Retnla, also known as Resistin-like molecule alpha or 'Found in inflammatory zone 1', is a secreted protein. It has been implicated in modulating inflammation, fibrosis, and cholesterol homeostasis. It is involved in various biological processes, and its expression is regulated by factors like food intake [1,3].

In a cardiac injury model, Retnla knockout (KO) mice showed preserved cardiac function, increased angiogenesis, and suppressed cardiomyocyte apoptosis compared to wild-type (WT) and transgenic (TG) mice. The KO mice had a higher number of cardiac macrophages, unsorted bone marrow cells (UBCs), and more phosphorylated histone H3(+) cells in the bone marrow, along with higher adiponectin in UBCs. Adoptive transfer of UBCs from KO mice to the WT infarcted heart improved cardiac function [2]. In hyperlipidemic mice, Retnla deficiency promoted hypercholesterolaemia and atherosclerosis, while overexpression reversed these effects by upregulating cholesterol-7-α-hydroxylase through induction of liver receptor homologue-1, thus enhancing cholesterol excretion as bile acids [3]. In helminth-infected Retnla(-/-) mice, stronger Th2 responses were observed, indicating that Retnla functions as a negative regulator of Th2-type immunity [4].

In conclusion, Retnla plays crucial roles in cardiac repair, cholesterol homeostasis, and Th2-type immunity. Studies using Retnla KO mouse models have revealed its significance in these biological processes, providing insights into potential therapeutic targets for related diseases such as cardiac injury, hyperlipidemia, and immune-mediated disorders.

References:

1. Lee, Mi-Ran, Shim, Dahee, Yoon, Jihye, Choi, Jae-Hoon, Oh, Goo Taeg. 2014. Retnla overexpression attenuates allergic inflammation of the airway. In PloS one, 9, e112666. doi:10.1371/journal.pone.0112666. https://pubmed.ncbi.nlm.nih.gov/25415454/

2. Kim, Yong Sook, Cho, Hyang Hee, Cho, Dong Im, Oh, Goo Taeg, Ahn, Youngkeun. 2021. The adipokine Retnla deficiency increases responsiveness to cardiac repair through adiponectin-rich bone marrow cells. In Cell death & disease, 12, 307. doi:10.1038/s41419-021-03593-z. https://pubmed.ncbi.nlm.nih.gov/33753732/

3. Lee, Mi-Ran, Lim, Chae-ji, Lee, You-Han, Choi, Jae-Hoon, Oh, Goo Taeg. 2014. The adipokine Retnla modulates cholesterol homeostasis in hyperlipidemic mice. In Nature communications, 5, 4410. doi:10.1038/ncomms5410. https://pubmed.ncbi.nlm.nih.gov/25022542/

4. Pesce, John T, Ramalingam, Thirumalai R, Wilson, Mark S, Urban, Joseph F, Wynn, Thomas A. 2009. Retnla (relmalpha/fizz1) suppresses helminth-induced Th2-type immunity. In PLoS pathogens, 5, e1000393. doi:10.1371/journal.ppat.1000393. https://pubmed.ncbi.nlm.nih.gov/19381262/