Mechanosensitive Piezo1 ion channel protein (PIEZO1 gene): update and extended mutation analysis of hereditary xerocytosis in India

Variant spectrum of PIEZO1 and KCNN4 in Japanese patients with dehydrated hereditary stomatocytosis

Hereditary stomatocytosis (HSt) is a type of congenital hemolytic anemia caused by abnormally increased cation permeability of erythrocyte membranes. Dehydrated HSt (DHSt) is the most common subtype of HSt and is diagnosed based on clinical and laboratory findings related to erythrocytes. PIEZO1 and KCNN4 have been recognized as causative genes, and many related variants have been reported. We analyzed the genomic background of 23 patients from 20 Japanese families suspected of having DHSt using a target capture sequence and identified pathogenic/likely pathogenic variants of PIEZO1 or KCNN4 in 12 families.

New KCNN4 Variants Associated With Anemia: Stomatocytosis Without Erythrocyte Dehydration

The K+ channel activated by the Ca2+, KCNN4, has been shown to contribute to red blood cell dehydration in the rare hereditary hemolytic anemia, the dehydrated hereditary stomatocytosis. We report two de novo mutations on KCNN4, We reported two de novo mutations on KCNN4, V222L and H340N, characterized at the molecular, cellular and clinical levels. Whereas both mutations were shown to increase the calcium sensitivity of the K+ channel, leading to channel opening for lower calcium concentrations compared to WT KCNN4 channel, there was no obvious red blood cell dehydration in patients carrying one or the other mutation. The clinical phenotype was greatly different between carriers of the mutated gene ranging from severe anemia for one patient to a single episode of anemia for the other patient or no documented sign of anemia for the parents who also carried the mutation. These data compared to already published KCNN4 mutations question the role of KCNN4 gain-of-function mutations in hydration status and viability of red blood cells in bloodstream.

Case Report: Whole Exome Sequencing Revealed Two Novel Mutations of PIEZO1 Implicated in Nonimmune Hydrops Fetalis

Nonimmune hydrops fetalis (NIHF) is a serious and complex fetal condition. Prenatal diagnosis of hydrops fetalis is not difficult by ultrasound. However, determining the underlying etiology of NIHF remains a challenge which is essential to address for prenatal counseling. We extracted DNA from a proband prenatally diagnosed unexplained NIHF. Trio-whole exome sequencing (WES) was performed to filter candidate causative variants. Two gene mutations were identified as a compound heterozygous state in the proband. Both variants located on the PIEZO1 gene: c.3895C > T, a missense mutation in exon 27 paternally inherited; c.4030_4032del, a maternally inherited in-frame deletion in exon 28. Both variants were first reported to be related to NIHF. PIEZO1 gene mutations, leading to an autosomal recessive congenital lymphatic dysplasia, which can present as NIHF and partial or complete resolution postnatally. In conclusion, WES can aid in the elucidation of the genetic cause of NIHF and has a positive effect on the assessment of prognosis.

Recent advances in the pathophysiology of PIEZO1-related hereditary xerocytosis

Hereditary xerocytosis is a rare red blood cell disease related to gain-of-function mutations in the FAM38A gene, encoding PIEZO1, in 90% of cases; PIEZO1 is a broadly expressed mechano-transducer that plays a major role in many cell systems and tissues that respond to mechanical stress. In erythrocytes, PIEZO1 adapts the intracellular ionic content and cell hydration status to the mechanical constraints induced by the environment. Until recently, the pathophysiology of hereditary xerocytosis was mainly believed to be based on the "PIEZO1-Gardos channel axis" in erythrocytes, according to which PIEZO1-activating mutations induce a calcium influx that secondarily activates the Gardos channel, leading to potassium and water efflux and subsequently to red blood cell dehydration. However, recent studies have demonstrated additional roles for PIEZO1 during early erythropoiesis and reticulocyte maturation, as well as roles in other tissues and cells such as lymphatic vessels, hepatocytes, macrophages and platelets that may affect the pathophysiology of the disease. These findings, presented and discussed in this review, broaden our understanding of hereditary xerocytosis beyond that of primarily being a red blood cell disease and identify potential therapeutic targets.

Impact of Next-Generation Sequencing on the Diagnosis and Treatment of Congenital Anemias

Congenital anemias are a wide spectrum of diseases including hypoproliferative anemia syndromes, dyserythropoietic anemias, sideroblastic anemias, red blood cell membrane and enzymatic defects, hemoglobinopathies, and thalassemia syndromes. The various congenital anemia syndromes may have similar clinical and laboratory presentations, making the diagnosis challenging. The traditional work-up, which includes a complete blood count, blood smears, bone marrow studies, flow cytometry, and the osmotic fragility test, does not always lead to the diagnosis. Specialized tests such as red blood cell enzyme activity and ektacytometry are not widely available. In addition, red blood cell transfusions may mask some of the laboratory characteristics. Therefore, genetic testing is crucial for accurate diagnosis of patients with congenital anemias. However, gene-by-gene testing is labor intensive because of the large number of genes involved. Thus, targeted next-generation sequencing using custom-made gene panels has been increasingly utilized, with a high success rate of diagnosis. Accurate genetic diagnosis is important for determining specific therapeutic modalities, as well as for avoiding splenectomy when contraindicated. In addition, molecular diagnosis can allow for genetic counseling and prenatal diagnosis in severe cases. We suggest a work-up scheme for patients with congenital anemias, including early incorporation of targeted next-generation sequencing panels.

A New Hope in Spinal Degenerative Diseases: Piezo1

As a newly discovered mechanosensitive ion channel protein, the piezo1 protein participates in the transmission of mechanical signals on the cell membrane and plays a vital role in mammalian biomechanics. Piezo1 has attracted widespread attention since it was discovered in 2010. In recent years, studies on piezo1 have gradually increased and deepened. In addition to the discovery that piezo1 is expressed in the respiratory, cardiovascular, gastrointestinal, and urinary systems, it is also stably expressed in cells such as mesenchymal stem cells (MSCs), osteoblasts, osteoclasts, chondrocytes, and nucleus pulposus cells that constitute vertebral bodies and intervertebral discs. They can all receive external mechanical stimulation through the piezo1 protein channel to affect cell proliferation, differentiation, migration, and apoptosis to promote the occurrence and development of lumbar degenerative diseases. Through reviewing the relevant literature of piezo1 in the abovementioned cells, this paper discusses the effect of piezo1 protein expression under mechanical stress stimuli on spinal degenerative disease, providing the molecular basis for the pathological mechanism of spinal degenerative disease and also a new basis, ideas, and methods for the prevention and treatment of this degenerative disease.

PIEZO1 might be involved in cerebral ischemia-reperfusion injury through ferroptosis regulation: a hypothesis

Stroke is associated with high mortality and extremely high disability rate. Regulating ferroptosis seems to be a promising way to treat ischemic stroke. After stroke, vasogenic edema exerts a mechanical force on surrounding structures, which could activate the mechanosensitive PIEZO1 channel. Our previous research has found that brain cortex PIEZO1 expression was increased in the rat model of middle cerebral artery occlusion (MCAO), and PIEZO1 regulated oxygen-glucose deprivation/reoxygenation (OGD/R) injury in neurons through the calcium signaling. Considering recent studies has identified HIF1α as an essential protein in PIEZO1/calcium signaling, ferroptosis regulation and cerebral ischemia, we herein hypothesize that PIEZO1 might be involved in cerebral ischemia-reperfusion injury through ferroptosis regulation.