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

Cellular zinc metabolism and zinc signaling: from biological functions to diseases and therapeutic targets

Zinc metabolism at the cellular level is critical for many biological processes in the body. A key observation is the disruption of cellular homeostasis, often coinciding with disease progression. As an essential factor in maintaining cellular equilibrium, cellular zinc has been increasingly spotlighted in the context of disease development. Extensive research suggests zinc's involvement in promoting malignancy and invasion in cancer cells, despite its low tissue concentration. This has led to a growing body of literature investigating zinc's cellular metabolism, particularly the functions of zinc transporters and storage mechanisms during cancer progression. Zinc transportation is under the control of two major transporter families: SLC30 (ZnT) for the excretion of zinc and SLC39 (ZIP) for the zinc intake. Additionally, the storage of this essential element is predominantly mediated by metallothioneins (MTs). This review consolidates knowledge on the critical functions of cellular zinc signaling and underscores potential molecular pathways linking zinc metabolism to disease progression, with a special focus on cancer. We also compile a summary of clinical trials involving zinc ions. Given the main localization of zinc transporters at the cell membrane, the potential for targeted therapies, including small molecules and monoclonal antibodies, offers promising avenues for future exploration.

MGAT5/TMEM163 variant is associated with prognosis in ursodeoxycholic acid-treated patients with primary biliary cholangitis

BACKGROUND

Primary biliary cholangitis (PBC) is a chronic immune-mediated liver disease. Previous genome-wide meta-analysis has identified the association between variants in TMEM163 with PBC. Here we aimed to evaluate the association between variants near the reported risk loci of TMEM163 at 2q21.3 and prognosis of PBC patients.

METHODS

We performed a retrospective analysis of 347 PBC patients treated with ursodeoxycholic acid (UDCA) for at least 1 year. We collected clinical data at diagnosis and 1 year after UDCA treatment. SNPs within 200 kb upstream and downstream of the lead variant were genotyped and screened.

RESULTS

We identified that rs661899 near MGAT5 and TMEM163 showed the strongest association with prognosis in PBC patients. Patients carrying the rs661899 T allele tended to respond incompletely to UDCA treatment and had worse performances in laboratory values including aspartate aminotransferase (53.5 vs 32 vs 28.5 U/L, p = 0.001), alkaline phosphate (157.25 vs 125 vs 113 U/L, p = 0.001), albumin (41.5 vs 42.3 vs 43.7 g/L, p = 0.008) and bilirubin (19.2 vs 14.9 vs 12.85 μmol/L, p = 0.001). GLOBE scores (p = 4.8 × 10-5) and UK-PBC risk scores (p = 4.6 × 10-4) were strongly correlated with rs661899 genotype. Patients with TT genotype had a higher risk for adverse events compared with CC genotype (p = 0.039) during the 1-year follow-up. Results were also verified in an independent cohort.

CONCLUSIONS

PBC patients carrying the rs661899 T allele are associated with poor prognosis and adverse outcomes after 1-year UDCA therapy.

From zinc homeostasis to disease progression: Unveiling the neurodegenerative puzzle

Zinc is a crucial trace element in the human body, playing a role in various physiological processes such as oxidative stress, neurotransmission, protein synthesis, and DNA repair. The zinc transporters (ZnTs) family members are responsible for exporting intracellular zinc, while Zrt- and Irt-like proteins (ZIPs) are involved in importing extracellular zinc. These processes are essential for maintaining cellular zinc homeostasis. Imbalances in zinc metabolism have been linked to the development of neurodegenerative diseases. Disruptions in zinc levels can impact the survival and activity of neurons, thereby contributing to the progression of neurodegenerative diseases through mechanisms like cell apoptosis regulation, protein phase separation, ferroptosis, oxidative stress, and neuroinflammation. Therefore, conducting a systematic review of the regulatory network of zinc and investigating the relationship between zinc dysmetabolism and neurodegenerative diseases can enhance our understanding of the pathogenesis of these diseases. Additionally, it may offer new insights and approaches for the treatment of neurodegenerative diseases.

Trace Metals and The Hemostatic System

In this narrative review we report the main relationships between trace metals and the hemostatic system since this aspect has seldom attracted the attention of the scientific community. A basic aspect to be considered is the importance of maintaining the fine control of all trace metals' levels since they have an important impact on the pathophysiology of the hemostatic system. It is worth noting that poor diet habits are responsible for most trace metal deficiencies, while pollution is responsible for dangerous exposure to them with a consequent negative impact on the general population. This appears of paramount importance in planning the implementation of food and nutrient support to ameliorate the hidden hunger and the quality of life of people especially in developing countries and limiting poisons both in the air and food. As it often happens, when damage to certain mechanisms takes a very long time to appear, no attention is paid to the importance of a systematic prevention to avoid late negative outcomes.

Loss of zinc transporters ZIP1 and ZIP3 augments platelet reactivity in response to thrombin and accelerates thrombus formation in vivo

Zinc (Zn2+) is considered as important mediator of immune cell function, thrombosis and haemostasis. However, our understanding of the transport mechanisms that regulate Zn2+ homeostasis in platelets is limited. Zn2+ transporters, ZIPs and ZnTs, are widely expressed in eukaryotic cells. Using mice globally lacking ZIP1 and ZIP3 (ZIP1/3 DKO), our aim was to explore the potential role of these Zn2+ transporters in maintaining platelet Zn2+ homeostasis and in the regulation of platelet function. While ICP-MS measurements indicated unaltered overall Zn2+ concentrations in platelets of ZIP1/3 DKO mice, we observed a significantly increased content of FluoZin3-stainable free Zn2+, which, however, appears to be released less efficiently upon thrombin-stimulated platelet activation. On the functional level, ZIP1/3 DKO platelets exhibited a hyperactive response towards threshold concentrations of G protein-coupled receptor (GPCR) agonists, while immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptor agonist signalling was unaffected. This resulted in enhanced platelet aggregation towards thrombin, bigger thrombus volume under flow ex vivo and faster in vivo thrombus formation in ZIP1/3 DKO mice. Molecularly, augmented GPCR responses were accompanied by enhanced Ca2+ and PKC, CamKII and ERK1/2 signalling. The current study thereby identifies ZIP1 and ZIP3 as important regulators for the maintenance of platelet Zn2+ homeostasis and function.

Variants in the zinc transporter TMEM163 cause a hypomyelinating leukodystrophy

Hypomyelinating leukodystrophies comprise a subclass of genetic disorders with deficient myelination of the CNS white matter. Here we report four unrelated families with a hypomyelinating leukodystrophy phenotype harbouring variants in TMEM163 (NM_030923.5). The initial clinical presentation resembled Pelizaeus-Merzbacher disease with congenital nystagmus, hypotonia, delayed global development and neuroimaging findings suggestive of significant and diffuse hypomyelination. Genomic testing identified three distinct heterozygous missense variants in TMEM163 with two unrelated individuals sharing the same de novo variant. TMEM163 is highly expressed in the CNS particularly in newly myelinating oligodendrocytes and was recently revealed to function as a zinc efflux transporter. All the variants identified lie in highly conserved residues in the cytoplasmic domain of the protein, and functional in vitro analysis of the mutant protein demonstrated significant impairment in the ability to efflux zinc out of the cell. Expression of the mutant proteins in an oligodendroglial cell line resulted in substantially reduced mRNA expression of key myelin genes, reduced branching and increased cell death. Our findings indicate that variants in TMEM163 cause a hypomyelinating leukodystrophy and uncover a novel role for zinc homeostasis in oligodendrocyte development and myelin formation.

Transmembrane 163 (TMEM163) protein interacts with specific mammalian SLC30 zinc efflux transporter family members

Recently, we reported that TMEM163 is a zinc efflux transporter that likely belongs to the mammalian solute carrier 30 (Slc30/ZnT) subfamily of the cation diffusion facilitator (CDF) protein superfamily. We hypothesized that human TMEM163 forms functional heterodimers with certain ZNT proteins based on their overlapping subcellular localization with TMEM163 and previous reports that some ZNT monomers interact with each other. In this study, we heterologously expressed individual constructs with a unique peptide tag containing TMEM163, ZNT1, ZNT2, ZNT3, and ZNT4 (negative control) or co-expressed TMEM163 with each ZNT in cultured cells for co-immunoprecipitation (co-IP) experiments. We also co-expressed TMEM163 with two different peptide tags as a positive co-IP control. Western blot analyses revealed that TMEM163 dimerizes with itself but that it also heterodimerizes with ZNT1, ZNT2, ZNT3, and ZNT4 proteins. Confocal microscopy revealed that TMEM163 and ZNT proteins partially co-localize in cells, suggesting that they exist as homodimers and heterodimers in their respective subcellular sites. Functional zinc flux assays using Fluozin-3 and Newport Green dyes show that TMEM163/ZNT heterodimers exhibit similar efflux function as TMEM163 homodimers. Cell surface biotinylation revealed that the plasma membrane localization of TMEM163 is not markedly influenced by ZNT co-expression. Overall, our results show that the interaction between TMEM163 and distinct ZNT proteins is physiologically relevant and that their heterodimerization may serve to increase the functional diversity of zinc effluxers within specific tissues or cell types.

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TMEM163 protein heterodimerizes with ZNT1, ZNT2, ZNT3 and ZNT4 zinc efflux transporters.

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Partial co-localization of TMEM163 and ZNT proteins in cells suggests distinct roles as homodimers and heterodimers.

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Zinc efflux activity of TMEM163 or ZNT protein homodimers did not differ from their TMEM163/ZNT heterodimer counterparts.

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TMEM163/ZNT heterodimerization attests to the role of TMEM163 as a bona fide SLC30 protein family member.

Identification of a Novel MLPH Missense Mutation in a Chinese Griscelli Syndrome 3 Patient

Melanophilin (MLPH) functions as a linker between RAB27A and myosin Va (MYO5A) in regulating skin pigmentation during the melanosome transport process. The MYO5A-MLPH-RAB27A ternary protein complex is required for anchoring mature melanosomes in the peripheral actin filaments of melanocytes for subsequent transfer to adjacent keratinocytes. Griscelli syndrome type 3 (GS3) is caused by mutations in the MLPH gene. So far, only five variants of MLPH associated with GS3 have been reported. Here, we reported the first patient with GS3 in a Chinese population. The proband carried a novel homozygous missense mutation (c.73G>C; p.D25H), residing in the conserved Slp homology domain of MLPH, and presented with hypopigmentation of the hair, eyebrows, and eyelashes. Light microscopy revealed the presence of abnormal pigment clumping in his hair shaft. In silico tools predicted this MLPH variant to be likely pathogenic. Using immunoblotting and immunofluorescence analysis, we demonstrated that the MLPH (D25H) variant had an inhibitory effect on melanosome transport by exhibiting perinuclear melanosome aggregation in melanocytes, and greatly reduced its binding to RAB27A, although the protein level of MLPH in the patient was not changed. Our findings suggest that MLPH (D25H) is a pathogenic variant that expands the genetic spectrum of the MLPH gene.

Functional Study of TMEM163 Gene Variants Associated with Hypomyelination Leukodystrophy

Hypomyelinating leukodystrophies (HLDs) are a rare group of heterogeneously genetic disorders characterized by persistent deficit of myelin observed on magnetic resonance imaging (MRI). To identify a new disease-associated gene of HLD, trio-based whole exome sequencing was performed for unexplained patients with HLD. Functional studies were performed to confirm the phenotypic effect of candidate protein variants. Two de novo heterozygous variants, c.227T>G p.(L76R) or c.227T>C p.(L76P) in TMEM163 were identified in two unrelated HLD patients. TMEM163 protein is a zinc efflux transporter localized within the plasma membrane, lysosomes, early endosomes, and other vesicular compartments. It has not been associated with hypomyelination. Functional zinc flux assays in HeLa cells stably-expressing TMEM163 protein variants, L76R and L76P, revealed distinct attenuation or enhancement of zinc efflux, respectively. Experiments using a zebrafish model with knockdown of tmem163a and tmem163b (morphants) showed that loss of tmem163 causes dysplasia of the larvae, locomotor disability and myelin deficit. Expression of human wild type TMEM163 mRNAs in morphants rescues the phenotype, while the TMEM163 L76P and L76R mutants aggravated the condition. Moreover, poor proliferation, elevated apoptosis of oligodendrocytes, and reduced oligodendrocytes and neurons were also observed in zebrafish morphants. Our findings suggest an unappreciated role for TMEM163 protein in myelin development and add TMEM163 to a growing list of genes associated with hypomyelination leukodystrophy.

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 15 subtypes 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.

Rebalancing the unbalanced aged immune system - A special focus on zinc

Nowadays, aging is understood as a dynamic and multifaceted dysregulation process that spares almost no human organ or cell. The immune system being among the most affected, it has been shown predominantly that its integrity determines the tightrope walk between the difference of escaping or suffering from age-related diseases. Next to drug-based anti-aging strategies, micronutrient intervention may represent an emerging but less radical way to slow immune aging. While a sufficient supply of a variety of micronutrients is undeniably important, adequate intake of the trace element zinc appears to tower over others in terms of reaching old age. Inconveniently, zinc deficiency prevalence among the elderly is high, which in turn contributes to increased susceptibility to infection, decreased anti-tumor immunity as well as attenuated response to vaccination. Driven by this research, this review aims to provide a comprehensive and up-to-date overview of the various rebalancing capabilities of zinc in the unbalanced immune system of the elderly. This includes an in-depth and cell type-centered discussion on the role of zinc in immunosenescence and inflammaging. We further address upcoming translational aspects e.g. how zinc deficiency promotes the flourishing of certain pathogenic taxa of the gut microbiome and how zinc supply counteracts such alterations in a manner that may contribute to longevity. In the light of the ongoing COVID-19 pandemic, we also briefly review current knowledge on the interdependency between age, zinc status, and respiratory infections. Based on two concrete examples and considering the latest findings in the field we conclude our remarks by outlining tremendous parallels between suboptimal zinc status and accelerated aging on the one hand and an optimized zinc status and successful aging on the other hand.