.

GENERAL PURPOSE: To review issues related to atopic dermatitis, including its classification, clinical presentation, potential triggers, and treatment options. TARGET AUDIENCE: This continuing education activity is intended for physicians, physician assistants, nurse practitioners, and registered nurses with an interest in skin and wound care. LEARNING OBJECTIVES/OUTCOMES: After participating in this educational activity, the participant will:1. Synthesize a differential diagnosis for atopic dermatitis (AD).2. Explain the classification of AD cases.3. Select triggers or exacerbating factors for AD.4. Explain pharmacologic and nonpharmacologic treatment options for patients with AD.

Atopic dermatitis is the most common eczematous inflammatory skin condition, presenting with lesions that typically appear as poorly demarcated erythematous and scaly papules and plaques. The lesions most commonly occur on flexural surfaces of the knees, elbows, and wrists and are associated with moderate to severe itching. This article focuses on the clinical presentation of atopic dermatitis and treatment options. Other related topics include epidemiology, pathogenesis, risk factors, triggers, and differential diagnoses.

Platelet VPS16B is dependent on VPS33B expression, as determined in two siblings with arthrogryposis, renal dysfunction, and cholestasis syndrome.

BACKGROUND: Platelet α-granule biogenesis in precursor megakaryocytes is critically dependent on VPS33B and VPS16B, as demonstrated by the platelet α-granule deficiency seen in the rare multisystem disorder arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome associated with biallelic pathogenic variants in VPS33B and VIPAS39 (encoding VPS16B). VPS33B and VPS16B are ubiquitously expressed proteins that are known to interact and play key roles in protein sorting and trafficking between subcellular locations. However, there remain significant gaps in our knowledge of the nature of these interactions in primary cells from patients with ARC syndrome. OBJECTIVES: To use primary cells from patients with ARC syndrome to better understand the interactions and roles of VPS33B and VPS16B in platelets and precursor megakaryocytes. PATIENTS/METHODS: The proband and his male sibling were clinically suspected to have ARC syndrome. Confirmatory genetic testing and platelet phenotyping, including electron microscopy and protein expression analysis, was performed with consent in a research setting. RESULTS: We describe the first case of ARC syndrome identified in Costa Rica, associated with a novel homozygous nonsense VPS33B variant that is linked with loss of expression of both VPS33B and VPS16B in platelets. CONCLUSION: These results indicate that stable expression of VPS16B in platelets, their precursor megakaryocytes, and other cells is dependent on VPS33B. We suggest that systematic evaluation of primary cells from patients with a range of VPS33B and VIPAS39 variants would help to elucidate the interactions and functions of these proteins.