Matriptase-2 and Hemojuvelin in Hepcidin Regulation: In Vivo Immunoblot Studies in Mask Mice

Abstract

Matriptase-2, a serine protease expressed in hepatocytes, is a negative regulator of hepcidin expression. The purpose of the study was to investigate the interaction of matriptase-2 with hemojuvelin protein in vivo. Mice lacking the matriptase-2 proteolytic activity (mask mice) display decreased content of hemojuvelin protein. Vice versa, the absence of hemojuvelin results in decreased liver content of matriptase-2, indicating that the two proteins interact. To further characterize the role of matriptase-2, we investigated iron metabolism in mask mice fed experimental diets. Administration of iron-enriched diet increased liver iron stores as well as hepcidin expression. Treatment of iron-overloaded mask mice with erythropoietin increased hemoglobin and hematocrit, indicating that the response to erythropoietin is intact in mask mice. Feeding of an iron-deficient diet to mask mice significantly increased spleen weight as well as the splenic content of erythroferrone and transferrin receptor proteins, indicating stress erythropoiesis. Liver hepcidin expression was decreased; expression of Id1 was not changed. Overall, the results suggest a complex interaction between matriptase-2 and hemojuvelin, and demonstrate that hepcidin can to some extent be regulated even in the absence of matriptase-2 proteolytic activity.

Matriptase-2 regulates iron homeostasis primarily by setting the basal levels of hepatic hepcidin expression through a nonproteolytic mechanism

“…To seek insights into the roles of Mt2 in the iron regulation of hepcidin, we first tested the extent to which the Tmprss6 −/− mice can elevate hepatic hepcidin expression in response to increased bodily iron load. Previous studies indicate that severe iron deficiency in mask mice can be corrected by feeding an iron-enriched diet with 2% carbonyl iron ( 11 , 45 ). To avoid gastrointestinal bleeding and other side effects of high dietary iron ( 55 ), we fed the Tmprss6 +/+ , Tmprss6 +/− , and Tmprss6 −/− mice a high iron diet containing ∼0.5% carbonyl iron (HID).…”

“…MT2 can bind to HJV through its stem region ( 38 ). In mask mice that lack detectable Mt2 protein, the increased hepcidin expression is associated with a decrease, rather than an increase, in hepatic Hjv protein ( 44 , 45 ). These findings support the idea that Mt2 suppression of hepcidin is not mediated through its proteolytic activity to cleave and to inactivate its substrates.…”

TMPRSS6 as a Therapeutic Target for Disorders of Erythropoiesis and Iron Homeostasis

“…TMPRSS6 is a critical negative regulator of the receptor complex that controls hepcidin transcription [15]. The exact mechanism of action of TMPRSS6 is still not understood, but TMPRSS6 interacts with HJV and possibly other components of the BMP receptor complex and acts as both an allosteric inhibitor and a protease that degrades components of the receptor complex [16][17][18]. As a result, TMPRSS6 decreases SMAD1/5/8 signaling and suppresses hepcidin transcription.…”

In Vitro Pharmacokinetic Behavior of Antiviral 3-Amidinophenylalanine Derivatives in Rat, Dog and Monkey Hepatocytes

“…Both matriptase and transmembrane serine protease 2 (TMPRSS2) belong to the type II transmembrane serine proteases (TTSPs), and these membrane-anchored enzymes are involved in several physiological and pathological processes [ 1 ]. Excessive TTSP activity can be correlated with the formation of several disorders, thus specific inhibition of matriptase- and TMPRSS2-caused proteolysis with 3-amidinophenylalanine (3-APhA) derivatives can be an effective pharmacological option to alleviate tumor formation and metastatic potential [ 2 ], to counteract cartilage damage [ 3 ] and to restore hepcidin-mediated tipped iron homeostasis [ 4 ].…”