Liver Endothelial Heg Regulates Vascular/Biliary Network Patterning and Metabolic Zonation Via Wnt Signaling.

BACKGROUND & AIMS: The liver has complex interconnecting blood vessel and biliary networks; however, how the vascular and biliary network form and regulate each other and liver function are not well-understood. We aimed to examine the role of Heg in mammalian liver development and functional maintenance. METHODS: Global (Heg-/-) or liver endothelial cell (EC)-specific deletion of Heg (Lyve1-Cre;Hegfl/fl ) mice were used to study the in vivo function of Heg in the liver. Carbon-ink anterograde and retrograde injection were used to visualize the 3-dimensional patterning of liver portal and biliary networks, respectively. RNA sequencing, histology, and molecular and biochemical assays were used to assess liver gene expression, protein distribution, liver injury response, and function. RESULTS: Heg deficiency in liver ECs led to a sparse liver vascular and biliary network. This network paucity does not compromise liver function under baseline conditions but did alter liver zonation. Molecular analysis revealed that endothelial Heg deficiency decreased expression of Wnt ligands/agonists including Wnt2, Wnt9b, and Rspo3 in ECs, which limits Axin2 mediated canonical Wnt signaling and the expression of cytochrome P450 enzymes in hepatocytes. Under chemical-induced stressed conditions, Heg-deficiency in liver ECs protected mice from drug-induced liver injuries. CONCLUSION: Our study found that endothelial Heg is essential for the 3-D patterning of the liver vascular and indirectly regulates biliary networks and proper liver zonation via its regulation of Wnt ligand production in liver endothelial cells. The endothelial Heg-initiated changes of the liver metabolic zonation and metabolic enzyme expression in hepatocytes was functionally relevant to xenobiotic metabolism and drug induced liver toxicity.

Cell Cycle Withdrawal Limit the Regenerative Potential of Neonatal Cardiomyocytes.

PURPOSE: The neonatal mouse possesses a transient capacity for cardiac regeneration during the first few days of life. The regenerative response of neonatal mouse is primarily mediated by pre-existing cardiomyocyte (CM) proliferation, which has been identified as the primary source of myocardial regeneration. Postnatal 4-day-old (P4) mouse CMs appear to undergo a rapid transition from hyperplastic to hypertrophic growth and binucleation. By 7 days following birth this regenerative potential is lost which coincidently correspond with CM cell cycle arrest and binucleation. CCM2-like (Ccm2l) plays pivotal roles in cardiovascular development and cardiac growth, indicating a potential function in heart regeneration postnatally. The aim of this study was to determine the cardiac regeneration ability of P4 neonatal mouse using a novel and more reproducible injury model and to determine whether Ccm2l has any functional roles in heart repair following ischemic injury. METHODS: We performed a modified left anterior descending artery (LAD) ligation procedure on P4 mice to examine cardiac regenerative responses at different time points. Additionally, we generated an endothelial-specific Ccm2l gain-of-function transgenic mouse to determine the role of Ccm2l in neonatal cardiac regeneration. RESULTS: We found that the P4 mouse heart harbor a robust regenerative response after injury that was through the proliferation of pre-existing CMs but cardiac hypertrophy and subsequent remodeling was still evident 60 days after LAD ligation. Furthermore, we show that endothelial-specific overexpression of Ccm2l does not promote CM proliferation and heart repair after LAD ligation. CONCLUSION: The neonatal heart at P4 harbors a robust but incomplete capacity for cardiac regeneration. Endothelial overexpression of Ccm2l has no effect on cardiac regeneration.

The lysosomal membrane protein LAMP-2 is dispensable for PINK1/Parkin-mediated mitophagy.

Selective autophagy for the elimination of aberrant mitochondria, termed mitophagy, can be regulated by the kinase PINK1 and the ubiquitin ligase Parkin. The lysosome-associated membrane protein 2 (LAMP-2) plays diverse functions in non-selective autophagy, chaperone-mediated autophagy and selective autophagy for the degradation of RNA/DNA. In the present study, we investigated whether LAMP-2 plays important roles during PINK1/Parkin-mediated mitophagy. The results obtained clearly show that knockdown of LAMP-2 does not cause defects in mitophagy in HeLa cells stably expressing Parkin, indicating that LAMP-2 is dispensable for PINK1/Parkin-mediated mitophagy. The present study is the first to determine the potential role of LAMP-2 in PINK1/Parkin-mediated mitophagy, thereby providing more insight into the sophisticated process of mitophagy.