Expression of an epidermal keratin protein in liver of transgenic mice causes structural and functional abnormalities.

Abstract

Abstract. To examine the role of keratin intermediate filament proteins in cell structure and function, transgenie mice were isolated that express a modified form of the human K14 keratin protein in liver hepatoeytes. A modified K14 eDNA (K14.P) sequence was linked downstream of the mouse transthyretin (TTR) gene promoter and enhancer elements to achieve targeted expression in hepatocytes. Hepatoeytes expressing high levels of the transgene were found to have abnormal keratin filament networks as detected by indirect immunofluorescenoe using an antibody specific for the transgene product. Light and electron microscopic level histological analysis of isolated liver tissue showed in many eases degenerative changes that included inflammatory infiltration, ballooning degeneration, an increase in fat containing vacuoles, and glycogen accumulation. These changes were most evident in older mice over four months of age. No indication of typical Mallory body structures were identified at either the light or electron microscopic level. To evaluate secretory function in transgenic livers, bile acid secretion rates were measured in isolated perfused liver and found to be approximately twofold lower than aged-matched controls. These findings indicate that expression of an abnormal keratin in liver epithelial cells in the in vivo setting can alter the structure and function of a tissue and suggest a role of the keratin network in cellular secretion.

Unique amino acid signatures that are evolutionarily conserved distinguish simple-type, epidermal and hair keratins

“…expressing epidermal keratins in simple-type epithelial tissues (Albers et al, 1995). This is further supported by the human variants in K8/K18 leading to introduction of cysteines into an otherwise cysteine-free K8.…”

“…However, K19 can rescue K18 loss (Hesse et al, 2000;Hesse et al, 2005), and replacement of the K14 with a chimeric keratin that consists of the K14 rod domain and the K10 head and tail domains predisposed mice to an accelerated development of skin cancer (Chen et al, 2006). Ectopic keratin expression can even lead to a gain-of-function phenotype as shown in mice overexpressing K16 in the skin, epidermal K14 in the liver or K1 in the pancreatic b-cell (Blessing et al, 1993;Takahashi et al, 1994;Albers et al, 1995). In that context, ectopic expression of a keratin pair, which to our knowledge has not been reported to date, is likely to be more physiologically informative.…”

Protein phosphatase inhibition in normal and keratin 8/18 assembly-incompetent mouse strains supports a functional role of keratin intermediate filaments in preserving hepatocyte integrity

“…In transgenic mice that express K14 in the liver with consequent hepatocyte IF disruption, inflammatory infiltration, ballooning degeneration, increased fat-containing vacuoles, and glycogen accumulation were also observed. 50 Liver fragility in mice lacking functional liver IFs has also been observed in a few other studies. 23,47 These results together with our present data would strongly imply a role of keratin IFs in intracellular organization.…”

Disturbances in hepatic cell-cycle regulation in mice with assembly-deficient keratins 8/18

“…14,15 Several transgenic mouse lines targeting epithelial keratins have been generated to study the requirement of keratins for the formation and function of simple epithelia. 12,[16][17][18][19][20][21][22] The targeted null mutation of K8 causes mid-gestational lethality with bleeding into the embryonic liver. 19 The lethality does not have a complete penetrance, because approximately half of the homozygous K8 null embryos escape lethality in mice with the FVB/n genetic background.…”