Seongho Kim. CSAM 2015;22:665-74. https://doi.org/10.5351/CSAM.2015.22.6.665

In the US, there have been more than 29.8 million confirmed COVID-19 cases and more than 542 400 deaths from this disease.¹ Nationwide, racial and ethnic disparities have been substantial. Data show that Black individuals represent 22% of cases to date while only representing 13% of the US population.² Trends have been similar in Michigan, where COVID-19 incidence has been higher among Black individuals (48 443 per 1 000 000 population) compared with White individuals (45 427 per 1 000 000 population) and all other racial/ethnic groups.³ COVID-19–related mortality has also been higher among Black individuals (2328 per 1 000 000 population) compared with White individuals (1329 per 1 000 000 population) and other racial/ethnic groups. Of note, Black individuals account for 14% of the population in Michigan but have represented 23% of COVID-19–related deaths to date.⁴

Alcohol consumption induces liver steatosis; therefore, this study investigated the possible role of adipose tissue dysfunction in the pathogenesis of alcoholic steatosis. Mice were pair-fed an alcohol or control liquid diet for 8 weeks to evaluate the alcohol effects on lipid metabolism at the adipose tissue-liver axis. Chronic alcohol exposure reduced adipose tissue mass and adipocyte size. Fatty acid release from adipose tissue explants was significantly increased in alcohol-fed mice in association with the activation of adipose triglyceride lipase and hormone-sensitive lipase. Alcohol exposure induced insulin intolerance and inactivated adipose protein phosphatase 1 in association with the up-regulation of phosphatase and tensin homolog (PTEN) and suppressor of cytokine signaling 3 (SOCS3). Alcohol exposure up-regulated fatty acid transport proteins and caused lipid accumulation in the liver. To define the mechanistic link between adipose triglyceride loss and hepatic triglyceride gain, mice were first administered heavy water for 5 weeks to label adipose triglycerides with deuterium, and then pair-fed alcohol or control diet for 2 weeks. Deposition of deuterium-labeled adipose triglycerides in the liver was analyzed using Fourier transform ion cyclotron mass spectrometry. Alcohol exposure increased more than a dozen deuterium-labeled triglyceride molecules in the liver by up to 6.3-fold. These data demonstrate for the first time that adipose triglycerides due to alcohol-induced hyperlipolysis are reverse transported and deposited in the liver.

The CXCL12/CXCR4 axis transactivates HER2 and promotes intraosseous tumor growth. To further explore the transactivation of HER2 by CXCL12, we investigated the role of small GTP protein Gαi2 in Src and HER2 phosphorylation in lipid raft membrane microdomains and the significance of CXCR4 in prostate cancer bone tumor growth. We used a variety of methods such as lipid raft isolation, invasion assays, an in vivo model of intratibial tumor growth, bone histomorphometry, and immunohistochemistry to determine the role of CXCR4 signaling in lipid raft membrane microdomains and effects of targeting of CXCR4 for bone tumor growth. We determined that (a) CXCL12/CXCR4 transactivation of EGFR and HER2 is confined to lipid raft membrane microdomains, (b) CXCL12 activation of HER2 and Src is mediated by small GTP proteins in lipid rafts, (c) inhibition of the CXCL12/CXCR4 axis through plerixafor abrogates the initial establishment of tumor growth without affecting the growth of established bone tumors, and (d) inhibition of EGFR signaling through gefitinib leads to inhibition of established bone tumor growth. These data suggest that lipid raft membrane microdomains are key sites for CXCL12/CXCR4 transactivation of HER2 via small GTP binding protein Gαi2 and Src kinase. The initial establishment of prostate cancer is supported by the endosteal niche, and blocking the CXCL12/CXCR4 axis of this niche along with its downstream signaling severely compromises initial establishment of tumors in the bone microenvironment, whereas expanding bone tumors are sensitive only to the members of growth factor receptor inhibition.