Raman spectroscopic detection of rapid, reversible, early-stage inflammatory cytokine-induced apoptosis of adult hippocampal progenitors/stem cells: a preliminary study

Abstract

The role of neuro-inflammation in diverse, acute and chronic brain pathologies is being increasingly recognized. Neuroinflammation is accompanied by increased levels of both pro- and anti-inflammatory cytokines; these have deleterious as well as protective/reparative effects. Inflammation has varying effects on neurogenesis and is a subject of intense contemporary interest.We show that TNF-a and IFN-g, used concomitantly, cause apoptosis of adult rat hippocampal progenitor/stem cells in vitro as detected by the TUNEL and MTT assays on time scales of several hours. We have coupled Raman spectroscopy to an optical trap to probe early changes of apoptosis in single, live neural stem cells that have been treated with pro-inflammatory cytokines, TNF-a and IFN-g. Our spectroscopic results on very early-stage apoptosis also show that cells can be divided into two groups: those that show an increase in the intensity of the DNA band and those that show the opposite. Changes caused by inflammation-induced denaturation of DNA are observed in the Raman spectra that correspond to very early stages of apoptosis, occurring on very fast time scales: as short as 10 minutes. Addition of the anti-inflammatory cytokine IL-10 either 10 min before or 10 min after treatment with TNF-a and IFN-g reverses the changes substantially. The findings of this preliminary study imply that inflammation may induce very rapid changes leading to cell death but that these are reversible, in the early stages at least.