Sunday, November 22, 2015

Normalizing T lymphocyte metabolism treats lupus autoimmunity

Glucose is metabolized in two pathways to fuel cellular functions: glycolysis, which splits glucose, yielding little energy but providing pyruvate and other materials for synthesis, and oxidative phosphorylation, which degrades glucose in the mitochondria and produces ~15-fold more energy. Glucose uptake is a limiting in activated T lymphocytes through CD28 costimulation.  Glucose metabolism is dysregulated in T lymphocytes of patients with the autoimmune disease Systemic Lupus Erythematosus (SLE, lupus, review).

These investigators blocked glycolysis with 2-deoxy-D-glucose (2DG) and oxidative phosphorylation with metformin (Met), and observed that disease was reduced and even reversed in mice “triple congenic” (TC) with three lupus-predisposing genetic regions: Sle1-Sle2-Sle3 (review).  2DG is glucose with its 2-hydroxl group replaced by a hydrogen, thereby blocking glycolysis.  Met is a small molecule that was discovered in 1920s to reduce blood glucose, probably by interfering with mitochondrial respiration.  The authors show here that Met reduces extracellular acidification rate (ECAR) and 2DG reduces oxygen consumption rate (OCR), both measures of glucose metabolism, in activated T cells (fig. 1).  

Anti-nuclear antibodies (ANA), a hallmark of lupus, are particularly dangerous because they damage glomeruli, the kidney’s filtration units, causing glomerular nephritis (GN).  The authors show a remarkable reduction in ANA and spleen size (fig. 4, panels, C, D and a portion of panel E shown here) as well as improvement in kidney pathology (fig. 4 panel I)
Although these metabolism inhibitors are not targeted to pathogenic T cells, there are no obvious adverse consequences for the animal or even the immune system.  Treated mice raise antibody responses following protein immunization, generating normal levels and avidities of circulating antibodies (supplemental).  Perhaps the limiting effect of glucose uptake by pathogenic, chronically activated T cells make them more sensitive to inhibition.  How treatment influences control of chronic infections (e.g., EBV, CMV) is also worth knowing.  There was no change in body weight on Met. 
Testing 2 other mouse models of lupus (NZB/W and chronic graft-vs-host (cGVH)), they found a mixture of responses.  For example, in cGVH, combined treatment doesn’t reduce spleens (though Met alone does), while treatment of NZB/W mice reduces ANA but doesn’t improve GN.  Human patients exhibit a range of symptoms and might also be expected to show a range of responses.  This is inspired and inspiring work that cuts across as many disciplines as it does organ systems and raises as many questions as hopes. 
Y. Yin, S.-C. Choi, Z. Xu, D. J. Perry, H. Seay, B. P. Croker, E. S. Sobel, T. M. Brusko, L. Morel, Normalization of CD4+ T cell metabolism reverses lupus. Sci. Transl. Med. 7, 274ra18 (2015).

Sunday, March 15, 2015

Stem Cells: Unstable in Culture

Stem Cells (SC) can differentiate into many different cell types, offering the potential of replacing failing cells, tissues, or even entire organs with new ones generated from the patient’s own or related donor SC (National Academy of Sciences Workshop summary).  To be useful for therapy in the clinic, it would be necessary to grow and expand SCs in culture.

The authors explored the proliferation of human embryonic SC (HESC), which are prepared from disrupted embryos, and the less-controversial human inducible pluripotent stem cells (hiPSCs), which can be prepared from several adult tissues, including blood, skin, and fat.  They obtained 1 HESC line, WA09, from the WiCell Research Institute and they generated 3 hiPSC lines from fetal dermal fibroblasts by over-expressing the ‘standard reprogramming factors’ (pluripotency-conferring genes, transduced OCT4/POU5F1, SOX2, KLF4, and MYC).

They compared four standard SC culture conditions: with or without a feeder cell layer and enzymatic or “mechanical” (dissection) disruption, with 6 replicate cultures per condition, for over 100 “passages” (transfers to fresh cultures). Previous studies cited here revealed genomic changes (small duplications) that are not detectable by karyotyping, particularly on chromosome 12, where the pluripotency-related gene NANOG is encoded, and chromosome 20, where the survival gene Bcl-xL is encoded.  In addition to measuring proliferation, telomere length, pluripotency by teratoma formation, they also analyzed over a million reference SNPs around the genome and used those SNPs to assess copy number variation (CNV). 

Not surprisingly, genomic changes increased with time in culture, both in aberration number (A) and total length (B) (Figure 2, shown, WA09 HESC: left duplications and right deletions).  The number of aberrations was lowest in “EcmMech” condition, i.e. cultures without feeder cells (only extracellular matrix, ECM), and disrupted mechanically (blue line).  The number and length of aberrations was worst with MefEnz (green line), cultured with feeder cells (mouse embryo fibroblasts, Mef) and disrupted enzymatically.  They conclude that there is a “need for careful assessment of the effects of culture conditions on cells intended for clinical therapies”.  

Increased Risk of Genetic and Epigenetic Instability in Human Embryonic Stem Cells Associated with Specific Culture Conditions  Garitaonandia et al. PLoS One 10(2), February 25, 2015

Saturday, January 24, 2015

Nurture Immunity: Immune system influenced more by environment than by genes

Differences in immune protection presumably explain why some people exposed to infection resist disease or recover while others succumb.  These authors sought to distinguish the influences of genes and environment on immunity. They compared the cellular and molecular components of the immune system among 210 twins: 78 monozygotic (MZ, “identical”) and 27 dizygotic (DZ, fraternal) pairs.  They measured 43 serum proteins and 72 immune cell populations repeatedly and longitudinally (over time) to assess actual variations and account for technical variations.  MZ twins, who have practically identical genomes, and DZ twins, who share half their genes, are especially valuable for assessing the relative contributions of “nature or nurture” (genes or environment) to phenotype.  Their analysis allowed them to detect as little as 20% heritability.

The levels of few proteins and cell populations are under strong genetic control, such as interleukin-6 and CD4+ “central memory” T cells, but most are only weakly heritable or not at all (Fig 1). They found that a common, chronic infection, by cytomegalovirus (CMV), influences the levels of most (58%) cell populations and proteins (Fig 5).  Variation between twins increased as they age, probably reflecting different environmental stimuli and epigenetic changes (Fig 4).  Most intriguing, they correlate the heritability of response to vaccines to the age of immunization, whereby early childhood vaccines are highly heritable while vaccines after early adolescence have no detectable heritability (Table 1, shown below).  

Brodin et al. Cell. 2015 Jan 15;160(1-2):37-47. Variation inthe human immune system is largely driven by non-heritable influences.