Glycerol-3-phosphate acyltransferases 3 and 4 direct glycerolipid synthesis and affect functionality in activated macrophages

Abstract

Macrophage classical M1 activation via TLR4 triggers a variety of responses to achieve the elimination of foreign pathogens. During this process, there is also an increase in lipid droplets which contain large quantities of triacylglycerol (TAG) and phospholipid (PL). The functional consequences of this increment in lipid mass are poorly understood. Here, we studied the contribution of glycerolipid synthesis to lipid accumulation, focusing specifically on the first and rate-limiting enzyme of the pathway: glycerol-3-phosphate acyltransferase (GPAT). Using bone marrow-derived macrophages (BMDMs) treated with Kdo2-lipid A, we showed that glycerolipid synthesis is induced during macrophage activation. GPAT4 protein level and GPAT3/GPAT4 enzymatic activity increase during this process, and these two isoforms were required for the accumulation of cell TAG and PL. The phagocytic capacity of Gpat3−/− and Gpat4−/− BMDM was impaired. Additionally, inhibiting fatty acid β-oxidation reduced phagocytosis only partially, suggesting that lipid accumulation is not necessary for the energy requirements for phagocytosis. Finally, Gpat4−/− BMDM expressed and released more pro-inflammatory cytokines and chemokines after macrophage activation, suggesting a role for GPAT4 in suppressing inflammatory responses. Together, these results provide evidence that glycerolipid synthesis directed by GPAT4 is important for the attenuation of the inflammatory response in activated macrophages.

Mycobacterium leprae promotes triacylglycerol de novo synthesis through induction of GPAT3 expression in human premonocytic THP-1 cells

“…We showed that intracellular localization of M. leprae to lipid droplets was clearly reduced in GPAT3 KO cells compared to wild-type cells. This observation is in agreement with a recent study showing that in bone marrow-derived macrophages from Gpat3 -/mice, not only was the formation of Kdo 2 -lipid A (KLA)-inducible lipid droplets suppressed, intriguingly, the phagocytic capacity of the macrophages was also reduced [42]. In the present study, however, we have clearly shown that GPAT3 does not affect the ability of THP-1 cells to undergo phagocytosis.…”

FATP4 inactivation in cultured macrophages attenuates M1- and ER stress-induced cytokine release via a metabolic shift towards triacylglycerides

“…We observed that M1-like activation of siCon cells led to an increase in Cer d18:1/24:1, Cer d18:1/24:0 (Figure 3B) and TAG (Figure 3C) levels, which were consistent with previous reports for TAGs [12] and Cer [42]. Remarkably, FATP4 KD further elevated the levels of TAGs and Cer d18:1/24:1.…”

“…Specifically, FATP4 inactivation induces a metabolic shift from GPLs and Cer towards TAGs as reported in skin fibroblasts [27] and skin [21,22] of Fatp4-null mice as well as in subcutaneous fat of adipose-specific Fatp4-deficient mice fed with high-fat diet [30]. As GPLs, SPLs, and TAGs are critical for macrophage functions [9][10][11][12][13][14], we hypothesized that FATP4 inactivation may affect the cytokine release by altering these lipids. Because of FATP4 localization in the ER [25,26], we chose a stress model which involves unfolded protein response (UPR) activation in the ER [31] in two in vitro systems using small interfering RNA (siRNA) against FATP4 in THP-1-derived macrophages and BMDMs of myeloid-specific Fatp4-deficient (Fatp4 M-/-) mice.…”

“…Fatty acids are utilized not only for the generation of ATP but also the activation of M1-like inflammatory response [8]. M1-like macrophage activation is also regulated by acylated lipids including phosphatidylcholine (PC) [9,10], phosphatidic acid [11], triacylglycerides (TAGs) [12,13], and ceramides (Cer) [14]. Moreover, IL-4induced polarization to M2-like macrophages is associated with alterations of lysophosphatidic acid [15] and sphingosine 1-phosphate [16].…”

Phospholipids containing ether-bound hydrocarbon-chains are essential for efficient phagocytosis and neutral lipids of the ester-type perturb development in Dictyostelium

“…Moreover, efficient phagocytosis depends on lipolysis ( Chandak et al, 2010 ). Thus, it is well conceivable that mammalian macrophages lacking GPAT3 or GPAT4 show compromised phagocytosis ( Quiroga et al, 2019 ). In Dictyostelium , however, phagocytosis does not seem to depend on a TAG reservoir, because in gpat − mutants phagocytosis is even increased, whether or not the cells are challenged with palmitic acid ( Fig.…”