Heat shock proteins (hsp) are well recognized for their protein folding activity. Additionally, hsp expression is enhanced during stress conditions to preserve cellular homeostasis. Hsp are also detected outside cells, released by an active mechanism independent of cell death. Extracellular hsp appear to act as signaling molecules as part of a systemic response to stress. Extracellular hsp do not contain a consensus signal for their secretion via the classical ER-Golgi compartment. Therefore, they are likely exported by an alternative mechanism requiring translocation across the plasma membrane. Since Hsp70, the major inducible hsp, has been detected on surface of stressed cells, we propose that membrane interaction is the first step in the export process. The question that emerges is how does this charged cytosolic protein interact with lipid membranes? Prior studies have shown that Hsp70 formed ion conductance pathways within artificial lipid bilayers. These early observations have been extended herewith using a liposome insertion assay. We showed that Hsp70 selectively interacted with negatively charged phospholipids, particularly phosphatidyl serine (PS), within liposomes, which was followed by insertion into the lipid bilayer, forming high-molecular weight oligomers. Hsp70 displayed a preference for less fluid lipid environments and the region embedded into the lipid membrane was mapped toward the Cterminus end of the molecule. The results from our studies provide evidence of an unexpected ability of a large, charged protein to become inserted into a lipid membrane. This observation provides a new paradigm for the interaction of proteins with lipid environments. In addition, it may explain the export mechanism of an increasing number of proteins that lack the consensus secretory signals.

About 2–3 million years ago, Alu‐mediated deletion of a critical exon in the CMAH gene became fixed in the hominin lineage ancestral to humans, possibly through a stepwise process of selection by pathogen targeting of the CMAH product (the sialic acid Neu5Gc), followed by reproductive isolation through female anti‐Neu5Gc antibodies. Loss of CMAH has occurred independently in some other lineages, but is functionally intact in Old World primates, including our closest relatives, the chimpanzee. Although the biophysical and biochemical ramifications of losing tens of millions of Neu5Gc hydroxy groups at most cell surfaces remains poorly understood, we do know that there are multiscale effects functionally relevant to both sides of the host–pathogen interface. Hominin CMAH loss might also contribute to understanding human evolution, at the time when our ancestors were starting to use stone tools, increasing their consumption of meat, and possibly hunting. Comparisons with chimpanzees within ethical and practical limitations have revealed some consequences of human CMAH loss, but more has been learned by using a mouse model with a human‐like Cmah inactivation. For example, such mice can develop antibodies against Neu5Gc that could affect inflammatory processes like cancer progression in the face of Neu5Gc metabolic incorporation from red meats, display a hyper‐reactive immune system, a human‐like tendency for delayed wound healing, late‐onset hearing loss, insulin resistance, susceptibility to muscular dystrophy pathologies, and increased sensitivity to multiple human‐adapted pathogens involving sialic acids. Further studies in such mice could provide a model for other human‐specific processes and pathologies involving sialic acid biology that have yet to be explored.

Humans and chimpanzees are more sensitive to endotoxin than mice or monkeys, but any underlying differences in inflammatory physiology have not been fully described or understood. We studied innate immune responses in Cmah−/− mice, emulating human loss of the gene encoding production of Neu5Gc, a major cell surface sialic acid. CMAH loss occurred ~2-3 million years ago, after the common ancestor of humans and chimpanzees, perhaps contributing to speciation of the genus Homo. Cmah−/− mice manifested a decreased survival in endotoxemia following bacterial lipopolysaccharide (LPS) injection. Macrophages from Cmah−/− mice secreted more inflammatory cytokines with LPS-stimulation and showed more phagocytic activity. Macrophages and whole blood from Cmah−/− mice also killed bacteria more effectively. Metabolic re-introduction of Neu5Gc into Cmah−/− macrophages suppressed these differences. Cmah−/− mice also showed enhanced bacterial clearance during sub-lethal lung infection. Although monocytes and monocyte-derived macrophages from humans and chimpanzees exhibited marginal differences in LPS responses, human monocyte-derived macrophages killed E. coli and ingested E. coli bioparticles better. Metabolic re-introduction of Neu5Gc into human macrophages suppressed these differences. While multiple mechanisms are likely involved, one cause is altered expression of C/EBPβ, a transcription factor affecting macrophage function. Loss of Neu5Gc in Homo likely had complex effects on immunity, providing greater capabilities to clear sub-lethal bacterial challenges, possibly at the cost of endotoxic shock risk. This trade-off may have provided a selective advantage when Homo transitioned to butchery using stone tools. The findings may also explain why the Cmah−/− state alters severity in mouse models of human disease.

Sepsis is a major clinical challenge, with therapy limited to supportive interventions. Therefore, the search for novel remedial approaches is of great importance. We addressed whether hyperbaric oxygen therapy (HBOT) could improve the outcome of sepsis using an acute experimental mouse model. Sepsis was induced in male CD-1 mice by cecal ligation and puncture (CLP) tailored to result in 80–90% mortality within 72 h of the insult. After CLP, mice were randomized into two groups receiving HBOT or not at different times after the initial insult or subjected to multiple HBOT treatments. HBOT conditions were 98% oxygen pressurized to 2.4 atmospheres for 1 h. HBOT within 1 h after CLP resulted in 52% survival in comparison with mice that did not receive the treatment (13% survival). Multiple HBOT at 1 and 6 h or 1, 6, and 21 h displayed an increase in survival of >50%, but they were not significantly different from a single treatment after 1 h of CLP. Treatments at 6 or 21 h after CLP, excluding the 1 h of treatment, did not show any protective effect. Early HBO treatment did not modify bacterial counts after CLP, but it was associated with decreased expression of TNF-α, IL-6, and IL-10 expression in the liver within 3 h after CLP. The decrease of cytokine expression was reproduced in cultured macrophages after exposure to HBOT. Early HBOT could be of benefit in the treatment of sepsis, and the protective mechanism may be related to a reduction in the systemic inflammatory response.