Affinage

NIPAL4

Magnesium transporter NIPA4 · UniProt Q0D2K0

Length
404 aa
Mass
44.0 kDa
Annotated
2026-06-10
18 papers in source corpus 8 papers cited in narrative 8 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

NIPAL4 (ichthyin) is a granular-layer epidermal protein required for the lipid processing that builds the stratum corneum permeability barrier (PMID:20016120, PMID:38692573). It is expressed specifically in the granular cell layer of the epidermis (PMID:20016120) and localizes to desmosomes and keratins in differentiating keratinocytes (PMID:22258272). Genetic loss of NIPAL4 — in patient keratinocytes, NIPAL4-deficient American Bulldogs, and Nipal4 knockout mice — produces intracellular lipid accumulation, abnormal lamellar bodies, discontinuous corneocyte lipid bilayers, and unprocessed lipid, establishing a direct role in lamellar-body-associated lipid processing (PMID:22258272, PMID:25322746). Comprehensive lipid profiling of knockout epidermis shows that NIPAL4-dependent Mg2+ transport in keratinocytes is required for normal production of multiple ceramide species, with depletion of ω-O-acylceramides and linoleate-containing ω-O-acyl hydroxy fatty acids and accumulation of ω-hydroxy ceramides, ω-hydroxy glucosylceramides, triglycerides, and free fatty acids (PMID:38692573); patient stratum corneum likewise shows reduced long-chain acylceramides (PMID:31836270). NIPAL4 functions in coordination with the lipoxygenase/transglutaminase arm of barrier formation, colocalizing with TGM1 in healthy upper epidermis and showing increased 12R-LOX/eLOX-3 colocalization upon its loss (PMID:22622417). Loss-of-function NIPAL4 mutations cause autosomal recessive congenital ichthyosis with dose-dependent ultrastructural severity, and oral retinoid treatment normalizes lipoxygenase expression and partially restores acylceramide levels (PMID:22622417, PMID:31836270, PMID:31347739).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 2009 Medium

    Establishing where NIPAL4 acts within the epidermis was the first step in linking it to barrier biology; cell-type-specific expression localized its function to the terminally differentiating layer.

    Evidence In situ hybridization of human epidermal sections

    PMID:20016120

    Open questions at the time
    • mRNA localization does not establish protein function or transport activity
    • does not identify lipid substrates or partners
  2. 2012 Medium

    Subcellular localization and a lipid-accumulation phenotype were needed to connect the protein to a process; ichthyin was placed at desmosomes/keratins and tied to defective lamellar body lipid processing.

    Evidence Confocal/electron microscopy, immunolabeling, and Nile red lipid staining of patient and control skin and keratinocytes

    PMID:22258272

    Open questions at the time
    • mechanism connecting desmosomal localization to lipid processing unresolved
    • no direct demonstration of transport activity
    • single-lab observation
  3. 2012 Medium

    Whether NIPAL4 acts in the known lipoxygenase/transglutaminase barrier pathway was unclear; proximity ligation placed ichthyin near TGM1 and showed perturbed 12R-LOX/eLOX-3 colocalization on its loss, integrating it into the LOX–TGM1 arm of barrier formation.

    Evidence In situ proximity ligation assay, immunofluorescence, and liarozole retinoid treatment of patient biopsies

    PMID:22622417

    Open questions at the time
    • proximity ligation indicates closeness, not direct physical interaction
    • molecular basis of LOX dysregulation not defined
    • retinoid mechanism of normalization unknown
  4. 2014 Medium

    A naturally occurring animal model was used to test causality of protein loss; absence of ichthyin in deficient dogs reproduced lamellar body and corneocyte lipid defects, confirming a direct loss-of-function link to lipid processing.

    Evidence Immunohistochemistry, electron microscopy, and linkage analysis in NIPAL4-deficient American Bulldogs

    PMID:25322746

    Open questions at the time
    • does not identify the biochemical step disrupted
    • transport substrate not measured
  5. 2019 Medium

    The specific lipid species affected in humans were undefined; ceramide profiling of patient stratum corneum showed reduced long-chain acylceramides with retinoid-responsive partial restoration, pinpointing acylceramide synthesis/processing as the affected output.

    Evidence Ceramide analysis of tape-stripped stratum corneum, RNA-seq, IHC, and EM in an ARCI patient with a frameshift mutation

    PMID:31836270

    Open questions at the time
    • single patient
    • enzymatic step at which acylceramide production fails not identified
  6. 2019 Medium

    Genotype–phenotype and structural questions were addressed: cohort ultrastructural phenotyping showed dose-dependent severity (ARCI EM type III), and modeling predicted a 9-TM transport channel whose narrowing by p.E178D would impair Mg2+ transport.

    Evidence Electron microscopy and mutation/mRNA analysis of six patients; separate in silico 3D homology modeling

    PMID:31347739 PMID:31876100

    Open questions at the time
    • predicted Mg2+ transport channel and the p.E178D effect are computational, lacking experimental transport assays
    • no experimental structure
  7. 2024 High

    Whether NIPAL4 loss broadly remodels epidermal lipids and links Mg2+ transport to ceramide metabolism was the central open question; knockout-mouse lipidomics defined comprehensive ceramide-class changes, establishing NIPAL4-dependent Mg2+ transport as required for normal barrier lipid production.

    Evidence Nipal4 knockout mouse with TLC and mass spectrometry of epidermal lipids

    PMID:38692573

    Open questions at the time
    • direct Mg2+ transport activity of NIPAL4 not measured biochemically
    • the Mg2+-dependent enzymes whose activity is altered are not identified
    • mechanism connecting Mg2+ flux to specific ceramide-modifying steps unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • Direct biochemical demonstration of NIPAL4 Mg2+ transport and identification of the Mg2+-dependent enzymatic steps in acylceramide synthesis that it supports remain unestablished.
  • no reconstituted or cellular transport assay confirming Mg2+ selectivity
  • no defined molecular link between Mg2+ availability and specific ceramide-processing enzymes
  • no experimental structure of the predicted transport channel

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 1
Localization
GO:0005886 plasma membrane 1
Pathway
R-HSA-1266738 Developmental Biology 2 R-HSA-1430728 Metabolism 2
Partners
TGM1

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2012 Ichthyin/NIPAL4 localizes to desmosomes and keratins in epidermis (both in patient keratinocytes with NIPAL4 mutations and healthy controls), as shown by confocal and electron microscopy of immunolabeled skin sections. Nile red lipid analysis revealed intracellular lipid accumulations in granular and cornified layer cells of patients but not controls, indicating NIPAL4 is involved in epidermal lipid metabolism, possibly through processing of lamellar bodies. Confocal microscopy, electron microscopy, immunolabeling, Nile red lipid staining of skin sections and cultured keratinocytes Archives of dermatological research Medium 22258272
2012 In epidermis from ARCI patients with NIPAL4 mutations, colocalization of 12R-LOX and eLOX-3 was increased ~3-fold compared to controls, and TGM1 and ichthyin colocalize in the upper epidermis of healthy skin (demonstrated by in situ proximity ligation assay). Treatment with the retinoid-mimetic drug liarozole normalized 12R-LOX expression and attenuated the LOX colocalization signal in NIPAL4-mutant patients. These data indicate ichthyin and TGM1 are functionally closely related in epidermal lipid processing. In situ proximity ligation assay, immunofluorescence on skin biopsies, retinoid treatment experiment The Journal of investigative dermatology Medium 22622417
2009 NIPAL4 mRNA is highly and specifically expressed in the granular cell layer of the epidermis, as determined by in situ hybridization of human epidermal sections. In situ hybridization (ISH) of human epidermis Dermatology (Basel, Switzerland) Medium 20016120
2014 Immunolabeling of skin from NIPAL4-deficient American Bulldogs revealed an absence of ichthyin protein in the epidermis, and ultrastructural analysis showed discontinuous lipid bilayers, unprocessed lipid within corneocytes, and abnormal lamellar bodies, establishing a direct link between NIPAL4 loss and epidermal lipid processing defects. Immunolabeling (immunohistochemistry), electron microscopy (ultrastructural analysis), linkage analysis Veterinary pathology Medium 25322746
2019 In an ARCI patient with a frameshift NIPAL4 mutation, ceramide analysis of stratum corneum tape strips revealed reduced amounts of acylceramides (CER[NS] with C66:2–C72:2) and relative increases in shorter-chain CER[NS], demonstrating that NIPAL4 loss alters stratum corneum acylceramide composition. Oral retinoid treatment restored CER[EOH] and CER[EOP] levels. Ceramide analysis of tape-stripped stratum corneum, RNA sequencing of patient skin, immunohistochemistry, electron microscopy Journal of dermatological science Medium 31836270
2024 In Nipal4 knockout mice, detailed lipid analysis by TLC and MS of the epidermis revealed compositional changes in many ceramide classes: decreases in ω-O-acylceramides and ω-O-acyl hydroxy fatty acids (containing linoleic acid), increases in ω-hydroxy ceramides, ω-hydroxy glucosylceramides, triglycerides, free fatty acids, and unusual ω-O-acylceramides (containing oleic acid or palmitic acid), as well as increases in 1-O-acylceramides. Cholesterol and protein-bound ceramides were largely unchanged. This establishes that NIPAL4-dependent Mg2+ transport in differentiating keratinocytes is required for normal production of multiple epidermal lipid species essential for skin barrier formation. Nipal4 knockout mouse model, thin-layer chromatography (TLC), mass spectrometry (MS) of epidermal lipids Journal of lipid research High 38692573
2019 Ultrastructural (electron microscopy) analysis of skin biopsies from six ARCI patients with NIPAL4 mutations revealed morphological abnormalities classified as ARCI EM type III. A patient with a homozygous splice site mutation causing complete loss of NIPAL4 mRNA showed additional ultrastructural aberrations and a more severe clinical phenotype, consistent with a dose-dependent role of NIPAL4 in epidermal structure. Electron microscopy (ultrastructural analysis), mutation analysis, mRNA expression analysis Human mutation Medium 31347739
2019 In silico 3D modeling of NIPAL4 predicted 9 transmembrane helices and a transport channel; a missense mutation p.E178D located in the second transmembrane helix was predicted to cause shrinkage of the transport channel, suggesting the structural basis for impaired Mg2+ transport. In silico secondary structure prediction, 3D homology modeling Molecular genetics & genomic medicine Low 31876100

Source papers

Stage 0 corpus · 18 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 The expression of epidermal lipoxygenases and transglutaminase-1 is perturbed by NIPAL4 mutations: indications of a common metabolic pathway essential for skin barrier homeostasis. The Journal of investigative dermatology 28 22622417
2009 NIPAL4/ichthyin is expressed in the granular layer of human epidermis and mutated in two Pakistani families with autosomal recessive ichthyosis. Dermatology (Basel, Switzerland) 24 20016120
2017 A Defect in NIPAL4 Is Associated with Autosomal Recessive Congenital Ichthyosis in American Bulldogs. PloS one 21 28122049
2014 Autosomal Recessive Congenital Ichthyosis in American Bulldogs Is Associated With NIPAL4 (ICHTHYIN) Deficiency. Veterinary pathology 20 25322746
2019 Reduced stratum corneum acylceramides in autosomal recessive congenital ichthyosis with a NIPAL4 mutation. Journal of dermatological science 19 31836270
2011 Manifestation of diffuse yellowish keratoderma on the palms and soles in autosomal recessive congenital ichthyosis patients may be indicative of mutations in NIPAL4. The Journal of dermatology 13 22098531
2012 Ichthyin/NIPAL4 localizes to keratins and desmosomes in epidermis and Ichthyin mutations affect epidermal lipid metabolism. Archives of dermatological research 12 22258272
2019 Genetical, clinical, and functional analysis of a large international cohort of patients with autosomal recessive congenital ichthyosis due to mutations in NIPAL4. Human mutation 11 31347739
2019 NIPAL4 deletion identified in an American Bully with autosomal recessive congenital ichthyosis and response to topical therapy. Veterinary medicine and science 7 30741495
2015 Novel mutation in NIPAL4 in a Romanian family with autosomal recessive congenital ichthyosis. Clinical and experimental dermatology 7 26456858
2024 Alteration of epidermal lipid composition as a result of deficiency in the magnesium transporter Nipal4. Journal of lipid research 6 38692573
2019 Identification of a novel missense mutation in NIPAL4 gene: First 3D model construction predicted its pathogenicity. Molecular genetics & genomic medicine 6 31876100
2021 Expanding the clinical phenotype associated with NIPAL4 mutation: Study of a Tunisian consanguineous family with erythrokeratodermia variabilis-Like Autosomal Recessive Congenital Ichthyosis. PloS one 5 34669720
2023 Lamellar ichthyosis with a novel NIPAL4 variant showing dramatic response to high-dose vitamin D therapy. Pediatric dermatology 3 38018299
2025 Erythrokeratodermia Variabilis due to a Compound Heterozygous Variants in the NIPAL4 Gene. Pediatric dermatology 1 40476394
2026 Identification of Pathogenic Variants in CYP4F22, FLG, ALOX12B, and NIPAL4 in a Case Series of Inherited Ichthyosis. International journal of molecular sciences 0 42196615
2025 AI-driven radiogenomic analysis of clear cell renal cell carcinoma: perinephric adipose tissue stranding as a key feature of the NIPAL4-associated imaging pattern. The Canadian journal of urology 0 41220353
2018 Hyperlipidemia secondary to acitretin therapy for lamellar ichthyosis associated with a NIPAL4 mutation improves on a plant-based diet and relapses on a standard Western diet. Clinical nutrition ESPEN 0 29576363

Missed literature

Know a paper Affinage missed for NIPAL4? Flag it for the maintainers and the community.

No submissions yet.