The present invention refers to an in vitro method for quantifying total cell RNA content, preferably total cell content of long-non-coding RNAs (IncRNA), more preferably total cell content of IncRNA molecules transcribed from telomeric or sub-telomeric sequences or present in telomeric regions, such as TERRA and/or TERC, using a labelled probe and flow cytometry.
1. In vitro method for quantifying total cell RNA content in a biological sample which comprises: a. Contacting a labelled probe with the cells to be analysed in a suitable hybridization media, b. Incubating the hybridization mixture at a temperature below 45 °C in order to avoid double stranded DNA denaturation and possible probe hybridization with the DNA, thus providing suitable conditions for the probe to hybridize only with the RNA, and protecting RNA integrity; c. Quantifying total RNA content by flow cytometry. 2. Method, according to claim 1, for analysing, measuring and/or quantifying total long-non-coding RNA cellular content. 3. Method, according to any of the previous claims, for analysing, measuring and/or quantifying total cell content of long non-coding RNA molecules transcribed from telomeric or sub-telomeric sequences or present in telomeric regions. 4. Method, according to any of the previous claims, for analysing, measuring and/or quantifying total cell content of the long non-coding RNAs TERRA and/or TERC. 5. Method, according to any of the previous claims, wherein the labelled probe is a fluorescent-labelled probe. 6. Method, according to any of the previous claims, wherein the fluorescent-labelled probe is a peptide nucleic acid (PNA) probe. 7. Method, according to any of the previous claims, for analysing, measuring and/or quantifying total cell content of long-non-coding RNAs in a biological sample obtained from a subject which comprises: a. Contacting a fluorescent-labelled peptide nucleic acid (PNA) probe with the biological sample in a suitable hybridization media, b. Incubating the hybridization media at a temperature below 45°C in order to avoid double stranded DNA denaturation and probe hybridization with the DNA, thus providing suitable conditions for the probe to hybridize with the RNA and protecting RNA integrity; c. Analysing, measuring and/or quantifying total cell content of long-non-coding RNAs by flow cytometry. 8. Method, according to any of the previous claims, for analysing, measuring and/or quantifying total cell content of the long-non-coding RNAs TERRA and/or TERC, in a biological sample obtained from a subject, which comprises: a. Contacting a fluorescent-labelled peptide nucleic acid (PNA) probe with the biological sample in a suitable hybridization media, b. Incubating the hybridization media at a temperature below 45°C in order to avoid double stranded DNA denaturation and probe hybridization with the DNA, thus providing suitable conditions for the probe to hybridize with the RNA and protecting RNA integrity; c. Analysing, measuring and/or quantifying total cell content of the long-non-coding RNAs TERRA and/or TERC by flow cytometry. 9. Method, according to any of the previous claims, wherein the step a) comprises collecting the cell pellet from the biological sample before contacting with the labelled probe. 10. Method, according to any of the previous claims, wherein the step b) further comprises the addition of an RNA protecting agent to prevent RNA degradation. 11. Method, according to any of the previous claims, wherein the biological sample is blood. 12. In vitro method for the diagnosis of diseases associated with telomere shortening or dysfunction which comprises analysing, measuring and/or quantifying total cell content of long-non-coding RNA molecules transcribed from telomeric or sub-telomeric sequences, or present on the telomeric sequences, following the method of any of the claims 1 to 11. 13. Method, according to claim 12, for the diagnosis of a diseases associated with telomere shortening which comprises analysing, measuring and/or quantifying total cell content of the long-non-coding RNA TERR and/or TERC, following the method of any of the claims 1 to 11.